JPH048960B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an apparatus for performing electroless plating on through holes of printed circuit boards.

(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.

(Problem 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, so in the past, compared to the traditional electroplating method, It was difficult to adhere the hole plating layer to a uniform thickness.

The present invention improves this by flowing the plating solution parallel to the substrate in the electroless plating tank and with an even flow rate distribution, thereby averaging the temperature and concentration distribution of the plating solution over the entire surface of the substrate, and allowing the plating solution to flow through the substrate in an electroless plating tank. The purpose is to form a hole plating layer with a uniform thickness.

(Means for Solving the Problems) According to the present invention, a plating tank for electroless plating is divided into two by a perforated plate, and a printed circuit board is immersed in one of the two. Discharge ports are opened on the back side of the plating tank facing the perforated plate on the side where the substrates are immersed, and on the bottom of the plating tank near this back side, and the end of the plating liquid circulation line on the liquid supply side is connected to the partitioned plating tank where the substrates are immersed. The side that is not immersed and the liquid discharge side end of the plating liquid circulation line are connected to the above-mentioned discharge port, and the printed circuit board to be through-hole plated is
The liquid discharge side end is immersed in the plating tank on the side connected thereto in a direction perpendicular to the perforated plate.

(Function) The plating liquid in the plating tank exits the plating tank via the plating liquid circulation line and returns to the plating tank. During this circulation process, the plating solution is heated and replenished. In the present invention, the plating solution is heated and replenished between the perforated plate of the plating tank and the solution supply end and solution discharge end of the plating solution circulation line. Since the plating liquid always passes through the perforated plate.

When passing through the perforated plate, the flow velocity of the plating liquid is relaxed and dispersed, and the flow velocity distribution is averaged.
In addition, the outlet of the plating tank opens at the back of the plating tank facing the perforated plate and at the bottom of the plating tank near the back, and since the perforated plate is installed along the direction perpendicular to the printed circuit board, the perforated The plating liquid that has passed through the plate flows parallel to the printed circuit board toward the outlet.

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 the mixing chamber 10, and the outlet of the mixing chamber 10 is connected to the confluence pipe 12.
The pipe is connected to the supply pipe 13 through the pipe.

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 main circulation line A, and from the back outlet 7 to the pump 16 and the heat exchanger 17.
A heat exchange line B is a route that passes through the merging pipe 12 and reaches the supply pipe 13. The main circulation line A and the heat exchange line B constitute a plating liquid circulation line, the supply pipe 13 is the liquid supply side end of the plating liquid circulation line, and the bottom discharge port 6 and the back discharge port 7 are the plating liquid circulation line. This corresponds to the liquid discharge side end of the plating liquid circulation line.

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 newly 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 nickel plating solution may be used instead of the electroless copper plating solution.

The liquid injection liquid and pumps 8 and 16 are driven, the plating liquid in the tank is discharged from the bottom outlet 6 and the back outlet 7, and the liquid in these plating liquid circulation lines passes through the main circulation line A and the heat exchange line B. It is returned to the plating tank 1 through the supply pipe 13 which is the supply end.

The liquid in the supply pipe 13 is dispersed from the entire surface of the perforated plate 14 while its flow rate is moderated by the perforated plate 14, and flows across the tank at a uniform flow rate on the front and back of each substrate 3 parallel to the plate surface, Discharge from the outlets 6 and 7 on the opposite side of the supply pipe 13, and repeat this process.

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 across the entire plating tank, and the plating liquid does not stagnate in one part.

The plating liquid flowing through the heat exchanger 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 exposed portion of the substrate 3 is heated. Metallic copper is deposited to form 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 deposits are adsorbed and removed by the filter 9 from the bottom outlet 6 through the main circulation line A. Ru.

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 replenished into the plating tank 1 via the mixing chamber 10 in fixed quantities from the automatic liquid supply device 11 through the main circulation line A. do.

The plating liquid flowing through the main circulation line A is connected to the confluence pipe 1
2, the plating liquid is mixed with high temperature plating liquid from the heating line B, and then the perforated plate 14 is mixed with the plating liquid from the common supply pipe 13.
When being dispersed into the tank, they are further mixed integrally by hitting the perforated plate 4.

This plating solution flows out from the surface of the perforated plate 14 in a vertical direction, that is, parallel to the printed circuit board 3, and flows at a uniform flow rate throughout the tank without generating convection or vortices and stagnation. 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 from the supply pipe 13.

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, the present invention provides a perforated plate 14 installed on the side of the printed circuit board 3 in the electroless plating tank 1 along a direction perpendicular to the printed circuit board 3,
The liquid supply side end of the plating liquid circulation line is connected to the plating tank 1 on the opposite side of the substrate 3 divided by the perforated plate 14, and the liquid discharge side end of the plating liquid circulation line is connected to the plating tank 1 on the opposite side from the substrate 3 divided by the perforated plate 14. Since it is configured to connect to the discharge ports 6 and 7 in the plating tank 1 on the board 3 side,
The plating liquid that returns to the tank from the plating liquid circulation line is
First, they hit the perforated plate 14 and are agitated and mixed while the flow rate is moderated, and then the flow rate is averaged over the entire surface of the perforated plate 14 and the mixture flows out in a dispersed manner. Moreover, in the present invention, the discharge ports 6 and 7 are opened at the back and bottom of the plating tank on the side opposite to the liquid supply side, so the plating liquid that has passed through the perforated plate 14 traverses the entire plating tank toward the end on the liquid discharge side. The current flows parallel to the substrate 3 as shown in FIG. Therefore, the plating solution does not stagnate in the vicinity of the substrate 3, but has an equal flow rate over the entire surface of the substrate 3, 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 drawings]

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 a plating tank, 3 is a printed circuit board, A is a main circulation line, B is a heat exchange line, 6 is a bottom outlet, 7 is a back outlet, 8 is a main circulation pump, 13 is a supply pipe,
14 is a perforated plate, and 16 is a heat exchange pump.

Claims (1)

[Claims] 1. A perforated plate is installed on the side of a printed circuit board in an electroless plating tank in which through-holes are to be plated along a direction perpendicular to the printed circuit board, and the inside of the plating tank is divided into two. , The liquid supply side end of the plating liquid circulation line is connected to one of the plating tanks on the side opposite to the printed circuit board side, and the porous plating tank is connected to the plating tank on the other side of the printed circuit board. A back side outlet and a bottom side outlet are opened at the back side of the plating tank facing the plate and at the bottom side of the plating tank near the back side of the plating tank, respectively, and the liquid discharge side end of the plating liquid circulation line is connected to these back side outlet and bottom side outlet. A through-hole plating device for printed circuit boards that connects.