JPS6310593Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a printed circuit board for a key switch used in electronic devices having a key switch, such as computers and television tuners.

A printed circuit board for a key switch is one in which a contact conductive layer having a predetermined pattern constituting a fixed contact of a key switch and a copper foil circuit for wiring between electronic components are formed on an insulating substrate such as a resin laminate. A required number of pairs of contact conductive layers are formed on the insulating substrate, and each contact conductive layer is connected to a contact connection portion of a predetermined copper foil circuit. When assembled into a device, a movable contact member made of conductive rubber or the like is arranged so as to short-circuit the pair of contact conductive layers, and a key operation member such as a push button is provided for each movable contact member. key switch is configured. Conventionally, the contact conductive layer of printed circuit boards for key switches has been made of gold plating on a base made of copper foil, but recently, in order to reduce costs, a contact conductive layer made of carbon paint has been used. I started to be able to do it. However, when the contact conductive layer is formed only with carbon paint, if an attempt is made to lower the resistance value of the contact conductive layer by using carbon paint with a high carbon content, the adhesion between the carbon paint and the substrate will deteriorate, and fine particles may It becomes impossible to print the contact conductive layer in a pattern.
Therefore, when the contact conductive layer is formed using carbon paint, the operational resistance of the switch inevitably increases to some extent, and the switch cannot be used for applications requiring low operational resistance. Further, when the contact conductive layer is formed using only carbon paint, there is a problem that electrical connection between the copper foil circuit and the contact conductive layer cannot be made satisfactorily. This is because the thickness of the carbon paint may become thin or break at the sharp edges of the copper foil circuit, and in the worst case, disconnection may occur. As this type of printed circuit board, one was proposed that used a contact conductive layer with a carbon paint layer layered on a base made of copper foil, but since the adhesion between the copper foil and carbon paint was poor, When a carbon paint layer is layered on top of a copper foil, the contact resistance between the two increases, making it difficult to reduce the operating resistance of the switch.

SUMMARY OF THE INVENTION An object of the present invention is to provide a printed circuit board for a key switch that allows the operating resistance of the switch to be lower than that of the prior art.

In order to achieve the above object, the present invention includes a first conductive layer made of silver paint containing flaky silver powder, and a second conductive layer made of carbon paint formed to cover the first conductive layer. A contact conductive layer is formed by the contact conductive layer. Since the silver paint layer and the carbon paint layer have good adhesion, the contact resistance between them can be made sufficiently small, and according to the present invention, the operating resistance of the switch can be made much smaller than before.

The printed circuit board of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a plan view showing a part of an embodiment of the present invention, in which numeral 1 denotes an insulating substrate made of a paper phenol laminate, a paper epoxy laminate, a glass epoxy laminate, etc. Copper foil circuits 2, 2' having a predetermined pattern are formed on the surface of 1 by etching. The copper foil circuits 2, 2' are connected to each other via a key switch, and these copper foil circuits have contact conductive layer connecting portions 2a, 2a' projecting in parallel in opposing directions. Contact conductive layers 3,
3' are connected to each other.

As shown in FIGS. 2 to 4, each contact conductive layer includes a first conductive layer 31 made of silver paint containing flaky silver powder formed on the surface of the substrate 1, and a first conductive layer 31 formed on the surface of the substrate 1. 31 and a second conductive layer 32 made of carbon paint formed to cover the conductive layer 31. Although the pattern of the contact conductive layer is arbitrary, in this embodiment, both the contact conductive layers 3 and 3' are formed in a substantially U-shaped pattern, and a central portion of each has a protrusion toward the copper foil circuits 2 and 2'. Copper foil circuit connection part 3a,
3a' are formed and these copper foil circuit connection parts 3a,
3a' is the contact conductive layer connection part 2a of the copper foil circuit 2, 2',
2a' is polymerized. The silver paint used here consists of flaky or flaky silver powder and a resin binder such as phenol resin or epoxy resin.
A mixture of 60:40 is suitable. A suitable carbon paint is, for example, a mixture of carbon powder and a resin binder in a ratio of 50:50.

