JPH0790238A - Electrically conductive resin paste - Google Patents

Abstract

PURPOSE:To provide an electrically conductive resin paste composed of silver powder, a specific epoxy compound and a curing agent at specific ratios, having excellent coating workability and low water-absorption, providing a cured product having low elastic modulus and free from cracking and useful for bonding a semiconductor element to a metal frame, etc. CONSTITUTION:This electrically conductive resin paste contains, as essential components, (A) 60-85wt.% of silver powder, (B) 3-20wt.% of an epoxy compound having naphthalene skeleton and expressed by the formula I (R1 and R2 are group of the formula II or H and at least one of R1 and R2 is group of the formula II; (n) is 0 or 1), e.g. 1,6-dihydroxynaphthalene diglycidyl ether and (C) a curing agent.

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 adhering semiconductor elements such as IC and 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, which has been conventionally about several mm on the long side, has been dramatically increased to about 10 mm. Further, as the lead frame, a copper material, which has good thermal conductivity and is inexpensive, is becoming the mainstream from the conventional 42 alloy. On the other hand, the semiconductor product mounting method is a surface mounting method, and the size of the semiconductor product itself is becoming smaller and thinner due to high-density mounting. In accordance with such trends in semiconductor products, the performance requirements for the constituent materials of semiconductor products are changing,
For the conductive resin paste for die bonding that joins the semiconductor element and the metal frame, not only the reliability of joining that has been conventionally required but also the thermal stress due to the difference in the coefficient of thermal expansion between the large chip and the copper frame is absorbed. Stress relaxation characteristics to relax, and solder crack resistance characteristics based on surface mounting in thin packages are beginning to be required.

Here, regarding the stress relaxation characteristic, the linear thermal expansion coefficient of silicon, which is the material of the semiconductor element, is 3 × 10 ⁻⁶ / ° C., whereas the linear thermal expansion coefficient of the copper frame is 20 × 10 ^−6.
Since the copper frame shrinks at a rate larger than that of silicon chips in the cooling process after heating and hardening the conductive resin paste for die bonding, chip warpage, and eventually chip cracking or die bonding This may cause peeling of the conductive resin paste or the like, which may be a cause of defective characteristics of semiconductor products such as IC and LSI. In order to absorb and relax such thermal stress, the conductive resin paste for die bonding needs to have a low elastic modulus, but the conventional epoxy-based conductive resin paste for die bonding is a thermosetting resin so The original cross-linking resulted in a higher elastic modulus, and the strain due to the difference in the coefficient of thermal expansion between the large chip and the copper frame could not be absorbed. On the other hand, the linear polymer type polyimide resin-based conductive resin paste for die-bonding has a smaller elastic modulus of the cured product than the epoxy-based conductive resin paste for die-bonding, and chip warpage is improved. However, when the polyimide resin is used as a conductive resin paste for die bonding, the viscosity is adjusted by dissolving it in a large amount of polar solvent such as N-methyl-2-pyrrolidone, N, N-dimethylformamide, etc. from the viewpoint of coating workability. Must. The amount of solvent at this time is 30% of the resin paste for die bonding.
When it is used for adhesion of semiconductor element and metal frame, voids are generated in the cured product as traces of solvent escaped during curing and heating, which causes decrease in adhesive strength, thermal conductivity and conductivity. It is not preferable in terms of reliability.

Further, due to a rapid increase in thermal stress at the time of mounting due to the miniaturization and thinning of the package size for surface mounting or high density mounting, not only the semiconductor sealing material but also the conductive resin paste for die bonding is used. Also, reflow crack resistance is required. The reflow crack resistance of the conductive resin paste for die bonding has a low elastic modulus near the reflow temperature in order to absorb and absorb stress during solder reflow, and a small water absorption rate in the pretreatment stage of solder reflow. In addition, it is necessary to show sufficient bonding strength even after absorbing water, but none of them including epoxy and polyimide resin paste satisfies these characteristics.

[0005]

SUMMARY OF THE INVENTION According to the present invention, even when a large chip such as an IC and a copper frame are combined, a chip crack or a characteristic defect of the IC due to the warp of the chip does not occur, and a solder reflow crack occurs in a thin package. Not to provide a highly reliable conductive resin paste.

