CN1054092A - Moisture resistant conductive adhesive and methods of making and using same - Google Patents

Abstract

And a conductive adhesive which has a very stable conductivity under high temperature conditions when the conductive mating surfaces are bonded, the adhesive comprising a carrier and a filler, the carrier having a volume shrinkage value of less than about 6.8%, the filler comprising agglomerates, particles, powders, flakes, particles of an outer plated nickel, and outer plated glass spheres, the filler having particle size and surface characteristics which provide for electrical contact stability due to moisture resistant contact on the electronic component leads. The volume shrinkage of the support between the unset and the set state is greater than 6.8%, thus placing the filler particles in compression, facilitating electrical contact of the surfaces to be joined, and bringing the particles themselves to a certain density, thereby enhancing the interaction between the particles.

Description

The applicant's pending and generally known application number is No. 07/436199, filed November 14, 1989, titled "Conductive Adhesive" and application number No. 07/533682, filed June 4, 1990, is a continuation of two U.S. patent applications entitled "Conductive Adhesives and Methods of Making and Using Same".

The present invention relates to a conductive adhesive or cement, and more particularly to a conductive adhesive having excellent long-term performance under conditions of high temperature and high humidity.

Conductive adhesives and glues are generally made from single or multi-component non-conductive carrier materials and conductive fillers such as metal or metal particles. While various binders can be used as carriers, multi-component resins, single-component solvent-based systems and mixtures thereof have been used. The resin has a long shelf life, good bonding characteristics, and can be cured with a variety of materials. Similarly, by removing the solvent in the one-component solvent-based system, the one-component solvent-based substance can be easily cured with various materials to form a bond with high strength and reliable performance. The above-mentioned fillers are generally noble metals of various particle sizes, such as gold or silver. Preferred fillers are mixtures of tabular and non-tabular particles of various particle sizes. The above-mentioned particles are mainly solid, and in some cases, may also be non-conductive bodies coated with metal. In general construction, the conductive filler may constitute about 75% or more of the total weight of the material containing the carrier, with the carrier making up the remaining 25% or less. It is generally believed that since the flakes tend to be arranged in a continuous overlapping relationship to form electron channels in the solidified carrier, the metal or metal-coated particles in the shape of flakes or lamellar crystals provide a strong support for this conductive adhesive. conductive properties. It is believed that non-flaky conductive fillers in the carrier will fill in the gaps between the flake particles to enhance conductivity.

Modern circuits can be fabricated into traditional rigid printed circuit boards (PCBs) using subtractive methods. In this method, a copper plate pattern and connection areas form an electrical circuit formed by etching a thin layer of copper attached to a rigid, non-conductive plate or substrate. The wires usually coated with solder on the electronic components pass through the fixed holes opened on the printed circuit board, and the wires coated with solder are connected to the connection area by lead/tin soldering, so as to connect the above electronic components to this on the circuit. It is also well known to make so-called "flexible circuits", in which circuits are formed on flexible sheets or substrates such as polyimide or polyester sheets, for example KAPTON™ polyimide of 1 to 5 mil thickness. Copper pattern and connection area. Electronic components are connected to such circuits by passing their wires through holding holes in the flexible sheet and connecting these wires to the connection pads with lead/tin solder. More recently, a surface mount device (SMC) has been developed in which the device wires are fixed only above the connection area and soldered in place to form a pair of headers. Surface mount technology can be used on both rigid and flexible substrates.

With the improvement of its performance under various temperature and humidity conditions, especially under the conditions of high temperature and high humidity, the traditional welding method has reached a considerable state of the art. However, in order to artificially form circuits on substrates, traditional soldering methods often require extensive chemical processing using various etchants and similar chemicals. Various fluxes and solvents may also be required for effective solder connections. In addition, traditional welding methods use a lot of heat in order to rapidly melt the welding material to form the joint. While rigid substrates and some expensive polyimides can be used to absorb the heat generated during soldering, flexible substrates have a relatively small cross-sectional height, low heat capacity, and ease of deformation, so less costly polymers are used Flexible substrates such as polyester are more prone to heat loss. For example, solder joints on flexible polyester substrates may cause localized "wrinkling" of the substrate, changes in the alignment of various bonded areas, and deformation of the entire substrate.

Attempts have therefore been made to use conductive inks, adhesives and glues to replace the traditional solder connections used in rigid and flexible substrates. For example, now people have printed conductive printed circuits including connection areas on flexible polyester substrates, and then bonded conductive terminals of surface mount component (SMC) circuit groups to the connection areas with conductive adhesives. The advantage of the above method is that the shape of the fabricated flexible printed circuit can be easily changed, so that it can be put into a special mounting case, so that the design of the case has great flexibility. In addition, it is estimated that successful solderless connection methods employing conductive printing, adhesives, and low-cost flexible substrates can greatly reduce costs compared to traditional soldering methods. "Conductive adhesive" as used herein means any compound or material used to form electrical and mechanical connections between elements such as wires and lands.

Although general conductive adhesives are generally not as conductive as solid metals and solder alloys, the conductivity of conductive adhesives (eg: 100 megohms per bonded joint vs. 10 megohms per soldered joint ohm) is large enough for many circuits. For example, when the element is a resistor or other component with a resistance value of hundreds or thousands of ohms or more, the influence of the contact resistance of about 1 ohm between the element lead and its connection area is almost negligible. Although contact resistance becomes more important in the use of low resistance circuits, circuits can usually be designed to accommodate a larger range of cumulative contact resistances. In addition to the resistance value of the contact resistance, the stability of the contact resistance with time and different environments is also an important aspect worth considering. Since a connection method that does not have the required stability is not suitable for many applications, there is a need for a connection method that can form a joint with a known resistance value in the range of It can be used stably for a long time and under different environmental conditions. Within the scope of a solderless connection method using a conductive adhesive, any joint that has been tested at a temperature of 60°C at a relative humidity (RH) of 90% is generally considered acceptable. After 1000 hours, the average value of the change in contact resistance is less than about 20-25%, preferably less than 15%. As used herein, the terms "moisture-resistant adhesive" and "moisture-resistant electrical contact" refer to a conductive adhesive, that is, a joint made using this conductive adhesive, at a relative humidity of 90%, Under the test condition of a temperature of 60°C, after 1000 hours, it has a stable contact resistance value, and the variation range of the resistance value does not exceed about 25% on average.

One factor that affects conductivity at the connection interface is the presence of non-conductive or resistive surface oxides that are exposed in contact with ambient air and moisture. In the solder connection method, the oxide at the interface between the solder-coated wire and the solder itself can be greatly removed by using a flux that reacts with the oxide and effectively removes the oxide , but also separate the air and moisture that circulate at the connection interface when the solder is cooling. In conductive adhesive attachment methods, fluxes are not used during the curing process, so it is desirable that the adhesive contain components that reduce the negative effects of surface oxides without the need for caustic cleaners or other treatments prior to forming the joint Methods to treat surfaces to be connected, such as lead wires of electronic components containing lead.

Although the initial volume resistivity of known silver-based conductive adhesives is satisfactory, such adhesives tend to increase the solder-plated wire due to the presence of non-conductive lead/tin oxides. resistivity at the interface. Consequently, the resistance value of the joint between the conductive adhesive and the solder-coated wire may vary considerably over time, especially in environments with high humidity. The resistance values in the above joints are particularly sensitive to continuous exposure to high temperature and high humidity. Since the aforementioned one- or two-component polymeric carriers used in conventional conductive adhesives naturally permeate moisture, connectors made with such adhesives are adversely affected by moisture to some extent. Although a circuit can be designed to accommodate the accumulated contact resistance, the change in resistance over time can adversely affect the overall electrical performance of the circuit. It is generally believed that the moisture in the carrier that penetrates the joint made of conductive adhesive will oxidize the metal at the interface of conductive adhesive and component wire, and the non-conductive oxide formed will make the The resistance increases.

