JPH0471358B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for forming a jumper circuit on a printed wiring board that provides a highly reliable conductive connection. [Prior Art] In response to the demand for higher density printed wiring, multilayer printed wiring boards on which jumper circuits are formed are often used. FIG. 2 shows an example of such printed wiring in a partial cross-sectional view. This printed wiring board has copper on the surface of an insulating substrate 10 (for example, a substrate made of various materials such as epoxy resin, phenolic resin, polyester resin, polyimide resin, or a composite material of these resins and glass fiber or paper). A conductor circuit 11 is formed by an appropriate method such as foil etching, metal plating, or screen printing with conductive paint, and a jumper circuit 14 is further formed on this through an insulating layer 12 by screen printing with conductive paint. Therefore, it is formed so as to be electrically connected to the conductive circuit 11. [Problems to be solved by the invention] In the conventional printed wiring board, the conductor circuit 11
is formed of a metal such as copper, nickel, or silver, and the jumper circuit 14 is generally formed by screen printing with conductive paint containing powder of a metal such as copper, nickel, or silver. In this case, if the metal of the conductor circuit 11 and the metal contained in the conductive paint are of the same type, no particular problem will occur and highly reliable conduction will occur between the conductor circuit 11 and the jumper circuit 14. If a connection can be made between different metals with different potential differences, for example, the conductor circuit 11 is formed of nickel metal,
When printed wiring in which the jumper circuit 14 is formed of conductive paint containing silver powder is used under high humidity, the conductor circuit 11 and the jumper circuit 1
A local battery is formed on the contact surface between the two metals due to the potential difference between different metals, causing problems such as electrolytic corrosion of the metals, increasing connection resistance, or poor conduction. In particular, galvanic corrosion becomes more pronounced as the potential difference between dissimilar metals increases. In addition, when the conductor circuit 11 is formed of metal foil, moisture seeping in from the substrate 10 side can be blocked to some extent by the metal foil layer, and the occurrence of electrolytic corrosion can be slightly delayed. However, if the conductive circuit 11 is formed of metal plating, the circuit 11 layer has almost no moisture blocking effect, and significant electrolytic corrosion occurs. The present invention was conceived in view of the above-mentioned current situation, and provides a jumper circuit that does not cause problems such as galvanic corrosion at the connection interface between the conductor circuit 11 and the jumper circuit 14 and provides a highly reliable conductive connection. The purpose is to provide a forming method. [Means for Solving the Problem] In order to achieve the above object, the method for forming a jumper circuit of the present invention provides a method for forming a jumper circuit, in which a conductive circuit is formed on a printed wiring board by metal plating, and the plated metal of the circuit is When a jumper circuit is formed using a conductive paint containing metals with different potential differences as conductive fillers, a conductive resin layer containing carbon powder is interposed at the connection portion between the metal plating circuit and the jumper circuit. . [Function] That is, the method for forming the jumper circuit of the present invention is as follows:
By interposing a carbon powder-containing conductive resin layer in the conductive connection between the conductive circuit and the jumper circuit, the formation of local batteries and the electrolytic corrosion caused by this are prevented, making highly reliable conductive connections possible. This is what I did. [Example] The present invention will be described in further detail below with reference to FIG. This is a partial sectional view showing an embodiment of the present invention when the basic structure of the conventional printed wiring board shown in FIGS. 1 and 2 is adopted, and the same reference numerals indicate the same components. Therefore, its explanation will be omitted.
The difference between FIG. 1 and FIG. 2 is that in FIG. 2, the conductor circuit 11 and jumper circuit 14 are in direct contact and conductively connected without any other intervening layer, whereas in FIG. In the illustrated embodiment of the present invention, a jumper circuit 14 is formed with a carbon powder-containing conductive resin layer 13 interposed therebetween, and the other components are the same between the two. According to the printed wiring board of FIG. 1 configured as described above, the different metals of the conductor circuit 11 and the jumper circuit 14 do not come into direct contact, so that even if moisture in the atmosphere were to infiltrate into the contact interface, Also, no local batteries are formed and therefore no galvanic corrosion occurs,
Problems such as an increase in connection resistance or disconnection do not occur. The printed wiring board used in the method for forming a jumper circuit of the present invention is not particularly limited, and various printed wiring boards on which conductor circuits are formed by metal plating commonly used in the industry can be used. There is no particular limitation on the insulating layer 12 formed on these printed wiring boards prior to forming the jumper circuit 14 on these printed wiring boards. For example, synthetic resins such as polybutadiene resins, phenolic resins, acrylic resins, epoxy resins, polyester resins, silicone resins, urethane resins, and melamine resins are dissolved in organic solvents, or organosol types are dispersed in water. A liquid material such as an emulsion type obtained by emulsion polymerization or an ultraviolet curing type made by combining a reactive monomer and a photosensitizer is used, and the liquid material is applied to the necessary areas on the printed wiring board (for example, excluding the connection areas of the jumper circuit). part) can be formed by screen printing to the required thickness. To form the carbon powder-containing conductive resin layer 13,
Advantageously, it is formed by screen printing using a known conductive paint consisting of conductive carbon powder and a synthetic resin binder. In this case, the thickness of the conductive resin layer 13 may be arbitrary, for example, 5.
The thickness can be changed over a wide range of ~100 μm or more, and especially when the thickness is formed to be flush with the surface of the insulating layer 12, the difference between the jumper circuit forming surface (the surface of the insulating layer 12) and the conductive resin layer This is particularly preferable because there is no difference in level between the wafer 13 and the wafer 13, making it extremely easy to form the jumper circuit that follows, and enabling reliable conductive connection. Further, the conductive resin layer 13 may be formed before the insulating layer 12 is formed. The jumper circuit 14 is formed using copper, nickel,
It can be formed by a screen printing method using a known conductive paint made of conductive metal powder such as silver and a synthetic resin binder. Example 1 A circuit pattern was printed on a paper-phenol substrate by screen printing using a paste consisting of 80% by weight of copper powder and 20% by weight of a phenolic resin binder, followed by curing treatment (150°C x 30 minutes, pattern film thickness).
20 μm), and then electroless nickel plating was applied on this circuit pattern to form a conductor circuit. A conductive paint consisting of 40% by weight of conductive carbon powder and 60% by weight of phenol resin binder was screen printed on the jumper circuit connection portion on the obtained conductor circuit, and cured (150°C x 30 minutes).
A carbon powder-containing conductive resin layer having a thickness of approximately 20 μm was formed. Next, an ultraviolet curable insulating layer forming paste was screen printed on the printed wiring board in the area excluding the conductive resin layer, and was cured by ultraviolet irradiation to form an insulating layer with a thickness of about 45 μm. Further, on top of this, a conductive silver paint consisting of 80% by weight of silver powder and 20% by weight of phenolic resin binder was screen printed to form a jumper circuit (curing conditions: 150°C x 30 minutes, circuit film thickness: approx.
20 μm). Regarding the printed wiring board obtained in this way, 60℃×
Under a humidity condition of 90% RH, the resistance change between the conductor circuits (conductor circuit → carbon powder-containing resin layer → jumper circuit → carbon powder-containing resin layer → conductor circuit) was measured, and the results are shown in Table 1. . Comparative Example 1 A printed wiring board on which a jumper circuit was formed was produced in exactly the same manner as in Example 1 except that the carbon powder-containing resin layer was removed, and the change in resistance was measured in the same manner.
(In this case, the conductor circuits are conductor circuit → jumper circuit → conductor circuit). The measurement results are shown in Table-1.

