KR870001547B1 - Process for regenerating electroless plating bath and a regenerating apparatus of electroless plating bath - Google Patents

Abstract

A process for regenerating electroless plating (EP) bath comprises (i) continuously or intermittently discharging a portion(or whole) of EP soln. from electroless-Cu-plating bath contg. EDTA to separate/ eliminate the Cu ion, (ii) adjusting pH to below 4.0 to recover chelating agent(EDTA), (iii) providing a cathod (Cu) and anode chambers (sepd. by ion-exchange membrane), putting neutral or alk. soln. (when with an anion-exchange membrane) or acidic soln. (when with a cation-exchange membrane) in a cathod chamber, introducing recovered chelating agent, and applying D.C. current, and (iv) recirculating the soln. of both electrode chambers to the electroless Cu plating bath.

Description

Electroless plating bath regeneration method and regeneration device

1 is an explanatory diagram of the present invention.

2 is a graph showing the recovery rate of EDTA (ethylenediaminetetraacetic acid).

3 is a graph showing the relationship between current density and anode dissolution efficiency.

4 is a graph showing the relationship between the concentration of copper ions (R) and anode dissolution efficiency for EDTA.

5 is a graph showing the relationship between anode electrolyte temperature and anode efficiency.

* Explanation of symbols for main parts of the drawings

12 electroless plating bath 21 copper precipitator

27: chelating agent recovery device 31: electrolytic device

37 ion exchange membrane 39 anode

41: cathode

The present invention relates to a method for regenerating an electroless plating bath containing a chelating agent, such as ethylenediaminetetraacetic acid (EDTA) or the like, as a result of dissolution of the anode as a chelating agent recovered in the device, in particular the plating bath. A method for regenerating an electroless plating bath comprising supplying the resulting copper ions in the form of an EDTA-copper compound and an apparatus used therein.

Electroless plating involves the accumulation of by-products in the plating bath where copper ions, hydride ions, pH regulators, and reducing agents are consumed and produced, whether used as a supercoat for electroplating or as such. This phenomenon is inevitable because the electroless plating reaction is a reverse reaction.

On the other hand, the quality of the electroless copper plated film greatly depends on the plating bath composition and plating conditions. That is, due to an increase in salt concentration due to by-products in the plating bath, the characteristics and quality of the electroless copper plating film are deteriorated, and the plating reaction rate is additionally changed.

In electroless copper plating for printed wiring boards, in particular printed wiring boards produced by the half-added or full-duplex method, through-holes and circuits are manufactured by conventional weight reduction methods in which the through-holes and circuits are mainly formed of electrolytic copper gratings. The electroless plated film obtained needs to be extremely excellent in physical properties compared with the physical properties of the electroless plated film which only acts as a conductive thin film for the right-hole. That is, if the physical properties of the electroless copper plated film are not the same as those of the copper film produced by the electroplating of the pyrophosphate copper plating bath and the copper sulfate plating bath, a printed wiring board having a quality equivalent to that of the electrocopper plating film is obtained. It is impossible to do this, and in order to control the characteristics of the plating film, it is very important to control the deposition rate of the plating such as electroless. In view of this, it is necessary to adjust the composition of the electroless copper plating bath in order to keep the concentration as uniform as possible and to reduce the reaction byproducts as much as possible.

The plating bath concentration control is determined in advance by the manual or automatic analysis of the plating bath component concentrations such as CU ²⁺ , OH ^- and reducing agent which decreases as the electroless plating reaction progresses, or as the time required for substrate throughput and plating. When it is assumed that the concentration has been reached, a separately prepared sulfuric copper solution, sodium hydroxide solution and, for example, a solid or liquid formaldehyde reducing agent are added and adjusted in a predetermined amount, respectively.

This, on the one hand, causes accumulation of alcohols such as sodium sulfate, sodium formate and methanol, ethanol and the like.

Considering the fact that the number of rejected products of the plated product increases with the increase of the reaction by-products, the empirically used to replace a new plating bath without using some or all of the plating baths with a certain plating bath life.

