JPS6151705A - Conductive adhesive sheet - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to adhesive sheets and fills having conductivity (hereinafter referred to as adhesive sheets), and its purpose is to achieve anisotropic conductivity and high conductivity through a simple adhesive operation. An object of the present invention is to provide a metal particle composite adhesive sheet for circuit connection that also has adhesive strength.

[Conventional technology]

Conventionally, as a method of bonding two types of circuits A and B and also obtaining electrical continuity between A and B, methods using soldering or conductive adhesive have been widely used.

However, since soldering is hard (and brittle), it has the disadvantage of low adhesion reliability and easily peeling off due to impact, etc.Also, since conductive adhesive must be applied only to the circuit area, it is difficult to Circuits have the disadvantage of being complicated to work with and lacking in reliability.Recently, adhesive sheets for circuit connections have been studied, and patent publications No. 51-20941, No. 55-104007, and No. 56-
This method has been proposed in Japanese Patent Publication No. 122193, Japanese Patent Publication No. 51-21192, and the like. In either case, the basic idea is to insert an adhesive sheet containing a conductive material between opposing circuits, apply pressure, or provide pressure/heating means to bond the circuits. At the same time, a conductive connection using a conductive material is obtained.

[Problem that the invention seeks to solve]

However, in such conventional methods, conduction between circuits is mainly caused by contact between multiple conductive materials, often metal particles, and the reliability of current methods is insufficient. Was. For example, as shown in Table 2 of Examples below, the resistance value with respect to temperature changes tended to increase at high temperatures. This is because the distance between conductive particles becomes substantially thicker due to thermal expansion of the adhesive due to temperature rise.
This phenomenon is due to a decrease in the contact area of particles. That is, this is a common drawback of conventional conductive adhesives for connecting circuits, which simply rely on contact between metal particles for conduction between circuits.

The present inventors have previously proposed an extremely transparent and conductive adhesive sheet for circuit connection that contains a very small amount of metal particles of a specific shape and particle size, but the above-mentioned drawbacks of the prior art have been solved. As a result of extensive research into ways to improve and enable reliable connections, we have arrived at the present invention.

Means for Solving Problem c] That is, the present invention provides a conductive adhesive sheet comprising an adhesive component and conductive particles, in which the adhesive component has an average particle size of 1 to 50 μm and a maximum particle diameter of 1 to 50 μm. The ratio of small diameter is α5
The conductive metal particles having a melting point of 100 to 250° C. are contained in an amount of 0.1 to 10% by volume, and the adhesive layer is
The present invention relates to a conductive adhesive sheet having a thickness of 110% or more of the average particle size of the conductive particles and a total light transmittance of 40% or more.

In the adhesive sheet of the present invention, since the adhesive is a thermoplastic polymer that softens at the melting point of the metal particles and exhibits adhesive properties, circuit connection work can be performed under heat sensitivity, and the adhesive The metal particles dispersed in the ingredients melt and the contact between the metal particles changes into a completely integrated structure, making it possible to obtain excellent connection workability, high adhesion strength, and stable high four-sidedness. can. Furthermore, the adhesive sheet of the present invention can obtain sufficient conductivity even with a very small amount of metal particles, and has high transparency. It has the advantage that it can be carried out by optical means.

The reason why the adhesive sheet of the present invention containing a small amount of metal particles exhibits high adhesive strength and high conductivity is not clear, but it is presumed as follows. In other words, the adhesive layer flows due to heating or heating/pressure adjustment during connection, and some of the metal particles protrude from the surface layer of the adhesive, that is, the interface with the circuit. The adhesive sheet itself can fully adapt to the surface of the circuit, and a high residual contact force can be obtained.Also, as will be described later, the metal particles embedded in the adhesive layer are more likely to contact each other in the thickness direction. However, since the interface is melted and integrated, high conductivity can be obtained.If there are many metal particles at the interface between the circuit and the adhesive, the contact area will decrease and the adhesive strength will decrease. Therefore, the connection reliability during use deteriorates, which does not meet the purpose of the present invention.According to the study results of the present inventors, the thickness of the adhesive layer was set to 110% of the particle size of the metal particles. It is preferable to set it as above.