〔Effect of the invention〕

The jumper circuit according to the present invention is formed separated from the conductor circuit by the carbon powder-containing conductive resin layer, so it is possible to maintain a stable conductive connection for a long time even under high humidity. It has the excellent effect of being possible. Therefore, it is not necessary to use the same metal for the conductor circuit and the jumper circuit, and even if the conductor circuit is formed by metal plating, a highly reliable printed wiring board can be obtained, so this method has extremely high practical value. It is.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a portion of an embodiment of a printed wiring board obtained by the jumper circuit forming method of the present invention. FIG. 2 is a sectional view of a portion of a printed wiring board on which a jumper circuit is formed using a conventional method. 10...Insulating substrate, 11...Conductor circuit, 12...
...Insulating layer, 13...Carbon powder-containing conductive resin layer, 14...Jumper circuit.

Claims (1)

[Scope of Claims] 1. When forming a jumper circuit on printed wiring on which a conductive circuit is formed by metal plating, using a conductive paint containing a metal having a different potential difference from that of the plating metal of the circuit as a conductive filler, A method for forming a jumper circuit, which comprises interposing a carbon powder-containing conductive resin layer at the connection between a metal plating circuit and a jumper circuit. 2. The jumper circuit according to claim 1, wherein the conductor circuit is formed by nickel plating, and the jumper circuit is formed by conductive paint containing silver powder as a conductive filler. How to form.