However, this method is not only costly, but also has disadvantages such as uneven quality and low productivity. In addition, as described above, there are many problems to be solved especially when a high quality electroless plating film is required. In addition, the problem of treating the plating bath used in the exchange of the plating bath is generated separately. More specifically, at such times, consideration should be given to treatments to make the chelating agent non-toxic in the plating bath used, such as, for example, COD (chemical oxygen demand) and BOD (biochemical oxygen demand) measures for chelating agents and similar rules. There is a need. Therefore, this method not only increases the cost of making non-toxic chelating agents non-toxic, but it is also inconsistent with social environmental requirements because it is difficult from the environmental pollution point of view to dispose of the used plating bath itself.

It is an object of the present invention to eliminate the aforementioned drawbacks arising from the prior art methods and to reduce the accumulation of reaction by-products and to allow for a stable electroless plating process and also to deal extensively with the treatment of the plating solution used. The present invention provides a method and apparatus for regenerating a bath.

Electroless plating bath regeneration method according to the present invention and silver engraving steps from (1) to (4) as follows:

(1) An operation step in which copper ions contents are removed from the plating bath after the chelating agent-free copper electroless plating bath is partially or completely removed from the electroless plating tank by combustion.

(2) An operation step of acidifying the thus-received solution to pH 4.0 or below to recover the chelating agent and recovering the precipitated chelating agent.

(3) By supplying the recovered chelating agent to the positive electrode cell having the positive electrode separated from the negative electrode cell having the negative electrode by the exchange membrane, when the neutral or alkaline electrolyte solution is supplied to the negative electrode cell described above, the above-mentioned distribution membrane is subjected to anion exchange or Although it becomes a cation exchange membrane, when the acidic electrolyte solution is supplied to this cathode cell, the above-mentioned distribution membrane becomes a cation exchange membrane, and an operation step of using a raw material between two electrodes.

(4) It is characterized by consisting of the operation step of recycling the solution in the above-mentioned positive electrode cell to the above-mentioned electroless plating tank. In addition, the regeneration apparatus of the electroless plating bath is a structural element for (a) to (c) the following means: (a) to decompose copper chelate contained in the electroless copper plating bath and to precipitate the copper ion. (B) a chelating agent recovery means for changing the pH of the solution to 4.0 or less to precipitate and recover the chelates; and (c) a cathode cell having an anode cell and an anode separated by an ion exchange membrane. It is characterized by consisting of an electrolytic means consisting of.

1 is an explanatory diagram of the present invention. The electroless plating bath 12 may contain copper ions, hydrate ions (PH regulators), reducing agents and chelating agents, and may also contain various auxiliary agents.

As electroless copper plating proceeds, copper ions, hydride ions and reducing agents are consumed, while sodium formate and methyl alcohol (if formaldehyde is used as reducing agent) are produced as by-products. In addition, sodium sulfate accumulates when copper ions are added as copper sulfate and when hydride ions are added as sodium hydroxide. Therefore, the consumed amount is supplied from the circulation system and the non-circulation system through the lines 13 and 15, respectively, and at the same time the plating tank continuously or intermittently part or all of the plating bath (containing the by-product). (11) Pull out.

The term "intermittent" as used herein includes the case of withdrawing the plating bath irregularly regardless of the predetermined cycle.

FIG. 1 illustrates an example in which a part of the plating bath flows out continuously as it overflows according to the supplied amount. The overflowing plating bath passes along the line 17 and is introduced into the copper precipitator 21 from the inlet via the filter 19 (which may be omitted). In the copper precipitation apparatus 21, copper ions are precipitated and removed. Separation of copper ions is performed by decomposing copper chelates by combining one or two or three of the following methods and by precipitating copper in the form of metal copper or coral copper.

(1) Copper, copper foil, copper powder or similar copper metal is added to the bath.

(2) A catalyst such as Pd ²⁺ or an analog thereof is added to the bath.

(3) The bath is kept at high temperature and high PH.

