JPH0468799B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an apparatus for circulating a plating solution in a plating tank when performing electroless plating on through holes of a printed circuit board.

(Prior Art) A printed circuit board with double-sided wiring provides conduction between both sides of the board by attaching a plating layer to the inner surface of a hole drilled in the board to form a through hole.

When forming a through hole, in the traditional electroplating method, a thin conductive layer is first applied to the inner surface of the hole by electroless plating, and then a plating layer is deposited thereon by electroplating. In contrast, in the electroless plating method, a predetermined plating layer is finished on the inner surface of the hole by electroless plating only, so the plating layer can be formed uniformly and the process can be shortened.

(Problems to be Solved by the Invention) However, in the case of electroless plating, the thickness of the plating layer varies significantly depending on the temperature and concentration of the plating solution, which makes it difficult to handle.

However, in the past, the plating solution tended to stagnate in a part of the plating tank, causing unevenness in the temperature and concentration of the solution there, which was one of the reasons why the thickness of the plating layer was not uniform.

The present invention improves this by flowing the plating solution parallel to the substrate in the electroless plating tank without stagnation, thereby controlling the temperature and concentration distribution of the plating solution in the tank. The purpose is to average the thickness and form the plating layer of the through hole to have a uniform thickness.

(Means for Solving the Problems) In the present invention, a printed circuit board is installed between the front plate and the back plate of the plating tank in a direction perpendicular to these,
A rear outlet and a bottom outlet are opened on the back plate and the bottom plate of the plating tank near the back plate, respectively.

The bottom discharge port is connected to one end of the first plating liquid circulation line, and the back discharge port is connected to one end of the second plating liquid circulation line, and the other ends of these first and second plating liquid circulation lines are connected to a common plating liquid circulation line. Connect it to the supply pipe, and connect this supply pipe closer to the front plate than the printed circuit board of the plating tank.

(Function) The plating liquid in the plating tank exits from the tank through the back outlet and the bottom outlet, passes through the first and second plating liquid circulation lines, and returns to the plating tank via the supply pipe.

During this circulation process, the plating solution is heated and replenished, but in the present invention, the supply pipe is connected closer to the front plate of the plating tank than the printed circuit board, and the supply pipe is connected to the rear outlet and the bottom outlet near it. Since the supply pipe is located on the opposite side of the printed circuit board, the plating liquid discharged from the supply pipe crosses the plating tank from the front side to the back side.

Since the printed circuit boards in the plating tank are installed along a direction perpendicular to the front and back plates, the plating liquid flows parallel to the surface of the printed circuit boards.

Therefore, the flow of the plating liquid in the plating tank is smooth and does not stagnate. Therefore, the temperature and concentration distribution of the plating liquid on the surface of the printed circuit board are averaged, and the thickness of the plating layer of the through hole becomes uniform.

(Example) An example of the present invention will be explained with reference to the drawings.1
is an electroless copper plating tank with a rectangular plane, and a substrate storage basket 2 is suspended in the tank from the open top surface.
A large number of substrates 3 in the cage are installed parallel to the short side direction of the plating tank 1. Catalyst fine particles are adhesively coated on the substrate 3 in advance, and a resist is printed on the upper surface according to the wiring pattern.

Then, the bottom plate 5 is gently inclined toward the back plate 4 that constitutes one long side of the plating tank 1, and the back plate 4 is
A plurality of bottom discharge ports 6 are opened at the deepest part of the bottom plate 5 near the bottom, and the same number of back discharge ports 7 as the bottom discharge ports 6 are opened in the back plate 4 at positions looking above the bottom discharge ports 6.

Next, these plurality of bottom discharge ports 6 are combined and piped to the suction side of one main circulation pump 8, and the discharge side thereof is passed through a filter 9 to a mixing chamber 10.
Piping is installed at the inlet of the pipe.

Reference numeral 11 denotes an automatic liquid replenisher, whose discharge pipe 11a is connected to a mixing chamber 10, and the outlet of the mixing chamber 10 is connected to a supply pipe 13 via a confluence pipe 12.

14 is a perforated plate installed in the tank parallel to the front plate 15 constituting the other long side of the plating tank 1;
The open end of the supply pipe 13 is attached between the perforated plate 14 and the front plate 15.

In addition, the plurality of back discharge ports 7 are combined and piped to the suction side of one heat exchange system pump 16, and the discharge side is piped to the supply pipe 13 from a known heat exchanger 17 via the above-mentioned merging pipe 12. do. The heat exchanger 17 has a structure in which a large number of plastic tubes 17a extending from the inflow side to the outflow side are housed in an outer cylinder 17b.
The fluid in the tube 17a is heated by injecting steam or hot water into the tube 7b, or the fluid in the tube 17a is cooled by injecting cold water.

Here, the route from the bottom outlet 6 to the supply pipe 13 via the pump 8, filter 9, mixing chamber 10, and merging pipe 12 is the first plating liquid circulation line A, and from the back outlet 7 to the pump 16, the heat exchanger The path leading to the supply pipe 13 via the container 17 and the confluence pipe 12 is the second plating liquid circulation line B.

Reference numeral 18 denotes a number of air diffuser pipes arranged at equal intervals along the short side of the bottom of the plating tank 1. These pipes are connected to an air pump (not shown) and diffuse countless air bubbles into the tank through a large number of small holes bored in the pipe wall. to suppress excessive liquid decomposition of the electroless copper plating solution, which will be described later.

Reference numeral 19 denotes an injection pipe for directly injecting plating liquid into the plating tank 1, and is connected to a liquid tank (not shown).

