JPH0456849B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a conductive thermosetting resin paste made of silver powder and liquid epoxy resin. More specifically, the present invention relates to a resin composition for solvent-free one-component mounting. Due to recent remarkable developments in the electronics industry, it has evolved into transistors, ICs, LSIs, and super LSIs.
As the degree of circuit integration in these semiconductor devices rapidly increases, mass production becomes possible, and as the prices of semiconductor products using these devices fall, improving workability and reducing costs in mass production become important issues. It's here. Conventionally, it has been common practice to bond semiconductor elements to substrate conductors and lead frames using the Au-Si eutectic method, and then seal them with a hermetic seal to produce semiconductor products. However, due to workability and cost considerations during mass production, a resin encapsulation method was developed, and as a result, an improved method of the Au/Si eutectic method in the mounting process was developed.
Methods using solder materials and mounting resins have begun to be taken up. However, the disadvantages of the soldering method include low reliability and easy contamination of the device's electrodes.
Its use is limited to power transistors and power IC elements that require high thermal conductivity. Mounting resin, on the other hand, has superior workability compared to the soldering method, and is superior to Au/Si methods in terms of characteristics such as reliability and heat-resistant adhesion, and its popularity is rapidly increasing. It is being done. Recently, chip mounting equipment has become more automated and faster, and the requirements for the characteristics necessary for one-component mounting resins that meet this trend are becoming more stringent. The properties necessary for a mounting resin are as follows. Mount strength: When heated to 350℃, -65~150℃ heat shock cycle, after hot water treatment, etc. Heat dissipation properties Electric conductivity Workability: quantitative injection using a dispenser,
Screen printing properties, stamping properties, etc. Curability: Excellent curing properties using oven method, hot plate method, etc. Boyd: Low. Reliability: There should be no defects in the moisture resistance current test, such as silver migration, changes in device characteristics due to gas generated from cured adhesive, corrosion of aluminum wiring due to ionic impurities such as halogens and alkali metals, etc. Wire bonding properties: Deterioration in bonding properties due to gas generated from cured products, contamination due to bleeding, etc. Pellet crack: Good buffer against stress caused by the difference in thermal expansion with the lead frame (especially in the case of copper alloy). In particular, chip mounting process equipment has recently become more automated and faster in order to enable mass production, and for this purpose, in addition to streamlining resin application through screen printing and stamping, the hot plate method has been developed. As the curing process began to take effect, a short cycle on a hot plate was required. This completely eliminates the oven curing process and replaces the wire bonding process.
When the curing is carried out on a hot plate at 300 to 450°C, curing is completed at the same time, thereby shortening and simplifying the process. Reliability requirements also tend to become more stringent, and in the past, the amounts of ionic impurities such as Cl ions and Na ions in the Pressure-Schucker test were at the level of several hundred ppm each; Broad improvements were strongly requested. As a result of various studies on these points, the present inventors found that liquid alicyclic epoxy resins and glycerinase epoxy resins are used in solvent-free, conductive resin pastes consisting of silver powder, liquid epoxy resin, curing agents, and curing accelerators. It is a mixture with a gel-type polyfunctional epoxy resin, and contains a hydrolyzable halogen group of 300 ppm or less (by weight, the same applies hereinafter).The hardening agent is finely powdered dicyandiamide, and the hardening accelerator is finely powdered dicyandiamide. By using a salt of a tertiary amine, the above conditions can be satisfied, leading to the present invention. In other words, since the composition of the present invention is a 100% resin-based composition that does not contain any volatile substances in principle, it can be injected in a fixed amount using a dispenser, and the viscosity does not change even after long periods of screen printing and stamping operations. is extremely small and has excellent tack-free properties for an extremely long time. On the other hand, it can be cured within 120 minutes in an oven at 300℃ or on a hot plate at 350℃.