The removal of copper can be accomplished by an electrolytic removal method in addition to the precipitation removal method described above. Copper ions contained in the above-described plating bath may be removed from the plating bath by, for example, having an insoluble anode and a cathode in the electroless copper plating solution to be treated and applying a direct current to fuse the copper cathode.

Therefore, the copper precipitation apparatus 21 may include a member for injecting copper powder, Pd ²⁺ , an alkaline agent, and the like, or a member for heating these materials, as well as accelerating the aforementioned reaction. It may also include a member for stirring the above-described material to make. In addition, the copper precipitator 21 may have a positive electrode and a negative electrode. In this way, when the precipitated copper is required, it is discharged from the valve 24.

The copper ion-precipitated solution thus obtained passes through the outlet and is introduced into the chelating agent recovery device 27 through line 23 via filter 25 (may be omitted).

Acid can be introduced into the chelating agent recovery device via line 28 to make the pH of the solution in the device sufficiently acidic to precipitate the chelating agent. Although depending on the chelating agent, the appropriate PH range is generally 4.0 or less, such as when the chelating agent is EDTA, preferably 2.0 or less, more preferably 1.0 or less. Ordinary acids may be used for this pH control. As the above-mentioned acid, sulfuric acid, hydrochloric acid, and the like may be mentioned. In FIG. 2, it is a graph which shows the relationship between the recovery rate and PH when EDTA is used as a chelating agent. From this graph it can be seen that EDTA can be recovered sufficiently at a pH of 2.0 or less and a more desirable recovery can be achieved at a pH of 1.0 or less. In this regard it should be noted that the pH control in this example proceeds to sulfuric acid.

As evident from the foregoing description, separation of the chelating agent from the electroless copper plating bath can be accomplished by decomposing the chelating agent and removing the chelating agent such that the contents are removed. Chelating agents that can be used in this process include, in addition to EDTA, many known compounds used in electroless copper plating, such as tartaric acid, potassium sodium (rosel salt), ethylediaminetetramine, triethanolamine, diethanolamine and the like. Can be. The recovered chelating agent is introduced into the anode cell 33 of the electrolytic device 31 through the line 29. In such cases the chelating agent may be washed and further dried if necessary. In addition, the recovered chelating agent may be supplied to the positive electrode cell 33 in a solid state, or may be introduced into the positive electrode cell 33 of the electrolytic apparatus 31 by a solution solution previously dissolved in an alkaline solution.

The electrolytic device 31 is comprised of the anode cell 33 and the cathode cell 35 which closed the compartment using the ion exchange membrane 37. As shown in FIG. The anode 39 is located in the anode cell 33, while the cathode 41 is located in the cathode cell 35. The negative electrode 41 is preferably made of a material such as stainless, carbon, or the like which is insoluble in the negative electrode electrolyte.

In the negative electrode cell 33, the recovered chelating agent is supplied in solid or liquid form. The PH is maintained at a value at which the chelating agent is dissolved in the solution in the positive electrode cell 33 or in the positive electrode electrolyte solution. In the case of EDTA, for example, the pH value is generally 4.0 or more, preferably 7.0 degrees or more.

The negative electrode cell 35 may accommodate an alkaline, neutral or acidic electrolyte solution. The distribution membrane 37 may be an anion exchange membrane or a cation exchange membrane when the neutral or alkaline electrolyte solution is supplied into the cathode cell 35, while the acidic electrolyte solution is supplied when the acidic electrolyte solution is supplied into the cathode chamber 35 (37). ) Becomes cation exchange. In other words, when the ion exchange membrane 37 is a cathode, the electrolyte solution contained in the cathode cell 35 may be either alkaline, neutral or acidic, whereas when the membrane 37 is the anode, the electrolyte solution may be neutral or alkaline. Becomes

In the case where electrolysis is conducted directly through a direct current between two electrodes, that is, between the anode 39 and the cathode 41, copper is dissolved in the anode and copper ions are generated in the anode cell 33. At the same time, they combine with the chelating agent supplied through the on-line 29 to form a copper compound. The complex is then recycled from line 13 to electroless plating tank 11. Current densities are generally in the range of 00.1 to 100 A / dm 2.