Conductive adhesive compositions known in the art generally include a polymer or carrier filled with conductive particles. For example, a mixture is described in the US4880570 patent, which comprises an adhesive with epoxy resin as the main component, a contact agent and conductive particles whose shape can minimize steric interference and provide conductivity; in US4859364 No. 1 patent describes a mixture of organic media filled with particles with a particle size of no more than 1 micron coated with conductive metal and conductive particles with a particle size of 0.3-1.0 microns; in US4859268 Described in the patent is a mixture of photosensitive resin polymer, plasticizer and spherical conductive particles. In US4814040 patent, a kind of adhesive layer is described, which includes certain particle size Conductive particles, that is, the particles can pass through the resistance layer and enter the metal mold by using the heat pressing method; a resin mixture is described in the US4732702 patent, which is filled with conductive metal powder or coated with a conductive film Inorganic insulating powder; US4716081 describes a mixture of plastics, rubber or resin filled with silver-plated metal particles, and US4701279 describes a thermoplastic synthetic rubber mixture filled with There are metal particles, a resin mixture is described in the US4696764 patent, which is filled with abrasives and conductive tiny particles; a polymer with polyester urethane as the main component is described in the US4624801 patent A mixture of polymers mixed with closed isocyanate and filled with conductive particles; an epoxy resin, hardener and metallic silver particle mixture is described in US4747968, and a A blend of acrylic, carboxylated vinyl, and epoxy polymers filled with metallic silver particles; a blend of thermoplastic setting polymers filled with sheet metal and conductive metal is described in US4566990 Or metal-coated fibers.

In summary, silver-filled polymer-based conductive adhesives have good performance in the moderate high-temperature range, but under relatively high humidity conditions, at the interface between the adhesive and the conductive wire, the adhesion of this adhesive becomes weak. Performance is worse. When under the condition of high humidity for a long time, the resistance between the interfaces is often unstable, that is, it will increase greatly. While many circuits will still function well with greatly increased resistivity in one or more of the joints, moisture sensitivity has been identified as a factor limiting the more widespread use of conductive adhesives in both rigid and flexible substrates.

In view of the above, it is an object of the present invention to provide a conductive adhesive having improved performance, especially when used to bond bumps under high temperature and/or high humidity conditions. Better characteristics when point contact, surface mount devices and other electronic components are attached to the substrate. The above-mentioned electronic components are coated with ordinary metals, such as solder and tin.

Another object of the present invention is to provide a moisture-resistant conductive adhesive, in which by improving the conductivity between the particles and forming an airtight surface contact between the filler and the surface to be connected, the load Volume shrinkage contributes to the form of conductive joints.

It is also an object of the present invention to provide a conductive adhesive comprising conductive particles dispersed in a carrier, the conductive particles have surface properties, and the particle size is conducive to the formation of conductive particles due to carrier shrinkage during curing. The filler particles are brought into air-tight surface contact between the surfaces to be joined.

The present invention provides a conductive adhesive for bonding between bonding surfaces and making electrical contact between them, the adhesive comprising a mixture containing a Dispersed fillers in the carrier. The above-mentioned carrier shrinks in volume during solidification, and the carrier has such an amount that when the carrier is present, the mixture can be effectively attached to the substrate. The aforementioned fillers include a content of conductive particles having a structure which, when the particles have a structure, helps to form a moisture-resistant electrical contact during solidification of the carrier.

The present invention also provides a method for making a moisture-resistant conductive joint, the steps of which include coating a mixture on the surface, the mixture includes an adhesive carrier and a filler, the carrier shrinks in volume during solidification, and the filler includes a certain amount of Conductive particles, and its structure helps to form a moisture-resistant electrical contact with the substrate.

The present invention provides an electrically conductive adhesive comprising a settable polymeric carrier that shrinks in volume between the unset and set states by greater than 6.8%, preferably at Between 7.5% and 65%. The conductive adhesive described above also includes a filler that includes conductive particles that help form a moisture-resistant electrical contact during the solidification of the carrier.

While not intending to be bound by any particular theory of invention or mode of action here, it is generally believed that the use of a carrier or adhesive that is between the non-set and set states and that has volume shrinkage properties and a shrinkage value greater than about 6.8% It can make the filler particles achieve good compactness. The above-mentioned filler particles are dispersed in the carrier, and have an appropriate content and a suitable structure, so that the electrical contact between the above-mentioned filler particles can be improved, and a gas isolation layer can be formed on the surface to be connected. It is also generally believed that during the solidification process, if the pressure is large enough, the carrier shrinks its internal particles into a compressed state, thereby not only bringing the above-mentioned particles into contact with each other, but also making them at the interface between the adhesive and the surface. Particles at the junction link together and penetrate impurities and non-conductive oxides that may be present on the surface. The above-mentioned particles maintain a certain content with respect to the support, and have structural surface characteristics and such a particle size that when subjected to the pressure generated by the volume shrinkage of the support during solidification, the use of such particles facilitates the formation of gaseous particles on the surface. close connection. A hermetic joint having a surface is believed to be demonstrated when the joint is mechanically pulled apart at the interface, exposing conductive particles protruding from the cured adhesive surface. The anti-moisture electrical contact is just the result of the gas isolation layer formed by the above-mentioned protruding particles pressed on the surface of the wire.

The carrier used in the adhesives of the present invention can be any material that shrinks effectively upon setting, is loaded with conductive particles, and has sufficient cohesive and cohesive strength to form a mechanically reliable joint. The above-mentioned carrier may comprise a solvent-based polymer system, or may form a mixture of two polymeric carriers, one of which has high volume shrinkage properties and the other has low volume shrinkage properties. The weight percentages of these two carriers in can be varied within the range effective to impart volume shrinkage properties to the mixture.

In one embodiment of the invention, the conductive filler particles are sintered agglomerates having a particle size distribution ranging from 10.6 microns to about 2.00 microns (average particle size 4.5 microns), the particles having a rough outer surface, characterized by Many dimples and ridge-like interfaces or protruding corners, the ratio of length, width and height is about 1:1:1. As the volume of the binder shrinks during the setting of the binder, it is believed that the surface roughness of the agglomerate helps to form an electrical contact that resists moisture and penetration into surface oxides or impurities on the wire surface. Such a sintered compact is a suitable electronic carrier since its appearance features can participate in the formation of moisture-resistant electrical contacts between, for example, particles, leads of electronic components and connection areas on the substrate. In another embodiment, moisture resistant electrical contacts can be made with other particles called "surface penetrating particles" so that the present application includes solid particles and metallized particles having a similar properties, including its particle size and rough surface characteristics.

In the most preferred embodiment, the carrier comprises a mixture of two epoxy resins and a non-reactive diluent, wherein the ratio of each component is adjusted so that the carrier is in a state between a non-set and a set state. The volume shrinkage value is greater than about 6.8%, preferably 7.5%-65%.

If necessary, a certain amount of wetting agent can be added to improve the wetting ability of the non-curing epoxy resin mixture during the coating process (the content generally accounts for 2-5% of the carrier).

