JPH0817052B2 - 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 adhering a semiconductor element such as IS or LSI to a substrate such as a metal frame, and more particularly to a resin paste having excellent storage stability.

[0002]

2. Description of the Related Art With the recent remarkable development of the electronics industry, it has evolved into transistors, ICs, LSIs and VLSIs, and the degree of integration of circuits in these semiconductor elements has rapidly increased and mass production has become possible. With the spread of semiconductor products using these, 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 has come to be taken up as an improvement of the Au—Si eutectic method in the mounting step.

However, the soldering 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 conductive resin paste is superior to the solder method in workability and reliability, and the demand for it is rapidly increasing.

Usually, such a resin paste is a dispersion of silver powder having a very large specific gravity in a resin having a small specific gravity, and therefore, precipitation and separation of the silver powder easily occur during storage. Therefore, the storage temperature needs to be an extremely low temperature of −10 ° C. or less, and it is necessary to maintain the extremely low temperature with dry ice or the like during transportation. Furthermore, it is necessary to return the temperature to room temperature at the time of use, but it takes at least 2 hours or more to return the temperature from -10 ° C or lower to room temperature.
In addition, water in the air may condense and mix into the paste, which may have a serious adverse effect on reliability.

[0005]

In order to solve such a problem of storage stability, the present invention has a normal viscosity near room temperature, but at a storage temperature of 5 ° C. or less, the viscosity is remarkably increased to separate silver powder. The present invention provides a conductive resin paste that does not occur.

[0006]

That is, according to the present invention, in a conductive resin paste containing an epoxy resin, a curing agent and silver powder as main components, 2,3,5-trimethyl-phenyl-1 of the following formula (1) is used. A conductive resin paste containing 4,4-diglycidyl ether as an essential component.

[0007]

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The present invention is characterized by using the crystallizing epoxy resin (1), but other epoxy resins can be used together. The epoxy resin used in combination is desired to be liquid because it must finally have good workability. Examples thereof include bisphenol A, bisphenol F, diglycidyl ether obtained by the reaction of phenol novolac and epichlorohydrin, which is liquid at room temperature, vinylcyclohexene dioxide, dicyclopentadiene dioxide, alicyclic diepoxy-azide. Cycloaliphatic epoxies such as paints, as well as conventional epoxies such as n-butyl glycidyl ether, versatic acid glycidyl ester, styrene oxide, phenyl glycidyl ether, butylphenyl glycidyl ether, cresyl glycidyl ether, dicyclopentadiene diepoxide. There is a resin diluent.

The amount of the crystallized epoxy resin of the formula (1) added is preferably 0.5 to 15% by weight based on the total amount of the conductive resin paste. If it exceeds 15% by weight, the epoxy resin will be completely crystallized, so that the viscosity at room temperature becomes high. On the other hand, if it is less than 0.5% by weight, the effect of increasing the viscosity at low temperature becomes small.

That is, by adding a small amount of the epoxy resin of the formula (1), crystallization starts at about 5 ° C. and the viscosity of the paste increases remarkably. Therefore, even if the paste is stored at a temperature of about 5 ° C. or lower for a long period of time, silver powder does not settle, and the paste has normal workability even when returned to room temperature.

The silver powder used in the present invention is preferably 50 μm or less. If it exceeds 50 μm, needle clogging occurs. The field of use of ionic impurities such as sodium and chlorine contained in silver powder is electronics, and it is desirable that the amount is 10 ppm or less from the viewpoint of reliability of LSI and the like. The shape of the silver powder is flake-shaped, spherical, etc., and any of them can be used together.

It is generally desirable that the curing agent used in the present invention has active hydrogen in its molecule. Examples thereof include novolac type phenolic resins and amine type curing agents such as imidazole and dicyandiamide, and are not particularly limited. It is also possible to use them in combination. Further, additives such as a curing accelerator, a pigment, a dye and a defoaming agent can be used in the resin composition of the present invention if necessary. The production method of the present invention includes, for example, premixing each component, kneading using a three-roll mill, obtaining a paste, and defoaming under vacuum.

[0013]

EXAMPLES The present invention will be specifically described below with reference to examples.
The mixing ratio is set to weight%.

Examples 1, 2 Diglycidyl ether obtained by the reaction of bisphenol A and epichlorohydrin (liquid at room temperature with an epoxy equivalent of 180, hereinafter epoxy resin A), cresyl glycidyl ether as a diluent, 2, 3, 5- Trimethyl-phenyl-1,4-diglycidyl ether (hereinafter epoxy resin B), imidazole (2P4MZ), silver powder (average particle size 4
μm) was mixed in a ratio shown in Table 1 and kneaded with a three-roll mill to obtain a conductive resin paste. After degassing this 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.

Evaluation Method Viscosity Using an E-type viscometer (3 ° cone), the viscosity was measured at 25 ° C. and 25 rpm to obtain the viscosity. The thixotropic value was measured at 25 ° C. and 0.5 rpm in the same manner as the above viscosity measurement, and the value calculated by the following formula was defined as the thixotropic degree. Thickness = (viscosity at 0.5 rpm) / (viscosity at 2.5 rpm) Volume resistivity The paste was applied on a slide glass to a width of 4 mm and a thickness of 30 μm, and cured on a heating plate at 200 ° C. for 60 seconds. Then, the volume resistivity of the cured product was measured. Threadability A 1mm diameter pin is 5mm deep into the conductive resin paste.
And it was pulled up at a speed of 300 mm / min, and the height when the paste was broken was measured. Sedimentability 15 g of a conductive resin paste was packed in a 5 cc syringe, refrigerated (5 ° C.) while lying sideways, and the sedimentation of silver powder in the paste was visually determined.

Examples 3 and 4 A conductive resin paste was obtained in the same manner as in Example 1 except that phenol novolac resin (hydroxyl group equivalent 104) was used instead of the imidazole of Example 1. Table 1 shows the evaluation results.

Comparative Examples 1 to 5 Conductive resin pastes were obtained in the same manner as in Example 1 with the compounding ratios shown in Table 1. The hydrophobic ultrafine silica particles blended in Comparative Examples 3 to 5 have an average particle size of 2 to 50 nm, and the viscosity of the paste increases as the amount of silica compounded increases.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

The conductive resin paste of the present invention is copper, 42
It can be used for bonding semiconductor elements such as ICs to metal frames such as alloys, ceramic substrates, and organic substrates such as glass epoxy, and has the same performance as conventional ones such as volume resistivity and viscosity change over time. Is. Further, in the case of storage in a refrigerator (5 ° C. or lower), a conductive resin paste in which silver powder does not settle can be obtained, as compared with the conventional ones which were likely to settle.

Claims (1)

[Claims] 1. A conductive resin paste containing an epoxy resin, a curing agent and silver powder as main components, wherein
A conductive resin paste comprising 3,5-trimethyl-phenyl-1,4-diglycidyl ether as an essential component. Embedded image