JPH04154192A - Plating of printed wiring board - Google Patents

Abstract

PURPOSE:To form an equalized plating layer within a through hole by installing a printed wiring board so that its exposed through hole may be located at an angle of 45 deg. and below to the liquid level of an electroless copper plating solution and vibrating said board. CONSTITUTION:A printed wiring board 2 is installed in such a manner that a through hole exposed side 2A, which calls for plating, may keep an angle thetaof 45 deg. and below to a liquid level 4A of an electroless copper plating solution 4. Then, an attempt is made to vibrate the board 2 by giving impact whose gravitational acceleration may range from 0.1 to 0.5G by means of a vibrator device, such as a hammer 7 of a hammering device. When air is supplied into a solution 4 from an air supply pipeline 8 so that the amount of dissolved oxygen in the solution 4 may range from 3 to 6ppm, the oxygen gas is mixed with the air bubbles comprising the reaction gas generated in the hole 1, which makes it possible to circulate through the hole with ease. As a result, the air bubbles easily flow out from the hole 1, which makes it possible to form an equalized electroless copper plating layer under such a state where no plating layer is lacking.

Description

[Detailed Description of the Invention] [Summary] Regarding the electroless copper plating method for printed wiring boards, the reaction gas generated in the through-hole during electroless copper plating is easily extracted from the inside of the through-hole to the outside, and the process is uniform. The purpose of the present invention is to provide a method for plating a conductor layer inside a through hole, in which a printed wiring board with a through hole drilled therein is immersed in a plating solution, and a conductor layer is plated inside the through hole. The printed wiring board to be plated is immersed at an angle such that the surface of the printed wiring board where the through holes are exposed is at an angle of 45 degrees or less with respect to the plating liquid level, and the printed wiring board is installed. The jig has a gravitational acceleration of 0.1 to 0.
The printed wiring board is vibrated by impact with a hammer in the range of 5G, and the amount of dissolved oxygen in the plating solution is 3 to 6 p.
The printed wiring board is plated while supplying oxygen gas to the plating solution so that the plating temperature becomes pm.

? INDUSTRIAL APPLICATION FIELD The present invention relates to a method for electroless copper plating of printed wiring boards.

When manufacturing multilayer printed wiring boards, prepregs made of semi-curing epoxy resin are installed on both sides of an intermediate layer base material with copper foil in a predetermined pattern formed on both sides of the base material. After installing the copper foil, the intermediate layer base material, prepreg, and copper foil are laminated under pressure, and then a through hole is provided that penetrates the intermediate layer base material, prepreg, and copper foil, and the inside of this through hole is filled with electroless copper. The process of forming a conductor layer in the through hole by plating and electrolytic copper plating is adopted.

In recent years, such printed wiring boards have been required to be formed with higher density in order to be used in high-speed computers.
Therefore, a high aspect ratio printed wiring board with a large number of laminated inner layer conductors and small through-hole diameters is required.Therefore, a technology is required to uniformly form a conductor layer within the minute through-holes by electroless copper plating. ing.

[Conventional technology]

Conventionally, as shown in Fig. 4, a method of forming an electroless copper plating layer with a uniform thickness in such a through hole is used.
The printed wiring board 2 with the through-holes 1 to be plated drilled therein is placed on the installation jig 3, immersed in the electroless copper plating solution 4, and the wiring board is rocked or the printed wiring board itself is turned over. A method is adopted to allow the hydrogen gas generated in the through hole during the plating process to escape from the inside of the through hole to the outside, so that the electroless copper plating layer is uniformly deposited within the through hole. Ta.

[Problem to be solved by the invention]

By the way, in a printed wiring board with a high aspect ratio (through hole diameter/printed wiring board thickness) of 15 or more, as shown in Fig. 5(a), it occurs within the through hole 1, and mainly The reaction gas consisting of hydrogen gas forms bubbles 5 and cannot be easily extracted from the printed wiring board 2 to the outside, but remains in the through hole. Therefore, as shown in FIG. 5(b), the electroless copper plating layer 6 is not formed at the part of the through hole 1 where the air bubbles have accumulated, causing the problem that the plating layer is missing at the part of the air bubble. There is.

