JPH07205395A - Conductive bonding agent - Google Patents

Abstract

PURPOSE:To obtain a conductive binder having a low resistance value by mixing metal flakes and conductive whiskers with a base material composed of a thermosetting resin and constituting a metal network of the conductive whiskers. CONSTITUTION:A conductive binder is constituted by mixing a large number of metal flakes 7 composed of an Ag/Pd alloy and a large number of conductive whiskers 8 composed of ZnO with an epoxy resin 6. Each of the whiskers 8 has four needle projections and these needle projections come into contact with the peripheral metal flakes 7 to form a metal network. At the time of use, for example, the conductive binder is thinly applied to the land part 10 of a printed circuit board 9 in a thickness of 150nm by printing and heated in such a state that the electrode 11 of an electronic part is bonded to the conductive binder layer to cure the epoxy resin to electrically and mechanically bond the electrode 11 of the electronic part to the land 10. Since each of the whiskers 8 have four needle projections, the contact ratio with the metal 7 flakes is increased and, that is, the metal network is formed and the resistance value of the conductive binder itself is made low.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive bonding agent used for bonding electronic parts to a circuit board and for other electrical bonding.

[0002]

2. Description of the Related Art Generally, in an electronic device, a conductive bonding agent is used for electrically and mechanically bonding an electronic component to a circuit board thereof. The conductive bonding agent has a low resistance, and It is desired that coating and heat treatment be easy.

Solder is generally used as the conductive bonding agent, but it is not suitable when the electrodes of electronic parts are bonded to the land of the circuit network of the circuit board by thin printing. In such a case, cream solder is used. However, when this cream solder is used, the temperature for reflow heating in the bonding step is high and the electronic component must be heat resistant.

For this reason, conventionally, a conductive bonding agent has been used in which a flake-shaped metal made of an Ag / Pd alloy is mixed in an epoxy resin and the flaky metal is brought into contact to obtain conductivity. ing. FIG. 4 shows the conductive bonding agent, in which 1 is an epoxy resin and 2 is a flake metal. Further, in the figure, 3 is a circuit board, 4 is a land, and 5 is an electrode of an electronic component.

[0005]

By the way, the conductive bonding agent obtained by mixing the flake-shaped metal with the epoxy resin obtains the conductivity by simply contacting the flake-shaped metals with each other, and there are few contact points. Therefore, the resistance value cannot be lowered, and the demand for a conductive adhesive having a lower resistance value cannot be satisfied. Further, even if the reflow heating was applied, the contact ratio did not increase, and the resistance value could not be reduced.

The present invention has been made in view of the above conventional problems, and an object thereof is to provide a conductive adhesive having a low resistance value.

[0007]

In order to achieve the above-mentioned object, the present invention uses a thermosetting resin such as an epoxy resin as a base material, and a flake metal or low temperature solder and a conductive whisker are added to the thermosetting resin. And a conductive bonding agent.

[0008]

In the conductive bonding agent having the above structure, the metal whiskers have rod-shaped or needle-shaped protrusions, and these needle-shaped protrusions connect flaky metal or low temperature solder. The contact ratio increases, and the metal whiskers are metal-bonded to the low-temperature solder by heating at a relatively low temperature of around 150 ° C., thereby lowering the resistance value of the conductive bonding agent.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 6 denotes an epoxy and a resin as a base material, and a large number of flake-shaped metals 7 made of an Ag / Pd alloy and a large number of conductive whiskers 8 made of ZnO are mixed in the epoxy resin 6 for conductive bonding. Make up the agent. In the figure, 9 is a circuit board, 10 is a land, and 11 is an electrode of an electronic component.

As shown in FIG. 2, the conductive whiskers 8 have four needle-like protrusions, and each needle-like protrusion makes contact with the flaky metal 7 around it to form a metal network. To do. In use, for example, the epoxy resin 6 is hardened by applying a thin print, for example, to a thickness of 150 μm on the land 10 of the circuit board 9 and heating the electrode 11 of the electronic component bonded thereto. And land 1
The electrode 11 of the electronic component is electrically and mechanically bonded to the electrode 0.
Since the conductive whiskers 8 have a size of 5 to 10 μm, there is no problem in the printing.

In this structure, since each conductive whisker 8 has four needle-shaped protrusions, the contact ratio with the flake-shaped metal 7 is increased, that is, a metal network is formed, and therefore the conductive joint is formed. The agent itself has a low resistance value. In addition, the conductive whiskers 8 are 4
The needle-like protrusions of the book increase the strength of the conductive bonding agent after curing, and the conductive bonding agent is not broken by mechanical vibration or the like. On the other hand, if the resistance value is the same as the conventional one, the amount of resin can be increased, so that the bonding strength can be improved.

Here, the resistance value of a conductive adhesive having a composition in which 20% by weight of flake metal and 20% by weight of conductive whiskers were mixed in 20 parts of epoxy resin was measured.
The resistance was 1.5 × 10 ⁻⁴ Ω, which was considerably lower than the conventional resistance value of 5.0 × 10 ⁻⁴ Ω shown in FIG.

Next, a second embodiment of the present invention will be described. In this embodiment, low-temperature solder particles are mixed with an epoxy resin together with a conductive whisker in place of the flake-shaped metal in the above-described embodiment to form a conductive bonding agent. The conductive bonding agent having this structure increases the contact ratio by the conductive whiskers similarly to the above-mentioned embodiment, but in addition to this, when heated in the bonding step, as shown in FIG. The low temperature solder particles 13 mixed around the whiskers 12 are welded and metal-bonded to the needle-like protrusions of the conductive whiskers 12 before the epoxy resin is cured as shown in FIG. 3B. Therefore, a more reliable metal network is established, and accordingly, the resistance of the conductive bonding agent is reduced. If the low-temperature solder particles 13 are made of Sn-In, for example, they can be melted at 117 [deg.] C., so that the electronic components can be used even if they are not highly heat-resistant. Of course, the conductive whiskers 12 increase the mechanical strength of the conductive bonding agent in addition to the formation of the metal network.

As described above, in the conductive bonding agent of each of the above-described embodiments, since the conductive material and the conductive whiskers are mixed in the thermosetting resin such as epoxy resin, the low resistance which is not found in the conventional conductive bonding agent or The amount of resin can be increased and the bonding strength can be increased.

Although the epoxy resin is used as the base material in the above embodiment, other thermosetting resins having similar properties may be used. Further, this conductive bonding agent may be used not only for bonding the circuit board and the electronic component but also for other bonding or as a conductive layer, and the present invention is not limited to the application of the above-mentioned embodiment.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the composition of a conductive bonding agent according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a conductive whisker used for the conductive bonding agent.

FIG. 3 (a) is a schematic view of the composition of a conductive bonding agent according to another embodiment of the present invention, and FIG. 3 (b) is a schematic view of the composition after heating the conductive bonding agent.

FIG. 4 is a sectional view showing the composition of a conventional conductive bonding agent.

[Explanation of symbols]

 6 Epoxy resin (thermosetting resin) 7 Flake metal 8 Conductive whisker

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location H01B 1/20 D H05K 3/32 B 8718-4E (72) Inventor Toshiaki Sugimura Kadoma City, Osaka 1006 Kadoma Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A conductive bonding agent, characterized in that a thermosetting resin is used as a base material, flaky metal and conductive whiskers are mixed in the base material, and a metal network is constituted by the conductive whiskers. 2. A conductive bonding agent comprising a thermosetting resin as a base material, low temperature solder particles and conductive whiskers being mixed in the base material, and a metal network being constituted by the conductive whiskers.