It is excellent because it can be cured within 30 seconds. Therefore, the mounting resin composition of the present invention is revolutionary in terms of workability and reliability compared to conventional products, and fulfills a long-held desire in the electronics industry. . The silver powder used in the present invention includes halogen ions,
The content of ionic impurities such as alkali metal ions is preferably 10 ppm or less, and the particle size is 0.1 to 50μ.
If necessary, it is a mixture of slightly coarse flakes or dendritic materials and slightly fine granular materials. Furthermore, a surfactant such as a metal soap may be added as a lubricant when producing silver powder, but in this case it is preferable to remove it in advance by washing with hot water or the like. Washing is also effective in removing contamination from the surface of silver particles and in activating it, but care must be taken since the particle size distribution may change considerably. The mixing ratio of silver powder in the present invention is preferably 70 to 95% (by weight, the same applies hereinafter) to the composition. If the amount is less than this, it is undesirable because it becomes easy to sediment and separate, and the conductivity becomes low.
Even if it is used in excess, the conductivity does not improve much, but the cost increases significantly, and the adhesive strength decreases significantly, which is not desirable. The epoxy resin used in the present invention is a mixture of a liquid alicyclic epoxy resin and a glycidyl type polyfunctional epoxy resin, and preferably contains 300 ppm or less of hydrolyzable halogen groups.
It is 200ppm or less. In general, liquid alicyclic epoxy resins do not use epihalohydrin as a raw material, so they essentially do not contain halogen groups as impurities. On the other hand, glycidyl-type epoxy resins use epihalohydrin as a raw material, so they contain a considerable amount of halogen groups as impurities, and typically contain 100 ppm or more of hydrolyzable halogen groups. For the purposes of the present invention, it is desirable that the amount is 1000 ppm or less, preferably 600 ppm or less. In the present invention, a mixture of both types of epoxy resins has a hydrolyzable halogen group content.
It is necessary that the content be 300 ppm or less in order to improve reliability as a mounting resin composition. As the alicyclic epoxy resin used in the present invention,
Epoxycyclohexylmethyl-epoxycyclohexanecarboxylic acid ester, bis(epoxycyclohexylmethyl) succinic acid, adipic acid,
Diesters of aliphatic dibasic acids such as sebacic acid,
These include vinyl cyclohexene dioxide, dicyclopentadiene dioxide, and lower alkyl derivatives thereof. Since the epoxy group of the alicyclic epoxy resin is not a terminal epoxy group but an internal epoxy group, acid anhydrides are particularly effective as curing agents, but amines are not so effective. However, when a glycidyl-type polyfunctional epoxy resin is used in combination as in the present invention, this becomes the starting point for ring-opening polymerization at high temperatures of 250°C or higher, and the curing reaction is smooth due to the copolymerization of both. It is thought that this will progress to. That is, although internal epoxy groups alone do not cure sufficiently with dicyandiamide, when they coexist with terminal epoxy groups, copolymerization between the two occurs, resulting in good curing. For the purpose of the present invention, epoxycyclohexylmethyl-epoxycyclohexane carboxylic acid ester type is particularly preferred since it has a high boiling point and low viscosity. Since the alicyclic epoxy resin is used, the stability at room temperature is superior to that of the glycidyl type, and a product with particularly excellent tack-free properties can be obtained. The glycidyl type epoxy resin used in the present invention needs to contain 2.5 or more epoxy groups per molecule. It is not desirable that the number of epoxy groups per molecule is 2.0 as in the usual Epivis type because sufficient heat resistance and fast curing properties cannot be obtained. However, a trifunctional or higher functionality and a bifunctional one may be appropriately blended to have an average functionality of 2.5 or more. As the glycidyl type epoxy resin used in the present invention, any glycidyl type epoxy resin can be used as long as it satisfies the above conditions, but the following types are particularly preferred. Phloroglucinol triglycidyl ether, triglycidyl ether of trihydroxybiphenyl, tetraglycidyl ether of tetrahydroxybiphenyl, tetraglycidyl ether of tetrahydroxybisphenol F,
