JPS6329886B2 - - 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. I came. 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, resin encapsulation methods were developed from the viewpoint of workability and cost during mass production, and along with this, methods using solder materials and mounting resins were taken up as an improvement method for the Au/Si eutectic method in the mounting process. I came. 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 demand for it 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 to 150℃ heat shock cycle, after hot water treatment, etc. Heat dissipation; electrical conductivity; workability; quantitative injection using a dispenser;
Ability to adapt to automation and speed-up of screen printing, stamping, etc. Curing properties: Short curing cycle using oven method, hot plate method, etc. Void: low. Reliability: There should be no defects in the moisture resistance current test, that is, there should be no change in device characteristics due to gas generated from the cured silver migration adhesive, and no corrosion of aluminum wiring due to ionic impurities such as halogen or alkali methane. Wire bonding: No deterioration in bonding performance due to gas generated from the cured product, no 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). Particularly recently, chip mounting process equipment is becoming more and more automated and faster in order to enable mass production. There is a growing demand for hardening. This completely eliminates the oven-type curing process and completes curing simultaneously during the wire bonding process performed on a hot plate, shortening the process.
It is intended to be simplified. In addition, demands for reliability tend to become even more stringent, and in the past, the amount of ionic impurities such as eluted Cl ions and Na ions in the Plessyer-Kutsker test was at a level of several hundred ppm each; Significant improvements were strongly requested. As a result of various studies by the present inventors regarding these points, the epoxy resin to be used in a conductive thermosetting resin paste consisting of silver powder, epoxy resin, curing agent, curing accelerator, and reactive diluent is as described below. The content of hydrolyzable halogen groups such as
By using a reactive diluent with a hydrolyzable halogen group content of 1000 ppm or less, preferably 600 ppm or less, the amount of halogen ions eluted from hot water in the cured product can be reduced as a mounting resin. (pressure test 20 hours) below 150ppm, preferably 80ppm
It became possible to do the following, and the reliability was significantly improved. In addition, the epoxy resin has an average functionality of 2.5 or more, the curing agent is pulverized dicyandiamide, the curing accelerator is a tertiary amine salt, and the reactive diluent is at least monofunctional. By using a resin with a boiling point of 250°C or higher and a viscosity of 10 poise/25°C or lower, it has good tack-free properties and can be used for long periods of resin supply and application (by stamping, screen printing, etc.). Above 200° to 450°C
The present invention has been achieved by making curing possible in a sufficiently fast cycle. The mounting resin composition of the present invention is dramatically superior to conventional products in terms of workability and reliability, 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 10 ppm or less, and the particle size is in the range of 0.1 to 50μ, with slightly coarse flakes or dendritic forms and slightly fine granular forms as appropriate. It is a mixture. Further, when producing silver powder, a metal soap or the like may be added as a lubricant as appropriate, 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 settle and separate, and the conductivity becomes low.If it is used more than this, the conductive performance does not improve much, but the cost increases significantly and the adhesive strength etc. decreases, so it is not desirable. . The epoxy resin used in the present invention must be liquid, have a hydrolyzable halogen group content of 600 ppm or less (preferably 300 ppm or less), and contain 2.5 or more epoxy groups per molecule. Note that the amount of ionic impurities such as halogen ions and alkali metal ions is preferably 10 ppm or less. 600ppm of hydrolyzable halogen in epoxy resin
There are various ways to achieve the following, but the first is
An example is as follows. Epoxy resin is produced by reacting polyactive hydrogen compounds such as polyhydric phenols, polybasic acids, etc. with epihalohydrin using quaternary ammonium hydroxide as a catalyst, and then ring-closing the resulting halohydrin group with an alcoholic alkali. Production method, halohydrin group remaining in epoxy resin,
A method for purifying epoxy resins in which mainly hydrolyzable halogen groups are ring-closed by heating with an equivalent amount of alcoholic alkali in an anhydrous state, and remaining halohydrin groups are reacted with an equivalent amount of fatty acid silver salt in an anhydrous state to form Agx. A method for producing an epoxy resin, in which polyphenols are previously allylized, and then the allyl group is epoxidized with an organic peracid, such as p-chlorobenzoic acid. For the purpose of the present invention, resins with a small amount of hydrolyzable halogen groups obtained by any method can be used in exactly the same manner, and therefore there are no restrictions on the method of reducing the amount. The epoxy resin used in the present invention has a hydrolyzable halogen group content of 600 ppm or less,
It is preferably 300 ppm, and may be adjusted to this level by appropriately blending two or more epoxy resins. Even if it is small in ordinary epoxy resin,
It is 600ppm or more, and usually contains 1000ppm or more. Therefore, it is not desirable for the purpose of the present invention to use ordinary commercially available epoxy resins as they are. Furthermore, the epoxy resin used in the present invention must contain an average of 2.5 or more epoxy groups per molecule. The number of epoxy groups per molecule is 2.0 as in the normal Epibis type, which has sufficient heat resistance.
