JPS6112871A - Method for continuously regenerating electroless copper plating solution - Google Patents

Abstract

PURPOSE:To regenerate continuously an electroless copper plating soln. and to keep the plating soln. in a favorable plating state at all times by cooling the plating soln. to a specified temp. or below to crystallize and remove harmful ions from the plating soln. CONSTITUTION:Part or the whole of an electroless copper plating soln. in a plating tank 1 is introduced continuously or intermittently into a concentrating tank 4, where it is concentrated. The concd. plating soln. is introduced into a cooling tank 6 and cooled to <=10 deg.C, preferably <=5 deg.C to crystallize harmful ions. The plating soln. regenerated by removing the harmful ions in the cooling tank 6 is recycled to the plating tank 1. By this method, the plating soln. can be regenerated continuously in a perfectly closed system from which the principal component and additives in the plating soln. are not discharged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for stably performing electroless copper plating processing by removing harmful ions accumulated in an electroless copper plating solution.

[Technical background of the invention and its problems]

Electroless copper plating solution is an aqueous solution containing copper salt, its complexing agent, alkali hydroxide, and formaldehyde as main components. This is a method of reducing and precipitating copper. As the copper salt, copper sulfate, copper chloride, steel acetate, etc. are used, and as the copper complexing agent, ethylenediaminetetraacetic acid (EDTA) or its salt, tartaric acid, some salt, etc. are used. Sodium hydroxide, potassium hydroxide, etc. are used as the alkali hydroxide. Formalin (37'%), paraformaldehyde, etc. are used as the reducing agent. In order to measure the stability of Sara K plating solution and improve the spreadability of electroless copper plating film,
Various additives such as 2°2'-dipyridyl, sodium cyanide 2-mercabutobenzothiazole, ethylenethiourea, rhodanine, metal sulfur compounds, and nonionic surfactants may be added.

The main components of electroless copper plating solution, copper ions, reducing agents, and hydroxide ions, are consumed during the plating reaction, so these components are analyzed and the consumed amount is replenished to maintain a constant component concentration in the solution. need to be kept.

Mainly for economic reasons, copper sulfate is used as a source of copper ions, formaldehyde is used as a reducing agent, and sodium hydroxide is used as a source of hydroxide ions. By replenishing these, the plating solution gradually contains sulfate ions, which are the counteranions of copper sulfate, formate ions, which are generated as a result of the oxidation reaction of formalin,
Harmful ions such as sodium ions, which are the counter cations of sodium hydroxide, accumulate, causing a decrease in the precipitation rate and decomposition of the liquid.

Conventionally, when using an electroless copper plating solution industrially, there are two methods: discarding part or all of the plating solution, and using an ion exchange membrane.

For the former, use the bath until it reaches a certain lifespan, and either discard the plating solution or measure the specific gravity of the plating solution. If the specific gravity of the plating solution becomes higher than the predetermined value, ion accumulation has progressed. The method is to reduce the concentration of accumulated ions by discarding a portion of the plating solution and replacing it with a new solution.The latter method involves electrodialysis using a positive ion exchange membrane to remove accumulated ions. Alternatively, after separating the copper ions and the complexing agent from the electroless copper plating solution, only the complexing agent is introduced into an anode chamber with copper as an anode to dissolve the copper and eliminate the copper. There is an anodic dissolution method that recycles copper into an electrolytic copper plating solution and prevents the accumulation of copper anions.

However, regarding the method of disposing of electroless copper plating solution,
'Since the copper ions are chelated, it is not easy to treat the waste liquid, and the cost of waste liquid treatment is high, and the expensive complexing agents and additives cannot be recovered and reused, making the plating cost extremely high. .

In addition, the method using an ion exchange membrane requires large and bulky equipment such as an ion exchange tank, an electrodialysis tank, and a concentrated liquid tank. Furthermore, the anodic melting method requires a large amount of formalin and alkali hydroxide (Vt) in the copper removal process, and has drawbacks such as requiring a large amount of energy for heating and cooling.