Tetraglycidyl ether of tetrahydroxybenzophenone, epoxidized novolak, epoxidized polyvinylphenol, triglycidyl isocyanurate, triglycidyl cyanurate, triglycidyl S-triazine, triglycidyl aminophenol, tetraglycidyl diaminodiphenyl Tri- or more polyfunctional epoxy resins such as methane, tetraglycidyl metaphenylene diamine, tetraglycidyl pyromellitic acid, triglycidyl trimellitic acid, and bifunctional epoxy resins blended therein;
For example, diglycidyl resorcin, diglycidyl bisphenol A, diglycidyl bisphenol F, diglycidyl bisphenol S, diglycidyl ether of dihydroxybenzophenone, diglycidyloxybenzoic acid, diglycidyl phthalic acid (o, m, p), diglycidylhydantoin, diglycidylaniline, diglycidyltoluidine, etc., or a condensation type resin thereof. In addition, as a special type, for example, those having glycidyl ether groups and nuclear-substituted glycidyl groups, such as epoxidized products of allylated polyphenols mainly composed of mono- to trinuclear bodies, by peracid, also meet the above conditions. If it is fulfilled, it can be used in the same way. In any type of epoxy resin used in the present invention, it is preferable that the content of ionic impurities such as halogen ions and alkali metal ions is 10 ppm or less. The curing agent used in the present invention needs to be latent, and dicyandiamide is most suitable. However, dicyandiamide is difficult to dissolve in resin, so if it is coarse, it may settle and become unevenly dispersed.
Since there is a risk of non-uniform curing, it is desirable that the material be finely pulverized, preferably wet-pulverized, so as to be uniformly dispersed. It is not preferred to use dicyandiamide as a solution since a volatile solvent will be included in the composition. The particle size of dicyandiamide used is 350
It is preferable that the material is made of mesh pass; if it is not such fine particles, a uniform cured product cannot be obtained;
This is not preferable because it may cause variations in performance. The above-mentioned pulverization is essential for improving the reliability of mounting resin. The curing accelerator used in the present invention is a salt of a tertiary amine, and at least one selected from the group of dimethylbenzylamine, tris(dimethylaminomethyl)phenol, alicyclic superbases, and imidazoles.
Desirably, it is a salt of a tertiary amine and a polyhydric phenol or a polybasic acid. Alicyclic superbases are trimethylene diamine, 1,
8-diazabicyclo(5,4,0)undecene-
7, dodecahydro-1,4,7,9-tetraazaphenarene, and the like. Imidazoles are those in which a substituent such as methyl, ethyl, propyl, a long-chain alkyl group up to _C17 , or a phenyl group is introduced at the 2- and/or 4-position. Those that form salts with these tertiary amines include phthalic acid (o, m, p), tetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, dimer acid, hexahydrophthalic acid, trimellitic acid, adipic acid, succinic acid, maleic acid,
polybasic acids such as itaconic acid, or resorcinol,
These are polyhydric phenols such as pyrogallol, hydroquinone, bisphenol A, bisphenol F, bisphenol S, and low-molecular-weight novolaks. The amount of these tertiary amine salts is desirably in the range of 0.1 to 10 parts per 100 parts (by weight, hereinafter the same) of the epoxy resin. If the amount is less than this, the accelerating effect will be insufficient, and if it is more than this, the curing will not be promoted so much, but the storage stability will deteriorate, so both are undesirable. Note that these tertiary amine salts tend to absorb moisture and carbon dioxide before use, which tends to deteriorate their performance. It is preferable that the amount of CO ₂ gas absorbed is 5% or less. Once it absorbs water,
