JPH09198916A - Conductive particles - Google Patents

Abstract

(57) [PROBLEMS] To provide conductive fine particles capable of easily bonding various substrates with high accuracy. SOLUTION: Spherical polymer particles 1 coated with a conductive layer 2
Of the spherical polymer particles 1 coated with the conductive layer 2 is covered with solder having a thickness of 5 to 30% of the radius of the spherical polymer particles 1.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to conductive fine particles having excellent conductivity.

[0002]

2. Description of the Related Art Conductive fine particles are conductive pastes used for joining lead electrodes, wiring boards, etc. in electronic parts, vertical conduction adhesives, anisotropic conductive adhesives, electromagnetic shielding conductive materials, etc. Is used for. Examples of such conductive fine particles include solder balls made of lead and tin, and particles made of a non-conductive material coated with a conductive material.

A solder ball composed of lead and tin can easily bond a lead electrode, a wiring board and the like by heating. However, for example, when joining different types of base materials, the stress applied to the joint portion caused by the difference in the coefficient of thermal expansion between the base materials cannot be absorbed by the solder balls.
There is a problem that peeling occurs at the interface between the solder ball and the base material, and it is difficult to obtain a satisfactory joint.

On the other hand, in the case of conductive fine particles in which particles made of a non-conductive material are coated with a conductive material, the particles made of a non-conductive material used have heat resistance, and the accuracy of bonding is lowered by heating. Since it is less likely to occur, in recent years, its use has become popular with the progress of miniaturization and thinning of electronic components.

Japanese Unexamined Patent Publication No. 5-287582 discloses a method of coating particles made of a non-conductive material with a conductive material by directly forming a copper plating layer on the surface of the non-conductive material by an electrolytic copper plating process. It is disclosed. This method does not require a conventional electroless copper plating step and can form a copper plating layer only by electrolytic copper plating, so that the processing steps can be simplified and the processing time can be shortened.
The productivity can be improved by improving the working environment.

However, since there is a large difference in the coefficient of thermal expansion, the compressive deformability and the like between the non-conductive material forming the central part of the conductive fine particles and the metal coating the surface of the conductive fine particles, there are large differences in temperature during use and compression. There is a problem that the formed copper plating layer is easily broken or peeled due to deformation or the like.

Japanese Unexamined Patent Publication (Kokai) No. 3-129607 discloses an anisotropic method in which resin particles whose surface is coated with a metal and low-melting metal particles such as zinc and tin are dispersed in a polymer material having thermal adhesiveness. A conductive film is disclosed. Among the conductive resins used in this anisotropic conductive film, the resin particles whose surface is coated with a metal include, for example, when the wiring conductor patterns are thermocompression-bonded, while keeping the intervals between the wiring conductor patterns constant. The low melting point metal particles have features such that they can be electrically connected, and the low melting point metal particles can easily confirm the crimping state while electrically connecting the wiring conductor patterns by melting. It has characteristics.

However, as described above, the resin particles whose surface is coated with a metal have a possibility that the metal layer on the surface may be broken or peeled off, and the low melting point metal particles are , And there is a possibility of causing uneven melting.

Japanese Unexamined Patent Publication (Kokai) No. 5-119337 discloses an interconnection method of electrode terminals using conductive fine particles whose surfaces are coated with an adhesive. This method of interconnecting electrode terminals is performed by spraying conductive particles whose surfaces are coated with an adhesive onto the first wiring board and fixing them by heating, then placing the second wiring board and then performing thermocompression bonding. Adhere and fix,
It interconnects the electrode terminals of the wiring board facing each other through conductive particles, and is more reliable than the conventional method of interconnecting electrode terminals using conductive particles coated with an adhesive. It has the characteristics of

However, the method of interconnecting the electrode terminals is such that the conductive particles having the surfaces coated with the adhesive are dispersed before the conductive particles having the surfaces coated with the adhesive are dispersed on the first wiring substrate. Therefore, there is a problem that the process becomes complicated.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned conventional problems, and an object thereof is to make it possible to easily bond various substrates with high accuracy. The purpose of the present invention is to provide fine particles.

[0012]

In order to achieve the above object, the conductive fine particles of the present invention are spherical polymer particles in which the surface of spherical polymer particles coated with a conductive layer is coated with the conductive layer. Is coated with solder having a thickness of 5 to 30% of the radius.

The material of the conductive layer used in the present invention is not particularly limited, and examples thereof include a conductive layer made of gold, nickel or the like.

The spherical polymer particles used in the present invention are not particularly limited, and examples thereof include polystyrene, polystyrene copolymers, polyacrylic acid esters, polyacrylic acid ester copolymers, phenol resins, silicone resins,
Examples thereof include those made of polyamide resin, polyester resin, polyvinyl chloride and the like. The shape of the spherical polymer particles is not particularly limited as long as it is spherical, and may be hollow, for example.

The method of coating the above-mentioned spherical polymer particles with the above-mentioned conductive layer is not particularly limited, but an electroless plating method or the like is preferable.

In the present invention, the surface of the spherical polymer particles coated with the conductive layer is coated with solder having a thickness of 5 to 30% of the radius of the spherical polymer particles coated with the conductive layer. It is a thing. When the thickness of the solder is less than 5% of the radius of the spherical polymer particles coated with the conductive layer,
When joining electrode terminals etc., the melting amount of solder decreases,
If sufficient bondability cannot be obtained and the radius of the spherical polymer particles coated with the conductive layer exceeds 30%, the melting amount of the solder increases, which may cause short circuit with the adjacent electrode terminal. It is limited to the above range.

