JPS6194391A - Conductive paste for formation of circuit - 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 This invention relates to improvements in conductive pastes for forming circuits.

Conventionally, for example, conductive paste for circuit formation has been used to form circuits on printed circuit boards. This conductive paste for circuit formation is composed of a mixture of about 80% by weight of a conductive metal such as Ag or Cu and about 20% by weight of a binder such as an epoxy resin or a phenol resin.

Circuit formation using this conductive paste for circuit formation is performed in the following procedure. - That is, after applying a conductive paste for circuit formation to a thickness of about 20 to 30 μm on a substrate through a screen of a predetermined pattern made of stainless steel or the like, it is heated at about 150 to 200°C for about 20 to 30 minutes. The conductive paste for circuit formation is cured for about 20 minutes.
A circuit is formed of a conductive metal film having a thickness of ~30μ.

The problem that (2) is trying to address However, in the circuit using the conductive paste for circuit formation described above, the conductive metal is bonded with a binder and baked onto the substrate.

The bonding force is not strong, and the mechanical strength against external forces such as tension is weak6. Therefore, when inserting electronic components into the formed circuit using an automatic insertion machine, etc., There were problems such as the circuit (conductive metal) being separated from the substrate by the IdJ or being partially damaged.

Furthermore, when a printed circuit board with electronic components mounted on a circuit falls, there is a problem in that the circuit peels off from the board due to the impact of the fall.

This invention was made in view of the above-mentioned problem, and its purpose is to improve the bonding properties of conductive metals.
An object of the present invention is to provide a conductive paste for forming a circuit, which enables the formation of a circuit with improved mechanical strength.

11 In order to achieve the above-mentioned object, the present invention provides a conductive paste for circuit formation, which is made by mixing a conductive metal and a binder, and which is a conductive paste that is intertwined with the conductive metal and has a binder. A conductive paste for forming a circuit is formed by mixing about 1 to 5% of whiskers to increase the bonding force between conductive metals.

According to this method, the circuit formed on the substrate is printed onto the substrate in a state in which the conductive metals are entangled with each other via whiskers and are firmly bonded. Therefore, the mechanical strength of the circuit against external forces such as tension is increased, and peeling and damage of the circuit when electronic components are inserted is prevented.

Furthermore, since the amount of whiskers mixed in is extremely small, the conductivity of the circuit is not inhibited.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a conductive paste for forming a circuit according to the present invention will be described below with reference to FIGS. 1 and 2.

In FIG. 1, reference numeral 1 indicates a printed circuit board, 2 indicates a printed circuit board 1, and 3 indicates a conductive paste for circuit formation which is applied to the substrate 2 to form a circuit. The conductive paste 3 for forming a circuit includes a binder made of an epoxy resin or a phenol resin of about 20 V%, a conductive metal made of Ag particles or Cu particles of about 79 to 751%, and a conductive metal intertwined with the conductive metal. and about 1 to 5 wt % of whiskers to increase the bonding force between conductive metals.

Whiskers are made of carbon silicon (SiC, carborundum), for example.
Or alumina, boron, etc. with a diameter of about 0.1 to 1 μm.
, formed as hair-like filaments or hair-like crystals with a length of about 10 μm. Therefore, the mixed whiskers are dispersed between the conductive metals, and the hair-like filaments are entangled with each conductive metal particle to firmly bond these particles.

Therefore, the mechanical strength of a circuit formed using this conductive paste 3 for circuit formation is significantly improved. In addition, the reason why the whisker mixing ratio is about 1 to 5wt% is that in Figure 2, where the horizontal axis is the whisker mixing ratio and the vertical axis is the tensile strength of the circuit, the whisker content is about 2wt%. The strength reached the highest value of 908 gf/mm'', which was 7 at 1 sushi%.
78gt/no”, 858gf/at 5%1t%
This is because it has been confirmed through experiments that it is am2. It was also found that these values increased by about 50% compared to the case where whiskers were not mixed. Note that 4 in FIG. 1 is N1 plating that is fixed to a circuit formed by a conductive paste for circuit formation.

Next, the effect will be explained.

A conductive paste 3 for circuit formation is applied to a thickness of about 20 to 30 μm on the substrate 2 through a screen (not shown) with a predetermined pattern made of stainless steel or the like.
When heated at 0 DEG C. for about 20 to 30 minutes, the circuit-forming conductive paste 3 hardens, and a circuit of a conductive metal film baked to a thickness of about 20 to 30 microns is formed on the substrate 2. In this case, in the above-mentioned coating process, the diameter of the whisker is about 1/10 to 1/100 of the length, so the whisker will not be caught on the mesh during screen printing. Therefore, the efficiency of screen printing does not decrease. Moreover, since the amount of whiskers mixed in is minute, even if it is non-conductive like silicon carbide, it has almost no effect on the conductivity of the circuit.

Furthermore, since the conductive metal particles are firmly bonded through the whiskers, the mechanical strength of the circuit is increased and peeling and breakage phenomena are prevented.

Effects of the Invention As explained above, the present invention provides a conductive paste for circuit formation, which is made by mixing a conductive metal and a binder, and which increases the bonding strength of the conductive metal by intertwining with the conductive metal. Since it is characterized in that about 1 to 5% of whiskers are mixed in, it is possible to obtain various effects as described below.

(1) A conductive paste for forming a circuit can be formed extremely easily by simply mixing a small amount of whiskers. Moreover, since the amount of whiskers mixed in is very small, even if the whiskers themselves are expensive, the increase in the price of the conductive paste itself for forming circuits is alleviated.

(2) Furthermore, since the mechanical strength of the formed circuit is significantly increased, peeling and damage of the circuit when inserting electronic components is prevented. Therefore, the efficiency of printed circuit board manufacturing can be significantly improved.

(3) Furthermore, even if a printed circuit board with electronic components and the like mounted on it is inadvertently dropped, the circuit will not peel off due to the impact of the fall. Therefore, the durability of the printed circuit board can be improved.

(4) Furthermore, even if the whiskers themselves are non-conductive, the amount of the whiskers mixed in is so small that the conductivity of the circuit is not inhibited.

Therefore, the reliability of the printed circuit board does not deteriorate.

[Brief explanation of the drawing]

1 and 2 show an embodiment of the present invention, FIG. 1 is a front sectional view of a printed circuit board on which a circuit is formed using the conductive paste for circuit formation according to the present invention, and FIG. 2 is a circuit diagram. It is a chart showing the relationship between the tensile strength of the conductive paste for formation and the whisker mixing ratio. 1... Printed board, 2... Board, 3... Conductive paste for circuit formation.

Claims (1)

[Scope of Claims] A conductive paste for forming a circuit made by mixing a conductive metal and a binder, the paste comprising about 1 to 5 wt% of the conductive metal that intertwines with the conductive metal to increase the bonding strength of the conductive metal. A conductive paste for circuit formation that is characterized by containing whiskers.