Since it is difficult to sufficiently purify CO ₂ gas, it is generally not preferable to purify it before use. In order to stabilize the curability of the mount resin, it is preferable to use one within the above range. In the present invention, a defoaming agent may be used as appropriate. As the defoaming agent, silicone-based, fluorine-based, or other types may be used. In any case, it is preferable that aromatic low-boiling point solvents are not included as much as possible. Also, it is preferable that the material is not silicone-based so as not to cause contact failure. Further, if necessary, a surface treatment agent such as a silicone type or a titanate type may be used in combination. This significantly improves quality resistance. It is desirable that the curing agent, curing accelerator, reactive diluent, etc. used in the present invention contain ionic impurities such as Cl ions and Na ions at 10 ppm or less. However, these raw materials essentially do not contain hydrolyzable halogen groups like epoxy resins, nor do they contain these ionic impurities, and can be purified by normal purification methods such as distillation and recrystallization. Therefore, one suitable for the purpose of the present invention can be obtained. The test method for ionic impurities is as follows. For chlorine ions, shake 15 g of a liquid sample with 20 ml of pure water for 2 hours, then centrifuge the aqueous layer and use it as a test solution. Next, test solution
Collect 15 c.c. with a whole pipette, add 4 ml of 6% iron alum aqueous solution and 2 ml of 0.3% thiocyanic acid/mercury ethanol solution, and dilute with pure water until the volume reaches 25 ml. The absorbance of the obtained test solution at a wavelength of 460 nm is measured using a spectrophotometer, and the concentration of chlorine ions contained as impurities is determined using a calibration curve prepared in advance in comparison with a blank test. For epoxy resins, mounting resin compositions, curing agents, etc., in the case of viscous liquids or solids, uniformly dissolve 15 g of the sample in 30 ml of toluene, and add 100 mL of pure water.
After shaking for 2 hours, the aqueous layer was centrifuged for detection, and the same procedure was followed. Sodium ions contained as impurities are determined from the absorbance of the above test solution at a wavelength of 330.2 nm using a flameless atomic absorption spectrometer, using a calibration curve prepared in advance for comparison with a blank test. To quantify hydrolyzable chlorine in epoxy resin, dissolve 0.5 g of resin in 30 ml of dioxane, then add 1N
Heat under reflux with 5 ml of KOH-ethanol solution for 30 minutes, then measure the amount of chlorine ions generated.
Determined by titration with _0.01AgNO3 . This value is defined as the amount of hydrolyzable chlorine. The conventional measurement method was to heat and reflux the 0.1N KOH methanol solution for 15 minutes, but this method is not preferable for the purposes of the present invention because it yields an underestimate of the amount of hydrolyzable chlorine. The manufacturing process of the mounting resin composition of the present invention is as follows. First, predetermined amounts of epoxy resin, curing agent, curing accelerator, etc. are weighed out and kneaded to form a uniform solution. In this case, for kneading, an appropriate combination of conventional stirring tanks, picklers, triple rolls, ink mills, etc. may be used. Next, a predetermined amount of silver powder is weighed out and kneaded with the resin solution to form a completely uniform paste. In this case as well, a stirring tank, a crusher, three rolls, etc. are used in combination as appropriate. Next, the paste-like resin composition is weighed and distributed into predetermined containers, and defoamed in a vacuum chamber to obtain a product. In this case, if the mounting resin layer is thick, it will not be possible to remove bubbles sufficiently, so it is preferable to make the layer as thin as possible. The resin composition thus obtained needs to be stored and transported at a temperature of -15°C or lower. If the temperature is higher than this, the shelf life will be significantly reduced, which is not preferable. The conductive resin paste of the present invention has the following features compared to conventional products. (1) High purity Since we use a high proportion of resin that essentially does not contain hydrolyzable chlorine groups,
