JPH0410755B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a wiring board for a thermal head, a contact type line sensor, etc.

(Prior Art) For example, a thermal head has conventionally been manufactured by accurately depositing an undercoat layer on an electric circuit shape made of a material such as chromium or a nickel-chromium alloy on an insulating substrate such as ceramic or glass. An intermediate conductive layer made of a material such as nickel or copper, which is aligned and laminated, and a plating layer made of gold, silver, etc., which is laminated in alignment with the pad part and external connection terminal part of the intermediate conductive layer. , and an intermediate conductive layer covering the areas where the plating layer does not exist, and is usually composed of an insulating protective layer made of a material such as silicon dioxide or tantalum pentoxide, an undercoat layer, and an intermediate conductive layer. The alignment of the layers and plating layers was performed by the following method.

That is, after forming an undercoat layer, an intermediate conductive layer, and a plating layer over the entire surface of an insulating substrate, the same etching mask is used to etch the electrical circuit shape, and then another etching mask is used to form the plating layer into an electrode terminal. This is a method of etching the shape.

In addition, the undercoat layer and the intermediate conductive layer are formed on the entire surface of the insulating substrate, and the plating layer is plated in the shape of an electrode terminal using a plating mask, and then the undercoat layer and the intermediate conductive layer are formed into an electrical circuit using an etching mask. Methods of etching into shapes are also known.

In addition, the protective layer is formed after processing the undercoat layer, intermediate conductive layer, and plating layer into a predetermined shape, and unlike the undercoat layer, intermediate conductive layer, or plating layer, this protective layer does not require accurate alignment. Because of that,
After it is formed on the entire surface of the substrate by a method such as sputtering, it is covered with an etching mask and etched into a desired shape, or it is sputtered on a substrate on which an electric circuit is formed through a mask. was forming.

(Problem to be Solved by the Invention) However, in either case, the protective layer of the plating layer cannot be precisely aligned, and therefore, there is no coating between the plating layer and the protective layer. However, there were often areas where the intermediate conductive layer was exposed. Furthermore, in either method, the side surfaces of the intermediate conductive layer are exposed without being covered with the plating layer. As mentioned above, since the intermediate conductive layer is made of nickel, copper, etc., there is a problem in that the exposed portion of the intermediate conductive layer is susceptible to disconnection due to oxidation or the like.

(Means for Solving the Problems) That is, the present invention provides, on an insulating substrate, a functional part that functions substantially exposed to the outside world, a pad part for fixing a wire connected to an electric component, and an external connection terminal part. an electrical circuit in the shape of an electrical circuit, an electrically insulating protective layer covering the electrical circuit of this functional part, and a plating layer laminated on the pad part and external connection terminal part and made of gold, silver, or an alloy thereof. In a method of manufacturing a wiring board, after forming an electric circuit using a thin film of an electrically conductive metal on an insulating substrate and electrically connecting the whole, the electric circuit is electrically insulated except for pads and external connection terminals. It is coated with a protective layer of an inorganic material, and then using this protective layer as a plating mask, gold and gold are applied to the pads and external connection terminals exposed on the surface.
It is characterized by electrolytically plating silver or an alloy thereof.

In such technical means, the term "wiring board" refers to a wiring board that has a functional part that is substantially exposed to the outside world and performs its functions, and examples thereof include a thermal head, a contact type line sensor, and the like. In addition, "substantially exposed to the outside world" means that the function acts on the outside world or is activated by an action from the outside world. It is a part that has a thermogenic antibody that functions to cause transfer and color development in the outside world upon contact, and in a contact type line sensor, it is a photosensitive part that functions by receiving light from the outside world.

In such a wiring board, a protective layer made of an electrically insulating inorganic material is provided to cover the functional layer, for example, to prevent wear and oxidation of the functional layer. When the wiring board is a thermal head, a protective layer of tantalum pentoxide or a two-layer structure of silicon dioxide and tantalum pentoxide can be used to prevent wear.

This protective layer is provided to cover the electric circuit except for the pad portion and the external connection terminal portion which are wire-bonded to the electric component. The protective layer can be formed by forming the entire surface of the insulating substrate on which the electric circuit is provided by a method such as vacuum evaporation or sputtering, and then etching it using a photosensitive resin as an etching mask. Alternatively, it may be formed by a lift-off method. Alternatively, the protective layer may be formed by vacuum evaporation or sputtering into a predetermined shape using a mask (mask evaporation or mask sputtering method). Preferably, the sputtering method is used. The protective layer may be formed to cover the electric circuit, but it is desirable to form the protective layer so as to cover not only the top surface but also the side surfaces of the electric circuit.

Then, using the protective layer thus formed as a plating mask, the entire electric circuit is connected to a power source, and gold, silver, or an alloy thereof is electrolytically plated on the pad portion and the external connection terminal portion. Plating with gold or the like may be applied directly onto the pad portions and external connection terminals of this electric circuit, but it may also be applied through nickel plating or the like.
The electrical circuits other than the pads and external connection terminals are covered with a protective layer, and the insulating substrate is exposed except for the electrical circuits, so metal will not adhere to the pads and external connection terminals. Metal is deposited only on the surface. The metal is deposited not only on the top surface of the pad portion and the external connection terminal portion but also on the side surfaces, completely covering the pad portion and the external connection terminal portion. At this time, if there is a disconnection, it is easy to determine whether or not there is a disconnection, since metal will not be deposited on the portions not connected to the power supply due to the disconnection.