[Purpose of the invention]

The present invention has been made in order to improve the above-mentioned conventional problems, and it is intended to enable continuous removal of harmful ions using a simple method.

[Summary of the invention]

The present invention deals with electroless copper plating solutions that contain harmful ions that accumulate during continuous plating operations in electroless copper plating solutions that are mainly composed of copper sulfate, its complexing agent, alkali hydroxide, and formaldehyde. It is characterized in that a part or all of the electroless copper plating solution is cooled continuously or intermittently to 10° C. or lower, preferably 5° C. or lower, to crystallize and remove harmful ions in the electroless copper plating solution.

That is, in the present invention, a plating solution containing sulfate ions, formate ions, and sodium ions accumulated in an electroless copper plating solution using copper sulfate as a copper ion source is cooled to 10 °C or less. By removing the solubility of sodium sulfate and sodium formate in the plating solution, the regeneration process was performed continuously, and the cause of the decomposition of the plating solution and the decrease in the precipitation rate was solved.

The principle of the present invention will be explained in detail below with reference to the flowchart shown in FIG. In chart 70 of FIG. 1, 1 is an electroless copper plated cypress, and 8.9.10 is a replenishment tank for replenishing copper sulfate, formalin, and sodium hydroxide, respectively. If plating is performed continuously while replenishing the necessary components of the electroless copper plating tank IK from these replenishment tanks, sulfate ions and formic acid ions will be present in the plating tank 1, which will interfere with the plating reaction.

Harmful ions such as sodium ions accumulate.

To regenerate electroless copper plating solution containing harmful ions, first pump the plating solution in electroless copper plating tank 1 to pump 2 and pipe 11.
The electroless copper plating solution is introduced into the concentration tank 4 via the . As for the structure of the concentration tank, methods such as reverse osmosis and depressurization are preferred because they do not adversely affect the plating solution. The plating solution concentrated in the concentration tank 4 is introduced into the cooling tank 6 via the pump 5 and piping 12, and is cooled to crystallize harmful ions. The cooling temperature is 10°C or less, preferably 5°C or less. The regenerated plating solution from which harmful ions have been removed in the cooling tank 6 is recycled to the electroless copper plating tank 1 via a pump 7 and piping 13. As described above, the electroless copper plating solution can be continuously regenerated.

[Embodiments of the invention]

The present invention will be explained in more detail below with reference to Examples.

Example 1 In the flow sheet shown in FIG. 1 explained above,
Electroless copper plating tank 1.2.5t with liquid capacity of 101
Concentrating tank having a liquid capacity of 4. Cooling tank 6 was used.

Of the 151 electroless copper plating solutions, 101 were used for plating, and the remaining 5 tons were used for regeneration processing such as concentration and cooling.

The electroless copper plating treatment was performed for about 6 hours per day, and the regeneration treatment was performed continuously.

In the electroless copper plating process, bath load 2=Odnl/l,
The bath temperature is 60°C and pHIZ3 is used to maintain the concentration in the liquid at a constant level by automatically replenishing the decreased concentration of the main component.

Electroless plating was performed under the same conditions, and the plating solution was continuously taken out and treated at 10° C. in a cooling tank, and then recycled to the plating bath and the plating process was repeated.

At this time, changes in concentration of accumulated components in the plating solution and changes in precipitation rate were as shown in graph iC of FIG. 2.

As is clear from the graph of FIG. 2, the effect of the cooling treatment is that the concentrations of sulfate ions, formate ions, and sodium ions become constant when the plating time is 40 hours or more. That is, this is because sodium sulfate and sodium formate reached saturation in the cooling tank and crystallized. Although the deposition rate was slightly decreased, #1 was able to be kept constant, and no decomposition of the plating solution occurred even after the plating time reached 100 hours. In this example, 1.2 # of harmful ions were recovered from inside the cooling tank.

