JPH0567672B2 - - Google Patents

Description

[Detailed description of the invention]

(1) Purpose of the invention [Industrial field of application] The present invention relates to lead wire contact adhesion, magnetic
Ceramic filling, silk screen printing,
A two-component low-temperature heat-curing type that can be used for a variety of purposes, such as repairing circuit boards, adhering molded carbon to metal, adhering various electronic elements to lead frames and alumina substrates, surface adhesion of PTC and metal, and adhesion between Nesa glass. Related to conductive epoxy adhesive. [Prior art] This type of two-component conductive epoxy adhesive can be used for conductive bonding of plastics (epoxy, phenolic resin, etc.) that could not be soldered in the past, for bonding Nesa glass used in liquid crystal display tubes, and for micro motors. It is an indispensable material for adhering phosphor bronze and carbon brushes, and for adhering lead wires for crystal resonators, SDC meters, etc. Recent developments in the semiconductor industry in particular have been remarkable, with ICs and LSIs being developed one after another and being mass-produced.
Previously, a method using Si eutectic was used, but in order to reduce costs and improve productivity, conductive adhesives made by mixing silver powder into epoxy resin have come into widespread use, and are currently the most popular die bonding method. being watched. However, this type of conventional two-component high-temperature heating conductive epoxy adhesive has a silver content of 70 to 90% by weight.
is common, and the mixing ratio of silver filler epoxy resin and curing agent is 1:1 or 1:2 and the diluting solvent is
Uses SH thinner and has a viscosity of 100,000 to 200,000
Indicates CPS and curing conditions are 100℃~130℃×1H (hour)
The temperature is 150°C x 0.5 hours, and the viscosity is high, and the kneading properties are poor, and the wettability related to adhesive strength is also poor. In other words, when designing the composition of epoxy conductive adhesives, the viscosity of the raw material epoxy resin is usually high, so when it is kneaded with silver filler, the viscosity increases further, making application workability with micro-dispensers, silk screen printing, etc. Solvents must be added as this may cause deterioration, and as a result, when surface adhesion is applied to the object to be coated, if a solvent is included, when heated and cured,
The curing agent tends to foam, resulting in property deterioration (variation in conductivity, decrease in adhesive strength), so it is desirable that conductive adhesives used for assembling and bonding electronic components be solvent-free and highly airtight. When used in components, care must be taken as trace amounts of volatile matter may have a negative effect on switch contacts and metal parts.In particular, products for die bonding of ICs and LSIs must be free of outgassing. Solvents have no choice but to be used to reduce viscosity, knowing that the viscosity will be reduced, and even though workability can be improved by adjusting the viscosity by adding a solvent when gluing in an open state, such as when bonding lead wires. Adhesives related to ICs and semiconductor elements are often surface-adhesive, and after adhesion, they are hermetically sealed with a synthetic resin or the like, which can cause defects due to residual solvent, so solvent-containing adhesives are not preferred. In addition, since the curing temperature is a high temperature heat curing type and it must be heated for a long time, the adhesive itself deteriorates and deteriorates, resulting in a tensile shear strength of only 29 to 62 kg/ ^cm2 . This is a drawback in that it has an adverse thermal effect on surrounding electronic components and deteriorates their electrical characteristics. [Problems to be Solved by the Invention] In view of the conventional drawbacks, the present invention lowers the adhesive viscosity to improve kneading properties, improves wettability and spreadability to increase adhesive strength, and achieves a low curing temperature and short heating time. The purpose of the present invention is to provide a two-component low temperature heat-curable conductive epoxy adhesive which has significantly improved curing conditions and suppresses as much as possible adverse thermal effects during adhesion. (2) Structure of the invention [Means for solving the problems] The two-component low-temperature heat-curing conductive epoxy adhesive of the present invention has a particle size of 5 to 5 as a conductive filler.
Bisphenol A-based silver filler epoxy resin with a weight ratio of 30 μm silver filler and binder resin dispersed and kneaded is 90-75:10-25, and an appropriate amount of reactive diluent such as pheniglycidyl ether is added. The weight percentage of the aliphatic polyamine curing agent such as triethylenetetraamine added during use of the bisphenol A-based silver filler epoxy resin
By adding 2 to 3 parts per 100 parts, the viscosity is lowered to 10,000 to 50,000 CPS, and the curing temperature is set to 50 to 80°C to increase adhesive strength. [Example] Examples of the present invention will be described below. The two-component low-temperature heat-curing conductive epoxy adhesive of the present invention is a polyamine-curing type of silver filler epoxy resin (hereinafter also referred to as the main ingredient), and is a cream-like paste with a viscosity of 10,000 to 50,000 CPS and is easy to work with. Since it contains no volatile solvents, there is no shrinkage during curing, and after curing it has high conductivity and strong adhesive strength, and is also suitable for filling and encapsulation. The epoxy resin that serves as the main binder is a low-viscosity liquid adjusted with a reactive diluent that adjusts the viscosity and imparts flexibility to the cured resin. The epoxy resin is based on bisphenol A, and its basic structure is as shown below.

