JPH0619078B2 - Conductive resin paste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is a conductive resin paste composed of silver powder, an epoxy resin, a curing agent, and a dimethylsiloxane compound that is a flexibility-imparting agent, and is used for semiconductors such as IC and LSI. The present invention relates to a conductive resin paste for adhering an element with a metal frame or the like. More specifically, a large chip such as an IC is bonded to a copper frame, and the characteristics of the IC such as a chip crack or a warp of the chip due to a difference in thermal expansion coefficient between the large chip and the copper frame during the heat treatment in the assembly process of the IC or the like. The present invention relates to a conductive resin paste that has excellent reaction relaxation characteristics and that prevents defects.

[Prior art]

With the recent remarkable development of the electronics industry, it has evolved into transistors, ICs, LSIs, and ultra-LSIs, and the degree of integration of circuits in these semiconductor elements has rapidly increased and mass production has become possible. With the spread of products, improvement of workability and cost reduction in mass production have become important problems. Conventionally, a semiconductor element is usually bonded to a conductor such as a metal frame by the Au-Si eutectic method and then sealed by a hermetic seal to obtain a semiconductor product. However, a resin sealing method has been developed from the viewpoint of workability during mass production and cost, and is now generalized. Along with this, a method using a solder material or a conductive resin paste, that is, a mounting resin has been taken up as an improvement of the Au-Si eutectic method in the mounting step. However, the solder method has low reliability, It is disadvantageous in that the electrodes of the device are easily contaminated, and its use is limited to devices such as power transistors and power ICs that require high thermal conductivity. On the other hand, the mounting resin is superior to the solder method in workability and reliability, and the demand for it is rapidly increasing.

More recently, due to the higher integration density of ICs and the like, the size of the chip has been increased. On the other hand, the 42 alloy frame, which is the lead frame that has been conventionally used, is expensive. Therefore, the copper frame is used for the purpose of cost reduction. It is getting started. When the size of a chip such as an IC becomes larger than about 4 to 5 mm square, heating during the assembly process of the IC causes a difference between the coefficient of thermal expansion of the chip and the coefficient of thermal expansion of the copper frame. When the -Si eutectic method is used, defective characteristics due to cracks and warpage of chips have become a problem. That is, the coefficient of thermal expansion of silicon, which is the material of the chip, is 3 × 10 ^-6 / ° C, whereas it is 8 × 10 ^-6 / ° C in the 42 alloy frame, but it is 20 × 10 ⁶ in the copper frame. ^-6 /
This is because it becomes as large as ℃. On the other hand, it is conceivable to use a mounting resin as the mounting method, but with the conventional epoxy resin paste, since the thermosetting resin is three-dimensionally cured, the elastic modulus is large, and the distortion between the chip and the copper frame is large. I didn't absorb it. On the other hand, the linear polymer type polyimide resin system has a smaller elastic modulus than the epoxy resin and the warpage of the chip is improved. However, in order to use a polyimide resin as a mounting resin, N-methyl-2-pyrrolidone, N.M. It must be dissolved in a large amount of polar solvent such as N-dimethylformamide to reduce the viscosity. The amount of solvent at this time is more than 30% by weight in the mount resin, and when it is used for bonding the chip and metal frame, voids are generated in the cured product as a trace of the solvent when curing and heating, and adhesion It is not preferable in terms of reliability, as it causes a decrease in strength, poor electrical and thermal conductivity.

For this reason, there has been a strong demand for a conductive resin paste that is excellent in applied relaxation characteristics such as absorbing the strain of a chip and a copper frame, and that is excellent in reliability without voids in a cured product.

[Object of the Invention]

The inventors of the present invention have found that even if a large chip such as an IC and a copper frame are combined, a characteristic defect of the IC due to a chip crack or a warp of the chip does not occur, and a void in a cured product that causes a defective reliability does not occur. As a result of diligent research to obtain a conductive resin paste, a conductive resin paste obtained by adding a specific dimethylsiloxane compound as a flexibility-imparting agent to an epoxy resin has a small elasticity of the cured product and It was found that the strain due to the difference in the coefficient of thermal expansion from the copper frame is absorbed and the applied relaxation is excellent, and that voids do not occur in the cured product, and the present invention has been completed.

