JPH0139234B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a printed wiring board having a horizontal circuit.

The conventional method for manufacturing printed wiring boards is to create a circuit on the copper foil surface of a copper-clad laminate by screen printing using etching resist, and then remove unnecessary copper other than the circuit by dissolving it with a ferric chloride solution. A common method is to further remove the etching resist with an alkaline aqueous solution or an organic solvent. However, in this method, unnecessary copper is dissolved and removed, so heavy copper is wasted, which is a big loss from a resource saving perspective.

On the other hand, various attempts have been made to solve this problem, but one method is to create a circuit using plating resist on a stainless steel plate, etc., and apply plating only to the exposed parts of the metal surface. A method has been proposed in which the resist is applied, the resist is then peeled off, and the circuit is then transferred to a substrate coated with adhesive. However, when this method is used, the following drawbacks occur.

(1) The process of removing the resist is required, which complicates the work, and the plating circuit may be damaged depending on the type of plating.

(2) It is necessary to apply adhesive evenly to the board surface, which is a complicated work if the board is a hard board, etc.
If uniform coating is not performed, unevenness will occur on the circuit surface.

(3) Since the adhesive is applied to the surface of the board, the board structure in the thickness direction of the obtained circuit board changes, resulting in warpage, etc.

(4) Since the plating circuit is transferred using an adhesive, the circuit on the resulting circuit board generally protrudes above the horizontal plane of the board, so it does not require sliding. Not suitable for circuits.
Regarding point (1) of the above-mentioned drawbacks, there is also a method of using a permanent protective film that is resistant to plating liquid as a resist, which ultimately becomes integrated with the circuit board without peeling off the resist coating. However, other problems and shortcomings remain unresolved.

The present invention seeks to eliminate the above-mentioned drawbacks while providing a method for making a circuit board with horizontal circuits without using adhesives during the board manufacturing process. The present invention will be specifically explained below.

The present invention first has the ability to eventually become a permanent protective film on a metal plate that can be plated with metal, and in addition, a coating that can be used as a plating resist is applied by screen printing, etc., to create a pattern in which the base metal is exposed only on the circuit surface. Form. In this case, any metal plate can be used as long as it can be plated with metal, but it is desirable to use various types of metal foils that can be easily peeled off. In this sense, stainless steel foil, iron foil, etc. are preferably used. Especially in the case of inexpensive iron foil, it can be removed by etching, so it is particularly preferably used in the present invention. Various types of resin pastes can be used as the resin paste for the photoresist and cover coat, but it is preferable to use a resin paste that makes up the prepreg used in this method because it has excellent adhesive properties, electrical performance of the coating film, and reduction in warping of the circuit board. It is preferable from the viewpoint of timeliness. Generally, in consideration of the above characteristics, pastes based on epoxy resins are preferably used. These screen-printed pastes are completely cured by heating, resulting in a strong coating that will not be damaged during metal plating. In this case, regarding the relationship between the plating thickness and the resist thickness, it is preferable that the resist thickness be slightly thicker than the desired plating thickness in the sense that thickening of the plating can be avoided in the case of fine line plating or the like.

Next, metal plating is applied to the resist-treated metal plate. Although the type of plating metal in this case can be selected as appropriate, electrolytic copper plating is generally used. Also, as for the plating that I am particularly interested in, if you first perform through metal plating, then apply base metal plating on top of that, and transfer this when creating the board, it is possible to create a circuit that has a through metal layer on the surface. It is. After drying, the plated metal plates thus obtained are laminated so that the plated surface is in contact with the prepreg surface. In this case, the number of prepreg sheets can be changed as appropriate depending on the desired substrate thickness. Although various types of prepreg can be used, our experimental results show that epoxy resin is impregnated into base materials such as glass cloth, glass nonwoven fabric, paper, cloth, etc., and dried, and the resin is cured to the B stage. The advanced one has excellent adhesion to metal and resist. Next, the laminate is heated and pressed by a press to completely cure the prepreg and at the same time firmly bond the plated metal and the cured resist. Furthermore, since the resin in the prepreg has fluidity at the initial stage of heating and pressing, even if there is a step between the metal plating part and the resist surface, it will be completely filled with resin, compared to when adhesive is applied. There is no mixing of air etc. The greatest feature of the present invention lies in this process, in that the circuit board can be obtained during the conventional thermosetting laminate manufacturing process. The top layer metal plate is then removed from the laminated structure obtained in this way.In the case of metal foil, it can be removed sufficiently by peeling, but if necessary, it can also be removed by etching. Preferably used when surface smoothness is required. The printed wiring board thus obtained is a so-called horizontal circuit board (flat board) in which the circuit is completely embedded in the board, and when a metal foil with a mirror surface is used, this mirror surface is completely transferred. It is a circuit board with a beautiful circuit. Furthermore, since no adhesive is used, the board structure is exactly the same as that of conventional boards, and a circuit board with no warping, twisting, etc. can be obtained. Also, unlike the conventional plating circuit transfer method, which is performed by applying adhesive to a once-made board, this method is very rational for creating a circuit during the board manufacturing process. Examples of the present invention are shown below, but these are merely examples and the present invention is not limited thereby.

Example A resist was coated onto a mirror-surfaced iron foil using an epoxy resin paste using a screen printing method, leaving only the circuit portion. The back side of the iron foil was coated with a resin to prevent plating.
The coat thickness was 20μ. Next, the obtained metal foil was heat treated in a 150°C heating oven for 1 hour,
The epoxy resin paste was completely cured. Next, the exposed portion of the base metal of the obtained metal plate was subjected to electrolytic plating in a copper sulfate bath to form copper plating to a thickness of 15 μm. It was dried after plating. Next, eight sheets of glass substrate epoxy resin prepreg were stacked on the circuit surface of the plated product, and heat pressing was performed at 150° C. for 60 minutes.
As a result, the laminate was completely integrated. The top layer cover on the surface of the resulting laminate with completely cured prepreg was removed, and then only the iron foil was removed by etching, yielding a printed wiring board with the copper-plated circuit and resist transferred to the board surface. . The obtained printed wiring board had a completely flat surface and also had an excellent horizontal circuit on which the mirror surface of the iron foil was transferred.

Claims (1)

[Claims] 1. A process of applying a permanent protective coating to the surface of a metal foil selected from stainless steel foil, iron foil, nickel foil, and zinc foil only to unnecessary parts of the printed wiring circuit.
(1), the step (2) of applying metal plating to the exposed portion of the base metal foil, and the surface composed of the permanent protective coating and metal plating facing the prepreg, which is an intermediate material for manufacturing the laminate. The process of laminating the required number of prepregs and curing them under heat and pressure.
A method for producing a printed wiring board, comprising the steps of (3) and (4) of removing only the base metal foil from the obtained laminate to produce a printed wiring board having a horizontal circuit on its surface. 2. The method for manufacturing a printed wiring board according to claim 1, wherein the permanent protective coating is a paste containing an epoxy resin as a main component. 3. Claim 1, wherein the metal plating is selected from copper plating, nickel plating, gold plating, and solder plating, or a combination thereof.
or the method for manufacturing a printed wiring board according to item 2. 4. The printed wiring board according to claim 1, 2, or 3, wherein the prepreg used is selected from glass epoxy prepreg, paper epoxy prepreg, phenol paper prepreg, and polyimide glass prepreg. manufacturing method. 5. The method for manufacturing a printed wiring board according to claim 1, 2, 3, or 4, wherein the removal of the base metal foil is etching removal. 6. The method for manufacturing a printed wiring board according to claim 1, 2, 3, or 4, wherein the removal of the base metal foil is by peeling.