In the preferred embodiment described above, the conductive particulate filler is a mixture of silver flakes, silver powder and silver agglomerate. The sintered agglomerates are particles with irregular shapes, the particles have many surface depressions forming many rough-edged convex corners or ridges, the ratio of the length, width and height of the above particles is about 1:1:1. Since silver oxide is conductive relative to insulating oxides of other materials, silver particles and silver-plated particles are preferred here; under the above conditions, gold, palladium and other noble metals also have good properties in this regard, but its Expensive. Nickel has proven to have good stability under high temperature and high humidity conditions, however, its initial resistance is high. When forming the bonded joint, at the appropriate level, the silver agglomerate penetrates into the non-conductive oxide on the surfaces to be joined and on the lead/tin plated wires. In general, the filler particles comprise from about 60% to about 90%, preferably about 75%, by weight of the total epoxy resin mixture/conductive filler particle composition.

The above and other objects and further scope of application of the present invention can be understood from the following detailed description with reference to the accompanying drawings.

Fig. 1 (Prior Art) is a table showing the increase in contact resistance in an environment with a relative humidity of 90% for the composition of the prior art.

Figure 2 is a photomicrograph at 5000X magnification of the silver agglomerate used in the composition of Example 2 showing many rough surface features.

Fig. 3A is a table showing the stability of contact resistance in an environment of 90% relative humidity according to the composition of Example 2 of the present invention, where the wires are cleaned with acetone before splicing.

Fig. 3B is another table showing the stability of contact resistance in an environment with a relative humidity of 90% according to the composition of Example 2 of the present invention, where the wires are cleaned with mineral acid before forming joints.

Fig. 4 is a table showing the stability of contact resistance in an environment of 90% relative humidity according to the composition of Example 3 of the present invention.

Fig. 5 is a table showing the stability of contact resistance in an environment of 90% relative humidity according to the composition of Example 4 of the present invention.

Fig. 6 is a table showing the stability of contact resistance in an environment with a relative humidity of 90% according to the composition of Example 5 of the present invention.

Fig. 7 is a table showing the stability of contact resistance in an environment of 90% relative humidity according to the composition of Example 6 of the present invention.

Fig. 8 is a table showing the stability of contact resistance in an environment of 90% relative humidity according to the composition of Example 7 of the present invention.

Fig. 9 is a table showing the stability of contact resistance in an environment of 90% relative humidity according to the composition of Example 8 of the present invention.

Fig. 10 is a table showing the stability of contact resistance in an environment of 90% relative humidity according to the composition of Example 9 of the present invention.

Fig. 11 is a table showing the stability of contact resistance in an environment of 90% relative humidity according to the composition of Example 10 of the present invention.

Fig. 12 is a table showing the stability of contact resistance in an environment of 90% relative humidity according to the composition of Example 11 of the present invention.

Fig. 13 is a table showing the stability of contact resistance in an environment of 90% relative humidity according to the composition of Example 12 of the present invention.

Fig. 14 is a table showing the stability of contact resistance in an environment of 90% relative humidity according to the composition of Example 13 of the present invention.

Many factors must be considered when developing conductive adhesives that perform better under adverse operating conditions, especially high temperature and high humidity. Since all polymeric supports are subject to moisture penetration to some extent, the conductive particle filler should be of such a nature that the formation of non-conductive oxides is kept to a minimum during prolonged exposure to humidity. In addition, the carrier should have the following characteristics, that is, not only to enhance the conductivity at the interface between the adhesive and the wire, but also to enhance the conductivity between the conductive particles in the filler; to meet this requirement, it is best to choose silver particles or silver plating Particulate fillers, although other noble metals and nickel may also be suitable for use.

Fillers such as silver agglomerates, silver particles, silver flakes, silver powder, and silver plated particles are used in the various compositions of the present invention provided below. The silver agglomerate described above is characterized by an irregular shape with a surface having many depressions between which ridges or ridges are formed. The ratio of length, width and height of the above-mentioned sintered mass is preferably 1:1:1, so it is believed that the above-mentioned sintered mass can act as force vectors, and these force vectors can be used even in a high-temperature and high-humidity environment. A gas barrier layer is formed at the connection interface and will penetrate through the oxide present on the connection surface to maintain a stable electrical contact. The plated particles used herein are silver-plated non-conductive inorganic spheres and non-conductive inorganic spheres coated with outer silver-plated non-noble metals and nickel. With the compaction phenomenon formed by the volume shrinkage of the polymer carrier, it is believed that the above-mentioned sintered agglomerate and the outer-coated metal particles form an initial electron flow path in the solidified carrier through direct surface-to-surface internal particle contact, and the above-mentioned sintered agglomerate The metal particles and outer plating are in contact with the wire surface of the connecting body and penetrate into it at the same time. For small particle size silver particles, which are characterized here as powder, it will facilitate the formation of conductive pathways between large particle size particles. As the volume of the carrier shrinks to generate internal pressure, the above-mentioned small powder particles, like in larger sintered agglomerates or particles, can penetrate individually or in groups at the interface between the adhesive and the component wire at the connection. any oxides or surface impurities present.

While moderate amounts of sintered agglomerate and powder particles having the above structure and bonded to the carrier provide a moisture-resistant electrical contact, it has also been found useful to have conductive particles in the form of flakes or lamellar crystals. Tabular grains are particles whose thickness dimension is substantially (ie, a grade or order of magnitude) smaller than their length and width. If the content is appropriate, the platelet particles will tend to overlap together or overlap each other front and back, thereby enhancing the conductivity of the system.

In order to internally densify the conductive particulate filler, the carrier should have a volume shrinkage characteristic of greater than about 6.8%. Other characteristics of the carrier should include good adhesion, wettability and good handling properties. Since many conductive adhesives are applied by screen printing, stencil printing, or similar techniques, the unset polymeric carrier should have some tack to render the final conductive adhesive suitable for application by the methods described above. The rheological properties of the carrier should be favorable for the stencil printing, plate printing or pneumatic deposition methods usually used when applying the conductive adhesive, and its suitable viscosity can be in the range of 50000-25000 (PS).

The following examples are representative compositions of conductive adhesives with moisture resistant electrical contacts.

The linear shrinkage value can be determined by applying a long strip of uncured adhesive to a flat surface, allowing it to set, and using the shrinkage value as a function of the uncured and cured linear lengths. The volume shrinkage characteristic between uncured and cured adhesives is determined by the following formula.

The dissolved concentration ρu of the uncured (carrier) epoxy resin is determined at room temperature from the weight W of a container filled with epoxy resin of known volume V and the known weight W of the empty container as follows:

ρu=(W-w)/V Formula 1

The concentration pu of the solidified epoxy resin was determined at room temperature according to Archimedes' principle (ASTMC693) using a METTLER density measuring instrument E-210250 and an OHAUS precision balance 160D. Determine the dry weight of the solidified epoxy resin sample in the air as A, and its weight in the liquid with known concentration ρl is ρ, then the concentration ρc of the solidified epoxy resin is:

ρc=(A/P)ρi Formula 2

By using the uncured and cured epoxy volumes determined using the pu values derived above, the volume shrinkage values Vs of the uncured and cured epoxy fingers can be determined. The volume Vu of the uncured epoxy resin is determined by measuring the weight W of the uncured epoxy resin sample. It can be determined according to the following formula:

Vu＝Ww/ρu Formula 3

The epoxy resin was then cured according to the treatment given below, and the weight Wc of the cured sample was determined. Calculate the volume Vc of the solidified epoxy resin according to the following formula.