Then, a specified amount of low temperature and inert electroless copper plating solution is injected into the plating tank 1 through the injection pipe 19. Electroless plating solution is a mixture of copper sulfate and caustic soda, and a solution of formalin, ethylenediaminetetraacid, and additives dissolved in pure water, and is activated at a high temperature exceeding a specified temperature. It decomposes into liquid and remains inactive at lower temperatures. In addition, when performing nickel plating, an electroless copper plating solution may be used instead of electroless copper plating.

After the liquid is injected, the pumps 8 and 16 are driven, and the plating liquid in the tank is discharged from the bottom outlet 6 and the back outlet 7, and the plating liquid is discharged from the first plating liquid circulation line A and the second plating liquid circulation line A.
After passing through the plating liquid circulation line B, the plating liquid is returned to the plating tank 1 through a common supply pipe 13 of these plating liquid circulation lines.

The liquid in the supply pipe 13 is dispersed and flows out from the entire surface of the perforated plate 14 while its flow velocity is moderated by the perforated plate 14.
Discharge from the outlet ports 6 and 7 on the opposite side of the supply pipe 13,
Repeat this.

Here, the discharge port opens not only on the bottom surface of the plating tank but also on the back surface, so the plating liquid flowing out from the perforated plate 14 also flows in the direction of the discharge port 7 on the back surface.
Don't concentrate on.

Therefore, the plating liquid flows horizontally across the entire plating tank in parallel to the printed circuit board, and the plating liquid does not stagnate in one place.

The plating liquid flowing through the second plating liquid circulation line B is heated by steam or hot water in the heat exchanger 17, and when the plating liquid in the tank exceeds a predetermined temperature, the liquid decomposes due to the catalytic action, and the palladium on the substrate 3 is heated. Metallic copper is deposited on the exposed portions, thereby forming through holes and wiring patterns.

Copper may precipitate around the catalyst separated from the substrate 3 and settle at the bottom of the plating tank 1, but such precipitates are adsorbed to the filter 9 from the bottom outlet 6 through the first plating liquid circulation line A. and removed.

The plating layer has a predetermined thickness (for example, 30 microns)
It takes a long time to finish the plating liquid, but during that time, the plating liquid that has evaporated or disappeared from the plating tank 1 is transferred to the plating tank through the mixing chamber 10 via the automatic liquid replenisher 11 and transferred to the plating tank by the first plating liquid circulation line A. Replenish to 1.

The plating liquid flowing through the first plating liquid circulation line A is mixed with the high temperature plating liquid from the heating line B in the confluence pipe 12, and then dispersed into the tank through the common supply pipe 13 through the perforated plate 14. Perforated plate 1
In Step 4, both are further mixed together.

Then, this plating liquid flows out from the plate surface of the perforated plate 14, flows parallel to the substrate, and does not generate convection or vortices on the way to stagnation, and flows at a uniform flow rate throughout the tank. Therefore, the concentration and temperature of the plating solution over the entire surface of the substrate 3 are distributed evenly, so that the thickness of the plating layer is uniform in both the through-holes close to the supply pipe 13 and the through-holes far away.

When the plating is completed, the substrate storage basket 2 is pulled up and moved to the cleaning process. After moving, cooling water is injected into the heat exchanger 17 while continuing to drive the pumps 8 and 16 to lower the temperature of the plating liquid, returning it to an inert state, and then discharging the plating liquid in the tank into the liquid tank. Instead, the plating tank 1 is cleaned by adding cleaning liquid.

(Effects of the Invention) In short, in the present invention, when circulating the plating liquid in the plating tank, the supply pipe for returning the plating liquid to the plating tank is connected near the front plate of the plating tank, and on the other hand, the plating liquid is transferred outside the tank. The plating liquid flows across the tank from the front plate side to the back plate side because the discharge ports for discharging the plating tank are opened in the back plate and the bottom plate of the plating tank as a back discharge port and a bottom face discharge port, respectively.

Furthermore, since the printed circuit board is installed in a direction perpendicular to the front and back plates, the plating liquid flows parallel to the printed circuit board and is not obstructed by the board.

Therefore, the plating solution does not stagnate near the substrate 3 but flows smoothly, and the temperature distribution and concentration distribution of the plating solution over the entire surface of the substrate 3 are averaged.

Therefore, according to the present invention, there is an effect that the thickness of the plating layer can be formed uniformly for all through holes located at any position within the tank.

[Brief explanation of the drawing]

FIG. 1 is a flow diagram of the entire through-hole plating apparatus for printed circuit boards embodying the present invention, FIG. 2 is a plan view of the plating tank, and FIG. 3 is a cross-sectional view of FIG. 2. 1 is the plating tank, 3 is the printed circuit board, A is the first plating liquid circulation line, B is the second plating liquid circulation line, 6 is the bottom outlet, 7 is the back outlet, 8 is the main circulation pump, 13 is the supply pipe , 14 is a perforated plate, and 16 is a heat exchange system pump.

Claims (1)

[Claims] 1 A large number of printed circuit boards on which through-hole plating is to be formed are installed at intervals in a direction perpendicular to the front plate and back plate of a plating tank for electroless plating, and the bottom plate of the plating layer close to the back plate and the back plate is installed. have a rear discharge port and a bottom discharge port respectively, the bottom discharge port is connected to one end of the first plating liquid circulation line, and the rear discharge port is connected to one end of the second plating liquid circulation line. 1st and 2nd
An electroless plating tank for forming through-hole plating, in which the other end of the plating liquid circulation line is connected to a common supply pipe, and this supply pipe is connected closer to the front plate than the printed circuit board of the plating tank. Metsuki liquid circulation device.