JPH04276694A - Manufacture of circuit substrate - Google Patents

Abstract

PURPOSE:To provide a forming method for a through hole having prevention of a malfunction at the time of a hole opening work and excellent reliability, working environment in a manufacture of a multilayer substrate used for various types of electronic devices. CONSTITUTION:In the case of a hole opening work for forming a through hole, a circuit substrate manufacturing sheet 3 in which colloidal graphite is impregnated in a base material, is superposed on a circuit substrate, a hole is opened in the substrate, and a through hole plating film is formed in the hole by an electric plating method. Before the plating, adhesive properties of a conductive layer in the hole is strengthened as required.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing circuit boards widely used in computers and various electronic devices.

0002

2. Description of the Related Art Hitherto, when forming through-holes in multilayer boards or high-precision circuit boards, holes have been drilled using precision drilling machines.

Normally, the substrate material used for this purpose is an epoxy resin containing a glass core, but since the glass transition temperature of the epoxy resin itself is not very high and it contains glass cloth inside, it is difficult to make holes during drilling. There was a problem in that the cutting drill heated up and a defect called smear occurred.

As one solution to this problem, a method has been proposed in which a paper impregnated with a water-soluble lubricant is sandwiched between the substrates during the drilling process. The reason for using a water-soluble lubricant is to remove the lubricant by washing with water in order to prevent partial plating failure during the through-hole electroless plating process after drilling.

[0005]

[Problems to be Solved by the Invention] The use of the above lubricant has a certain effect of extending the life of the drill and suppressing the occurrence of smear, but since the lubricant is required to be water-soluble, it is difficult to use it. There were limitations to the materials used, and the lubricating effect was also limited.

[0006]Furthermore, formalin odor is generated during the electroless plating process performed after the hole drilling process, causing a deterioration of the working environment.

[0007]

[Means for Solving the Problems] As a means for solving the above-mentioned problems, the present invention includes a process of stacking a sheet impregnated with colloidal graphite with a rotating board and making holes in the circuit board, and a process of making holes in the circuit board. The method is characterized by comprising a plating step of forming through-hole plating in the hole by a plating method.

[0008]

[Operation] By using a sheet impregnated with colloidal graphite when drilling a hole in a substrate, the frictional resistance of the drill is reduced, thereby reducing the occurrence of smearing and extending the life of the drill.

Furthermore, as a secondary effect, the fine graphite powder is pressed against the side wall of the hole during hole drilling to form a continuous conductive film, which eliminates the need for conventional multilayer boards or double-sided boards. The primary through-hole plating process using electrolytic plating is no longer necessary, and through-hole plating can be performed directly using electroplating.

[0010] Therefore, the process time is significantly shortened, and the mechanical properties of the plating film are improved, so that the through-hole reliability is improved. Furthermore, the problem of air pollution caused by formalin from electroless plating solution, which was a problem in the working environment, can be solved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a circuit board according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view showing the process of drilling holes in a multilayer substrate according to this embodiment. In FIG. 1, in order to make holes in the panel-plated four-layer board 1,
An aluminum plate 4 for heat dissipation is placed on top of the circuit board manufacturing sheet 3 made of paper impregnated with colloidal graphite 2, and holes are drilled with a drill 5.

[0013] By employing this sheet 3 for manufacturing circuit boards, it was possible to drill holes many times without generating smear. Figure 2 shows the frequency of smear occurrence depending on whether or not a circuit board manufacturing sheet was used. From FIG. 2, it can be seen that by using the circuit board manufacturing sheet, the occurrence of smear is significantly reduced, especially when the number of shots is large.

On the other hand, as a result of the hole-drilling according to the present invention, a conductive layer 6 made of rolled colloidal graphite is formed in the resin portion within the hole. Thereafter, the inside of the hole was cleaned and through-hole plating was performed directly using electroplating to complete the through-hole.

In FIG. 1, for ease of understanding, parts such as the colloidal graphite 2 and the conductive layer 6 are shown enlarged. Further, in FIG. 1, the side surfaces of the drill hole are shown as smooth straight lines for convenience, but in reality, the side surfaces have fine irregularities, so that the adhesion of the plating film to the side walls is good.

[0016] In order to further improve the adhesion of the through-hole plating film to the substrate, it is very effective to subject the inside of the hole to plasma treatment subsequent to cleaning the inside of the hole. However, if the plasma treatment time is longer than necessary,
Care must be taken because the graphite may be oxidized and disappear, and the conductivity within the through hole may be lost and the plating film may not adhere. Plasma treatment can be performed by electric discharge in a low vacuum.

Another method for improving the adhesion of a plating film is anodization. In this case, the graphite surface can be treated by applying electricity in an electrolytic solution using the panel-plated substrate as an anode.

The circuit board manufacturing sheet 3 to be used over the substrate can be manufactured by applying a colloidal graphite dispersion onto paper and drying it, or by dipping the paper in the dispersion and drying it. can. Colloidal graphite generally has a particle size of 1 μm or less, and can be obtained commercially in a state dispersed in a solvent such as water or various alcohols. Note that the base material to be impregnated with colloidal graphite is not necessarily limited to paper, and nonwoven fabrics made of heat-resistant fibers can also be used, but paper is optimal in consideration of cost, uniformity, etc.

Furthermore, when drilling a plurality of circuit boards by stacking them, it is also effective to sandwich the above material between the boards, in addition to between the aluminum plate 4 and the board.

[0020] In order to examine the through-hole reliability of the four-layer board 1 manufactured through the above process, the board was
A heat shock test was conducted in which the sample was alternately immersed in oil at 0°C and solvent at 5°C. As a result, the substrate of the present invention has a
While the substrates were able to withstand more than 0 tests, the substrates manufactured using the conventional process broke after 200 to 400 tests, with large variations.

[0021]

[Effects of the Invention] As can be seen from the above explanation, by using the circuit board manufacturing sheet of the present invention, it is possible to not only prevent the occurrence of smear defects, but also to improve the electroless plating process, which was previously indispensable for through-hole plating. becomes unnecessary. Therefore, through-hole reliability is improved, and environmental deterioration due to formalin odor can be prevented, which has great industrial effects.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view illustrating a method for manufacturing a circuit board according to an embodiment of the present invention.

[Figure 2] Characteristic diagram showing the frequency of smear occurrence depending on whether or not a circuit board manufacturing sheet is used in the same example

[Explanation of symbols]

1 4 layer board 2 Colloidal graphite 3 Sheet for circuit board manufacturing 4 Aluminum plate 5 Drill 6 Conductive layer

Claims (3)

[Claims] 1. A method comprising: a step of stacking a sheet impregnated with colloidal graphite and a circuit board to form a hole in the circuit board; and a plating step of forming through-hole plating in the hole by electroplating. A method for manufacturing a circuit board characterized by: 2. The method of manufacturing a circuit board according to claim 1, further comprising the step of subjecting the circuit board to plasma treatment or anodic oxidation treatment after the hole-drilling step. 3. A sheet used in the method of manufacturing a circuit board according to claim 1, which is made of paper impregnated with colloidal graphite.