Vc＝Wc/ρc Formula 4

Then calculate the percentage value Vs of volume shrinkage according to the following formula:

Vs=[(Vu-Vc)/Vu](100) Formula 5

Example 1

As a typical example of the change in contact resistance at 90% relative humidity, the conductive adhesive is produced by Emerson & Cuming of Lexingbon, MA, and sold under the designation "AMICON ^TM CSM-933-65-1" . According to the instructions given by the manufacturer, the conductive adhesive is used to connect a 68-pin surface mount device, [68-Pin swrface-mount device (SMD)], two 44-pin surface mount devices and a 10-pin surface mount device on the test circuit. A resistor series string is connected in series, and the adhesive is placed at a temperature of 140°C for 10 minutes. The legs of each surface mount device are connected in series through the resistive element in the surface mount device and the total contact resistance, which is obtained by subtracting the total series resistance of the internal components of the device from the measured total resistance. Likewise, the resistance value of the resistor string can also be obtained by subtracting the cumulative value of the resistances making up the resistor string from the total series resistance value to obtain the cumulative contact resistance value. When tested with the control circuit, the resistance values of the internal components in the surface mount device and the individual resistors in the resistor string are stable over the range of test temperature and humidity. The initial contact resistance value (ohm) measured under the test conditions of room temperature and relative humidity of 90% and a temperature of 60°C is shown in Figure 1. Afterwards, under the test conditions of relative humidity of 90% and temperature of 60°C, after standing for 15.5, 24, 39 and 63 hours, the resistivity was measured respectively. As shown in Figure 1, all contact resistance ohmic values increase with time at 90% relative humidity, and estimates corresponding to 1000 hours show that for 68-leg surface-mounted devices and two 44-leg surface-mounted devices, the contact resistance Values increase significantly, while contact resistance values increase less for resistor strings.

From an analysis of the data presented in Figure 1, it can be concluded that the electrical resistance of contacts made with prior art conductive adhesives increases significantly after prolonged exposure to high relative humidity.

Example 2

A conductive adhesive was prepared with a conductive filler including 3 silver particles A, B, C. The particles are silver flakes with a Fisher particle size (FSSS) of 0.90-1.30 microns, a vibration density (measured with a Tap-Pak volume meter) of 0.3-3.5 g/cc, and a Scott apparent density of 30-35g/in ³ , surface area 0.3-0.6m ² /g, particle size distribution 90%<14.000 microns, 50%<7.00 microns, 10%<2.00 microns. Particle size distribution data given here were determined using a Leeds and Northrop Microtrac. A suitable particle A is "Silver Flake #53" which is commercially available from the Electronic Materials Division of Metz Metallurgical Company, South Ploir field.

Particle B is a silver agglomerate having a Fisher Particle Size (FSSS) of 0.6 microns, a vibration density (measured with a Tap-Pak volumeter) of 1.85 g/cc and a Scott appaTent density of 16.7g/in ³ , surface area 1.62m ² /g, particle size distribution: 100%<10.6 microns, 90%<8.10 microns, 50%<4.4 microns. 10%<1.40 microns, the average particle size is 4.5 microns. A suitable particle B can be selected as "SPS-100 silver powder", which is commercially available from Metz Metallurgical Company. The sintered block shown in the photomicrograph in Figure 2 has many rough surface features.

Particle C is a silver powder with a Fisher Particle Size (FSSS) of 0.7 micron, a vibrational density (measured with a Tap-Pak volumeter) of 2.75 g/cc, and a Scott apparent density of 17.5 g/cc. m ² , the surface area is 1.84m ² /g, the particle size distribution is 100%<5.25 microns, 90%<3.16 microns, 50%<1.25 microns. A suitable particle C is "fine silver powder S-ED" commercially available from Metz Metallurgical Company.

Particles A, B, and C are mixed according to the following weight percentages, particle A accounts for 40%, particle B accounts for 30%, and particle C accounts for 30%, thereby forming a metallic silver filler mixed with the carrier.

The carrier is a polymer blend comprising two epoxy resins, Epoxy A and Epoxy B. Epoxy resin A is bisphenol F epoxy resin, such as "Aratronic 5046", a bisphenol F diglycidyl ether, and its viscosity is 1400CPS at 25°C. The aforementioned epoxy resins are commercially available from CibaGeigy Corporation. Epoxy resin B is a liquid phenol novolac epoxy resin (phenol epoxy novolac resin), such as Quatrex 2010, a phenol novolac epoxy resin with a relatively high viscosity of 25000-45000CPS at 52°C , the above resins are commercially available from Dow Chemical Company, Midland, MI.

Common hardeners such as imidazole can also be included in the polymer carrier, for example, the brand is "CURIMID ^TM -CN", located in MA, N-(α-cyanoethyl)-2-ethanediol produced by Poly Organix, New buport base, 4-methylimidazole.

Coupling or wetting agents may also be included in the polymeric vehicle. To improve the wetting properties of the unset material. A typical coupling agent is γ-shrink certain oil propoxytrimethoxysilane. Above-mentioned coupling agent can be bought by the Vnion Carbide company that sells trade mark as " A187 ". Another adjuvant which may be incorporated into the polymeric carrier of the present invention is gamma-butyrolactone, which is commercially available from Aldrich Chemical Company, Milwaukee, WI, and which acts as a diluent to adjust viscosity.

The conductive adhesive mixture was prepared with the following composition:

Composition Amount of each batch - weight percentage (%)

(standard weight unit)

Epoxy resin A 8.275

Epoxy resin B 8.275

Hardener 3.973

Thinner 1.985

Coupler 0.993

Total weight of epoxy resin = 23.5%

Particle A 30.600

Particle B 22.950

Particle C 22.950

Total weight of silver content = 76.5%

The silver content value of 76.5% given here is an optimum value for commonly used techniques, such as stencil printing, screen printing, tampo printing, spray coating, etc. If the above-mentioned value is lower than 74%, the conductivity of the above-mentioned conductive adhesive mixture under various test conditions is unstable, and the resistance value increases by an order of magnitude. If the above value is higher than 78%, the above conductive adhesive mixture, although suitable for application by spraying, is too viscous for application by stencil printing and screen printing.

The volume shrinkage value of the above polymer carrier was determined to be 17%. In the first experiment, the wires were first cleaned with acetone. A mixture of the above components was used to connect a 68-leg surface mount device (SMD), a 44-leg surface mount device and a resistor string connected in series in each of the six test circuits described in Example 1 (Test Circuits 1-6) .

Under the test conditions of room temperature and relative humidity of 90%, and a temperature of 60°C, the contact resistance was tested, and the measured values are shown in Figure 3A. Afterwards, the resistivity was measured respectively under the test conditions of relative humidity of 90% and temperature of 60°C. As shown in the "increase percentage" (%) column in Figure 3A, under the condition of relative humidity of 90%, after 1002 hours, except for one group of contact resistance ohmic values which increased by more than 11%, all other contact resistance ohmic values changed very little Small.

In the second test, the lead wires of the above-mentioned devices were first cleaned with mineral acid, and then joints were formed using the composition of this example in the above-mentioned manner. Under the test conditions of room temperature and relative humidity of 90%, and a temperature of 60°C, the contact resistance was measured, and the measured values are shown in Figure 3B. After that, the resistivity was measured after 14.5, 117.5, 149, 297 and 969 hours under the test conditions of relative humidity of 90% and temperature of 60°C. As shown in the "Increase Percentage" column shown in Figure 3B, under the condition of 90% relative humidity, after 969 hours, except for only one set of contact resistances whose ohm increase exceeds 12%, all other contact resistance ohms The value changes little.

Example 3

Three kinds of conductive particle fillers of silver particles A, B and C were used to prepare conductive adhesives. Above-mentioned particle A, B, C are identical with described in example 2, and particle A, B, C account for 40% by particle A, and particle B accounts for 30%, and particle C accounts for 30% by weight and mixes equally, forms and carrier phase Mixed stuffing.

