JPH04287395A - Electrolytic plating method for multilayered printed board - Google Patents

Abstract

PURPOSE:To provide an electroplating method which can form an electrolytic plated layer having a uniform thickness in the through hole of a multilayered printed board having a high aspect ratio. CONSTITUTION:A multilayered substrate 2 which is formed by piling up printed board forming materials in a multilayered structure and provided with an inner layer conductor 1 formed by opening a through hole 3 is dipped in an electrolytic copper plating bath 7. In the bath 7, an electrode 8 and current supplying section 6 are respectively provided in the bath 7 and to the part of the conductor 1 extended toward the end section of the substrate 2 for performing electrolytic plating on the substrate 2 by supplying an electric current between the section 6 and electrode 8.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic plating method for multilayer printed circuit boards, and more particularly to an electrolytic plating method for multilayer printed circuit boards with a high aspect ratio.

[0002] Multilayer printed circuit boards on which electronic components are mounted are
There is a growing demand for higher densities, and this requires products that are formed by laminating many inner layer conductors and have small through holes.As a result, products with high aspect ratios (printed circuit boards) are required. There is a trend toward demand for multilayer printed circuit boards with a thickness of 100 mm/diameter of through-holes).

0003

2. Description of the Related Art A method for manufacturing such a multilayer printed circuit board is as shown in FIG. A multilayer substrate 2 having a large number of them is formed, and through holes 3 are formed in this multilayer substrate.

Next, this multilayer board 2 is immersed in an electroless copper plating solution to form an electroless copper plating layer 4 in the through hole 3, and then a surface copper foil 5 is extended to the peripheral edge of the multilayer board 2. A current supply section 6 for electrolytic copper plating is provided. Next, as shown in FIG. 2(b), this multilayer substrate 2 is immersed in an electrolytic copper plating solution 7 so as to face an electrode 8 made of a copper plate.

[0005] Electrolytic copper plating is formed in the through holes 3 by applying a DC voltage between the electrodes 8 and the multilayer substrate 2 so that the electrodes 8 are positive and the multilayer substrate 2 is negative.

[0006]

[Problems to be Solved by the Invention] However, as shown in FIGS. 2(a) and 2(b), the thickness of the electroless copper plating layer 4 provided in the above-mentioned through hole 3 is extremely thin, about 1 μm. As the aspect ratio of the multilayer board 2 increases, when the current supply section 6 is provided in the surface copper foil 5, the above-mentioned Since the thickness of the electrolytic copper plating layer 4 is extremely thin,
The resistance from the current supply section 6 to the vicinity of the center of the through hole in the depth direction increases. Therefore, the amount of current supplied near the center of the through hole in the depth direction decreases, the current density decreases, and the thickness of the electrolytic copper plating layer 9 that is formed decreases so that the through hole is exposed on the multilayer board. Part A
It has the disadvantage that it is thinner than it is.

Furthermore, in a multilayer board with a high aspect ratio, the thickness of the printed board is 3.2 mm, and the diameter of the hole is 0.3 mm.
Due to the extremely small size of 5 mm, electrolytic copper plating is not sufficiently supplied, so there is the above-mentioned tendency.

Further, as shown in FIG. 2(b), the electric field generated in the electrolytic copper plating solution 7 between the electrode 8 and the multilayer substrate 2 becomes as shown in FIG. 11, and the through holes are exposed on the multilayer substrate. It concentrates on the part A where the irradiation occurs and the corner parts of the surface of the multilayer substrate. Therefore, the thickness of the electrolytic copper plating layer 9 at the center of the through hole 3 in the depth direction tends to be thinner than the portion A of the through hole exposed on the multilayer board, and the conduction inside the through hole is prevented. This has the disadvantage that it becomes incomplete, resulting in a multilayer printed circuit board with poor connections.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for electrolytic copper plating of a multilayer printed circuit board, which eliminates the above-mentioned drawbacks and forms an electrolytic copper plating layer of uniform thickness on the inner wall of a through hole. .