The metal particles of the present invention have a diameter of 1 to 50 μm, a ratio of the minimum diameter to the maximum diameter of the particles of 0.5 to 1.0, and contain 61 to 10% of KO in the adhesive. As for the particle size, a maximum diameter of 1 to 50 μm is appropriate. If the diameter is 1 μm or less, a large amount of metal particles are required, resulting in a significant decrease in adhesive strength.

If the thickness is 50 μm or more, a smooth adhesive surface that is compatible with the adherend cannot be obtained due to the relationship with the thickness of the adhesive sheet layer, and therefore sufficient adhesiveness cannot be obtained.

Regarding the shape, the ratio of the minimum diameter to the maximum diameter (hereinafter referred to as particle size ratio) is about 0.5 to 1.0.

If it is outside this range, the balance between conductivity and adhesiveness will shift. A typical example that satisfies this range is a bispherical shape, but there is no particular limitation as long as it satisfies the above conditions. There may be protrusions or irregularities on the particle surface.

Moreover, the particle size shall be the overall average particle size. A convenient method for measuring the particle shape and diameter is, for example, using an electron microscope.

If the metal particles are, for example, spherical, the adhesive sheet becomes fluidized by heating or heating and pressure during connection, and a portion of the spherical particles can exist in contact with the circuit surface.

On the other hand, in the case of flaky particles, for example, the long sides of the particles are present along the ascending path surface, and the metal particles occupy most of the ascending path surface, resulting in a large decrease in adhesion. Furthermore, in connection of extremely fine circuits, if metal particles are arranged in the plane direction of the circuit, the insulation between adjacent circuits will deteriorate, which is not preferable.

These metal particles used have a melting point in the range of 100 to 250°C. If the melting point is lower than 100° C., it is not preferable because the reliability of connection between circuits at high temperatures decreases. Moreover, if the temperature exceeds 250° C., it is not practical because it narrows the cavity temperature when the circuit is connected and the components attached to the circuit are adversely affected by the high heat. As these metal particles, various eutectic alloys or non-eutectic low melting point alloys can be used. For example, Pb
8a9%/5n11.1% (melting point 250°C), expressed in the same way below, P b 82.6/Cd17.4 (2
48℃) Pb85/Au15 (215”C), Tl 9
17/Na 6.3 (238°C), TI 92/As
8 (220°C), TlP9.4/LiCL6 (211°C
), TI 82.9/Cd 17.1 (203°C),
11977Mg5 (203℃), T180/5b20 (
195°C), TI 52.5/B i 47.5 (1
88℃), TlP &5/Ki5 (173℃), T1
757Au27 (131℃), B197/Na5 (21
8℃), Bi76.5/215Tl (198℃),
B l 60/Cd40 (144℃), B157/5n
43 (139°C), B156.5/Pb4i5 (125
℃), 5n (232℃), 5n67.7/Cd32.3
(177℃), 5n56.5/TJ4i5 (170℃)
, I n 97.2/Zn 2.8 (144°C),
1n74/Cd26 (123°C), B157/Pb11
/5n42 (135℃), B156/5n40/Zn4
(130℃), B i 5 59 / S n 21
9 / Sn 25.9 / Cd 2 (L2 (103
°C), Sn 48/In52 (117 °C), In (15
7℃), Ag5/Pb 15/In80 (149℃)
, Pb38/5n62 (183°C), Pb47/5n5
0/S63 (186℃), Pb50/1n50 (18
0℃) Pb50/5n50 (183℃) Pb
10/5n90 (183℃) Aui5/Pb9&5(2
21℃) Pb5/5n95 (183℃), Ag10
/In90 (204℃) pb60/5n40 (1
83℃) 5n95/5b5 (232℃), etc.

The appropriate amount of metal particles in the adhesive is 0.1 to 10% by volume. If it is less than 0.1%, satisfactory conductivity cannot be obtained.
If it exceeds 0 volume%, the insulation in the direction adjacent to the circuit will decrease.
Furthermore, the adhesive strength is greatly reduced and the transparency of the adhesive sheet cannot be obtained.

