JPH1072678A - Electroless plating device and plating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain good plating free from blobs and unequalness by providing the entire part of the bottom of a plating cell with a fine air bubble generating source and an atm. foam generating source in the upper part of this source. SOLUTION: The bottom of the plating cell 1 is provided with the air bubble generating source 2 consisting of a perforated board made of a fluororesin for generating fine air bubbles of a diameter of 5 to 100μm over the entire part thereof and is provided with the air bubble generating source 3 having holes 3A for generating the large bubbles of a diameter of 1 to 3cm apart a distance of about 10cm in the lower part of a piping above this source. As a result, a plating liquid 5 is forcibly stirred and the air bubbles are dispersed and are made uniform so that the concn. of dissolved oxygen is maintained at 2 to 4ppm. In such a case, the ventilation quantity of the fine air bubbles is specified to 1 to 21/min of plating liquid 11 and the ratio of the fine air bubbles to the atm. foam is preferably specified to 2:1. The application of the plating which is free from the blobs and unequalness and has the improved quality is thus made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an electroless plating apparatus and a plating method.

[0002]

2. Description of the Related Art When forming a conductor pattern on a printed wiring board, electroless plating using copper sulfate, formaldehyde, or the like is mainly used. In electroless plating,
It is necessary to make the microscopic plating reaction occur uniformly on the entire surface of the object to be plated. Further, at the time of plating, it is necessary to occlude hydrogen gas generated by the plating reaction into the plating film and to prevent the generation of monovalent copper which causes abnormal deposition. Further, the generation of fine copper particles due to the disproportionation reaction in the plating bath significantly lowers the stability of the bath. As a method of reducing the physical properties of these plating films and improving the stability of the bath, a method of agitating the entire plating bath including the surface of the body to be plated with air is mainly used.

[0003] As a plating apparatus for stirring a plating bath,
For example, there is one disclosed in JP-A-3-145793. This device, as shown in FIG.
A bubble generator 11 for blowing gas to the bottom of a plating tank 1A of a plating apparatus in which the printed wiring board 7 and the electrodes 14 are arranged, and a horizontal space between the bubble generator 11 and the lower end of the printed wiring board 7 Provide the held bubble adjustment plate 13, set the distance to the upper end of the bubble generator to 10 to 15 cm,
The diameter of the bubble ejection port of the bubble generator is 3 mm, and air is sent from the gas pump 12 to generate bubbles. The bubbles passing through the holes of the bubble adjusting plate 13 collide and combine in the process of passing through the holes.
mm.

[0004]

In the conventional plating apparatus using the bubble adjusting plate, only large bubbles are used, so that the dispersibility of the bubbles is deteriorated and the bottom of the plating tank with insufficient air agitation is insufficient. However, there is a disadvantage that the plating solution cannot be stabilized and copper is deposited in the tank.
Further, when sufficient air agitation is not performed between the objects to be plated, for example, U.S. Pat. S. Pat, 4,152,467
As described in (1979), in the region where the dissolved oxygen concentration in the plating solution is as low as 2 ppm or less, abnormal bump-like precipitation occurs on the surface to be plated. On the other hand, in a region where the air is excessively supplied and the dissolved oxygen concentration is as high as 4 ppm or more, the surface of the electroless plating is rendered inconducting, and the physical properties of the plating film are deteriorated.

An object of the present invention is to provide an electroless plating apparatus and a plating method capable of removing the above-mentioned drawbacks, stabilizing a plating solution, and performing high-quality plating without bumps and unevenness. is there.

[0006]

The electroless plating apparatus according to the first invention is provided on the entire bottom of the plating tank and has a diameter of 5 to 10 mm.
A microbubble source that generates microbubbles of 0 μm, and a large bubble generator that is provided at a predetermined distance above the microbubble sources and that generates large bubbles having a diameter of 1 to 3 cm. Is what you do.

According to a second aspect of the present invention, there is provided a plating method for generating a fine bubble having a diameter of 5 to 100 μm on the entire bottom of a plating tank, and a fine bubble having a diameter of 1 mm above the fine bubble generating source at a predetermined distance. In a plating method in which a large bubble generating source for generating large bubbles of about 3 cm is provided, and the plating solution is subjected to electroless plating while stirring, the air flow rate of the fine bubbles is set at 1 to 2 l / min per liter of the plating solution. It is characterized by things.

