JPS6158289A - Printed circuit board - 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 Field of Industrial Application The present invention relates to a printed wiring board used in a wide range of electronic equipment such as television receivers and magnetic recording/reproducing devices.

2. Description of the Related Art Conventional configurations and their problems In recent years, with the widespread use of electronic equipment, the demand for printed wiring boards has increased rapidly.

Under these circumstances, the demand for lower prices of printed wiring boards is increasing more and more, and various printed wiring boards have been developed to meet this purpose.

In general, a printed wiring board has a circuit conductor layer formed on the main surface of an insulating substrate, and various electric circuit elements are mounted on this board and soldered to the circuit conductor layer to create the intended electronic circuit. The structure is as follows.

Printed wiring boards have conventionally been manufactured using various methods, but the manufacturing methods can be broadly divided into two.

One of them is called the etched foil method, which uses a so-called copper-clad laminate as a starting material in which electrolytic copper foil is bonded to the entire surface of an insulating substrate, and removes unnecessary portions of the copper foil by dissolving and removing it by etching.

However, with this etched foil method.

Etch the unnecessary parts of the copper foil! There are disadvantages such as a large loss of conductive material due to dissolution and removal, and a large-scale equipment for waste liquid treatment because the conductive material is produced through a wet process such as etching.

On the other hand, another method is used to solve the problems of the etched foil method described above, and is commonly called the additive method.

The printed wiring board produced by this additive method uses an insulating substrate as a starting material to which no copper foil is bonded, and the required circuit conductor layer is directly formed on the main surface of the insulating substrate.

Currently, various manufacturing processes are being implemented using this additive method, and a typical one is shown in FIG.

This is the simplest manufacturing method among the additive methods, in which a conductive paste is applied onto an insulating substrate by screen printing to directly form a circuit conductor layer.

That is, as shown in FIG. 1, an insulating substrate 1 made of synthetic resin such as a paper phenol laminate or a glass epoxy laminate.
A conductive paste made by dispersing and mixing fine powder of copper or silver in a thermosetting resin such as epoxy resin is applied onto the main surface of the board in the desired circuit shape using a screen printing method, and this conductive paste is heated at high temperature. The circuit conductor layer 2 is formed by heating and curing in the wafer.

However, in printed wiring boards manufactured by this method, the circuit conductor layer is formed using conductive paste, so the resistance value of the circuit conductor layer is generally higher than that of metal foil, and it may be difficult to solder the circuit conductor layer. Because of the inconvenience that it cannot be used, its use has been extremely limited.

OBJECTS OF THE INVENTION The object of the present invention is to provide a method for producing an additive printed wiring board using a conductive paste, and in view of the above-mentioned conventional drawbacks,
An object of the present invention is to provide a printed wiring board having a circuit conductor layer with solderability.The present invention provides a printed wiring board in which a desired circuit conductor layer is formed on at least one main surface of an insulating substrate using a conductive paste. form,
A conductive metal layer that can be soldered is formed only in the part of the circuit conductor layer that requires soldering,
As a result, a printed wiring board with solderability of the circuit conductor layer can be obtained.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Figures 2-G are sectional views of essential parts for explaining the main manufacturing steps of a printed wiring board in an embodiment of the present invention.

In FIG. 2, 3 is an insulating substrate, 4 is a circuit conductor layer made of conductive paste, 6 is a metal mask, and 6 is a conductive metal layer.

The manufacturing process of the printed wiring board of this embodiment configured as described above will be explained in detail below.

First, as shown in FIG. 2, a conductive paste is applied onto the main surface of the insulating substrate 3 in the desired wiring circuit shape by screen printing, and the circuit conductor layer 4 is formed by heating and curing at a high temperature. do.

In this step, as the insulating substrate 3, a synthetic resin insulating substrate such as a paper phenol laminate, a glass epoxy laminate, or a ceramic insulating substrate such as alumina was used.

On the other hand, conductive paste is generally made by mixing and dispersing highly conductive metal powder such as silver or copper in insulating resin such as acrylic resin or epoxy resin. Disperse fine powder in epoxy resin,
We used a liquid-based, high-temperature curing conductive paste that uses isidazole as a hardening agent, has low conductor resistance, and cannot be soldered. Then, this conductive paste was applied onto a glass epoxy laminate to a thickness of 26 to 30 μm by screen printing and cured at 16°C for 60 minutes to form a circuit conductor layer 4.

The reason why we used a conductive paste of a high temperature curing type that cannot be soldered is to ensure the heat resistance of the circuit conductor layer, adhesion to the insulating substrate, and sufficient mechanical strength as a circuit conductor layer. This is because, if a solderable conductive paste is used, the characteristics as a circuit conductor layer described above cannot be fully satisfied because it is a low temperature curing type.