The carrier includes a single epoxy resin, which is a liquid bisphenol A epoxy resin, such as "Quantrex 1010", which has a viscosity of 11000-14000 cps at 25°C and is available from Dow Chemical Company.

The polymer carrier can also include hardener [N-(2-cyano(ethyl)-2-ethyl, 4-methylimidazole], γ-glycidyloxytrimethoxysilane, and diluent γ- Butyrolactone.

The conductive adhesive is prepared according to the following composition:

Composition Amount of each batch - weight percentage (%)

(standard weight unit)

Epoxy resin A 16.55

Hardener 3.97

Coupler 0.99

Thinner 1.99

Total weight of epoxy resin = 23.50%

Particle A 30.600

Particle B 22.950

Particle C 22.950

Total weight of silver content = 76.5%

The volume shrinkage value of the polymeric carrier described above was 13%, and the carrier was used to connect the 68-leg surface mount device (SMD) in each of the two test circuits (test circuits 1-2) described in Example 1, and the 44-leg surface mount device (SMD). A fixed device and a resistor string connected in series. Under the test conditions of room temperature and relative humidity of 90%, and a temperature of 60 °C, the contact resistance was measured, and the measured values are shown in Figure 4. Afterwards, under the test conditions of relative humidity of 90% and temperature of 60°C, the resistivity was measured after 15, 65 and 141 hours respectively. As shown in the "increase percentage" column in Figure 4, under the condition of a relative humidity of 90%, after 141 hours, except for the ohmic value of the two groups of contact resistances that increased by more than 2%, the ohmic values of all other contact resistances changed very small.

Example 4

A conductive adhesive was prepared using two conductive particle fillers of silver particles A and C, which were the same as those used in Example 2.

Particles A and C need to be mixed according to the following weight percentages, that is, particle A accounts for 40% and particle C accounts for 60% to form a filler mixed with a carrier.

The carrier is a mixture containing two epoxy resins, namely epoxy resin A and epoxy resin B. Epoxy A is a bisphenol F epoxy such as "Aratronic 5046" and Epoxy B is a liquid phenol novolac epoxy such as Quatrex 2010.

The polymer carrier can also include hardeners [such as N-2(2-cyanoethyl)-2-2yl, 4-methylimidazole], coupling agents (γ-glycidylpropylfluorosilane) and diluents (such as gamma-butyrolactone).

The conductive adhesive is prepared according to the following composition:

Composition Amount of each batch - weight percentage (%)

(standard weight unit)

Epoxy resin A 8.21

Epoxy resin B 8.21

Hardener 3.94

Thinner 0.66

Coupler 0.99

Total weight of epoxy resin = 22.0%

Particle A 31.20

Particle C 46.80

Total weight of silver content = 78.0%

The volume shrinkage value of the polymeric carrier described above was 10%, and the carrier was used to connect the 68-leg surface mount device and the 44-leg surface mount device in each of the 6 test circuits (test circuits 1-6) described in Example 1. and resistor strings connected in series. Under the test conditions of room temperature and relative humidity of 90%, and a temperature of 60 °C, the contact resistance was measured, and the measured values are shown in Figure 5. Afterwards, under the test conditions of relative humidity of 90% and temperature of 60°C, the resistivity was measured after 62, 136, and 1073 hours respectively. As shown in the "increase percentage" column in Figure 5, under the condition of a relative humidity of 90%, after 1598 hours, except for only one group of contact resistance ohms that increased by more than 19%, the ohms of all other contact resistances The value changes little.

Example 5

Conductive adhesives were prepared using three conductive fillers of silver particles A, B and C which were the same as particles A, B and C described in Example 2. Particles A, B and C were mixed in the following weight percentages, namely 40% particle A, 30% particle B and 30% particle C to form a filler mixed with the carrier. The carrier consists of a single epoxy/solvent composition which is a bisphenol A epoxy resin such as "EPONOL(R) 53-BH-35", a high molecular weight epoxy resin available from Available from Shell Chemical Company, Hoastom, TX. In the product model provided by the manufacturer, epoxy resin accounts for about 35% of the total product, and the remaining ingredients are composed of 75% methyl ethyl ketone (MEK) and 25% propylene glycol methyl ether ( PGME) solution. Prior to formulating the conductive adhesive of Example 5, methyl ethyl ketone (MEK) and propylene glycol methyl ether (PGME) were eliminated and replaced with ethyl 2-butoxyacetate, as available from Aldrich Chemical Company.

Prepare conductive adhesive mixture of the present invention by following composition:

Composition Amount of each batch - weight percentage (%)

(standard weight unit)

Epoxy resin 12.921

Solvent 23.996

Total weight of epoxy resin = 36.917%

Particle A 25.233

Particle B 18.925

Particle C 46.80

The total weight of silver content = 63.083%

The volume shrinkage value of the polymeric carrier described above was 65%, and the carrier was used to connect the 68-leg surface mount device, 44-leg surface mount device in each of the 6 test circuits (test circuits 1-6) described in Example 1. and resistor strings connected in series. Under the test conditions of room temperature and relative humidity of 90%, and a temperature of 60°C, the contact resistance was measured, and the measured values are shown in Figure 6. Afterwards, the relative humidity is 90%, and the temperature is 60°C under the test conditions, and the resistivity is measured after 6, 13, 349, and 1530 hours; The relative humidity is 90%, and after 1530 hours, except for only one group of contact resistance whose growth rate exceeds 10%, the ohm value of all other contact resistances changes very little.

Example 6

A conductive adhesive was prepared using three fillers of silver particles A, B and C which were the same particles A, B and C used in Example 2. Particles A and C are mixed according to the following weight percentages, that is, particle A accounts for 40%, particle B accounts for 30%, and particle C accounts for 30%, thereby forming a filler mixed with the carrier.

The vehicle consists of a single epoxy/solvent composition. The epoxy resin is an epoxy novolac resin such as "Quatrex 2010", a phenol novolac epoxy resin having a relatively high viscosity of 25,000-45,000 CPS at 25°C, commercially available from Dow Chemical Company. The solvent ethyl 2-(2-ethoxyethoxy)acetate is commercially available under the trademark "Carbitol" from Eastman Kodak Company, Rochester, NY. The above solvent is also called diethylene glycol-ethyl acetate. Hardeners (such as N-(2-cyanide)-2-ethyl, 4-methylimidazole) and coupling agents (such as γ-glycidylpropoxytrimethoxysilane) can also be included in the polymer carrier .

Prepare the conductive adhesive according to the following composition:

Composition Amount of each batch - weight percentage (%)

(standard weight unit)

Epoxy resin 14.79

Solvent 6.34

Hardener 1.18

Coupler 0.89

Total weight of epoxy resin = 23.20%

Particle A 30.72

Particle B 23.04

Particle C 23.04

Total weight of silver content = 76.8%

The volume shrinkage value of the polymeric carrier described above was 25%, and the carrier was used to connect the 68-leg surface mount device, 44-leg surface mount device in each of the 6 test circuits (test circuits 1-6) described in Example 1. and resistor strings connected in series. Under the test conditions of room temperature and relative humidity of 90%, and a temperature of 60°C, the contact resistance was measured, and the measured values are shown in Figure 7. Under the test conditions of relative humidity of 90% and temperature of 60°C, after 14, 16 and 1025 hours, the resistivity was tested respectively. As shown in the "Percentage Increase" column listed in Figure 7, after 1025 hours at 90% relative humidity, the ohmic values of all contact resistances changed very little.