The purpose is to provide a conductive resin paste that satisfies electrical characteristics, mechanical characteristics, impurity concentration, and other characteristics as a mounting resin, has excellent reliability, and has excellent stress relaxation characteristics. To provide.

[Structure of Invention]

The present invention provides a conductive resin paste comprising silver powder (A), epoxy resin (B), curing agent (C) and flexibility-imparting agent (D), wherein the flexibility-imparting agent has a carboxyl group of 0.5 to 0.5.
A dimethylsiloxane compound having 10% by weight and a number average molecular weight of 1,200 to 25,000, (A), (B),
The weight ratio of (C) and (D) is (A) / {(B) + (C)
+ (D)} = 60/40 to 90/10 and {(B) + (C)}
/(D)=100/0.5 to 100/20, which is a conductive resin paste.

The silver powder used in the present invention preferably has a content of ionic impurities such as halogen ions and alkali metal ions of 10
It is desirable to be less than ppm. Further, as the particle size, flaky, dendritic or spherical particles are used. It is also possible to use a mixture of relatively coarse silver powder and fine silver powder, and various shapes may be appropriately mixed.

The epoxy resin used in the present invention may be an ordinary epoxy resin, but the content of hydrolyzable halogen groups is preferably 500 ppm or less. The following types are used as the type.

Phloroglucinol triglycidyl ether, trihydrooxybiphenyl triglycidyl ether, tetrahydroxybiphenyl tetraglycidyl ether, tetrahydroxybisphenol F tetraglycidyl ether, tetrahydroxybenzophenone tetraglycidyl ether, epoxidized novolak, epoxidation Polyvinylphenol, triglycidyl isocyanurate, triglycidyl cyanurate, triglycidyl S-triazine, triglycidyl aminophenol, tetraglycidyl diaminodiphenylmethane, tetraglycidyl pyromellitic acid, triglycidyl trimellitic acid, diglycidyl Resorcin, diglycidyl bisphenol A, diglycidyl bisphenol F, diglyce Diyl bisphenol S, diglycidyl ether of dihydroxybenzophenone, diglycidyl oxybenzoic acid, diglycidyl phthalic acid (omp); diglycidyl hydantoin, diglycidyl aniline, diglycidyl toluidine, etc. Can be used alone or in combination of two or more.

A low-viscosity epoxy resin generally called a reaction diluent may be used in combination with the above epoxy resin. For example, cycloaliphatic epoxy compounds of vinyl cyclohexene dioxide, polyolefin epoxides such as diglycidyl phenyl glycidyl ether and divinylbenzene diepoxide, glycidyl amines such as diglycidyl aniline and diglycidyl toluidine, butyl glycidyl ether,
Examples thereof include glycidyl ethers such as phenyl glycidyl ether and cresyl glycidyl ether, and other glycidyl esters.

The curing agent used in the present invention may be an ordinary one, and includes polyhydric phenols, aromatic polybasic acids, aromatic polyamines and the like.

As the polyphenols, an amorphous resinous substance which is an initial condensate of phenols and aldehydes and contains as little free phenol as possible is preferable. For example, a low molecular weight liquid novolak mainly composed of dinuclear and trinuclear bodies obtained by reacting monohydric phenols such as phenol, cresol and xylenol with formaldehyde in dilute aqueous solution under strong acidity and dihydric phenols Examples thereof include initial condensates under acidic conditions with polyfunctional aldehydes such as acrolein and glyoxal, and initial condensates under acidic conditions with polyhydric phenols such as resorcin, catechol and hydroquinone and formaldehyde.

As the aromatic polybasic acid, there are polybasic acids such as pyromellitic anhydride and trimellitic anhydride, and 2 to 3 thereof.
A polybasic acid derivative in which the molecule is linked by an ester bond with a difunctional or trifunctional polyol, or a difunctional acid anhydride such as maleic anhydride, phthalic anhydride, endomethylenetetrahydrophthalic anhydride, or hexahydrophthalic anhydride. Examples thereof include a eutectic mixture with the above polybasic acid.