0010

[Means for Solving the Problems] The electrolytic plating method for a multilayer printed circuit board of the present invention is to electrolytically plate a multilayer board having an inner layer conductor formed by laminating printed board forming materials into a multilayer structure and drilling through holes. At the same time, an electrode is provided in the electrolytic solution, a region including the inner layer conductor is selectively led out toward an end of the substrate, and a current supply section is provided to connect to the inner layer conductor. The present invention is characterized in that electrolytic plating is performed on the multilayer substrate by passing current between the current supply portion and the current supply portion led out from the inner layer conductor.

[0011]

According to the method of the present invention, the substrate region including the inner layer conductor is selectively led out toward the end of the substrate, and a current for electrolytic plating is supplied from a current supply section connected to the inner layer conductor. In this way, the largest amount of current is supplied in the center of the depth direction of the through-hole where it is most difficult to supply current, with no resistance, and the electrolytic copper plating layer is passed through with a uniform thickness. Formed in the entire area within the hole.

0012

Embodiments Hereinafter, embodiments of the present invention will be explained in detail with reference to the drawings. As shown in FIG. 1(a), only the portion of the multilayer substrate 2 where the inner layer conductor 1 is formed is provided so as to protrude from the end of the multilayer substrate 2. As shown in FIG. In this structure, after forming the multilayer substrate 2, the inner layer conductor 1 is removed by polishing or etching the front and back surfaces of the substrate.
A current supply section 6 for supplying current for electrolytic copper plating is provided to the exposed area of the inner layer conductor.

Next, as shown in FIG. 1(b), electrolytic copper plating is performed by immersing it in an electrolytic copper plating solution 7 with the current supply section 6 being negative and the electrode 8 being positive. In this way, the current for electrolytic plating is directly supplied via the inner layer conductor 1 to the central part of the through hole 3 in the depth direction where it is most difficult to supply current, so Since the current density is uniform along the through hole 3, an electrolytic copper plating layer 9 having a uniform thickness is formed over the entire area within the through hole 3.

Although this embodiment has been described using electrolytic copper plating as an example, the present invention can be applied to any electrolytic plating of printed circuit boards such as electrolytic solder plating.

[0015]

[Effects of the Invention] As described above, according to the method of the present invention, the largest amount of current is supplied to the center of the through hole in the depth direction, where it is most difficult to supply current, with no resistance. Since the current for electrolytic plating is uniformly supplied along the depth direction of the through-hole, the thickness of the electrolytic copper plating layer formed inside the through-hole is uniform, resulting in high reliability with no disconnection. This has the effect of producing a multilayer printed circuit board with a high aspect ratio.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an embodiment of the method of the present invention.

FIG. 2 is an explanatory diagram of a conventional method.

[Explanation of symbols]

1 Inner layer conductor 2 Multilayer board 3 Through hole 4 Electroless copper plating layer 5 Surface copper foil 6 Current supply section 7 Electrolytic copper plating solution 8 Electrode 9 Electrolytic copper plating layer

Claims (1)

[Claims] Claim 1: A multilayer board (2) having an inner layer conductor (1) formed by laminating printed board forming materials into a multilayer structure and forming through holes (3), and an electrolytic solution (7)
At the same time, the electrode (8) is immersed in the electrolyte (7).
) is provided, and a current supply section (6) connected to the inner layer conductor is provided at a location where the region including the inner layer conductor (1) is selectively drawn out toward the end of the substrate, and a current supply section (6) connected to the inner layer conductor is provided, and a current supply section (6) connected to the inner layer conductor is provided at a location where the region including the inner layer conductor (1) is selectively led out toward the end of the substrate. A method for electrolytic plating of a multilayer printed circuit board, characterized in that electrolytic plating is performed on a multilayer circuit board (2) by passing current between a current supply section (6) led out from a conductor (1).