When the pH of the solution in the cathode cell 35 is alkaline and an anion exchange membrane is used, as the electrolysis proceeds, OH ^- ions pass through the ion exchange membrane 37 (anion exchange membrane) to reach the anode cell 33. As a result, the consumed copper ions (consumed in the form of complexing compounds) and hydride ions are supplied into the plating tank 11 through the line 13. In this case, it is very convenient in that hydride ions required for electroless plating are supplied together with copper ions. However, cation exchange membranes are more readily available on the market than anion exchange membranes.

When the pH of the solution in the negative electrode cell 35 is acidic or neutral and the ion exchange membrane 37 is the negative electrode, there is no OH ion supplied from the negative electrode cell. Although OH ions need to be supplied separately, they can be easily supplied in the form of NaOH or an analog thereof.

As is apparent from the foregoing description, copper ions (in the form of complexes) or else OH ⁻ ions are supplied from line 13 and the reducing agent and the necessary auxiliaries are routed through line 13 or line 15 '. Is supplied from. The above description is given for the case where copper ions are separated, chelating agent recovery, and electrolytic copper dissolution are operated in a separate tank. However, it should be noted that each of the aforementioned operations may be performed in one tank.

3 is a graph showing the relationship between current density and anode dissolution efficiency. This experiment shows that the ion exchange membrane is an anion exchange membrane and EDTA of 0.08 water 1ι. The electrolytic apparatus shown in FIG. 1 injecting 4Na into the anode cell and injecting NaOH of 0.1 water 1ι into the cathode cell, and using a copper plate of 0.5 dm 2 as the anode and 18-8 stainless steel of 0.5 dm 2 as the cathode Was carried out at a liquid temperature of 50 ° C.

4 is a graph showing the relationship between (R) (R = [EDTA] / [Cu ²⁺ ]) and the anode dissolution efficiency of the concentration of copper ions with respect to EDTA. This experiment proceeded in exactly the same way as in FIG. 3 except for changing the concentration of EDTA. The experimental results show that when the concentration of EDTA, a chelating agent for copper, is high, copper is dissolved in large amounts, resulting in high current efficiency. Therefore, the pH of the chelating agent can be kept higher than the predetermined value, so that copper dissolution and supply can be performed at higher efficiency.

5 is a graph showing the relationship between the liquid temperature in the anode cell and the anode dissolution efficiency. The experiment was conducted under the following conditions. That is, the composition of both cells was the same as that of FIG. 2, and the intensity 2A was used for the electric charge 3600 Coolung, the anode current density 3A / dm 2 and the cathode current density 4A / dm 2. From the results of this experiment, it can be seen that when the liquid temperature in the anode cell becomes higher, copper is dissolved with extremely high current efficiency. Therefore, the present invention is more effective for producing printed wiring boards using, for example, electroless plating. The reason is that it is very ideal to use the plating bath at a very high temperature in the electroless plating where the physical properties of the high-speed plating and the plating film are strictly required.

The other combination of the electrolyte solution and the ion exchange membrane contained in the cathode cell, that is, the cation exchange membrane and the acid, neutral or alkaline electrolyte solution, was tested on the anode dissolution efficiency using another combination of the anion exchange membrane and the neutral electrolyte solution with water. Results similar to those shown in FIGS.

As described above, the present invention extracts at least a portion of the electroless plating bath from the plating tank, recovers the chelating agent from the plating tank, and supplies the copper consumed in the form of a complex compound using the recovered chelating agent. By-products of sodium sulfate, sodium formate, and alcohol accumulation can be greatly reduced, and in particular, the accumulation of sodium sulfate can be reduced to almost zero, which greatly extends the life of the electroless plating bath and provides a high quality electroless plating film. It can be obtained stably.

In the prior art, the COD and BOD measures of the waste plating bath have caused serious environmental pollution problems.

On the contrary, according to the present invention, the life of the plating bath can be extended without discarding the plating bath, and in addition, it is possible to recover expensive phosphorus chelating agents such as EDTA and to effectively recycle them.