This is undesirable because rapid curing cannot be achieved. However, 3
It is also possible to use a combination of a functional or higher functionality and a difunctional one to have an average functionality of 2.5 or more. Any epoxy resin that satisfies the above conditions can be used in the present invention, but the following types are preferred. Phlorogrunol triglycidyl ether,
Triglycidyl ether of trihydroxybiphenyl, tetraglycidyl ether of tetrahydrocibiphenyl, tetraglycidyl ether of tetrahydroxybisphenol F, tetraglycidyl ether of tetrahydroxybenzophenone, epoxidized novolac, epoxidized polyvinylphenol , triglycidyl isocyanurate, triglycidyl cyanurate, triglycidyl S-triazine, triglycidyl aminophenol, tetraglycidyl diaminodiphenylmethane, tetraglycidyl metaphenylene diamine, tetraglycidyl pyromellitic acid, triglycidyl 3, such as diltrimellitic acid
or higher polyfunctional epoxy resins and bifunctional epoxy resins blended therewith, such as diglycidyl resorcin, diglycidyl bisphenol A, diglycidyl bisphenol F,
Diglycidyl bisphenol S, diglycidyl ether of dihydroxybenzophenone, diglycidyloxybenzoic acid, diglycidyl phthalic acid (o, m, p), diglycidyl hydantoin, diglycidyl aniline, diglycidyl toluidine, etc. or a condensation type resin of these. In addition, special types of allyl polyphenols, such as epoxidized products of mono- to tri-nuclear compounds with peracid, which have a glycidyl ether group and a glycidyl group substituted with a nucleus, also meet the above conditions. If so, you can use it in the same way. Among these, liquid polyglycidylated products of low molecular weight polyphenols are particularly preferred in terms of reactivity, workability and physical properties. 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 necessary 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 the dicyandiamide used is preferably 350 mesh pass. If the powder is not such a fine powder, a uniform cured product cannot be obtained and there is a risk of variations in performance, which is not preferable. 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.
Salts of tertiary amines and polyhydric phenols and polybasic acids are desirable. Alicyclic superbases are trimethylene diamine, 1,
These include 8-diaza-bicyclo-(5,4,0)undecene-7, dodecahydro-1,4,7,9btetraazaphenalene, 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, hexahydrophthalic acid, trimellitic acid, adipic acid, succinic acid, Polybasic acids such as maleic acid and itaconic acid or resorcinol, pyrogallol,
These are polyhydric phenols such as hydroquinone, bisphenol A, bisphenol F, bisphenol S, and low-molecular-weight novolaks. The amount of these tertiary amine salts is preferably in the range of 0.1 to 10 parts per 100 parts (by weight, the same applies hereinafter) 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 there is a risk that the storage stability will deteriorate, so both are undesirable. Note that these tertiary amine salts tend to absorb moisture or carbon dioxide before use, which tends to cause their performance to deteriorate. Therefore, especially when used in the present invention, water absorption of 10% (by weight) is recommended. Hereinafter, 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 a resin 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 defoamers 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. The reactive diluent used in the present invention has at least one terminal epoxy group per molecule, has a boiling point of 250°C or higher,
Preferably, it has a temperature of 300°C or more, a low viscosity of 10 poise/25°C or less, and a content of hydrolyzable halogen groups of 1000 ppm or less, preferably 600 ppm or less. If the boiling point is low, when screen printing or stamping is carried out continuously for a long time, it will gradually volatilize and increase the viscosity, which will gradually deteriorate the workability over time, which is not desirable. Further, if the viscosity is higher than this, the dilution effect cannot be sufficiently achieved, which is not preferable. Generally, high boiling point epoxy compounds used as diluents are unsuitable if they have a large number of hydrolyzable halogen groups, such as glycidyl ether of polyether polyol, and for the purpose of the present invention, _C10 to C Monoglycidyl ethers of ₂₀ long-chain fatty acids are suitable because they meet all of the above conditions. Similarly, polyglycidyl ether type dimer acids are also effective. Note that a monofunctional diluent may reduce the crosslinking density of the cured product and deteriorate its performance under heat, so it is necessary to use it in as small a quantity as possible. The curing agent, curing accelerator, and reactive diluent used in the present invention all need to 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 mm 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 is centrifuged and used as a test solution. Sodium ions contained as impurities are determined from the absorbance at a wavelength of 330.2 nm using the above test solution and a flameless atomic absorption spectrometer in comparison with a blank test using a calibration curve prepared in advance. To quantify hydrolyzable chlorine in epoxy resin, dissolve 0.5 g of resin in 30 ml of dioxane, then add 1N