Example 7

A conductive adhesive was prepared using three fillers of silver particles A, B and C which were the same as the particles A, B and C used in Example 2. Particles A, B, and C are mixed according to the following weight percentages, particle A accounts for 40%, particle B accounts for 30%, and particle C accounts for 30%, thereby forming a metallic silver filler mixed with the carrier.

The carrier comprises a mixture of two epoxy resins, Epoxy A and Epoxy B. Epoxy A is a bisphenol A epoxy resin such as "Eponol 53" described above, and the epoxy resin is a liquid phenol novolac epoxy resin such as "Quatrex 1010" described above.

The polymeric carrier may also include hardeners I and II. Hardener I is polyoxypropylene diamine, which is commercially available from Texaco Chemical Company under the designation "Jeffamine D-230". Hardener II is triethylene glycol diamine, which is commercially available from Texaco Chemical Company under the trade designation "Jeffamine EDR148".

The polymeric carrier may also include accelerators to increase the efficiency of setting. Suitable accelerators such as aliphatic amine mixtures are commercially available from Texaco Chemical Company under the designation "399". Commercially available from Texaco Chemical Company under the designation "Jeffamine T-5000".

Conductive adhesives were prepared according to the following composition:

Composition Amount of each batch - weight percentage (%)

(standard weight unit)

Epoxy resin A 13.50

Epoxy resin B 8.94

Hardener Ⅰ 2.59

Hardener II 0.36

Accelerator 0.27

Adhesion Accelerator 1.34

Total weight of epoxy resin = 27.00%

Particle A 25.20

Particle B 21.90

Granules C 21.90

Total weight of silver content = 73.00%

The volume shrinkage value of the polymeric carrier described above was 19%, and the carrier was used to connect the 68-leg surface mount device, 44-leg surface mount device in each of the 6 test circuits (test circuits 1-6) described in Example 1. and resistor strings connected in series. Under the test conditions of room temperature and temperature of 60°C and relative humidity of 90%, the contact resistance was measured, and the measured values are shown in Figure 8. Afterwards, under the test conditions that the relative humidity is 90% and the temperature is 60°C, the resistivity is measured after 15, 19, and 981 hours respectively; After 1598 hours, except for a group of contact resistance values whose growth rate exceeds 8%, the ohm values of all other contact resistances change very little.

Example 8

Conductive adhesives were prepared using conductive particle fillers of two types of conductive particles, Particles A and D. Particle A is the same as Particle A used in Example 1. Particles D are silver-plated nickel particles with an average particle size of 28 microns and an actual particle size distribution of 90% < 48.19 microns, 50% < 27.97 microns and 10% < 12.36 microns. Granules D can be selected from those manufactured by Novamet Specialty Products, Inc., 681 Law Lins Road, Wyckof, New York 07481 (201-891-7976).

Particles A and D are desirably mixed in the following weight percentages, namely 80% particle A and 20% particle D, thereby forming a filler mixed with the carrier.

The carrier is a mixture containing two epoxy resins, Epoxy A and Epoxy B. Epoxy A is a bisphenol F epoxy such as "Aratronic 5046" and Epoxy B is a liquid phenol novolac epoxy such as "Quatrex 2010".

The polymeric carrier may also include a hardener [such as N-(2-cyanoethyl)-2-ethyl, 4-methylimidazole] and a coupling agent (γ-glycidylpropoxytrimethoxysilane).

Prepare the conductive adhesive according to the following composition:

Composition Amount of each batch - weight percentage (%)

(standard weight unit)

Epoxy resin A 7.50

Epoxy resin B 7.50

Hardener 3.60

Coupler 0.90

Total weight of epoxy resin = 19.5%

Particle A 64.40

Particle B 16.10

Total weight of silver content = 80.5%

The volume shrinkage of the polymeric carrier described above was 7.6%, and the carrier was used to connect the 68-leg surface mount device, 44-leg surface mount device in each of the 6 test circuits (test circuits 1-6) described in Example 1. and resistor strings connected in series. Under the test conditions of room temperature, relative humidity of 90%, and temperature of 60°C, the contact resistance was measured, and the measured values are shown in Figure 9. Afterwards, the resistivity was measured after 119, 503, and 1146 hours under the test conditions of a relative humidity of 90% and a temperature of 60°C. As shown in the "increase percentage" column in Figure 9, at a relative humidity of 90%, after 1146 hours, except for a group of contact resistance values with a growth rate of more than 15%, the ohm values of all other contact resistances have little change .

Example 9

The conductive adhesive was prepared using conductive particle fillers of two kinds of conductive particles, namely particles A and E, the above particle A being the same as the particle A used in Example 1. Particle E is a silver-plated particle containing about 32% (by weight) silver. The particle has a Scott apparent density of 3.66 g/in ³ , a surface area of 0.22 m ² /g, and a powder resistivity of 0.4 ( m ohm·cm), the average particle size is 21μ, and the actual particle size distribution is 90%<29.3μm, 90%<19.5μm and 10%<13.9μm. Granules E can be selected from those sold under the trade designation "Cordueto-O-Fil Silver Nickel" manufactured by Potter Industries, Inc., Carlstadf, NJ.

Particles A and E were mixed in the following weight percentages, 80% of particle A and 20% of particle E, to form the filler mixed with the carrier.

The carrier mainly includes a mixture containing two epoxy resins, namely epoxy resin A and epoxy resin B. Epoxy A is a bisphenol F epoxy such as "Aratronic 5046" and Epoxy B is a liquid phenol novolac epoxy such as "Quatrex 2010".

The polymer carrier may also include a hardener [such as N-(2-cyanoethyl)-2-ethyl, 4-methylimidazole] and a coupling agent (such as γ-glycidylpropoxytrimethoxysilane).

Prepare conductive adhesive according to the following composition

Composition Amount of each batch - weight percentage (%)

(standard weight unit)

Epoxy resin A 7.50

Epoxy resin B 7.50

Hardener 3.60

Coupler 0.90

Total weight of epoxy resin = 19.5%

Particle A 64.60

Granular E 16.10

Silver content total weight = 80.5

The volume shrinkage value of the polymer carrier described above was determined to be 7.6%, and the carrier was used to connect the 68-leg surface mount device (SMD) in each of the 6 test circuits (Test Circuits 1-6) as described in Example 1, A 44-leg surface mount device and a resistor string connected in series. Under the test conditions of room temperature and temperature of 60°C and a relative humidity of 90%, the contact resistance was measured, and the measured values are shown in Figure 10. Afterwards, under the test conditions of relative humidity of 90% and temperature of 60°C, after 65, 453, and 1096 hours, the resistivities were respectively measured. As shown in the "increase percentage" column in Figure 10, under the condition of relative humidity of 90%, after 1096 hours, except for a group of contact resistance whose growth rate exceeds 14%, all other contact resistance ohmic values have little change .

Example 10

The conductive adhesive was prepared by using conductive particle fillers containing two kinds of conductive particles, namely conductive particles A and F, the above particle A being the same as the particle A used in Example 1. Particle F is a silver-coated glass sphere containing approximately 23.8% silver, having a Scott apparent density of 0.81 g/in ³ powder resistivity, willi-ohm cm, and an average particle size of 13 Micron, the actual particle size distribution is 90%<20.0 micron, 50%<12.1 micron and 10%<7.1 micron. Particle F can be selected from the particles produced by Potter Industries, Carlstadt, NJ07072, and the marketed brand is "Conducto-O-Fil silver-coated glass ball". Particles A and F were mixed in the following weight percentages, 92% of particles and 8% of particles F, to form a filler mixed with a carrier.

