JPH06120639A - Electroless copper plating method - Google Patents

Abstract

PURPOSE:To eliminate irregularities, voids, and copper flakes from the surface of an object to be plated by providing air diffuser pipes having different bubble diameters, stirring the plating liquid uniformly and circulating the plating liquid at high speed, thereby preventing the stability of the plating liquid from lowering. CONSTITUTION:A gas generator A is an air diffuser pipe 1 having a large number of ejection ports comprising a plurality of Teflon(R) resin tubes, for example. A gas containing oxygen is then jetted through the ejection ports obliquely downward toward the bottom of a plating bath 6. The narrower the interval of the air diffuser pipe 1 or the ejection port, the further lower part from the liquid level 12 can be stirred well resulting in uniform temperature and concentration of the plating liquid 8. A gas generator B comprises a plurality of sintered Teflon(R) pipes 5 and radiates countless microbubbles. When dissolved oxygen is fed into the plating liquid 8, the stability of the plating liquid 8 is enhanced and irregularities or copper flake phenomenon can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless copper plating method for forming a good copper plating film on the surface of a printed wiring board and the inner surface of a through hole.

[0002]

2. Description of the Related Art Conventionally, electroless copper plating consists of a copper salt, a complexing agent, a reducing agent and a pH adjusting agent, but the resulting plating film is very brittle and the plating solution is unstable and undergoes a self-decomposition reaction. Cheap. Therefore, various additives are added to supplement these. For example, cyanide, 2-2 ′ dipyridyl, polyether, polyester and other surfactants are known. By the way, an electroless plating apparatus for accommodating the plating solution is provided with an air diffuser for supplying an oxygen-containing gas to the bottom of the plating tank in order to keep the plating solution agitated and the dissolved oxygen constant. It is trying to make it.
Further, the air diffusing tube has a large number of jet outlets (2 to 5 mm) for jetting air obliquely downward toward the bottom of the tank, and the interval is 50.
˜100 mm, and the ejection port is provided along the longitudinal direction of the printed wiring board that is the object to be plated. Then, the printed wiring board is electroless plated while swinging back and forth. Further, the plating apparatus circulates the plating solution by a pump through a filter for removing foreign matters in the plating solution and a heat exchanger for the purpose of heating,
The number of circulations usually depends on the tank capacity, but it is 5 to 1 per hour.
It was common to carry out electroless copper plating under a fluidized state of about 0 times.

[0003]

However, the above-mentioned prior art has the following problems. That is, although the above-mentioned additives improve elongation and tensile strength, which are mechanical properties of the plating film, suppress the plating speed, or when the plating speed is used with emphasis, the mechanical properties of the plating film deteriorate. In addition, there is a problem that the stability of the plating solution is deteriorated. In addition, some additives are highly toxic and unfavorable for waste liquid treatment, and if a mechanical analysis method is applied to manage the additives, the equipment becomes expensive and maintenance costs increase, and further, it is consumed during plating. It was not always easy to handle, such as the need for analytical supply. On the other hand, blowing an oxygen-containing gas, such as air, into the electroless copper plating solution is disclosed in
It is described in Japanese Patent Publication No. 6-9063 and is known to be effective in stabilizing an electroless copper plating solution. But,
It is impossible to improve the mechanical properties only by blowing the oxygen-containing gas.

[0004]

The electroless copper plating method of the present invention is a conventional method in which a plating solution is uniformly stirred with an oxygen-containing gas to improve the dissolution efficiency of oxygen and to circulate the solution at a high speed. It is characterized in that electroless copper plating with good stability of liquid and good mechanical properties, which was difficult to achieve, can be obtained at high speed. The electroless plating solution is preferably an electroless copper plating solution containing basic components such as copper ions, a copper ion complexing agent, a reducing agent, and a pH adjusting agent, to which only 2-2 ′ dipyridyl is added. In the present invention, in the lower part of the plating tank for performing electroless copper plating by immersing the object to be plated in the plating solution, a plurality of diffuser pipes for ejecting oxygen-containing gas are provided, and plating is performed via the diffuser pipes of each stage. Uniform agitation can be obtained by making the bubble diameters of the oxygen-containing gas ejected into the liquid different. Further, the supply conditions of the oxygen-containing gas jetted into the plating solution are preferably sufficient stirring and pressure and flow rate capable of maintaining a desired dissolved oxygen concentration constant even if the specific gravity of the plating solution becomes high. Further, the plating solution is added to the plating bath capacity of 5 to 5 per hour.
By circulating it 0 times, preferably 30 times or more to promote mass transfer of various plating solution components, it is possible to stably obtain a good plating film at a high plating speed. Further, it is preferable to have a structure in which the plating solution flows in the plating tank without causing stagnation. By doing so, it is possible to easily stabilize the plating solution, control the temperature, and manage the concentration.

[0005]

In the electroless copper plating apparatus according to the present invention, since the diffusing tubes having different bubble diameters are provided to uniformly stir the plating solution and circulate the plating solution at high speed, the stability of the plating solution is lowered. There is nothing to do. Therefore, the surface of the object to be plated does not have roughness, voids, copper flutter, and the like.