[Chemical] Electrolytic silver powder and reduced silver powder are used for the silver powder with a particle size of 5 to 30 μm, preferably 5 to 10 μm, which is precisely kneaded and dispersed with the conductor mixed with the base material, that is, the epoxy resin, but the proportion of silver filler to the base material is The weight ratio is 10-25:90-75, preferably 17:83. Electrolytic silver powder is produced by re-electrolyzing electrolytic silver to precipitate it in a dendritic form, and is a silver powder with high purity and good moldability. Further, the reduced silver powder is obtained by adding a reducing agent such as formalin to a silver salt aqueous solution, reducing and precipitating it, and drying this to obtain a powder. The properties of these silver powders include fine particle size, excellent dispersibility, and no cohesion. The curing agent is generally selected based on the viscosity of the mixture, pot life, curing conditions, adhesive strength, etc., and triethylenetetraamine, etc., which does not cause blistering and can perform the curing reaction in small amounts, is generally selected. An aliphatic polyamine curing agent is used. Triethylenetetraamine (TTA=
The chemical structural formula of triethylene tetramine is as shown below. H ₂ N CH ₂ CH ₂ N CH ₂ CH ₂ N CH ₂ CH ₂
The main agent and curing agent that are mixed at the NH ₂ site undergo curing through a chemical reaction, and chemical equivalence is required for the curing reaction. In other words, in order for the epoxy groups of the epoxy resin and the amine groups of the polyamine to combine in just the right amount and form a three-dimensional strong structure, the chemical equivalents of each must be calculated, but the amount of curing agent must be calculated based on 100 parts of the base resin. Figure 1 shows a correlation characteristic diagram that is the test result of adhesive strength when Based on FIG. 1, 2 parts (by weight) of the curing agent was calculated as the optimum standard value for 100 parts (by weight) of the main agent. Therefore, as shown in FIG. 1, if the distribution ratio of the base agent and curing agent to be mixed is too much or too little than the standard value, the adhesive strength will be affected. [Characteristics of the Invention] The basic characteristics required of a conductive adhesive are conductivity due to the shape of the silver filler, such as scale-like shape and particle size, and adhesive strength due to the resin. It is important that these two characteristics do not deteriorate over time and maintain long-term reliability. Test examples of the characteristics of the present invention will be explained below. General properties As shown in Table 1 below.

[Table] Curing conditions are determined by the combination of heating temperature and time. For example, curing proceeds at room temperature (25°C), but it takes more than 48 hours, and the conductivity is not satisfactory. Therefore, heating to at least 50°C is required. Table 2 below shows the test results when the base resin: curing agent was mixed at a ratio of 100:2.

[Table] However, the * mark indicates the heating time when the specified temperature is reached. Furthermore, the relationship between curing temperature and volume resistivity when mixed at a blending ratio of base resin: curing agent = 100:2 is shown in the second graph.
Figure 3 shows the relationship between conductivity when heating at a low temperature of 50°C and varying the heating time. Adhesive Strength The following Table 3 shows the test results when the materials were mixed at a blending ratio of base resin: curing agent = 100:2 and were measured after being left at room temperature for 24 hours at 80°C for 15 minutes as curing conditions.

[Table] However, * indicates damage inside the adhesive layer. Heat Resistance In a heat resistance test at 190℃, the adhesive strength remains almost unchanged. Table 4 shows the results of a heat resistance test after mixing at a blending ratio of main ingredient: curing agent = 100:2, curing conditions at 80°C for 15 minutes, and leaving it at room temperature for 24 hours.