These curing agents may be used in combination of two or more, if necessary.

The flexible additive used in the present invention has a carboxyl group of 0.5.
It is a dimethylsiloxane compound having a number average molecular weight of 1,200 to 25,000 and having a content of ˜10% by weight.

It is well known that a dimethylsiloxane compound generally has a small elastic modulus and an excellent stress relaxation property. However, the adhesiveness and moisture resistance were poor, and it could not be used as a mounting resin. On the other hand, the epoxy resin is excellent in adhesiveness and moisture resistance, but inferior in stress relaxation property.

The present invention is to add a dimethylsiloxane compound having excellent stress relaxation property to an epoxy resin having excellent adhesiveness and moisture resistance. At this time, the dimethylsiloxane compound may have a carboxyl group. If necessary, this functional group reacts with the epoxy resin to form a uniform cured product, and a resin having a small elastic modulus, excellent stress relaxation property, and excellent adhesiveness and moisture resistance can be obtained.

Having a carboxyl group in the dimethylsiloxane compound,
It is an important point of the present invention to react with the epoxy resin, and if the epoxy resin does not have a functional group that reacts with the epoxy resin, the epoxy resin and the dimethylsiloxane compound are separated in the paste resin of the mounting resin, which causes workability. It becomes unsuitable, the cured product is not uniform, the adhesiveness is low, and the moisture resistance is poor.

Furthermore, it is necessary that the proportion of carboxyl groups in the dimethylsiloxane compound is 0.5 to 10% by weight. If this proportion is less than 0.5% by weight, the amount of functional groups is too small, so it is sufficient for the epoxy resin. The cured product does not become uniform without reacting, and the adhesiveness and moisture resistance decrease. On the other hand, when the proportion of carboxyl groups exceeds 10% by weight, the amount of functional groups is too large and the crosslink density of the cured product becomes high when it reacts with the epoxy resin, resulting in a high elastic modulus and stress relaxation characteristics of the dimethylsiloxane compound. Is not exhibited, and the stress relaxation property of the cured product decreases.

Further, the number average molecular weight of the dimethylsiloxane compound used here must be 1,200 to 25,000.
As the molecular weight of the dimethylsiloxane compound increases, its stress relaxation property improves, but if the number average molecular weight exceeds 25,000, the compatibility with the epoxy resin in the paste state deteriorates, causing separation, which makes it unsuitable for workability. However, the cured product is not uniform and the adhesiveness and moisture resistance are poor. On the other hand, when the number average molecular weight of the dimethylsiloxane compound is less than 1,200, the stress relaxation property is insufficient because the molecular weight is too small.
The stress relaxation property of the cured product decreases.

The silver powder (A) of the conductive resin paste and the epoxy resin (B) which is a resin component, the curing agent (C), and the flexibility-imparting agent (D) in the present invention have a weight ratio of (A) / {(B) +. (C) +
(D)} = 60/40 to 90/10 is preferable, and even if the proportion of silver powder (A) is higher than this, improvement in electrical conductivity cannot be obtained for the added amount, and the cost is also high. . On the other hand, when the amount of the silver powder (A) is less than this range, the electrical conductivity, which is an important characteristic of the conductive resin paste, decreases.

The weight ratio of the epoxy resin (B), the curing agent (C) and the flexibility-adding agent (D) in the resin component is {(B) + (C)} /
(D) = 100 / 0.5 to 100/20 is preferable, and when the ratio of the flexibility-imparting agent (D) is increased, the drawbacks of the dimethylsiloxane compound, that is, the decrease in adhesion and moisture resistance, occur. On the other hand, when the amount of the flexibility-imparting agent (D) is less than this ratio range, the stress relaxation property which is a characteristic of the dimethylsiloxane compound is not imparted to the cured resin paste for mounting.

Further, in the present invention, if necessary, a curing accelerator, a defoaming agent, etc. may be added. Further, for adjusting the viscosity, a solvent may be added to the cured product within the range where voids do not occur.