[0006]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a gas generator A is an air diffusing tube 1 having a large number of ejection ports 2, and is composed of a plurality of tubes (diameter 10 mmφ) made of, for example, Teflon resin. The diameter of the spout 2 is 1 to 5 mmφ and is 20 m
Oxygen-containing gas is jetted obliquely downward toward the bottom of the plating tank 6 at m intervals. The narrower the distance between the diffuser pipes 1 and the distance between the ejection ports 2, the greater the stirring intensity during that time, and the better the stirring can be done to a portion considerably lower than the liquid surface 12, thereby making the temperature and concentration of the plating solution uniform. Can be planned. In the gas generator B, a plurality of Teflon sintered tubes 5 are arranged, and innumerable fine bubbles 10 are radially formed.
Generates 0 μm or less, which allows dissolved oxygen to be supplied into the plating solution, improves the stability of the plating solution, and causes the roughness of the surface of the object to be plated and the copper falling phenomenon on the tank wall. Can be prevented. Further, the supply conditions of the oxygen-containing gas ejected into the plating solution are preferably sufficient stirring and pressure and flow rate capable of maintaining a desired dissolved oxygen concentration constant even when the specific gravity of the plating solution becomes high. That is, the electroless plating apparatus of this example is shown in FIG.
As shown in FIG. 3, the gas generators A and B having different bubble diameters ejected in the plating solution 8 are arranged at the bottom of the plating tank 6, and a rack 7 containing a printed wiring board, which is an object to be plated 8, is provided. Are arranged in a one-to-one correspondence. As for the distance relationship between the gas generators A and B and the object 8 to be plated and the liquid surface, the distance between the gas generators A and B and the object 8 to be plated is 50 mm.
With the above, the water depth from the liquid surface to the gas generators A and B is 1
It is desirable that it is 000 mm or less. In FIG.
Reference numeral 6 denotes a plating tank for accommodating the plating solution, and in the portion connected to the pipe 14, the taper gradually increases so that the plating solution blows out at a uniform speed as it goes forward. Further, 7 is a printed wiring board which is an object to be plated, 13 is a gas generator for stirring the plating solution,
Reference numeral 15 is a pump for circulating the plating solution, 16 is a filter for capturing foreign matter in the plating solution, 17 is a heat exchanger for heating or cooling the plating solution, and 18 is a replenisher injection device for copper sulfate, sodium hydroxide, formalin, etc. Indicates. The basic composition of the plating solution used here is 10 g / l of copper sulfate, EDTA
4Na 40 g / l, 37% formalin 3 ml / l, sodium hydroxide pH 12.3, 2-2'-dipyridyl 30
It consists of mg / l. Then, after the stainless steel plate whose surface has been polished smoothly was treated with a catalyst for electroless copper plating, electroless plating was performed using electroless copper plating having the above composition to obtain a plating film having a thickness of 30 to 35 μm. . The plated film was peeled from the stainless plate, cut into a test piece having a width of 12.7 mm, and the mechanical properties of the plated film were evaluated by a tensile tester. Table 1 shows the values of the elongation rate and the tensile strength before breaking measured as described above. From these results, it is clear that in Examples 2 and 3, the mechanical properties of the plating film were improved as compared with the comparative example. Furthermore, there was no roughness on the surface of the substrate and no copper deposition phenomenon, and the stability of the plating solution was extremely excellent.

[0007]

[Table 1]

[0008]

As described above, according to the present invention, plating solution management is easy and expensive, and a mechanically good plating film is efficiently plated without using a special additive. It is possible to provide an electroless copper plating method that can be performed.

[Brief description of drawings]

FIG. 1 is a top view of a gas generator in an electroless plating apparatus that is an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an electroless plating bath according to an embodiment of the present invention.

FIG. 3 is a schematic view of an electroless plating apparatus according to an embodiment of the present invention.

[Explanation of symbols]

1. Air diffuser 2. Spout 3. Header 4. Oxygen-containing gas introduction pipe 5. Teflon sintered tube 6. Plating tank 7. Plated object 8. Plating solution 9. Compressor 10. Flow control valve 11. Flow meter 12. Liquid level 13. Gas generator 14. Piping 15. Circulation pump 16. Filter 17. Heat exchanger 18. Chemical injection device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ikuro Funayama 1500 Ogawa, Shimodate City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Electronic Components Division

Claims (4)

[Claims] 1. A method of immersing a printed circuit board in an electroless copper plating solution to perform copper plating on both sides and through holes of the board, wherein the electroless plating solution is circulated at high speed while stirring with an oxygen-containing gas. A method for electroless plating a printed wiring board, which comprises: 2. In the stirring containing oxygen gas, a plurality of diffusion tubes for ejecting the oxygen-containing gas are provided, and the bubble diameters ejected into the plating solution through the diffusion tubes at each stage are made different. The electroless plating method according to claim 1. 3. The electroless plating method according to claim 2, wherein at least one of the air diffusers is a fine bubble having a bubble diameter of 100 μm or less. 4. A method of flowing a plating solution, wherein the total amount of the plating solution in the plating tank is circulated at a high speed of 5 to 50 times per hour, preferably 30 times or more. The electroless copper plating method according to any one of the above.