The solder coating is preferably uniform. If the solder coating is non-uniform, melting during heating becomes non-uniform, and it may be difficult to obtain a highly reliable joint.

The particle size of the conductive fine particles of the present invention is not particularly limited, but is preferably 1 to 1000 μm. If it is less than 1 μm, it may be difficult to make the aggregated particles generated in the electroless plating step into single particles,
If it exceeds m, the conductive layer coated with the spherical polymer particles may be cracked and may be easily separated from the spherical polymer particles.

The radius of the spherical polymer particles coated with the conductive layer is 5 times the radius of the spherical polymer particles coated with the conductive layer.
As a method of coating a solder having a thickness of ~ 30%,
Although not particularly limited, preferably, an electroplating method or the like can be mentioned, whereby thick-film solder plating can be obtained.

The conductive fine particles of the present invention are, for example, as shown in FIG. 1, plated with gold, nickel or the like on the surface of the spherical polymer particles by an electroless plating method to form a conductive layer. It can be obtained by plating the spherical polymer particles coated with the conductive layer with solder by an electroplating method. In the figure, 1 is a spherical polymer particle, 2 is a conductive layer, and 3 is a solder plating layer.

For joining the wiring boards using the conductive fine particles of the present invention, for example, after the conductive fine particles are uniformly dispersed on the first wiring board, the second wiring board is uniformly dispersed. It is carried out by melting the solder by heating the conductive fine particles relative to each other.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

(Examples 1 to 3, Comparative Examples 1 and 2) On the surface of spherical polymer particles (“Micropearl NI” manufactured by Sekisui Fine Chemical Co., Ltd.) having the properties shown in Table 1 and coated with a nickel conductive layer. Electroplating was performed using an electroplating device (“Flow loop looper RP-1” manufactured by Uemura Kogyo Co., Ltd.), and a solder (weight ratio: Pb / Sn = 60/40) plating layer having a thickness shown in Table 1 was coated. Conductive fine particles were obtained.

(Examples 4, 5 and Comparative Examples 3, 4) Spherical polymer particles (“Micropearl AU” manufactured by Sekisui Fine Chemical Co., Ltd.) having the properties shown in Table 1 and coated with a gold conductive layer were used. Except for the above, in the same manner as in Example 1, conductive fine particles coated with a solder (weight ratio: Pb / Sn = 60/40) plating layer having a thickness shown in Table 1 were obtained.

[0025]

[Table 1]

The following performance evaluations were conducted on the electroconductive fine particles obtained in the above Examples and Comparative Examples, and the results are shown in Table 2. (1) Thickness of solder plating layer The conductive fine particles are washed and dried, and then polished to form a hemispherical shape, and the polished surface of this hemispherical object is observed with a magnifying glass to measure the thickness of the solder plating layer. did.

(2) Bonding Strength The above conductive fine particles are compounded in postflux (“F-40” manufactured by Harima Chemicals Co., Ltd.) so that the area projection ratio of the particles is 6%, and this compound is prescribed. Screen printing was performed on the electrode patterns of FPC (flexible printed circuit) connection terminals having pitch electrode patterns. Another FPC joint terminal having a similar electrode pattern is superposed on this joint terminal so that the electrode patterns correspond to each other, and 1
A sample was prepared by heating and welding at 200 ° C. while pressurizing at kg / cm ² and laminating the electrode patterns of the two FPC bonding terminals. Using this sample, the joint strength was measured by a 180-degree tensile test.

(3) Insulation Resistance Between Lines, Connection Resistance Using the same sample as in (2), the electric resistance between adjacent electrodes was measured by an electric resistance measuring device to obtain the insulation resistance between lines. In addition, using the same sample as (2), the first FP
The electrical resistance between the C electrode and the corresponding second electrode was measured by an electrical resistance measuring device and used as the connection resistance.

[0029]

[Table 2]

As is clear from Table 2, when the thickness of the solder plating layer is less than 5% of the diameter of the spherical polymer particles coated with the conductive layer, the bonding force between the solder plating particles is insufficient and the conductive layer is coated. If the diameter of the spherical polymer particles exceeds 30%, the insulation resistance between wires is lowered. Further, when the spherical polymer particles coated with the conductive layer are fine particles having a particle size of about 1 μm, they are aggregated and it is difficult to form a single particle, and it is not possible to obtain conductive fine particles. In addition, spherical polymer particles coated with a conductive layer,
When the particles became large particles of about 1000 μm, the conductive layer was cracked and the conductive layer was peeled off, so that the conductive fine particles could not be obtained.

[0031]

EFFECT OF THE INVENTION Since the electroconductive fine particles of the present invention have the above-mentioned constitution, they can easily join the joining terminals and the like with high accuracy without using an adhesive or the like, and have excellent electroconductivity. Therefore, it is suitable for BGA applications, bonding between different kinds of substrates, and the like.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of conductive fine particles of the present invention.

[Explanation of symbols]

 1 Spherical polymer particles 2 Conductive layer 3 Solder plating layer

Claims (1)

[Claims] 1. The surface of spherical polymer particles coated with a conductive layer has a radius of 5 of the spherical polymer particles coated with the conductive layer.
Conductive fine particles coated with solder having a thickness of -30%.