Heat with 5 ml of KOH-ethanol solution for 30 minutes and reflux, then calculate 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, and reactive diluent are weighed out and kneaded to form a uniform solution. In this case, for kneading, an appropriate combination of conventional stirring tanks, crushers, 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. This is undesirable as the increase in temperature will significantly reduce the shelf life. The conductive resin paste of the present invention has the following features compared to conventional products. (1) The amount of ionic impurities such as chlorine ions and sodium ions eluted from the cured product according to the pressure test (20 hours) is at a much lower level. Therefore, the corrosion caused by ionic impurities in the aluminum wiring during the humidity resistance current test has been significantly reduced, and in terms of reliability, it is far superior to conventional products. (2) It is possible to cure the chip in a sufficiently short cycle on a hot plate, which greatly shortens the chip mounting process. However, curing in an oven is of course possible, and curing is possible by any method. (3) It has good tack-free properties, and can be used not only for injection using a dispenser, but also for long-term automatic operations such as screen printing and stamping. (4) Other considerations include mounting strength, heat dissipation, conductivity,
Its performance is comparable to that of conventional products in that it does not emit harmful gases. Therefore, the conductive resin paste of the present invention has 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 200℃ for 30 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 as the test solution. 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 The epoxy resin was epoxidized phenol borax (number average molecular weight: 540, epoxy equivalent: 170, number of epoxy groups/molecule: 3.1, hydrolyzable chloro group;
580ppm) 70 parts, the reactive diluent is glycidyl esters of _C14 long chain fatty acids (hydrolyzable chlorine groups)
900 ppm) 30 parts, 4.0 parts of dicyandiamide, which had been pre-pulverized to 350 mesh pass as a hardening agent, and 1,8 diaza-bicyclo (5,4,
0) 0.5 part of undecene-7 resorcinol salt and 0.01 part of a fluororesin antifoaming agent are stirred to form a uniform dispersion.
Further, 400 parts of silver powder is added and kneaded using a crusher, and finally 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 degassed 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 in a heating oven at 200°C for 120 minutes. The performance of various mounting resins is shown in Table 1. Note that when the above-mentioned epoxy resin is used as commercially available without purification, the amount of hydrolyzable chloro groups is 1200 ppm. If this is used as is, the amount of chlorine ions after hot water extraction will be 210 ppm.
This value is undesirable for precision electronics devices from the viewpoint of reliability. Example 2 The epoxy resin was an Epibis liquid epoxy resin (number average molecular weight: 380, epoxy equivalent: 190, number of epoxy groups/molecule: 2.0, hydrolyzable chlorine group;
200ppm) and triglycidyl ether of phloroglucin (number average molecular weight: 360, epoxy equivalent;
130, number of epoxy groups/molecule; 2.7, hydrolyzable chlorine group; 700 ppm) in a ratio of 1.0/3.0. The reactive diluent, curing agent, curing accelerator, and antifoaming agent are the same as in Example 1. The formulation, paste properties, curing conditions, and performance of the cured product are shown in Table 1. Example 3 Epoxy resin is epoxidized allylated bisphenol F with peracid (number average molecular weight: 400,
Epoxy equivalent: 125, number of epoxy groups/molecule;
A mixture of 3.0, hydrolyzable chloro group (absent) and the epoxidized phenol novolak of Example 1 in a ratio of 1.0/1.0 is used. The curing agent, curing accelerator, and antifoaming agent are the same as in Example 1. The formulation, paste properties, and performance of the cured product are shown in Table 1. Comparative Example All other raw materials are the same as in Example 1 except that phenyl glycidyl ether is used as the reactive diluent. The formulation, paste properties, curing conditions, and properties of the cured product are shown in Table 1. The tack-free properties deteriorated, making it impossible and undesirable to operate screen printing and stamping continuously for a long time.

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Claims (1)

[Claims] 1. A conductive resin paste consisting of silver powder, liquid epoxy resin, curing agent, curing accelerator, and reactive diluent, in which the epoxy resin has a hydrolyzable halogen group content of 600 ppm or less (by weight), and the epoxy resin has an average of 2.5 or more per molecule,
The curing agent is dicyandiamide, the curing accelerator is a tertiary amine salt, and the reactive diluent has at least one epoxy group per molecule, has a boiling point of 250°C or higher, and 10 poise/25°C or lower. A conductive resin paste having a viscosity of 1,000 ppm or less, and a content of hydrolyzable halogen groups of 1000 ppm or less.