Experimental Example

EDTA. 4Na 30g / ι

CuSO ₄ . 5H ₂ O 6g / ι

Para-formaldehyde 7g / ι

PH (adjusted with NaOH) 11.8

Glass-epoxy copper-craramimate was electroless plated using the plating bath composition (capacity: 5ι) described above at 50 ° C. At this time, sodium sulfate was added to jade in the amounts shown in the first table to observe the effect.

TABLE 1

It can be seen from Table 1 that the deposition rate depends on the amount of sodium sulfate added and the crack formation rate increases as the amount of sodium sulfate increases.

EXAMPLE

The glass-epoxy copper-cladrate is degreased with 40 g / ι sodium trihydrogen phosphate and corroded with 100 g / ι ammonium persulfate, then activated with a moloid solution of palladium and tin or 50 g / ι sulfuric acid. Subsequently, electroless plating was carried out by a conventional method under a load of 1 dm 2 / ι for 12 days under the following conditions.

Plating bath composition:

Copper sulfate 10g / ι

Formaldehyde 10g / ι

Plating bath temperature 50 ℃

EDTA 50g / ι

Sodium hydroxide pH is adjusted to 12

In the conventional method, the concentration of sodium sulfate was increased by supplying copper ions and hydride ions by supplementing copper sulfate and sodium hydroxide. The method of the present invention uses an anion exchange membrane in a manner using the system shown in FIG. 1, uses a plating bath of the above-mentioned composition, injects 0.1 g / ι of NaOH into the cathode cell of the electrolytic apparatus, and serves as a cathode. Also, a stainless plate was used as the cathode, electricity was used at an anode current density of 2.5 A / dm 2, and an anode current density of 4 A / dm 2, and the recovered EDTA was supplied to the anode cell.

However, no increase in the concentration of sodium sulfate was observed.

EDTA extracts a portion of the plating bath, adjusts the pH to 14 so that copper ions are deposited and removed, and then adds copper foil, and then adjusts the pH to 2.0 by adding H ₂ SO ₄ to the filtrate. Precipitated and recovered by filtration.

The results thus obtained are listed next.

Claims (7)

(A) A part or all of the electroless plating solution is continuously or intermittently discharged from the electroless copper plating bath containing ethylenediamine tetraacetic acid as a chelating agent to separate and remove copper ions from the liquid. The chelating agent is precipitated and recovered by making acid less than or equal to PH 4.0, and (c) it is divided into ion exchange membrane, and the anode chamber with copper as anode and the cathode chamber with cathode are installed. (A) If the ion exchange membrane is an anion exchange membrane) or an acidic solution (if the ion exchange membrane is a cation exchange membrane), and while a recovery chelating agent is introduced into the anode chamber, a DC current is applied between the anodes. A method for regenerating an electroless plating bath, characterized by recycling to an electroless copper plating bath. 2. The method for regenerating an electroless plating bath according to claim 1, wherein in step (a), copper ions in the plating bath are precipitated with metal copper or copper oxide to remove copper ions. The regeneration method of an electroless plating bath according to claim 2, wherein (a) metal copper is added to the electroless copper plating bath to precipitate copper ions. The method for regenerating an electroless plating bath according to claim 2, wherein in step (a), the copper plating solution is made alkaline and metal copper is added to precipitate copper ions. The regeneration method according to claim 1, wherein in step (a), the electroless copper plating solution is electrolyzed to remove copper ions. The regeneration method according to claim 1, wherein in step (b), the electroless copper plating solution is made acidic with a pH of 2.0 or less to precipitate and recover the chelate. (A) Copper precipitator which decomposes copper chelate in plating solution such as electroless, which contains ethylene diaminetetraacetate as chelating agent, and precipitates copper components. A chelating agent recovery device for precipitating and recovering (C) an anode chamber and a cathode chamber separated by an ion exchange membrane are installed, and the anode chamber is made of copper, and the cathode chamber is composed of an electrolytic apparatus having a cathode disposed therein. An electroless copper plating solution reproducing apparatus.

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