Examples of the adhesive polymer used in the present invention include ethylene-vinyl acetate copolymer, polyethylene, and ethylene-vinyl acetate copolymer.
Propylene copolymer L Ethylene-acrylic ester copolymer, acrylic ester rubber, polyisobutylene, atactic polypropylene, polyvinyl butyral, styrene-butadiene copolymer, polybutadiene, ethylene cellulose, polyamide resin, polyurethane, etc. Used alone or in combination of 2 [i or more.

In addition, tackifiers, commonly used plasticizers, crosslinking agents, anti-aging agents, antioxidants, etc. can be used as necessary. Examples of the tackifier include rosin resins such as rosin, hydrogenated rosin, estercam, and maleic acid-modified rosin, petroleum resins, xylene resins, coumaron-indene resins, and the like. These tackifiers may be used alone or in combination.
It may be used in combination at 8°C or higher.

The adhesive sheet is manufactured by dissolving an adhesive composition consisting of a polymer and other additives used as necessary in a bath agent or by heat-melting it to a liquid state, and then milling the Kinkai particles using a conventional method such as a ball mill. A metal particle mixed adhesive composition is obtained by mixing according to the method described above.

At this time, for example, a surfactant or the like may be used as a dispersant for the metal particles, if necessary.

The metal particle mixed adhesive composition is coated and dried on a separator made of paper or plastic film, which has been subjected to peeling treatment as necessary, using a roll coater or the like, thereby taking advantage of the volume reduction in the thickness direction of the meat. As a result, a metal particle mixed adhesive sheet having metal particles arranged more densely in the thickness direction is obtained. In this case, it is also possible to wrap the film using only the adhesive layer without using a separator. The thickness of the adhesive sheet is determined relative to the size of the metal particles used and the characteristics of the adhesive sheet.

That is, in order to sufficiently hold the metal particles with an adhesive, the adhesive needs to have a minimum particle size of 110% or more of the particle size of the metal particles. 1
If it is less than 10%, the metal particles are not protected by the adhesive, resulting in deterioration in conductivity due to oxidation or corrosion. Further, due to the characteristics of the adhesive sheet, a thickness of 5 to 100 μm is required.

If it is less than 5 μm, sufficient adhesion cannot be obtained, and 100 t1
If it is more than m, it is not practical because a large amount of metal particles must be mixed in order to obtain sufficient conductivity. For the adhesive sheet layer, a conductive or non-conductive core material made of, for example, non-woven fabric may be used as required.

The obtained adhesive sheet surface may be covered with a separator to prevent the adhesion of dust, etc., if necessary, or it may be continuously rolled up using a double-sided separator.

The adhesive sheet thus obtained has considerable transparency. When the adhesive sheet has transparency, quality control during manufacturing can be easily performed and the adhesive sheet has a good appearance. Furthermore, when adhering display elements, etc., it becomes possible to adopt a configuration in which the adherend can be seen through.

A method of bonding a circuit using the obtained adhesive sheet is, for example, by temporarily pasting the adhesive sheet on circuit A, peeling off the separator if there is a separator, and applying circuit B to that surface by heat press or heating roll. You can paste it with etc. At this time, both circuits A and B are strongly connected by the softening and flow of the adhesive, and at the same time, a stable four-way circuit can be formed in the contact layer M by melting the metal particles.

EXAMPLES The present invention will be explained in more detail below with reference to Examples.

The amount of adhesive compounded is all for one mound. Further, the particle size of the metal particles was determined from observation using a scanning electron microscope.