The carrier mainly consists of a mixture containing two epoxy resins, epoxy resin A and epoxy resin B. Epoxy A is a bisphenol F epoxy resin such as Aratronic 5046, and Epoxy B is a liquid phenol novolac epoxy resin such as Quatrex 2010.

The polymer carrier can also include common hardeners [such as N-(2-cyanoethyl)-2-ethyl, 4-methylimidazole] and coupling agents (such as γ-glycidylpropoxytrimethoxysilane) .

Prepare the conductive adhesive according to the following composition:

Composition Amount of each batch - weight percentage (%)

(standard weight unit)

Epoxy resin A 7.88

Epoxy resin B 7.88

Hardener 3.78

Coupler 0.96

Total weight of epoxy resin = 20.5%

Particle A 73.14

Particle F 6.36

Total weight of silver content = 79.5%

The volume shrinkage value of the polymer carrier was 7.6%, and the carrier was used to connect the 68-leg surface mount device (SMD) in each of the 6 test circuits (Test Circuits 1-6) described in Example 1. Surface mount devices and series connected resistor strings. Under the test conditions of room temperature, relative humidity of 90%, and temperature of 60°C, the contact resistance was measured, and the measured values are shown in Figure 11. Afterwards, the resistivity was measured after 65, 453, 1096 hours under the test conditions of a relative humidity of 90% and a temperature of 60°C. As shown in the "increase percentage" column shown in Figure 11, at a relative humidity of 90%, after 1096 hours, except for the growth rate of only the second group of contact resistance exceeding 15%, the ohm value of all other contact resistances has little change.

In some test runs of Examples 2 to 10 (results not shown), high humidity caused pooling of hot liquid water and total corrosion of the wires on the outside of the bonded joint, invalidating the test results.

Example 11

Adopt the conductive particle filler that contains two kinds of silver particles A and B to prepare conductive adhesive, particle A and particle B are identical with the particle A and B adopted in example 2, they are mixed by following weight percentage, and particle A accounts for 40%, Particle B constituted 60% to form a filler mixed with the carrier.

The carrier includes a mixture of synthetic rubber-modified epoxy resins including bisphenol F epoxy resin, such as Aratronic 5046, a bisphenol F diglycidyl ether, which has a viscosity of about 1400CPS at 25°C , the above-mentioned resin can be bought from Ciba-Geigy Company; liquid phenol novolac epoxy resin, the content of this resin is the same as that of the above-mentioned bisphenol F epoxy resin, the resin can be "Quatrex2010", and the viscosity at 52°C About 25,000-45000CPS, it can be bought from Dow Chemical Company; Butadiene acrylonitrile synthetic rubber modifier, such as Heloxy Wc-8005, has a viscosity of about 50,000-1,000 at 25°C, 000CPS, it is produced by Wilming-tom Chemical Company located in Delaware, USA.

Also can include imidazole type hardener in the polymer carrier, such as Curimid-CN, namely NC ₂ -cyanoethyl)-2-ethyl-4-methylimidazole; Thinner such as γ-butyrolactone; And coupling agent, Such as A-187, that is, γ-glycidyl propoxytrimethoxysilane.

Prepare the conductive adhesive according to the following composition:

Composition Primary content

(Ww)

Bisphenol F 5.05

(Linear) Novolak Epoxy Resin 5.05

Butadiene rubber 5.32

Hardener 3.19

Thinner 1.59

Coupler 0.80

Total Carriers = 21.0

Particle A 31.60

Particle B 47.40

Total amount of filler = 79.0

The polymer carrier has a volume shrinkage value of 10% and a bend diameter of 0.50 inches (this value was determined in the case of bending a strip approximately 4.5 mil thick around a rod of the smallest possible diameter that does not produce cracked or damaged). The above carrier was used to connect a 68-pin surface mount device (SMD), a 44-pin surface mount device and a series connected resistor string in each of the 3 test circuits described in Example 1 (Test Circuits 1-3). At room temperature and under the test conditions of 90% relative humidity and 60°C, the contact resistance was measured, and the measured values are shown in Figure 12. Then, under the test conditions of relative humidity of 90% and temperature of 60° C., the resistivity was measured after 1031 hours. As shown in the "Percentage Increase" column listed in Figure 12, after 1031 hours, all contact resistance ohmic values changed little or decreased.

Example 13

Adopt the conductive particle filler that contains two kinds of silver particles A and B to prepare conductive adhesive, particle A and B are identical with particle A and B adopted in example 2, they are mixed by following weight percentage, particle A accounts for 40%, particle B accounts for 60%, thus forming a filler mixed with a carrier.

The carrier includes an unfilled polyurethane such as Calthane NF 1300, which is available from Cal Polymers, California, USA. The above-mentioned rubber is composed of one part of aromatic isocyanate [4,4-diphenylmethane diisocyanate and about 20% (weight percent) of polymer with higher molecular weight] and three parts of butadiene homopolymer (hyroxyl A mixture of terminated polybutadiene.

A small amount of solvent, such as diethylene glycol-ether acetate [2-(2-ethoxyethoxy)]ethyl acetate, may also be included in the polymeric vehicle to adjust the viscosity.

Prepare the conductive adhesive according to the following composition:

Composition Amount per batch

(Ww)

Polyurethane elastomer 15.85

Solvent 1.05

Total Carrier Weight = 16.90

Particle A 33.24

Particle B 49.86

Total weight of filler = 83.10

The above polymeric carrier has a volume shrinkage value of 7.7% and a bend diameter of 0.25 inches (this value was determined when a 4.5 mil thick strip was bent around a rod of the smallest diameter possible without the strip being cracking and damage), the above-mentioned carrier is used to connect the 68-leg surface mount device, the 44-leg surface mount device and the series connection resistor in each circuit connected by the two test circuits described in Example 1 (Test Circuit 1-2) string. Under the test conditions of room temperature and relative humidity of 90%, and a temperature of 60°C, the contact resistance was measured, and the test values are shown in Figure 13. After that, the resistivity was measured after 429.5 hours under the test conditions of relative humidity of 90% and temperature of 60°C. As shown in the column "Increase Percentage" in Fig. 13, after 429.5 hours, all contact resistance ohmic values changed little or decreased somewhat.

Example 13

Adopt the conductive particle filler that contains two kinds of silver particles A and B to prepare conductive adhesive, particle A and B are identical with particle A and B used in example 2, they are mixed by following weight percentage, particle A accounts for 40%, particle B accounts for 60%, thus forming a filler mixed with a carrier.

Carriers include silicone resins such as "SR 900", a silicone conformal coating available from the Silicone Products Division of General Electric Company, New York, USA. The above-mentioned coating includes a 50% silicone resin solution and toluene solvent, and the viscosity of the above-mentioned solution is about 500 CPS at 25°C.

A small amount of another solvent such as Aromatic 150, a heavy aromatic solvent naphtha available from Exxon Chemical Company, Texas, USA, may also be included in the polymeric vehicle.