[Table] However, the sample was steel/steel bonded. Relationship between temperature and strength Main agent: hardening agent = 100:2 mixture ratio, curing condition: 80℃ x 15 minutes, strength test after being left at room temperature for 24 hours and measured at each temperature and after being left at room temperature for 1 hour and 30 minutes The results are shown in Figure 4. Relationship between coating thickness/width and volume resistivity The following Table 5 shows the measurement test results after mixing base resin: curing agent at a mixing ratio of 100:2 and curing at 80°C for 15 minutes and leaving it at room temperature for 24 hours. .

[Table] However, the sample is applied to the substrate PMMA (acrylic board). [How to Use the Invention] Examples of how to use the adhesive of the present invention will be described below. In order to achieve good performance, it is important to accurately measure the base agent and curing agent and stir and mix them well. Mixing ratio: Main agent: Hardening agent = 100:2 (wt%) Mixing guide: Main agent: 1g Hardening agent: 1 drop (approximately 0.02g) Mix both well. Curing conditions (standard value) 50℃ x 2 hours...1.5 x 10 ^-2 Ω-cm 80℃ x 15 minutes... 5 x 10 ^-4 Ω-cm Sustaining pot life As new, mix a predetermined amount of main ingredient: curing agent Then, freeze it immediately. For example, put it in a -20℃ freezer.
After leaving it for 120 hours (5 days), it was taken out and returned to room temperature while stirring, and used according to the normal curing procedure. No abnormality was observed in the performance. Adjustment of viscosity using a solvent If further adjustment of the viscosity is unavoidably necessary due to the convenience of deimapensing, use the mixture of the present invention5.
% (by weight) with toluene or ethyl acetate. (3) Effects of the invention Thus, the adhesive of the present invention can be heated at a low temperature of 50 to 80°C.
Curing takes place at °C. It is a creamy paste that is easy to mix and does not drip. Suitable for filling and encapsulation as there is no shrinkage after curing. Stable and high conductivity can be obtained. It has strong adhesion and is compatible with many new materials. Excellent heat and moisture resistance. Viscosity can be adjusted using solvent. Good dispensability. Excellent concealment power. It has various features compared to conventional products, such as a long shelf life and being effective for about one year at room temperature. Since the present invention cures at a low temperature and heats for a short time, it maintains quality and reliability without adversely affecting the adhesive itself, the parts to be bonded, or surrounding parts, and generally increases adhesive strength by 20% compared to conventional products. In addition, it has an excellent technological innovation impact effect on the electronic industry, such as improving workability, saving energy and cost, and establishing a mass production system.

[Brief explanation of the drawing]

Figure 1 is an adhesive force correlation characteristic diagram when the amount of curing agent is varied with respect to 100 parts of resin in an example of the present invention, and Figure 2 is a correlation characteristic diagram between curing temperature and volume resistivity. , Figure 3 is a correlation characteristic diagram of conductivity when heating time is varied at the same low temperature heating of 50℃, Figure 4 is the correlation between each temperature and tensile shear strength after being left at room temperature for 1 hour and 30 minutes. It is a characteristic line diagram.

Claims (1)

[Claims] 1 A silver filler with a particle size of 5 to 30 μm as a conductive filler and a binder resin obtained by dispersing and kneading the silver filler in a weight ratio of 90 to 75:10 to 25 and an appropriate amount of a reactive diluent added. The weight percentage of the aliphatic polyamine curing agent added to the phenol A-based silver filler epoxy resin during use is 2 to 3 parts per 100 parts of the bisphenol A-based silver filler epoxy resin,
Two-component low-temperature heat-curing conductive epoxy adhesive 2 with lower viscosity and increased adhesive strength by curing temperature between 50°C and 80°C Phenyglycidyl ether is used as the reactive diluent A two-component low-temperature heat-curable conductive epoxy adhesive 3 according to claim 1, wherein triethylenetetraamine is used as the aliphatic polyamine curing agent. A two-component low-temperature heat-curable conductive epoxy adhesive according to item 4 or item 2. The lower viscosity is a patent claim of 10,000 to 50,000 CPS, which has high kneading properties and good wettability for increasing adhesive strength. A two-component low-temperature heat-curable conductive epoxy adhesive according to item 1, item 2, or item 3.