The present invention solves the above-mentioned problems, and allows bubbles caused by the reaction gas generated in the through-hole to be easily drawn out from inside the through-hole, thereby forming a uniform plating layer inside the through-hole. The purpose of the present invention is to provide a method for plating printed wiring boards.

[Means to solve the problem]

The method for plating a printed wiring board of the present invention that achieves the above object is characterized in that the printed wiring board to be plated is placed so that the surface of the printed wiring board where the through hole is exposed is at an angle of 45 degrees or less with respect to the level of the plating solution. The installation jig for the printed wiring board is immersed at an angle so that the gravitational acceleration is 0.1 to 0.
．． The printed wiring board is vibrated by impact with a hammer in the range of 5G, and the amount of dissolved oxygen in the plating solution is 3 to 6.
The method is characterized in that the printed wiring board is plated while supplying oxygen gas to the plating solution so that the printed wiring board becomes pllllll.

[Function] When the printed wiring board 2 is immersed in the electroless copper plating solution 4 as shown in FIG. 4, that is, the through hole 1 to be plated is perpendicular to the liquid level 4A (installation angle θ - 90 degrees of the printed wiring board installation jig 3). When the through hole is tilted at an angle of 45 degrees or less, the air bubbles in the through hole can easily escape from the inside of the through hole to the outside without being affected by gravity.

In addition, the surface 2A of the printed wiring board 2 where the through holes 1 are exposed is 45 mm with respect to the liquid level 4A of the electroless copper plating solution.
If the tilt is more than 45 degrees, that is, if θ is 45 degrees or more, bubbles 5
It becomes difficult for the bubbles to come out to the top, and the bubbles become trapped in the through-holes, causing the electroless copper plating layer to be missing.

Furthermore, even if the installation jig 3 of this printed wiring board 2 is hit with a hammer 7 with a gravitational acceleration of 0.1 G or less to give a shock and give vibration to this printed wiring board, the vibration force is weak, so the reactive gas The bubbles will be drawn out from the through hole 1. Also, when the hammer 7 is applied with a gravitational acceleration of 0.5G or more and vibration is applied, the bubbles of the reaction gas will stick together and be drawn out from inside the through hole. It becomes difficult.

Therefore, by impacting the installation jig with a gravitational acceleration in the range of 0.1 to 0.5 G, air bubbles in the through hole can be removed most easily and the plating layer is less likely to be missing.

In addition, the amount of dissolved oxygen in the electroless copper plating solution 4 is 3 to Eipp.
When oxygen gas is supplied into the electroless copper plating solution by pumping air through the pipe 8 to the electroless copper plating solution 4 so that the oxygen gas is mixed with the bubbles of the reaction gas in the through hole, bubbles are generated. becomes easier to move, and the plating solution moves with good circulation within the through-hole. Further, if the dissolved oxygen content is 6 ppm or more, there is a problem that additives in the electroless copper plating solution will decompose and the plating rate will decrease, so it is set in the above range of 3 to 6 ppm.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a detailed explanatory diagram of the present invention.

As shown in the figure, in the method of the present invention, a surface 2A of the printed wiring board 2 where the through holes 1 to be plated are exposed.
is installed so as to maintain an angle θ of 45 degrees or less with respect to the liquid level 4^ of the electroless copper plating solution 4.

Then, this printed wiring board 2 is moved to a vibration device such as a hammer 7 of a hammering device, so that the gravitational acceleration is 0.1 to 0.5G.
Apply a shock and vibrate so that

In addition, when air is supplied to the electroless copper plating solution from the air supply piping 8 so that the amount of dissolved oxygen in the electroless copper plating solution 4 becomes 3 to 6 ppm, this oxygen gas and the gas generated in the through hole are generated. The electroless copper plating solution mixes with bubbles made of hydrogen gas as a reaction gas, and the electroless copper plating solution easily circulates through the through-hole, allowing the bubbles to easily escape from the inside of the through-hole to the outside, resulting in no missing plating layer inside the through-hole. A uniform electroless copper plating layer is formed within the through hole.