The amount of ionic impurities, including hydrothermally decomposable ones, is extremely low. Therefore, the corrosion of the aluminum wiring during the moisture resistance current test has been significantly reduced, and reliability has further improved. (2) Good tack-free property. It has good stability at room temperature and can be used for screen printing, stamping, etc. for long periods of time. (3) Fast curing at high temperatures. Rapid curing is possible within 30 seconds at 350℃ on a hot plate. (4) Strong adhesive strength at high temperatures. The mount strength is particularly high at high temperatures above 350℃. (5) Other performances such as heat dissipation, electrical conductivity, low voids, no silver migration, no contamination by generated gas, no failures such as pellet cracks, etc. are comparable to conventional products. Therefore, the conductive resin paste of the present invention is of extremely high industrial value and meets the wishes of the electronics industry, which has recently become increasingly demanding in performance. The method for measuring hydrothermally decomposable chlorine ions using the Plessyer Kutsker test is as follows. Cure the mounting resin at 300℃ for 60 minutes,
Next, the cured product is pulverized. 2g of the obtained powder sample
Add 3 ml of ethanol to the decomposition crucible and soak thoroughly. Next, add 40ml of pure water, seal completely and treat at 125℃ for 20 hours. After treatment, centrifuge if necessary, and use the supernatant for detection. The chloride ion concentration and sodium ion concentration in the test solution are determined according to the above method. Examples will be described below. Example 1 Alicyclic epoxy resin is 3,4 epoxycyclohexylmethyl/3,4 epoxycyclohexane carboxylic acid ester (viscosity: 4 poise/25°C, epoxy equivalent: 135, number average molecular weight: 280, number of epoxy groups/ Molecule; 2.0, no hydrolyzable chloride) 80
Glycidyl type polyfunctional epoxy resin is epoxidized phenol novolak (number average molecular weight: 680, epoxy equivalent: 180, number of epoxy groups/molecule: 3.6, hydrolyzable chlorine group: 900 ppm)
20 parts, 5.0 parts of pre-pulverized dicyandiamide of 350 mesh pass as a hardening agent, 0.5 parts of resorcinol salt of triethylenediamine as a hardening accelerator,
Stir 0.01 part of a fluororesin antifoaming agent to make a uniform dispersion. Furthermore, 400 parts of silver powder was added and kneaded using a grinder.
Finally, it is passed through three rolls to obtain a uniform paste-like mounting resin composition. The resulting paste-like mounting resin composition is spread in a vat to a liquid thickness of 20 mm or less, and defoamed in a vacuum chamber at room temperature under high vacuum of 5 mmHg or less. The defoamed resin composition is automatically supplied quantitatively onto the lead frame by screen printing or stamping to mount the chip. The resin is cured by leaving it on a hot plate at 350°C for 30 seconds. The performance of various mounting resins is shown in Table 1. In addition, in the above epoxy resin, do not use a glycidyl type polyfunctional epoxy resin together.
It is not desirable to use only an alicyclic epoxy resin because it is difficult to cure it with the above-mentioned curing agent and curing accelerator. Example 2 The same alicyclic epoxy resin as in Example 1 was used, and the glycidyl type polyfunctional epoxy was triglycidyl ether of phloroglucin (number average molecular weight: 370, epoxy equivalent: 135, number of epoxy groups/molecule; 2.6, hydrolyzable chlorine group; 800ppm)
Use. The curing agent, curing accelerator, and antifoaming agent are the same as in Example 1. The formulation, paste form, curing conditions, and performance of the cured product are shown in Table 1. Comparative Example Both the alicyclic epoxy resin and the glycidyl type polyfunctional epoxy resin are the same as in Example 1. Methyltetrahydrophthalic anhydride was used as a curing agent, and pentamethylene diethylene triamine was used as a curing accelerator. The formulation, paste properties, curing conditions, and performance of the cured product are shown in Table 1. In this case, since the curing agent is volatile, it is difficult to cure at high temperature in a short time, and the temperature is 80 to 120℃.
An extremely long curing cycle of more than 10 hours is required.

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Claims (1)

[Claims] 1 A conductive resin composition consisting of silver powder, a liquid epoxy resin, a curing agent, and a curing accelerator, where the liquid epoxy resin is a mixture of a liquid alicyclic epoxy resin and a glycidyl type polyfunctional epoxy resin. A conductive resin paste further characterized in that the content of hydrolyzable halogen groups is 300 ppm (by weight) or less, the curing agent is dicyandiamide, and the curing accelerator is a tertiary amine salt.