JP2974902B2 - Conductive resin paste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive resin paste for bonding a semiconductor element such as an IC or an LSI to a metal frame or the like.

[0002]

2. Description of the Related Art With the remarkable development of the electronics industry in recent years, the degree of integration of circuits in transistors, ICs, LSIs, VLSIs and semiconductor devices has been rapidly increasing.
For this reason, the size of the semiconductor element has been dramatically increased to about several tens mm, whereas the long side in the related art was about several mm. In addition, the lead frame is also mainly made of inexpensive copper material with good thermal conductivity from the conventional 42 alloy. On the other hand, the mounting method of semiconductor products is the surface mounting method. The size is getting smaller and thinner. In accordance with the trend of such semiconductor products, the required performance of constituent materials of the semiconductor products is also changing, and even for the resin bonding paste for bonding the semiconductor element and the metal frame, only the conventionally required bonding reliability is required. Instead, a stress relaxation property for absorbing and relaxing thermal stress based on a difference in thermal expansion coefficient between a large chip and a copper frame, and further, a solder crack resistance property based on surface mounting in a thin package are beginning to be required.

Here, the stress relaxation characteristic is such that the linear thermal expansion coefficient of silicon, which is a material of a semiconductor element, is 3 × 10 ⁻⁶ / ° C., while the linear thermal expansion coefficient of a copper frame is 20 × 10 ⁻⁶ / ° C.
° C, which is one order of magnitude higher, so that in the cooling process after heating and curing the die bonding resin paste, the copper frame shrinks at a greater rate than the silicon chip, resulting in chip warpage and chip cracking or die bonding resin paste. Causes peeling, etc., IC, L
There is a possibility that it may be a cause of poor characteristics of semiconductor products such as SI. In order to absorb and alleviate such thermal stress, it is necessary to make the die bonding resin paste have a low elastic modulus. However, conventional epoxy die bonding resin pastes are three-dimensionally cross-linked due to the thermosetting resin and are not elastic. The rate became high, and the strain based on the difference in the coefficient of thermal expansion between the large chip and the copper frame could not be absorbed. On the other hand, in the linear polymer type polyimide resin-based die bonding resin paste, the elasticity of the cured product is smaller than that of the epoxy-based die bonding resin paste, and the warpage of the chip is improved.
However, when a polyimide resin is used as the resin paste for die bonding, the viscosity must be adjusted by dissolving in a large amount of a polar solvent such as N-methyl-2-pyrrolidone, N, N-dimethylformamide from the viewpoint of coating workability. Must. At this time, the amount of the solvent is as much as 30% by weight of the resin paste for die bonding, and when used for bonding a semiconductor element to a metal frame, voids are generated in the cured product as traces of the solvent at the time of curing and heating. This is unfavorable in terms of reliability because it causes a decrease in strength, thermal conductivity and conductivity.

[0004] In addition, due to the rapid increase in thermal stress during mounting based on the miniaturization and thinning of the package size for surface mounting or high-density mounting, not only semiconductor encapsulants but also resin pastes for die bonding have been used. There is a demand for reflow crack resistance. The reflow crack resistance of the die bonding resin paste has a low elastic modulus near the reflow temperature to relax and absorb the stress during solder reflow, and the water absorption at the pretreatment stage of solder reflow is small, and However, it is necessary to show a sufficient bonding strength, especially a strength in a peeling direction in a heated state, but none of these properties including epoxy and polyimide resin pastes satisfy these properties.

[0005]

According to the present invention, even when a large chip such as an IC is combined with a copper frame, characteristic cracks such as an IC due to chip crack or chip warpage do not occur, and solder reflow crack occurs in a thin package. It is intended to provide a highly reliable conductive resin paste that does not have a high reliability.

[0006]

The present invention provides (A) a silver powder,
(B) Epoxy resin liquid at room temperature, (C) 3 per molecule
In a conductive resin paste containing a compound having two phenolic hydroxyl groups as essential components, (A) 60 to 85% by weight of silver powder is contained in all conductive resin pastes, and (C) three phenolic hydroxyl groups are contained in one molecule. 0.1 to
A conductive resin paste characterized by containing 20% by weight, which has been used conventionally by using a compound having good coating workability and having three phenolic hydroxyl groups in one molecule as a curing agent. Compared with the case of curing with phenol novolak resin, the crosslinked density of the cured product is lowered and the elastic modulus is low, so even the combination of large chip such as IC and LSI and copper frame absorbs the strain based on the difference in thermal expansion coefficient. It has excellent stress relaxation characteristics. Also, since the free volume of the cured product is small, the water absorption is small, and since the adhesive strength in the peeling direction in a heated state is large,
The conductive resin paste layer hardly peels off due to thermal stress during solder reflow, and is excellent in reflow crack resistance.