[0006]

The present invention provides (A) silver powder,
(B) An epoxy compound having a naphthalene skeleton represented by the following formula (1), a curing agent (C) as an essential component, 60 to 85% by weight of silver powder in the total conductive resin paste, and an epoxy compound having a naphthalene skeleton. 3 to 20% by weight of a conductive resin paste,

[0007]

[Chemical 2]

By introducing a naphthalene skeleton into the epoxy compound, which has good coating workability and is the main component, the crosslink density of the cured product decreases and the elastic modulus becomes low, so IC and LS
Even a combination of a large chip such as I and a copper frame absorbs strain due to the difference in coefficient of thermal expansion and has excellent stress relaxation characteristics. Further, the cured product has a low elastic modulus at high temperature, a low water absorption rate due to the introduction of a non-polar naphthalene ring, and an excellent reflow crack resistance with a small decrease in adhesive strength due to water absorption.

Since the silver powder used in the present invention is used in electronic and electrical fields, it is desirable that the amount of ionic impurities such as halogen ions and alkali metal ions be 10 ppm or less. Further, as the shape, a flake shape, a resin shape, or a spherical shape can be used alone or in combination. Further, regarding the particle size, it is usually preferable that the average particle size is 2 to 10 μm and the maximum particle size is about 50 μm or less, and relatively fine silver powder and coarse silver powder may be mixed and used. 60 silver powder
If it is less than 5% by weight, the electrical conductivity of the cured product will decrease, and if it exceeds 85% by weight, the viscosity of the resin paste will be too high, and this will cause deterioration of coating workability, which is not preferable.

The epoxy compound having a naphthalene skeleton represented by the formula (1) used in the present invention has a long distance between cross-linking points due to the introduction of a non-polar naphthalene ring, resulting in a low elastic modulus of a cured product and a high temperature. It has the characteristics that the elastic modulus can be lowered, the water absorption rate is low, and the decrease in adhesive strength due to water absorption is small. Here, n is 0 or 1, and if n is 2 or more, the viscosity of the conductive resin becomes too high, which is not preferable. R ₁ and R ₂ are glycidyl ether groups or hydrogen, and at least one of them is a glycidyl ether group. Among the epoxy compounds having a naphthalene skeleton represented by the formula (1), 1,6-dihydroxynaphthalene diglycidyl ether is preferable. The epoxy compound having a naphthalene skeleton is contained in the total conductive resin paste in an amount of 3 to 20% by weight. If it is less than 3% by weight, the effect of the epoxy compound having a naphthalene skeleton is not sufficiently exhibited,
If it exceeds 20% by weight, the epoxy compound itself having a naphthalene skeleton has a high viscosity, so that the viscosity of the conductive resin paste becomes too high and the coating workability deteriorates.

Further, in the present invention, in addition to the epoxy compound having a naphthalene skeleton, it can be used in combination with a usual epoxy resin as described below, if necessary. Examples of the epoxy resin that can be used in combination include fatty acids such as bisphenol A, bisphenol F, phenol novolac resin, polyglycidyl ether obtained by reacting cresol novolac resins with epichlorohydrin, butanediol diglycidyl ether, neopentyl glycol diglycidyl ether. Group epoxies, heterocyclic epoxies such as diglycidyl hydantoin, vinyl cyclohexene dioxide, dicyclopentadiene dioxide, alicyclic epoxies such as alicyclic diepoxy-adipate, and n-butyl glycidyl ether, glycidyl versatic acid Ester, styrene oxide, ethylhexyl glycidyl ether, phenyl glycidyl ether, cresyl glycidyl ether, butyl phenyl glycidyl There are those generally used as diluents in epoxy resins such as ethers, it also alone or in combination can be used in combination.

Further, in the present invention, phenol novolac resins, polyamides, aromatic or aliphatic polyamines,
Latent amine compounds such as dicyandiamide, dihydrazines and maleonitrile derivatives, ordinary epoxy resin curing agents such as imidazole derivatives, and ordinary curing accelerators such as tertiary amines, triphenylphosphine and tetraphenylphosphine tetraphenylborate. They can be used alone or as a mixture. In the present invention, a flexibility-imparting agent, a defoaming agent, a coupling agent and the like can be used if necessary. The production method of the present invention includes, for example, premixing the respective components, kneading using a three-roll mill, and degassing under vacuum after kneading to obtain a resin paste.

The present invention will be specifically described below with reference to examples. The mixing ratio is parts by weight. Examples 1 to 4 Flake silver powder having a particle size of 1 to 30 μm and an average particle size of 3 μm, 1,6-dihydroxynaphthalene diglycidyl ether (epoxy equivalent 141, liquid at room temperature, hereinafter naphthalene epoxy A), bisphenol A and epichlorohydrin. Diglycidyl bisphenol A obtained by the reaction of
(Epoxy equivalent 180, liquid at room temperature, hereinafter bis A epoxy), cresyl glycidyl ether (epoxy equivalent 18
5), phenol novolac resin (hydroxyl group equivalent 104,
(Softening point 85 ° C.), dicyandiamide, and diazabicycloundecene were mixed in the proportions shown in Table 1, and kneaded with a three-roll to obtain a conductive resin paste. After defoaming this conductive resin paste in a vacuum chamber at 2 mmHg for 30 minutes, various performances were evaluated by the following methods.