Examples 1 to 8, Comparative Examples 1 to 5 Ethylene-vinyl acetate copolymer (vinyl acetate 4%, MI
A5) 100 parts and a rosin-based tackifier (softening point 70°C)
) were each dissolved in 300 parts of toluene. The metal particles shown in Table 1 were added to this solution (the amount added is indicated by the volume fraction per resin isomorphic content), and the mixture was stirred and mixed in a ball mill for 48 hours to obtain an adhesive mixture. coated on treated polyester film),
The bath agent was completely removed by drying at 120°C for 3 minutes. The obtained adhesive sheet was attached to a 5US430BA plate (thickness: 500 μm).
), peel off the separator and add 35μ
Layer m copper foils and apply pressure 10k at the bonding temperature shown in Table 1.
The mixture was heated and pressurized for 20 seconds at a pressure of 100 g/p to obtain a composite consisting of SUS/metal particle mixed adhesive sheet/copper foil. The adhesive strength of this product is shown in Table 1.

The penetration resistance is determined by the adhesive sheet SUS 430BA
and 0.5a[lI] of aluminum foil were adhered, and the resistance in the thickness direction of the adhesive sheet was measured and converted to volume resistivity (Table 1)
. The foam layer resistance was determined by bonding an adhesive film onto an insulating polyester film of 50 μm, and measuring the resistance in the longitudinal direction of the adhesive film with an inter-electrode distance Q of 5 cm and a test piece width of 0.5 cm.
It was measured at 5 cm and converted into volume resistivity using the following formula.

S: Cross-sectional area of sample (Gll') R: Actual measurement of resistance fi (Ω) l: Distance between electrodes (cm) Adhesive strength + 2 JIS Z-0237VC compliant Sita 180
Although this was a multi-peel peeling method, the peeling rate was 5Qn++u/min. The measurement was carried out at 20° C. and 65% R) 1 with the steel foil bent at 90 degrees.

The total light transmittance was measured according to JIS K-6714 using a digital turbidity meter NDH-20D manufactured by Nippon Denshoku Kogyo ■.

1-Jig:,! 1 Examples 9 to 11, Comparative Examples 6 to 7 Styrene-butadiene block copolymer (MI2.6
) 100 parts and 50 parts of an aromatic adhesion promoter with a softening point of 120°C
Table 2.
The metal particles shown in 1 were added and mixed in a ball mill for 48 hours to obtain an adhesive solution containing metal particles. This liquid mixture was applied onto a separator (silicon-treated polyester film) using a bar coater and dried at 120° C. for 3 minutes to completely remove the solvent and obtain an adhesive sheet.

Next, line width α1mro, pitch Q, 2ru
A flexible circuit with a circuit width of 1QQ+nm having a circuit width of 1 (FPC), the above adhesive film cut into pieces with an adhesive width of 3 mm and a length of 100 cm was inserted between two sheets of 1 (FPC), and the circuit of the upper and lower two FPCs was inspected under a microscope. After proper alignment, apply a pressure of 5k.
The circuit was connected by applying pressure and heating at g/an' for 10 seconds. The contact M temperatures are as shown in Table 2, and were determined by adjusting the hot plate temperature of the press. At this time, since the adhesive sheet was transparent, it was possible to align the circuits extremely easily with the help of transmitted light. Table 2 shows the electrical characteristics of the connected circuit.
It was shown to.

[Effects of the Invention] As detailed above, the adhesive sheet of the present invention containing a very small amount of specific conductive metal particles can be used as a highly adhesive and highly conductive circuit connection material.

Furthermore, the dependence of the connection resistance on temperature changes is small and is extremely stable. Furthermore, since the adhesive sheet is transparent, it has the advantage that minute alignment of circuits can be easily performed with the aid of transmitted light.

Claims (1)

[Scope of Claims] 1. In a conductive adhesive sheet comprising an adhesive component and conductive particles, the adhesive component has an average particle size of 1 to 50 μm;
The conductive metal particles have a ratio of the minimum diameter to the maximum diameter of the particles of 0.5 to 1.0 and a melting point of 100°C to 250°C.
1 to 10% by volume, the adhesive layer has a thickness of 110% or more of the average particle diameter of the conductive particles, and has a total light transmittance of 40% or more. 2. The conductive adhesive sheet according to claim 1, wherein the adhesive component is a heat-sensitive adhesive sheet whose main component is a thermoplastic polymer that softens and exhibits adhesive properties at the melting point of the metal particles. .