When the first conductive layer 31 is formed using silver paint as described above and the first conductive layer is covered with the second conductive layer 32 made of carbon paint, the difference between the silver paint layer and the carbon paint layer is Due to good adhesion,
By reducing the contact resistance between both layers, the operating resistance can be lowered. Furthermore, when the first conductive layer is formed of copper foil, the thickness of the second conductive layer may become thinner or breakage may occur near the sharp edges. When the first conductive layer is formed using silver paint, there is no such problem because there are no sharp edges in the first conductive layer, and the first conductive layer is always reliably coated with the second conductive layer. Can be coated. Therefore, the first conductive layer made of silver paint can be completely protected by the second conductive layer made of chemically stable carbon paint, and the contact conductive layer can be prevented from deteriorating over time. Additionally, it was confirmed that when silver paint containing flaky silver powder is applied to a copper foil circuit, it is less likely to break due to the edges of the copper foil circuit, compared to silver paint containing granular silver powder. has been done. This is because flaky silver powder has a high surface resistance, which limits the amount of silver powder movement in the resin binder, and prevents the silver powder from moving significantly at the edges of the copper foil. It is assumed that he is deaf.

It was difficult to reduce the operating resistance of the switch to 500 Ω or less when the contact conductive layer was formed only with carbon paint, but after drying, it was possible to reduce the operating resistance of the switch to less than 500 Ω using silver paint made by mixing flaky silver powder and resin binder at a ratio of 60:40. A first conductive layer with a film thickness of 10 to 15μ is formed, and the film thickness after drying is approximately
When a second conductive layer of 15 μm was formed, the operating resistance of the switch using the contact conductive layer of the present invention was 50 μm.
It has become clear that it is possible to reduce the operating resistance to 1/10 of the conventional resistance. In the above implementation, the sheet resistance of the first conductive layer was approximately 100 mΩ/□, and the sheet resistance of the second conductive layer was approximately 50 mΩ/□.

In FIG. 2, reference numeral 4 indicates an example of a movable contact member used when constructing a key switch using the printed circuit board of the above embodiment. The contact conductive layer 3 is operated by the operating member;
3' and a position away from the contact conductive layers 3, 3'.

Although only a part of the printed circuit board is shown in Figure 1, the required number of contact conductive layers with a similar pattern are actually provided on the board, and copper foil is connected to each contact conductive layer. Copper foil circuits are provided in a predetermined pattern to which circuits and other electronic components are connected. Further, in the above example, the circuit is formed only on one side of the substrate, but it goes without saying that the present invention can also be applied to a case where the circuit is formed on both sides of the substrate.

In the above embodiment, the copper foil circuits 2, 2' have connection parts 2a,
Although the contact conductive layer 2a' is provided in a protruding manner, a portion of the contact conductive layer may be overlapped and connected to a predetermined portion of the copper foil circuit without providing such a connecting portion in particular.

As described above, according to the present invention, a double structure contact conductive layer is used in which a first conductive layer made of a silver paint containing flaky silver powder is covered with a second conductive layer made of a carbon paint, and a first conductive layer is used. And since the adhesion of the second conductive layer is improved, the contact resistance of both layers can be sufficiently reduced to reduce the resistance value of the contact conductive layer, and the operating resistance of the key switch can be significantly lowered than before. There is an advantage that it can be done. In particular, if the first conductive layer is formed from a silver paint containing flaky silver powder, even when the copper foil circuit connection portion of the contact conductive layer is superposed on the contact conductive layer connection portion of the copper foil circuit, the sharpness of the copper foil circuit Since the first conductive layer is not easily cut by the edge portion, there is an advantage that the electrical connection between the contact conductive layer and the copper foil circuit can be ensured.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a part of an embodiment of the present invention, and FIGS. 2 and 3 are respectively -
An enlarged sectional view taken along the line and an enlarged sectional view taken along the - line,
FIG. 4 is a sectional end view taken along the line -- in FIG. 3. 1...Insulating board, 2, 2'...Copper foil circuit, 3,
3'...Contact conductive layer, 31...First conductive layer, 3
2...Second conductive layer.

Claims (1)

[Scope of utility model registration request] In a printed circuit board for a key switch comprising a key switch contact conductive layer and a copper foil circuit connected to the contact conductive layer formed on an insulating substrate, the contact conductive layer includes a first layer made of a silver paint containing flaky silver powder. and a second conductive layer made of carbon paint formed to cover the first conductive layer, and the copper foil circuit connection portion of the contact conductive layer is the contact conductive layer connection of the copper foil circuit. A printed circuit board for a key switch, characterized in that part of the printed circuit board is polymerized.