The manufacturing process of the conductive resin paste is as follows.

The silver powder (A), the epoxy resin (B), the curing agent (C), the flexibility-imparting agent (D) are weighed, and if necessary, a curing accelerator, a defoaming agent, a solvent, etc. are added to the stirrer, A pestle, a mortar, three rolls, a kneader, etc. are used alone or in appropriate combination to form a uniform paste.

As a method of using the conductive resin paste of the present invention, it can be applied to a metal frame with a Tsuno King dispenser or the like, and after chip mounting of an IC or the like, it can be heat-cured and bonded in an open state or on a hot platen.

〔The invention's effect〕

The conductive resin paste of the present invention can be used for bonding a semiconductor element such as an IC to a metal frame such as copper or 42 alloy, a ceramic substrate, an organic substrate such as glass epoxy, and particularly a large chip on the copper frame. It is suitable for bonding and can prevent characteristic defects such as IC due to chip crack and chip distortion during heat treatment in the IC assembly process due to the difference in coefficient of thermal expansion between the copper frame and the silicon chip. It is a mounting resin that has excellent stress relaxation characteristics, has no voids in the cured product, and has excellent reliability.

The present invention will be described below with reference to examples.

〔Example〕

Example 1 Halogen group content of 250 parts by weight based on 100 parts by weight of epoxy resin
65 parts by weight of epoxidized phenol novolac (number average molecular weight: 500, epoxy equivalent: 170) of ppm and 35 parts by weight of a glycidyl ester of a C ₁₄ long-chain fatty acid having a halogen group content of 130 ppm were preliminarily used as a curing agent in a 350 mesh pass. 4 parts by weight of finely powdered dicyandiamide, as a flexibility-imparting agent (Here, X = 23 and Y = 2, and both are randomly polymerized.) 10 parts by weight of a dimethylsiloxane compound having the structure: 1,8 diazabicyclo (5,4,0) undecene-as a curing accelerator 0.5 parts by weight of the resorcinol salt of 7 was stirred to form a uniform dispersion liquid, 400 parts of silver powder was further added, and the mixture was kneaded with a three-roll mill to obtain a uniform mounting resin paste.

The obtained paste was applied on a copper frame, a 10 mm square silicon chip was mounted, and chip crack and chip strain when cured at 90 minutes / 150 ° C. were examined.

The chip strain is measured by measuring the height from the line connecting both ends of the chip to the top of the warp vertically.

Further, in the void test of the cured product, the paste was applied on a copper frame, a 5 mm square glass piece was mounted, cured at 90 minutes / 150 ° C., and then the cured product was observed from above the glass piece.

These results are shown in Table 1 together with other properties. The cured paste obtained had no chip cracks, a small chip strain of 4 μm, excellent stress relaxation characteristics, no voids in the cured products, and other properties sufficiently satisfying as a mounting resin.

Example 2 100 parts by weight of epoxidized phenol novolac (number average molecular weight: 460, epoxy equivalent: 170) having a halogen group content of 250 ppm as an epoxy resin, and 65 parts by weight of phenol novolac (number average molecular weight: 590) as a curing agent, As a flexibility-imparting agent (Here, both are randomly polymerized with X = 119 and Y = 8.) 8 parts by weight of the dimethylsiloxane compound having the structure: 0.8 parts by weight of the same curing accelerator as in Example 1, solvent As a mixture of 60 parts by weight of n-butyl cellosolve acetate,
A uniform dispersion was prepared, 700 parts by weight of silver powder was further added, and the mixture was kneaded with a triple roll to obtain a uniform resin paste for mounting.

The results of examining the characteristics of the obtained paste in the same manner as in Example 1 are shown in Table 1.

There are no chip cracks, the chip strain is as small as 4 μm, the stress relaxation characteristics are excellent, there are no voids in the cured product, and other characteristics are sufficiently satisfied as a mounting resin.

[Example 3] Similar to Example 1, only the flexibility-imparting agent was added. (Here, X = 96 and Y = 2, both of which are randomly polymerized.) Table 1 shows the characteristic results of the mounting resin paste obtained as 15 parts by weight of the dimethylsiloxane compound having the structure.

