JPS6011120B2 - How to plate printed circuit boards - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in a plating method for improving the uniformity of the plating thickness within the through-holes when plating through-holes in printed circuit boards.

BACKGROUND ART Conventionally, multilayer printed circuit boards, in which a plurality of printed circuit boards on which conductor patterns have been formed in advance are heated and pressed together with a prepreg adhesive sandwiched therebetween, have been widely used in electronic devices. In order to form a circuit in this multilayer printed circuit board, it is necessary to electrically connect conductors in each layer, and through-hole plating has been used as a means for this purpose. In this method, a hole with a diameter of a fraction of the thickness of a multilayer printed circuit board is drilled through the conductor in each layer, and the inner surface of the hole is plated to establish continuity between the conductors. Because it is thin and long, it is difficult to obtain uniform fin attachment within the hole. On the other hand, in the past, the key of the plating liquid or the rocking of the plated object were used to improve the through-hole plating characteristics, the so-called throwing power value (through-hole internal plating thickness ÷ surface plating layer x 1).
00) has been improved. However, when the ratio of the substrate thickness to the through-hole protrusion becomes 2 or more, the plating thickness B at the center of the through-hole 2 becomes thinner than the plating thickness A at the surface of the substrate 1, as shown in FIG. . This is because the metal ions cannot be sufficiently supplied into the through-holes by stirring and pouring alone, and the ion concentration of the plating liquid in the through-holes gradually decreases as the plating progresses. In response, high pressure is applied to supply plating liquid into the through hole,
Plating with low current for a long period of time has improved to some extent, but these methods require large equipment or a long time, and furthermore, the effect is not noticeable when the through-hole diameter to plate thickness ratio is 4 or more. do not have. Therefore, there is a need for the development of a simple and effective plating method that compensates for these drawbacks. The present invention was devised based on this request. For this reason, the present invention is characterized in that in through-hole plating applied to a printed circuit board, plating is performed while periodically applying impact to the printed circuit board submerged in the plating solution.

Hereinafter, embodiments of the present invention will be described in detail based on the accompanying drawings. FIG. 2 shows an apparatus for carrying out the method of the invention. In the figure, 3 is a air piston whose rod 4 makes periodic reciprocating motion, and the printed circuit board 1
An impact is applied to the object from the direction of arrow P. In this embodiment, the impact is applied directly to the board, but the impact may also be applied to a jig for mounting the printed circuit board. Next, the operation when plating is performed using this device will be explained.

In FIG. 2, a printed circuit board 1 is immersed in a plating solution and plated. During the plating work, the wear piston 3 periodically impacts the printed circuit board 1 in the direction of arrow P. Due to this first impact, new plating liquid enters the through hole in the direction of arrow Q, as shown in a, and pushes out the old plating liquid (hatched in the figure). Next, due to the second impact, the wood plating solution further pushes out the old plating solution as shown in b. In this way, the plating liquid in the through hole is renewed by several impacts. This method is simpler and more effective than the conventional method shown in Fig. 3, in which the plating liquid in the through-holes 2 is not refreshed by simply swinging the printed circuit board 1 in the direction of arrows x and Y. is remarkable. Also, this is the same as if oil is supplied to the end of a long piston, the oil is distributed throughout the piston due to the reciprocating movement of the piston, and instead of the movement of the piston, impact is used in the present invention. However, when applying an impact to a printed circuit board, it is necessary to pay attention to the impact force and impact period, and to set conditions for the impact force depending on the size and thickness of the board. Regarding the shock cycle, high-frequency shocks have the disadvantage that the movement of the liquid is obstructed because the next opposite vibration comes before the new liquid is delivered, so the shock applied should not exceed 400 times/minute. The most effective vibration frequency is preferably in the range of 10 to 200 vibrations/minute. Next, an actual example will be explained.

A printed circuit board with a ratio of board thickness to through hole diameter of 3 was used, and when plating was performed while applying impact 120 times/minute with an air piston, a throwing power value of 80 to 90% was obtained. This is a significant improvement over the throwing power of 60 to 70% in the conventional method. As explained above, the plating method of the present invention uniformizes the plating thickness within the through hole by periodically applying impact to the printed circuit board during plating work, improves the throwing power value, and spreads the plating. This improves the reliability of the electrical connection of the through-hole.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a conventional through hole, Fig. 2 is a schematic illustration of an apparatus for carrying out the method of plating a printed circuit board according to the present invention, and Fig. 3 is a schematic illustration of a method of plating a sub-button. It is a diagram. 1... Board, 2... Through hole. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 In through-hole plating on printed circuit boards,
A method for plating a printed circuit board, characterized in that plating is performed while periodically applying impact to a printed circuit board immersed in a plating solution.