Next, as shown in FIG. 2B, a metal mask 6 is superimposed on the circuit conductor layer 4 formed of conductive paste, and the through hole of the metal mask 6 is passed through the through hole of the metal mask 6 using a vacuum evaporation method.
A solderable conductive metal layer 6 is deposited on a portion of the circuit conductor layer 4 as shown in FIG.

The metal mask 6 used in this step is as shown in FIG.

That is, this metal mask 6 uses a metal plate 6a that is chemically stable and has excellent mechanical strength such as rigidity, and is compatible with the circuit conductor layer made of conductive paste using punching processing and photoetching technology. Through holes 6b having various sizes and shapes are provided at predetermined positions. In this embodiment, the metal plate 6& has a thickness of 0.1χ
A metal mask was prepared using a stainless steel plate (SUS-304) with through holes 6b formed at predetermined positions by photoetching. On the other hand, copper is selected as the conductive metal layer 6 that can be soldered, and in forming the conductive metal layer e.

Using vacuum evaporation technology.

The method is to form a circuit conductor layer 4 using conductive paste.
A predetermined shape is formed at the position where the upper conductive metal layer 6 is to be attached.
The metal masks provided with the through holes 6b having the same size are positioned and overlapped, and then set in a vacuum evaporation device and left in a high vacuum for a predetermined period of time.
A conductive metal layer 6 made of metallic copper was deposited to a thickness of approximately 6 μm only on a portion of the circuit conductor layer 4 through the conductor layer 4b. In this case, copper adhered to the entire surface of the metal mask, but this copper was removed from the metal mask by each tucking method.

The vacuum evaporation technology used in this example is an improved version of the conventional evaporation technology, which has high speed (5000 i/min) and excellent adhesion and throwing power. In the embodiment, as shown in FIG. 4, a circuit conductor layer 4 is formed on both the front and back surfaces of an insulating substrate 3 using conductive paste, a hole 7 is provided through both circuit conductor layers 4, and a metal mask is similarly formed. A double-sided printed wiring board in which a conductive metal layer 6 that can be soldered is formed only on a part of the circuit conductor layer 4 on the inner wall surface of the through hole 7 and its surrounding area by vapor deposition, and a through hole connection is made. It was created.

The printed wiring board obtained by such a method had extremely good reliability in through-hole connection.

In this way, in the printed wiring board according to the present invention, a conductive metal layer is selectively formed only in the parts that require soldering, and the circuit conductor layer is formed of conductive paste in other parts that do not require soldering. However, when forming a conductive metal layer on the entire circuit conductor layer made of conductive paste by vacuum evaporation,
Not only is it difficult to align the metal mask and the circuit conductor layer, but there are also disadvantages such as large dimensional restrictions on the wiring circuit when creating the metal mask.

Effects of the Invention As is clear from the above explanation, the printed wiring board according to the present invention comprises first printing a conductive paste on at least one main surface of an insulating substrate to form a desired circuit conductor layer, and then forming the desired circuit conductor layer on at least one main surface of an insulating substrate. A conductive metal layer that can be soldered by vacuum evaporation through a metal mask is constructed only in the portions of the circuit conductor layer that require soldering.

Therefore, the printed wiring board according to the present invention can achieve a completely dry manufacturing process, can perform good soldering only on the necessary parts of the circuit conductor layer made of conductive paste, and can have a conductor resistance of the circuit conductor layer. It is possible to obtain remarkable effects not found in conventional examples, such as being able to lower the value.

[Brief explanation of drawings]

FIG. 1 is a sectional view of main parts of a conventional printed wiring board. Figures 2 M to C are cross-sectional views of main parts in the main manufacturing process of a printed wiring board according to an embodiment of the present invention, Figure 3 is a perspective view of a metal mask used in the present invention, and Figure 4 is a cross-sectional view of a printed wiring board according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of main parts of a printed wiring board in an embodiment of the present invention. 3...Insulating substrate, 4...Circuit conductor layer made of conductive paste, 6...Metal mask, 6a
...Metal plate, 6b...Through hole, 6...
. . . Conductive metal layer, 7 . . . Through hole. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
figure

Claims (4)

[Claims] (1) Forming a desired circuit conductor layer using conductive paste on at least one principal surface of an insulating substrate, and forming a conductive metal layer that can be soldered only on a portion of the circuit conductor layer that requires soldering. A printed wiring board featuring (2) A hole passing through the circuit conductor layer formed of conductive paste is provided, and a conductive metal layer that can be soldered is formed on the inner wall surface of the through hole and a part of the circuit conductor layer around it. A printed wiring board according to claim 1. (3) Claim 1 characterized in that solder does not adhere to the circuit conductor layer formed of conductive paste.
Printed wiring board as described in section. (4) The printed wiring board according to claim 1, wherein the solderable conductive metal layer is formed by vacuum deposition.