[0008] Since the plating reaction is performed microscopically, it is necessary to stir the air with fine bubbles, and the size of the bubbles is 100
μm or less is appropriate. If it is 100 μm or more, the deposition of copper is adversely affected and plating becomes uneven. If it is less than 5 μm, it is difficult to produce a fine bubble generation source for generating bubbles of 5 μm or less. However, the dispersibility of the bubbles in the bath is insufficient with only the fine bubbles, and it is necessary to perform forced stirring with large bubbles. Large bubble size is 1-3cm
Is appropriate, and when it is 1 cm or less, stirring becomes insufficient. On the other hand, if it is 3 cm or more, fine bubbles may be absorbed and stirring may be too strong.

FIG. 2 shows the results of an examination of the relationship between the dissolved oxygen concentration and the amount of air flow of the fine bubbles. From FIG. 2, it is found that the flow rate for adjusting the dissolved oxygen concentration to 2 to 4 ppm is the plating solution 1
It is 0.7 to 2.5 l / min with respect to l, but preferably 1 to 2 l / min.

[0010]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of an electroless plating apparatus for explaining an embodiment of the present invention.

Referring to FIG. 1, the electroless plating apparatus of this embodiment is provided on the entire bottom of a plating tank 1 and has a diameter of 5 mm.
A microbubble source 2 made of a porous board made of a fluororesin for generating microbubbles of about 100 μm, and a large bubble having a long diameter of 1 to 3 cm provided at a distance of about 10 cm above the microbubble source 2 A large bubble generation source 3 having pores 3A (0.5 mm in diameter) at the bottom of the pipe,
It mainly comprises a steam pipe 4 for heating the plating solution 5 provided between the large bubble generation source 3 and the fine bubble generation source 2. In FIG. 1, 6 is a pipe for circulating the plating solution which has overflowed, 7 is a printed wiring board, and 8A and 8B are pipes for generating bubbles.

Next, a method of electroless plating a printed wiring board will be described with reference to FIG. An electroless plating solution 5 containing PH: 12 to 12.5 containing copper sulfate, NaOH, and formaldehyde as main components is placed in a plating tank 1 having a bath capacity of 180 l.
The printed wiring board 7 was plated with copper at a bath temperature of 60 to 70 ° C. At this time, fine bubbles of 100 μm or less are generated from the fine bubble generating source 2 at the bottom of the plating tank 1 and large bubbles having a diameter of 1 to 3 cm are generated from the large bubble generating source 3, respectively. Was improved so that the dissolved oxygen concentration was maintained at 2 to 4 ppm. The total air flow is 270 l / min, the air flow of fine bubbles is 180 l / min, and the air flow of large bubbles is 90 l.
/ Min. In order to maintain the dissolved oxygen amount at 2 to 4 ppm, the air flow rate of fine bubbles is 1 to 2 l / mi with respect to 1 l of plating solution.
When n was set, the preferable ratio of fine bubbles to large bubbles was about 2: 1.

[0013]

As described above, the present invention provides a fine bubble generating source for generating fine bubbles having a diameter of 5 to 100 μm at the bottom of a plating tank and a large bubble generating source for generating large bubbles having a long diameter of 1 to 3 cm. The plating rate is set to 1 to 2 l / min with respect to 1 liter of the electroless plating solution, and plating is performed while stirring the plating solution together with the large bubbles, thereby performing plating with improved quality without bumps and unevenness. Became possible.

[Brief description of the drawings]

FIG. 1 is a sectional view of an electroless plating apparatus for explaining an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the amount of air bubbling and the concentration of dissolved oxygen.

FIG. 3 is a sectional view of a plating apparatus having a conventional bubble generator.

[Explanation of symbols]

 1.1A Plating tank 2 Fine air bubble generation source 3 Large air bubble generation source 3A Pores 4 Steam piping 5,5A Plating solution 6 Plating solution circulation piping 7 Printed wiring board 8A, 8B Bubble generation piping 11 Bubble generator 12 Gas pump 13 Bubbles Adjustment plate 14 electrodes

Claims (2)

[Claims] Claims: 1. A plating tank having a diameter of 5 to be provided over the entire bottom of a plating tank.
A microbubble source for generating microbubbles of 100 μm;
An electroless plating apparatus comprising: a large bubble generation source provided at a predetermined distance above the fine bubble generation source and configured to generate large bubbles having a diameter of 1 to 3 cm. 2. The entire bottom of the plating tank has a diameter of 5 to 100 μm.
m, and a diameter of 1 to 3 cm at a predetermined distance above the fine bubble source.
A large-bubble generating source for generating large bubbles, and performing electroless plating while stirring the plating solution, wherein the air flow rate of the fine bubbles is 1 to 2 per liter of the plating solution.
1 / min.