JPH09137276A - Method for removing iron component from electroless copper plating liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of the gritty texture of a product by withdrawing a part of an electroless copper plating liquid from a plating cell, subjecting this liquid to circulation filtration in a filter device provided with an ultrafilter membrane and returning the permeated plating liquid to this plating cell. SOLUTION: A part of the plating liquid is withdrawn by a withdrawing pump 3 from the electroless plating cell 2 and is introduced into a filtering and circulating vessel 4. The plating liquid is continuously passed through the ultrafilter membrane 6 by an ultrafiltering and circulating pump 5. The permeated liquid 7 permeated through the filter membrane 6 is returned to the plating cell 2. The different metals concentrated and left in the circulating vessel 4 are discharged as the concd. plating liquid 8 to the outside of the system while the introduction of the plating liquid is temporarily stopped. Since the ultrafilter member has a very small pore size, the superfine particulates of the iron components in the plating liquid are removable. The ultrafilter membrane is of a cross flow filtration system and is, therefore, hardly clogged. The troubles, such as intrusion of the different metals into the plating liquid to contaminate the liquid with these metals and particularly the degradation in the plating rate by the contamination with the iron component and liquid dissolution, are prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing an iron component which is a plating inhibiting substance in an electroless copper plating solution for printed wiring boards and plastics.

[0002]

2. Description of the Related Art Conventionally, electroless copper plating has been widely used for forming circuits on printed wiring boards and conducting plastics. This electroless copper plating method generally deposits copper ions as a copper foil or a copper wiring circuit according to the following equation.

[0003]

[Chemical 1] CuSO ₄ ＋ 2HCHO ＋ 4NaOH → Cu ＋ Na ₂ SO ₄ ＋ 2HCOO
Na + 2H ₂ O + H ₂

The characteristics of the deposited copper foil as a product are that the accumulation of reaction products such as sodium sulfate (Na ₂ SO ₄ ) and sodium formate, the elution of organic substances from the plastic resin as the base material, and the production environment. It is said to be affected by the inclusion of dust, etc. In particular, contamination due to mixing of dissimilar metals caused by raw materials and environmental dust has a negative effect on the plating characteristics and appearance, such as a decrease in the plating deposition rate, instability of the plating solution, or abnormal plating deposition. Removal technology was desired.

As one of the techniques for removing them, for example, Kobayashi and Honma's research paper “Microfiltration Effect of Electroless Copper Plating;
Surface Technology, VoL, 44, No. 10, 1993 ”, it is shown that removal of fine particles with a 0.2 μm precision filter can reduce abnormal deposition of plating.

[0006]

However, in the ordinary filament filter system, the finer the filter pore size, the finer the particles are, and the finer particles are accumulated on the filter. Has been confirmed to fall into obstruction. Therefore, it was almost impossible to remove finer different kinds of fine metal particles and metal particles by the ordinary filter method.

[0007]

The present invention provides a method for removing fine flock-like iron components in an electroless copper plating solution.
It is intended to provide a method in which the plating solution is circulated and filtered through an ultrafiltration membrane, concentrated at the same time, and periodically discharged out of the system. That is, this is a method in which a part of the plating solution in the plating tank is intermittently or continuously withdrawn, the solution is circulated and filtered by a filtration device provided with an ultrafiltration membrane, and only the permeation plating solution is returned to the plating tank again. .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The ultrafiltration membrane is usually 0.01 μm.
This is a pore size of the order of magnitude and is used for removing and concentrating fine particles and for removing and concentrating polymer compounds. Unlike ordinary filtration membranes, it is a so-called cross-flow filtration system and has the characteristic of being less likely to be clogged. Further, the shape includes a hollow tube type of a thin tube, a tuber type of a thick tube, a flat film type, a spiral type wound with a flat film, and the like, and any of them can be used, but it is required that they have heat resistance and alkali resistance.

Problems caused by mixing different kinds of metals into the electroless copper plating solution include various defective phenomena. According to the plating experiments conducted by the inventors, the metal components such as cobalt, molybdenum, zinc, and nickel were not problematic even when mixed in about 20 ppm, but when the content of iron was about 5 ppm or more, the deposited copper foil It was found that abnormal deposition with uneven thickness and roughness occurred, and when the concentration reached about 20 ppm, the blue plating solution turned green and the plating reaction stopped. At this time, in the plating solution containing 5 ppm or more of iron component, suspended particles were not noticeable at first, but fine floc growth could be confirmed when left for several hours, and when this floc was filtered, iron was mainly contained in the filter paper. A solid product was obtained. That is, it is considered that the cause of the roughness of the plated product is that the fine flocs in the growth process of the solid matter are dispersed and adhere to the surface of the product to be plated to cause the roughness. Therefore, it is of course possible to avoid mixing iron from materials and equipment as much as possible, but it is important to quickly remove fine suspended particles even if mixed to form fine solid matter. It was a problem. Regarding the removal of iron from the electroless plating solution according to the present invention, the result of confirming the effect based on the examples shows that ultrafine iron component fine particles have a nominal pore diameter of 0.01 μm and a molecular weight fraction of 10,0.
It was found that an ultrafiltration membrane of No. 00 could be used for sufficient separation. Since the separated iron component is concentrated in the circulation tank by repeatedly circulating and filtering, it can be removed by discharging it out of the system at regular intervals. At the same time, other insoluble suspended substances could be similarly removed, and no abnormal deposition on the plated product was observed.

[0010]

EXAMPLES Examples will be described below with reference to FIG. Electroless copper plating bath 2 for manufacturing printed wiring board 1 (about 5,
(000 liters) of a part of the plating solution is drawn by the drawing pump 3 and the filtration circulation tank 4 (about 500 liters)
Was introduced into SLP-1053 (Asahi Kasei Kogyo Co., Ltd., trade name), which is a hollow fiber type ultrafiltration membrane 6 with an ultrafiltration circulation pump 5, and an average pressure of 2.5 kg / cm ^2. The solution was continuously passed through. The transparent plating solution 7 was returned to the plating tank 2. As a result, the iron concentration of the plating solution, which had an initial concentration of 1.6 mg / l, gradually decreased to 0.55 mg after 5 hours.
/ L, and conversely 12.1 mg / l in the filtration circulation tank
It was confirmed that it was possible to separate and concentrate. For the iron component concentrated in the circulation tank, the introduction of the temporary plating solution was stopped, the permeation plating solution was returned to the plating tank as much as possible, and then the reduced concentrated plating solution 8 was discharged out of the system.

[0011]

EFFECTS OF THE INVENTION Although the electroless plating and the filtration of the electroplating solution with a filter have been carried out conventionally, it cannot be said that the object of removal is strictly defined, and it is difficult to obtain a substantial effect. . According to the present invention, contamination by mixing different kinds of metals into the plating solution that is possible from all sides, particularly the reduction of the plating rate in the plating production due to the contamination of the iron component, and the prevention of troubles such as solution decomposition, It has become possible to suppress the occurrence of graininess on the product.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing one embodiment of the present invention.

[Explanation of symbols]

1. Printed wiring board 2. Electroless copper plating bath 3. Plating solution drawing pump 4. Filtration circulation tank 5. Ultrafiltration circulation pump 6. Ultrafiltration membrane 7. Transparent plating solution 8. Concentrated plating solution

Claims (1)

[Claims] 1. A part of the electroless copper plating solution in a plating tank is intermittently or continuously withdrawn, and the extracted plating solution is circulated and filtered by a filtration device provided with an ultrafiltration membrane to obtain only a permeation plating solution. Is returned to the plating bath again, and a method for removing iron components from the electroless copper plating solution.