Figure 2 shows the acceleration G of the hammer impact in the method of the present invention.
This diagram shows the relationship between the rate of occurrence of through holes with missing plating layers, and the dimensions of the printed wiring board used in the method of the present invention are 615.
ma+X520 mm, plate thickness 7.2 mm, through hole diameter 0.35 mm, number of through holes 8~
There are 90,000 pieces and 71 pieces, and the inclination angle θ of the printed wiring board is 4.
It was set to 5 degrees.

Furthermore, the incidence of missing through holes in the plated layer was calculated as shown in equation (1).

Occurrence rate (ppm) - (Number of through holes with missing plating layer/Number of through holes inspected) x 1 million (1) Second
As shown in the figure, the gravitational acceleration of the hammer is 0.1 to 0.5.
It is shown that in the range of G, the rate of occurrence of through holes with missing plating layers decreases rapidly.

FIG. 3 is a diagram showing the relationship between the amount of dissolved oxygen (ppm) in the plating solution and the rate of occurrence of through holes with missing plating layers in the method of the present invention. This is the value when the hammer is installed at an inclination angle of 45 degrees and the gravitational acceleration of the hammer is 0.3G.

As shown in the figure, when the amount of dissolved oxygen was 3 to 6 ppm relative to the electroless copper plating solution, the rate of occurrence of through holes in which the plating layer was missing was significantly reduced to 1 ppm or less.

As described above, as a result of applying electroless copper plating to through holes of printed wiring boards using the method of the present invention, conventionally,
In the case of a printed wiring board with a high aspect ratio of 21, the incidence of through holes with missing plating layers is 2.
The one with 0 ppa+ (number of through holes with missing plating layer/number of inspected through holes) was 1/20 of the ippm.
This resulted in a significant decrease.

Note that the method of the present invention is not limited to electroless copper plating, but can also be applied to electroless nickel plating and electroless gold plating.

Further, similar effects can be obtained when applied to electrolytic metal plating such as electrolytic copper plating or electrolytic nickel plating.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, even in high aspect ratio printed wiring boards, bubbles caused by reactive gases generated during the electroless copper plating process can be sufficiently removed.
Since the electroless copper plating solution can reliably penetrate into the through-holes, the phenomenon of missing metal layers in the through-holes is almost eliminated, resulting in high-quality, highly reliable printed wiring boards. arise.

[Brief explanation of the drawing]

Figure 1 is a detailed explanatory diagram of the present invention. Figure 2 is a diagram showing the relationship between the acceleration of hammer impact and the rate of occurrence of plated layer missing through holes. Figure 3 is a graph showing the amount of dissolved oxygen in the electroless copper plating solution and the plated layer. Relationship diagram with the incidence of missing through holes, Figure 4 is an explanatory diagram showing the conventional method, and Figures 5 (a) and 5 (g)) are explanatory diagrams of inconvenient conditions in the conventional method. It is. In the figure, 1 is a through hole, 2 is a printed wiring board, surface, 3 is an installation jig, 4 is an electroless copper plating solution, liquid level, 5 is a bubble, 6 is an electroless copper plating layer, 7 is a copper plating layer, 8 indicates piping. 2A is 4A is ha book suke 1 猷 saki < pe complete D

Claims (3)

[Claims] (1) Immerse the printed wiring board (2) with the through holes (1) in the plating solution (4).
1) When plating a conductive layer inside the printed wiring board (2) to be plated, the through hole (1)
Plating of a printed wiring board, characterized in that the printed wiring board is immersed at an angle of 45 degrees or less with respect to the liquid level (4A) of the plating solution so that the exposed surface (2A) of the printed wiring board Method. (2) Installation jig (
3) is plated while vibrating the printed wiring board (2) by impacting it with an impact means (7) having a gravitational acceleration of 0.1 to 0.5 G. plating method for printed wiring boards. (3) The printed wiring board is plated while supplying oxygen gas to the plating solution so that the amount of dissolved oxygen in the plating solution is 3 to 6 ppm.
The method for plating a printed wiring board according to 1) or (2).