Viscosity: E type viscometer (3 ° cone)
Was measured at 25 ° C. and 2.5 rpm to obtain the viscosity. String pullability: Diameter of 1mmφ into conductive resin paste
Was inserted 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 broken was measured. Volume resistivity: 4m width paste on slide glass
m, thickness of 30 μm, and 60 in 200 ° C oven
After curing for a minute, the volume resistivity of the cured product was measured. Elastic Modulus: Paste 10m wide on Teflon sheet
m, length about 150 mm, thickness 0.1 mm, 20
After curing in an oven at 0 ° C. for 60 minutes, the modulus of elasticity was calculated from the initial gradient of the stress-strain curve obtained by measuring with a tensile tester at a test length of 100 mm and a tensile speed of 1 mm / min. Water absorption: 50 × 5 paste on Teflon sheet
After coating so as to be 0 × 0.1 mm and curing in an oven at 200 ° C. for 60 minutes, water absorption treatment was performed at 85 ° C., 85% for 72 hours, and the water absorption rate was calculated from the weight change before and after the treatment. Adhesive strength: A 5 × 5 mm silicon chip was mounted on a copper frame using a paste and placed in an oven at 200 ° C. 6
Cured for 0 minutes. After curing using push-pull gauge 24
The die shear strength during heating at 0 ° C was measured. Also, the cured sample was subjected to water absorption treatment at 85 ° C, 85% for 72 hours, and then
The die shear strength during heating at 0 ° C was measured. Package crack resistance: A package molded under the following conditions using a biphenol type epoxy / phenol novolac-based encapsulating material containing about 78% silica filler is treated at 85 ° C., 85% for 168 hours for water absorption, and then subjected to IR reflow ( At 240 ° C. for 10 seconds, the number of internal cracks was measured by observing the cross section and used as an index of package crack resistance. Package: 80pQFP (14 x 20 x
2mmt) Chip size: 7.5 x 7.5mm (Aluminum wiring only) Lead frame: 42 Alloy molding: 175 ° C, 2 minutes Post mold cure: 175 ° C, 4 hours

Example 5 Instead of the 1,6-dihydroxynaphthalene diglycidyl ether of Examples 1 to 4, dihydroxynaphthalene 2 was used.
A tetrafunctional compound obtained by glycidyl etherification of a compound in which molecules are bound with a methylene group (epoxy equivalent 161, softening point 9
A conductive resin paste was prepared and evaluated in the same manner as in Examples 1 to 4 except that naphthalene epoxy B) was used at 1 ° C. The evaluation results are shown in Table 1. Example 6 A conductive resin paste was prepared and evaluated in the same manner as in Examples 1 to 4 except that triphenylphosphine was used as the curing accelerator. The evaluation results are shown in Table 1. Example 7 A conductive resin paste was prepared and evaluated in the same manner as in Examples 1 to 4 except that 2-methyl-4-ethylimidazole (hereinafter 2P4MZ) was used as a curing agent. The evaluation results are shown in Table 1.

Comparative Examples 1 to 4 A conductive resin paste was prepared in the same manner as in Example 1 with the compounding ratios shown in Table 2. The evaluation results are shown in Table 2.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

EFFECTS OF THE INVENTION The conductive resin paste of the present invention has good workability during dispense application, has a low elastic modulus of the cured product, and has a metal frame made of copper, 42 alloy or the like, a ceramic substrate, an organic material such as glass epoxy. It can be used for bonding semiconductor elements such as IC and LSI to a substrate. It is especially suitable for bonding large chips to a copper frame, can prevent characteristic defects such as IC and LSI due to the difference in thermal expansion coefficient between the copper frame and the silicon chip, and further has a low water absorption of the cured product. 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 the adhesive strength is less likely to drop due to water absorption.

Claims (2)

[Claims] 1. An (A) silver powder, (B) an epoxy compound having a naphthalene skeleton represented by the following formula (1), and (C) a curing agent as essential components, and the silver powder in the total conductive resin paste is 60 to 85. %, And an epoxy compound having a naphthalene skeleton is 3 to 20% by weight. [Chemical 1] 2. The conductive resin paste according to claim 1, wherein the epoxy compound having a naphthalene skeleton is 1,6-dihydroxynaphthalene diglycidyl ether.