Since the silver powder used in the present invention is used in the fields of electronics and electricity, the amount of ionic impurities such as halogen ions and alkali metal ions is desirably 10 ppm or less. Flakes, dendrites or spheres can be used alone or in combination. Furthermore, regarding the particle size, the average particle size is usually 2 to 10 μm,
The maximum particle size is preferably about 50 μm, and a mixture of relatively fine silver powder and coarse silver powder may be used. 6 silver powder
If the amount is less than 0% by weight, the electrical conductivity of the cured product decreases,
If the content exceeds 5% by weight, the viscosity of the resin paste becomes too high, which causes a reduction in coating workability, which is not preferable.

Although the epoxy resin used in the present invention is limited to a liquid at room temperature, a solvent is required for kneading with silver powder unless the resin is liquid at room temperature. The solvent is not preferable because it causes bubbles and lowers the adhesive strength and thermal conductivity of the cured product. The epoxy resin which is liquid at ordinary temperature used in the present invention includes, for example, a resin which is solid at ordinary temperature and shows a stable liquid at ordinary temperature by being mixed with the epoxy resin which is liquid at ordinary temperature.

The epoxy resins used in the present invention include bisphenol A, bisphenol F, phenol novolak, polyglycidyl ether obtained by the reaction of cresol novolaks with epichlorohydrin, 1,6
-Aliphatic epoxies such as dihydroxynaphthalenediglycidyl ether, butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, heterocyclic epoxies such as diglycidyl hydantoin, vinylcyclohexenedioxide, dicyclopentadienedioxide, alicyclic die Cycloaliphatic epoxies such as epoxy-adipate, and also normal such as n-butyl glycidyl ether, glycidyl versatate, styrene oxide, ethylhexyl glycidyl ether, phenyl glycidyl ether, cresyl glycidyl ether, butylphenyl glycidyl ether, etc. Some are used as diluents for epoxy resins,
These may be used alone or as a mixture.

The curing agent used in the present invention is a compound having three phenolic hydroxyl groups in one molecule, and is contained in the entire conductive resin paste in an amount of 0.1 to 20% by weight. With phenol novolak resins that have been used in the past, the cross-linking density of the cured product increases, so the elastic modulus increases, the stress relaxation characteristics decrease, and the free volume of the cured product increases, which increases the water absorption. Not preferred.
In addition, a compound having two phenolic hydroxyl groups in one molecule has a low cross-linking density of the cured product, a low elastic modulus, a small free volume of the cured product and a low water absorption, but a small cohesive force of the cured product. Particularly, the adhesive strength in the peeling direction in a heated state is reduced. When the compounding amount of the compound having three phenolic hydroxyl groups in one molecule is less than 0.1% by weight in the total conductive resin paste, low stress and low water absorption required, and 20% by weight cannot be expected. If it exceeds, the amount of the curing agent becomes too large, and after the curing, excess phenolic hydroxyl groups remain in an unreacted state, so that the water absorption of the cured product becomes large. It is not preferable because the strength becomes extremely low. Examples of the compound having three phenolic hydroxyl groups in one molecule include, in addition to the compound of the formula (1), a trinuclear phenol novolak resin,
There are trinuclear cresol novolak resins, compounds represented by the formula (2) and the like, and these may be used alone or as a mixture.

[0011]

Embedded image (R in the formula (1) is hydrogen or an alkyl group)

[0012]

Embedded image

When the compound represented by the formula (1) is used,
It may be used in combination with another compound having three phenolic hydroxyl groups in one molecule or a phenol novolak compound, but the compounding amount is preferably 2 to 7% by weight in the total conductive resin paste. preferable. When the amount of the compound represented by the formula (1) is less than 2% by weight, the required performance cannot be sufficiently exerted. When the amount exceeds 7% by weight, stringing at the time of applying the conductive resin paste tends to occur.

If necessary, other curing agents such as a latent amine curing agent may be used in combination with a general epoxy resin such as a tertiary amine, imidazoles, triphenylphosphine, tetraphenylphosphine tetraphenylborate and the like. A compound known as a curing accelerator with a phenolic curing agent can also be added. In the present invention, a flexibility-imparting agent, an antifoaming agent, a coupling agent, and the like can be used as necessary. The production method of the present invention includes, for example, preliminarily mixing the components, kneading them using a three-roll mill, kneading and then defoaming under vacuum to obtain a resin paste.

Hereinafter, the present invention will be described specifically with reference to examples. The mixing ratio is shown in parts by weight.

【Example】

Examples 1 to 4 Flaky silver powder having a particle size of 1 to 30 μm and an average particle size of 3 μm,
Diglycidyl bisphenol A (epoxy equivalent: 180, liquid at room temperature, hereinafter referred to as bis-A epoxy), cresyl glycidyl ether (epoxy equivalent: 185), tris (p-hydroxyphenyl) ethane (hydroxyl group) obtained by the reaction of bisphenol A with epichlorohydrin Equivalent 1
02, hereinafter referred to as trifunctional phenol A), bisphenol A (hydroxyl equivalent 114), dicyandiamide, and diazabicycloundecene were mixed in the ratio shown in Table 1, and kneaded with three rolls to obtain a conductive resin paste. After defoaming the conductive resin paste in a vacuum chamber at 2 mmHg for 30 minutes, various performances were evaluated by the following methods.
Table 1 shows the evaluation results.