If the electric circuit is not electrically connected in its entirety, a temporary wiring section or special wiring is provided on the outer periphery of the wiring board or at an appropriate position, and when the manufacturing of the wiring board is completed. Then, the temporary wiring portion or special wiring may be removed by mechanical cutting, laser beam cutting, partial etching, or the like.

Insulating substrates that can be used in the present invention include substrates made of ceramic, glass, and the like. In addition, the electric circuit can be formed in the same manner as before, for example, by using an undercoat layer such as chromium, nickel, etc.
After forming an intermediate conductive layer such as copper on the entire surface of an insulating substrate by a method such as vacuum evaporation, sputtering, CVD, or ion plating, the layer is etched into the shape of an electric circuit using a photosensitive resin or the like as an etching mask. I can do it.

(Function) According to the present invention, a protective layer made of an electrically insulating inorganic material is partially provided on a pre-formed electric circuit, and this is used as a plating mask to electrolytically plate the pad portions and external connection terminals with gold or silver. Since this plating layer completely covers the electrical circuit parts exposed on the outside, the electrical circuit parts are not exposed to the outside air, and the plating liquid such as gold should be kept to the minimum necessary.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

The drawings show a thermal head; FIG. 1 is a perspective view of the main parts thereof, FIG. 2 is a plan view thereof, and FIG. 3 is a sectional view.

As insulating substrate 1, attach a 3 inch square to an alumina substrate.
The glaze layer 13 having a thickness of 0.82 mm was applied on three sides.

Next, the heating resistor 14 is sputtered.
Chromium is vacuum-deposited to a thickness of 0.5 μm to form an undercoat layer 2, and copper is further deposited to a thickness of 0.1 μm.
The intermediate conductive layer 3 was formed by vacuum deposition to a thickness of 1 μm.

Next, the undercoat layer and the intermediate conductive layer were processed into the shape of an electric circuit by etching using the photosensitive resin as an etching mask. Such an electrical circuit is
It has a shape that includes pad parts 8a and 8b for fixing IC component connection wires around the functional part 6 and IC mounting part 7, and external connection terminals 9. Moreover, in order to electrically connect the whole, there is a temporary wiring part 10 on the outer periphery. (Figure 2). Note that 12 is a small cutting line, and after plating, a single wiring board is completed by cutting from this small cutting line 12. It is located on this outer periphery of the temporary wiring section 10 and is mechanically cut and removed after cutting.

Next, the pad portion 8 is formed using a mask sputtering method.
Protective layer 5 was formed by forming silicon dioxide to a thickness of 2 μm and tantalum pentoxide to a thickness of 5 μm on substantially the entire surface 11 excluding a, 8b and external connection terminals 9. Note that since the wiring parts 8c and 8d around the functional part 6 are areas not related to wire bonding, these parts were also covered with the protective layer 5.

Furthermore, this protective layer 5 is used as a plating resist,
Nickel was plated to a thickness of 1 μm at 0.5 A/dm ² for 20 minutes, and gold was plated at 0.7 A/dm ² for 7 minutes.

Finally, excess plating was removed with a needle tip, and the temporary wiring section 10 was cut with a laser beam to produce a wiring board.

In the obtained wiring board, the electric circuit was completely covered with the plating layer and the protective layer, and no disconnection occurred for a long period of time.

(Effects) According to the present invention, it is possible to obtain a wiring board in which the electric circuit is completely covered with the plating layer and the protective layer not only on the top surface but also on the side surfaces, and the electric circuit is not exposed to the outside air. It is possible to obtain a wiring board that is less likely to cause wire breakage and can be used while being substantially exposed to the outside for a long period of time.

In addition, the amount of plating liquid used can be kept to a minimum, and if there is a wire breakage, it can be easily discovered during the plating process.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention; FIG. 1 is a perspective view of the main part thereof, FIG. 2 is a plan view thereof, and FIG. 3 is a sectional view thereof. DESCRIPTION OF SYMBOLS 1... Insulating substrate, 2... Undercoat layer, 3... Intermediate conductive layer, 4... Plating layer, 5... Insulating protective layer,
6... Functional section, 7... IC mounting section, 8... Wiring section,
9... External connection terminal section, 10... Temporary wiring section, 11
...Protective layer portion, 12...Small cutting line, 13...
Glaze layer, 14... heating resistor layer.

Claims (1)

[Scope of Claims] 1. An electric circuit having a shape on an insulating substrate, which has a functional part that is substantially exposed to the outside and functions, a pad part for fixing a wire connected to an electric component, and an external connection terminal part; In a method for manufacturing a wiring board, the wiring board has an electrically insulating protective layer that covers an electrical circuit in a functional part, and a plating layer that is laminated on a pad part and an external connection terminal part and is made of gold, silver, or an alloy thereof. After an electrical circuit is formed on the board using a thin film of electrically conductive metal, the entire part is electrically connected, and then the electrical circuit is covered with a protective layer of electrically insulating inorganic material, except for the pads and external connection terminals. Next, using this protective layer as a plating mask, gold and gold were applied to the pads and external connection terminals exposed on the surface.
A method for manufacturing a wiring board, characterized by electrolytically plating silver or an alloy thereof.