JPH047120B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an apparatus for forming through-holes by performing electroless plating on 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 comparison, the electroless plating method finishes a predetermined plating layer on the inner surface of the hole by electroless plating only, so it has the advantage that 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 differs significantly depending on the temperature and concentration of the plating solution, so compared to the traditional electroplating method, the thickness of the plating layer differs significantly. It was difficult to apply the plating layer to a uniform thickness.

The present invention improves this by flowing electroless copper plating solution at a constant temperature and concentration in parallel to the substrate in the plating bath, thereby making the flow rate of the plating solution uniform over the entire substrate. The purpose is to equalize the temperature and concentration distribution of the plating liquid and form the plating layer of the through hole to a uniform thickness.

(Means for Solving the Problems) The present invention provides a back outlet and a bottom outlet in the back plate and the bottom plate near the back plate of a plating tank for electroless copper plating, respectively, and connects the back outlet to a heat exchanger system pump. , the supply pipe is connected through a heat exchanger and a merging pipe, and the bottom outlet is connected to the merging pipe through a main circulation pump, a filter, and a mixing chamber, and a liquid replenisher is connected to the mixing chamber. The open end of the supply pipe is attached between the perforated plate and the front plate in the plating tank, and a number of substrates are installed at intervals in a direction perpendicular to the rear plate of the front plate.

(Function) In the present invention, the plating liquid in the plating tank exits from the back outlet, is heated by a heat exchanger, reaches the merging pipe, and exits from the bottom outlet, is filtered by a filter, and then receives liquid replenishment. and reaches the confluence pipe, where both are mixed in the supply pipe and returned to the plating tank.

Therefore, the plating liquid whose temperature and concentration have been adjusted is returned to the plating tank.

Then, this plating solution is dispersed through the perforated plate, flows parallel to the printed circuit board, and exits the tank again through the rear and bottom discharge ports.

Therefore, the plating solution does not swirl or stagnate around the printed circuit board, so that the temperature and concentration of the plating solution over the entire surface of the board are uniform.

(Embodiment) The present invention will be explained based on the embodiment shown in the drawings. 1 is a plating tank with a rectangular plane, and a substrate storage basket 2 is suspended in the tank from the open upper surface of the plating tank.
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, each bottom discharge port 6 is merged into the main circulation pump 8.
The suction side of the mixing chamber 10 is piped to the suction side of the mixing chamber 10, and the discharge side thereof is piped to the inlet of the mixing chamber 10 through the filter 9. 1
1 is an automatic liquid replenisher whose discharge pipe 11a is connected to the mixing chamber 10, and the mixing chamber 1
The outlet of No. 0 is connected to a supply pipe 13 via a confluence pipe 12. Reference numeral 14 denotes a perforated plate installed in the tank parallel to the front plate 15 that constitutes the other long side of the plating tank 1, and the supply pipe 1 is installed between the perforated plate 14 and the front plate 15.
Attach the open end of step 3.

In addition, the rear discharge port 7 is merged with the heat exchange system pump 16.
The suction side of the pump is connected to the suction side, and the discharge side thereof is connected to the supply pipe 13 via a known heat exchanger 17, the above-mentioned merging pipe 12, and the like. 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, and the fluid in the tubes 17a is heated by steam or injection into the outer cylinder 17b, or Cold water is injected to cool the fluid in tube 17a.

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.

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

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

Then, a specified amount of low temperature, 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, mixed with a solution of formalin, ethylenediaminetetraacid, and additives dissolved in pure water. It decomposes and remains activated at lower temperatures. In addition, when performing nickel plating, an electroless nickel plating solution may be used instead of the electroless copper plating solution.

After the liquid is injected, the pumps 8 and 16 are driven to discharge the plating liquid in the tank from the bottom outlet 6 and the back outlet 7, and the plating liquid is returned to the plating tank 1 from the supply pipe 13 via the main circulation line A and heat exchange line B. return.

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 sides of each substrate 3 parallel to the plate surface, and is supplied. the outlet 6 on the opposite side of the pipe 13;
Drain from step 7 and repeat.

Then, 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 exposed to metal. Copper is deposited, thereby forming a through hole.

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 specified thickness (e.g. 30 microns)
It takes a long time to finish the plating solution, but during that time, the plating solution that has evaporated or disappeared due to the plating layer 1 is replenished into the plating tank 1 via the mixing chamber 10 via the automatic liquid replenisher 11 in fixed quantities through the main circulation line A. do. Incidentally, only the missing component in the plating solution, for example, copper sulfate, may be replenished from the replenisher 11.

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 heat exchanger line B, and then the perforated plate 14 is mixed with the plating liquid from the common supply pipe 13.
When dispersing into the tank, the two are further mixed together.

Therefore, the temperature and concentration of the plating liquid passing through the perforated plate 4 are uniform, and the plating liquid flows parallel to the substrate 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 tank 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 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 and return it to an inert state, and then the plating liquid in the tank is discharged 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 rear surface discharge port 7 and a bottom surface discharge port 6 which are respectively opened in the rear panel 4 of the plating tank 1 for electroless copper plating and the bottom panel 5 near the rear panel 4. is connected to the supply pipe 13 via the heat exchange system pump 16, heat exchanger 17 and merging pipe 12, and the bottom outlet 6 is connected to the main circulation pump 8 and filter 9.
A liquid replenisher 11 is connected to the mixing chamber 10, and the open end of the supply pipe 13 is connected to the perforated plate 14 in the plating tank 1 and the front plate 15. A large number of boards 3 are installed at intervals in a direction perpendicular to the back plate 4 of the front plate 15, and the supply pipe 13
This is characterized in that the plating liquid that has passed through the perforated plate 14 is distributed parallel to the plate surface of the substrate 3.

Therefore, according to the present invention, the high temperature and low concentration plating liquid of the heat exchange line B discharged from the heat exchanger 17,
The low-temperature, high-concentration plating liquid from the main circulation line A discharged from the mixing chamber 10 is transferred to the confluence pipe 12.
The temperature, concentration and flow rate of the plating liquid after passing through the perforated plate 4 are uniform, as the plating liquid is completely and integrally mixed twice before the perforated plate 14 and the flow rate is averaged by the perforated plate 14. Moreover, this plating liquid flows parallel to the substrate 3 toward the rear outlet 7 and the bottom outlet 6 on the opposite side from the supply pipe 13, does not stagnate in the tank, and has the same flow rate over the entire surface of the substrate 3. The temperature distribution and concentration distribution of the plating liquid over the entire plate surface are averaged. This results in the effect that the thickness of the plating layer can be made uniform throughout the through holes located at any position within the tank.

In addition, a filter 9 is installed in the main circulation line A connected to the bottom discharge port 6, and during the plating liquid circulation, the precipitate in the plating tank 1 is adsorbed and removed from the bottom lung discharge port 6 by the discharge filter 9, so that the plating liquid is removed. This has the effect of keeping it clean.

[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 Open a back outlet and a bottom outlet on the back plate and bottom plate near the back plate of the plating tank for electroless copper plating, respectively, and connect the back outlet to the supply pipe via the heat exchange system pump, heat exchanger, and merging pipe. At the same time, the bottom outlet is connected to the above-mentioned confluence pipe via the main circulation pump, filter and mixing chamber, and a liquid replenisher is connected to the mixing chamber, and the open end of the supply pipe is connected to the plating tank. This is a printed circuit board through-hole plating device that is installed between a perforated plate and a front plate, and consists of a number of boards spaced apart in a direction perpendicular to the front and back plates.