Viscosity: 2 using an E-type viscometer (3 ° cone)
The value at 5 ° C. and 2.5 rpm was measured and defined as viscosity. Stringing property: A pin having a diameter of 1 mmφ was put into a conductive resin paste to a depth of 5 mm, the pin was pulled up at a speed of 300 mm / min, and the height when the paste was cut was measured. Volume resistivity: paste 4 mm wide on a glass slide,
The composition was applied to a thickness of 30 μm and cured in an oven at 200 ° C. for 60 minutes, and then the volume resistivity of the cured product was measured. Elastic modulus: 10 × 150 × paste on Teflon sheet
Apply in 0.1mm and oven in 200 ℃ 6
After curing for 0 minutes, test length 100m with tensile tester
m, a load-displacement curve was measured at a test speed of 1 mm / min, and the elastic modulus was calculated from the initial gradient. Water absorption: paste 50 × 50 × on Teflon sheet
Apply to 0.1mm and oven at 200 ℃ 60
After curing for minutes, a water absorption treatment was performed at 85 ° C. and 85% for 72 hours, and the water absorption was calculated from the weight change before and after the treatment. Chip warpage: A 6 × 15 × 0.3 mm silicon chip was mounted on a copper frame (200 μm thick) with a conductive resin paste, and cured at 200 ° C. for 60 minutes. ). Adhesive strength (1): A 5 × 5 mm silicon chip was mounted on a copper frame using a paste and cured in a 200 ° C. oven for 60 minutes. Use a push-pull gauge after curing 2
The hot die shear strength at 40 ° C. was measured. The cured sample was subjected to a water absorption treatment at 85 ° C.
The hot die shear strength at 0 ° C. was measured. Adhesive strength (2): A 9 × 9 mm silicon chip was mounted on a copper frame using a paste and cured in a 200 ° C. oven for 60 minutes. After curing, the strength in the peeling direction was measured at 240 ° C. using a push-pull gauge.

Example 5 α, α-bis (4-hydroxyphenyl) -4- (4-hydroxy-α, α-dimethylbenzyl) -ethylbenzene (having a hydroxyl equivalent of 141) represented by the formula (2) as a curing accelerator to be used: A conductive resin paste was prepared and evaluated in the same manner as in Examples 1 to 4, except that trifunctional phenol B was used. Table 1 shows the evaluation results. Example 6 A conductive resin paste was prepared in the same manner as in Examples 1 to 4, except that 1,6-dihydroxynaphthalenediglycidyl ether (epoxy equivalent: 141, liquid at room temperature, hereinafter referred to as naphthalene epoxy) was used as the epoxy resin to be used. And evaluated. Table 1 shows the evaluation results. Example 7 A conductive resin paste was prepared and evaluated in the same manner as in Examples 1 to 4, except that triphenylphosphine was used as a curing accelerator to be used. Table 1 shows the evaluation results. Comparative Examples 1 to 5 Conductive resin pastes were produced in exactly the same manner as in the examples with the mixing ratios shown in Table 2. In Comparative Example 5, a phenol novolak resin (having a hydroxyl equivalent of 104, a softening point of 8
5 ° C.). Table 2 shows the evaluation results.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

The conductive resin paste of the present invention has good workability at the time of dispensing application, has a low elasticity of a cured product, a metal frame of copper or 42 alloy, a ceramic substrate,
It can be used for bonding semiconductor elements such as ICs and LSIs to organic substrates such as glass epoxy. In particular, it is suitable for bonding large chips to a copper frame, and can prevent poor characteristics of IC, LSI, etc. based on the difference in the coefficient of thermal expansion between the copper frame and the silicon chip.
This is a highly reliable conductive resin paste for bonding semiconductor elements, which has never existed before and does not cause cracks during soldering even when used in a thin package because of a small decrease in adhesive strength due to water absorption.

Claims (3)

(57) [Claims] 1. A conductive resin paste comprising (A) a silver powder, (B) an epoxy resin liquid at room temperature, and (C) a compound having three phenolic hydroxyl groups in one molecule as essential components. (A) Silver powder in resin paste is 60-8
5% by weight, (C) a conductive resin paste containing 0.1 to 20% by weight of a compound having three phenolic hydroxyl groups in one molecule. 2. The compound (C) having three phenolic hydroxyl groups in one molecule represented by the following formula (1).
The conductive resin paste as described in the above. 3. The (C) compound having three phenolic hydroxyl groups in one molecule is a compound represented by the following formula (1) and is contained in an amount of 2 to 7% by weight in the total conductive resin paste. Or the conductive resin paste according to claim 2. Embedded image (R in the formula (1) is hydrogen or an alkyl group)