There are no chip cracks, the chip strain is as small as 4 μm, the stress relaxation characteristics are excellent, there are no voids in the cured product, and other characteristics are sufficiently satisfied as a mounting resin.

[Comparative Examples 1 and 2] Similar to Example 1, only the flexibility-imparting agent was used. (Here, X and Y are randomly polymerized.) X = 8, Y = 2 (Comparative Example 2) The results of characteristics of the mounting resin paste obtained as 10 parts by weight of the dimethylsiloxane compound having the structure are shown in Table 1. It was shown to.

In Comparative Example 1, the amount of carboxyl groups was small, and in Comparative Example 2, the number average molecular weight was small, so that the chip strain was large.

Comparative Examples 3 and 4 In the same manner as in Example 2, only the flexibility-imparting agent was added. (Where X and Y are randomly polymerized) X = 349, Y = 8 (Table 1 shows the characteristic results of the mounting resin paste obtained as 8 parts by weight of the dimethylsiloxane compound having the structure of Comparative Row 4). In Comparative Example 3, since the amount of carboxyl groups was too large, the crosslink density increased and the chip strain was large, and in Comparative Example 4, the number average molecular weight was too large, so the flexibility-imparting agent was separated from the epoxy resin and was uniform. It did not become a cured product and the chip adhesion was weak.

Comparative Example 5 Similar to Example 1, only the flexibility-imparting agent does not react with the epoxy resin.

As 10 parts by weight of the dimethylsiloxane compound having the structure
The results of the characteristics of the mounting resin paste thus obtained are shown in Table 1.

The chip had large distortion and the chip adhesion was weak.

[Comparative Example 6] Table 1 shows the characteristic results of the mounting resin paste obtained in the same manner as in Example 1 except that only the flexibility-imparting agent was removed.

Chip cracks were generated when the flexibility-imparting agent was not added.

Comparative Example 7 113 parts by weight of a polyimide resin of pyromellitic acid / diaminodiphenyl ether condensation type (polyamic acid type and 15% by weight N-methyl-2-pyrrolidone solution) and 80 parts by weight of silver powder were used in the same manner as in Example 1. Table 1 shows the characteristic results of the mounting resin paste obtained by kneading with.

Although the chip strain was as small as 5 μm, there were many voids in the cured product and the adhesive strength was weak.

[Comparative Examples 8 and 9] Similar to Example 1, in Comparative Example 8, the flexibility-imparting agent 0.
3 parts by weight, and in Comparative Example 9, 30 parts by weight to obtain a mounting resin paste.

The results of these characteristics are shown in Table 1. When the amount of the flexibility-imparting agent added was small, the chip strain was as large as 19 μm, and when the amount added was large, the adhesive strength was weak.

[Comparative Example 10] In the same manner as in Example 1, 220 parts by weight of silver powder alone was used to obtain a mounting resin paste.

The results of these characteristics are shown in Table 1. Since the amount of silver powder is small,
The volume resistivity is 1 × 10 ^-1 Ω-cm or more, which is not suitable as a mounting resin paste.

[Comparative Example 11] In the same manner as in Example 1, an epoxy resin alone was used as an epoxidized phenol novolac having a halogen group content of 1,900 ppm (number molecular weight: 520, epoxy equivalent: 170) to obtain a mounting resin paste.

The results of this characteristic are shown in Table 1.
It was as high as 53 ppm, and the PCT reliability was also poor.

Claims (1)

[Claims] 1. A conductive resin paste comprising silver powder (A), epoxy resin (B), curing agent (C) and flexibility-imparting agent (D), wherein the flexibility-imparting agent has a carboxyl group of 0.5.
A dimethylsiloxane compound having a number average molecular weight of 1,200 to 25,000, having an amount of up to 10% by weight, (A),
The weight ratio of (B), (C) and (D) is (A) / {(B)
+ (C) + (D)} = 60/40 to 90/10, and the weight ratio of (D) is (D) / {(B) + (C)} = 0.
A conductive resin paste characterized by being 5/100 to 20/100.