The compositions of the plating solution and replenisher used in the electroless copper plating process are as follows.

(1) Electroless copper plating solution Cu 80. -5 H3O0,03mot/lE D
T A 4 N a O, 06mot/1
Amount to make NaOH pH 113 - 537 Thiformin 0.1mot/lα, α1
Shihilicil 10mf/L 2-mercaptobenzothiazole 1.0mW/1 (
2) Copper ion replenisher.

Cu 804.5 LO0,8 mob/Lα, α1 divirid # somr/z (3) Formalin replenisher 37 Formalin 250 ml/LCu S 0
4 ・5HsO0,4mo 171 (4) Hydroxyl ion replenisher N a OH10mo L/L Example 2 This example conducts electroless plating under the same conditions using the same electroless copper plating replenisher as in Example 1. The plating solution was continuously taken out, treated in combination with the concentration treatment and the cooling treatment in Example 2, recycled to the plating bath again, and the plating treatment was repeated. At this time, changes in concentration of accumulated components in the plating solution and changes in precipitation rate were as shown in the graph of FIG.

The concentration process was carried out at a liquid temperature of 50 DEG C. and under a reduced pressure of about 250 Hf, and the distillation tube was maintained until the ratio of distillate to concentrate was 10.

As is clear from FIG. 3, the effect of using the concentration treatment and the cooling treatment in combination was almost the same as that of the example.

In this example, 1.5 tons of harmful ions were recovered from the inside of the cooling tank.

Comparative Example 1 Using the same electroless copper plating solution and replenisher as in Example 1, the changes in the concentration of accumulated components in the plating solution and the changes in the deposition rate when the electroless copper plating process was performed continuously were as follows. 4
As shown in the graph in the figure) 7'C.

As is clear from the table in FIG. 2, in this example, the deposition rate decreased due to increased accumulation of sulfate ions, formate ions, and sodium ions, and the plating solution decomposed after a plating time of 80 hours. In addition, harmful ions crystallized during heat exchange in the plating solution controller, making it impossible to stably control tb due to pipe damage.

As is clear from the above explanation, examples, and comparative examples, according to the present invention, it is possible to continuously regenerate and use electroless copper plating solution using extremely simple processing equipment and operations. It is possible to solve the problem of a decrease in the deposition rate due to the accumulation of ions and the decomposition of the bath, and also to maintain a good plating state at all times.

Furthermore, it is possible to construct a completely closed system in which the main components and additives of the electroless copper plating solution are not discharged outside the system.

[Brief explanation of the drawing]

FIG. 1 is a flowchart for explaining the present invention in detail. FIGS. 2, 3, and 4 are tables showing changes in deposition rate and concentration of harmful ions accumulated in the plating solution with respect to plating time. 1... Electroless copper plating tank, 2,5.7... Pump. 3... Valve, 4... Concentrating tank, 6... Cooling tank, 8, 9
, 10... Replenishment tank, 11... Liquid introduction pipe to the concentration tank, 12... Liquid introduction pipe to the cooling tank, 13... Liquid introduction pipe to the electroless copper plating tank. Agent: Patent Attorney Noriyuki Chika (and 1 other person) 2nd figure, Kisouya [H] 8th figure: CHE

Claims (2)

[Claims] (1) In an electroless copper plating solution whose main components are copper sulfate, its complexing agent, alkali hydroxide, and formaldehyde, harmful ions generated during continuous use of electroless copper plating are A step of continuously or intermittently taking out part or all of the copper plating solution, cooling it to 10°C or less, and crystallizing harmful ions in the electroless copper plating solution to remove them from the electroless copper plating solution (b). A method for continuously regenerating an electroless copper plating solution, characterized in that electroless copper plating is performed while removing the solution that has passed through step (a) through a step of recycling it into an electroless copper plating bath. (2) The method for continuously regenerating an electroless copper plating solution according to claim 1, wherein the electroless copper plating solution is concentrated in steps (1) and (a) and then cooled.