Prepare the conductive adhesive according to the following composition:

Composition Amount per batch

(Ww)

Silicone resin "SR 900" 22.50

Solvent "Aromatic 150" 4.50

Total carrier weight = 27.00

Particle A 29.20

Particle B 43.80

Total packing weight = 73.00

The above polymeric carrier has a volume shrinkage value of 25.0% and a bend diameter of 0.25 inches (this value was determined in the case of bending a strip of about 4.5 mil thickness around a rod of the smallest diameter possible, and the strip without cracking or damage). The carriers described above were used to connect a 68-leg surface mount (SMD), a 44-leg surface mount and series connected resistor strings in each of the 3 test circuits described in Example 1 (Test Circuits 1-3). Also in both circuits (Test Circuit 1-2), tests were performed on series connected resistors connected resistor strings. Under the test conditions of room temperature and relative temperature of 90%, and a temperature of 60°C, the contact resistance was tested, and the test values are shown in Figure 14. Thereafter, the resistivity was measured after 192.5 hours under the test conditions of a relative humidity of 90% and a temperature of 60°C. As shown in the "increase percentage" column in Fig. 14, after 192.5 hours, all contact resistance ohmic values changed little or decreased.

It is an advantage of the present invention to provide a conductive adhesive mixture which has very stable electrical conductivity and very stable electrical resistance characteristics under high humidity conditions. The reason why the present invention has the above-mentioned features is because a kind of binder with such a volume shrinkage range is provided. When the carrier volume shrinkage value is located in the volume shrinkage range, the contact between the particles can be ensured, and the particles contact with the joint surface to form a reliable joint.

Without departing from the spirit and scope of the present invention defined by the appended claims of this specification, and their legal equivalents, various improvements can be made to the above-mentioned conductive adhesive of the present invention, but the above-mentioned Alterations and modifications will be apparent to those of ordinary skill in the art.

Illustration:

NCR growth rate

INIHAL initial

RMIEMP Indoor temperature

60℃/90%RH relative humidity 90%, 60℃

Claims (29)

1. An electrically conductive adhesive for bonding surfaces to be bonded and making electrical contact between them, characterized in that the adhesive comprises a mixture containing a shrinkable Dispersed filler in an adhesive carrier, the content of the carrier can make the mixture effectively bonded to the surface, the filler includes a certain content of conductive particles, and its structure can help when the carrier solidifies. A moisture-resistant electrical contact is formed. 2. Adhesive according to claim 1, characterized in that the carrier shrinks in volume during solidification by a value of at least 6.8%. 3. The adhesive of claim 1, wherein the carrier has a volume shrinkage value in the range of about 7.5% to 65%. 4. The adhesive according to claim 3, wherein at least a portion of said conductive particles are selected from the group consisting of agglomerates, surface-impregnated particles and tabular particles. 5. The adhesive according to claim 5, characterized in that the adhesive further includes powdered conductive particles to improve the electrical contact between the particles. 6. The adhesive according to claim 5, characterized in that the thickness of the plate-shaped conductive particles is an order of magnitude smaller than its length, and the Fisher particle size (FSSS) of the particles is about 0.9-1.3 microns. The tap density is about 3.0-3.5g/cc, the Scott density is about 30-35g/in ³ , and the surface area is about 0.3-0.6m ² /g. 7. The adhesive according to claim 4, characterized in that the conductive particles of the sintered agglomerate have surface roughness, and the average particle diameter thereof is 10.6-2.0 microns. 8. The adhesive according to claim 7, characterized in that the Fisher particles of the agglomerate conductive particles measure a particle size of about 0.6 microns, a bulk density of about 1.85 g/cc, and a Scott density of about 16.7 g /in ³ , the surface area is about 1.62m ² /g. 9. The adhesive according to claim 5, characterized in that the Fisher particle size of the powdered conductive particles is about 0.75 microns, the bulk density is about 2.70 g/cc, and the Scott density is 20.1 g/in ³ , the surface area is about 1.41m ² /g. 10. The adhesive according to claim 4, characterized in that said conductive filler comprises conductive flake particles, the thickness of which is an order of magnitude smaller than its length and width, said conductive filler further comprising at least one of the following particles A sort of: (a) Conductive sintered blocks with rough surface features; (b) silver-plated nickel particles; (c) silver-coated glass spheres; and (d) fine silver particles 11. The adhesive of claim 10 wherein the silver plated nickel particles have an average particle size of about 28 microns. 12. The adhesive of claim 10, wherein the silver-plated nickel particles have a silver content of about 32% by weight, a Scott density of about 3.66g/in ³ , and a surface area of about 0.22m ² /g, the powder resistivity is about 0.4 (m ohm cm), and the average particle size is about 21 microns. 13. The adhesive of claim 9, wherein the silver-coated glass sphere has a silver content of about 23.82% by weight, a Scott density of about 0.81 g/in ³ , and a powder resistivity of about 2.63 (m ohm cm), the average particle size is about 13 microns. 14. The adhesive of claim 4, wherein said carrier is a settable polymer carrier having a volume shrinkage value of 10%. 15. The adhesive of claim 14, wherein the polymeric carrier comprises one or more epoxy resins. 16. The adhesive of claim 15, wherein said epoxy resin carrier is selected from the group consisting of: (a) Bisphenol F epoxy resin (b) Liquid phenol novolac epoxy resins; (c) Bisphenol A epoxy resin and mixtures of the above ingredients. 17. The adhesive according to claim 14, characterized in that the filler accounts for 60-90% by weight of the total weight of the carrier and the filler. 18. A method of manufacturing a moisture-resistant conductive joint, the steps comprising: The surface is coated with a conductive adhesive comprising filler particles dispersed in an adhesive carrier which shrinks upon setting; providing an amount of said carrier to render said adhesive effective ground bonding to the substrate; the filler has a certain content and has a structure that helps to form a moisture-resistant electrical contact; the shrinkage of the carrier will form the electrical contact. 19. A method of forming a moisture-resistant conductive contact, the steps comprising: Apply the adhesive according to claim 4 on the surface to solidify the carrier, so that the carrier shrinks, so that the filler particles are in a compressed state and form an anti-moisture electrical contact with the surface. 20. A method of forming a moisture-resistant electrical contact, the steps comprising: Applying the adhesive according to claim 10 to the surface, allowing the carrier to solidify, causes the carrier to shrink, so that the filler particles are in a compressed state and form a moisture-resistant electrical contact with the surface. 21. A method of forming a moisture-resistant conductive contact, the steps comprising: Applying the adhesive according to claim 5 on the surface, allowing the carrier to solidify, causing the carrier to shrink, so that the filler particles are in a compressed state and form a moisture-resistant electrical contact with the surface. 22. A method of forming a moisture-resistant conductive contact, the steps comprising: Applying the adhesive of claim 16 to the surface, allowing the carrier to set, causes the carrier to shrink, thereby placing the filler particles in a compressed state and forming a moisture-resistant electrical contact with the surface. 23. The adhesive according to claim 1, wherein said carrier is selected from the group consisting of epoxy resin modified by synthetic rubber, polyimide resin and silicone resin, and the volume shrinkage value of the carrier is about 7-25%. 24. The adhesive according to claim 23, characterized in that said filler is a mixture of plate-shaped and sintered block-shaped conductive particles, and the filler accounts for about 60-90% of the adhesive by weight. 25. The adhesive according to claim 24, wherein the filler mixture comprises about 60% by weight of flake-shaped conductive particles and about 40% by weight of sintered agglomerate conductive particles. 26. The binder according to claim 25, characterized in that the flake particles are "6" and the sintered agglomerates are "7". 27. The adhesive according to claim 25, wherein the carrier accounts for about 21% by weight of the adhesive, which includes about 5% by weight of the total weight of the adhesive. Phenol F, about 5% epoxy novolac resin, about 5% butadiene rubber, about 5% hardener, thinner and coupling agent. 28. The adhesive according to claim 25, wherein the carrier accounts for about 17% of the adhesive by weight, and the main component is polyurethane. 29. The adhesive according to claim 25, wherein the carrier accounts for about 27% by weight of the adhesive, and its main component is a mixture of silicone and toluene.

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