CA1083304A

CA1083304A - Process for the elimination of undesirable by- products from copperplating baths

Info

Publication number: CA1083304A
Application number: CA271,560A
Authority: CA
Inventors: Horst Schafer
Original assignee: Kollmorgen Technologies Corp
Current assignee: Kollmorgen Technologies Corp
Priority date: 1976-02-14
Filing date: 1977-02-11
Publication date: 1980-08-12
Also published as: DE2606025B1; GB1521013A; NL178611B; AT347751B; NL178611C; ATA86577A; FR2340992A1; DE2606025C2; FR2340992B1; SE7701619L; NL7701408A

Abstract

ABSTRACT

A process is described for the removal from copperplating baths of undesirable by-products which impair further copper-plating. This process involves continuously distilling off from at least part of the copperplating bath sufficient water so that the solubility limits of the undesirable by-products are exceeded. The by-products are precipitated and collected at the bottom of the tank thus permitting the separate removal of residual solution and precipitated by-products. This process is considerably more economical than previously known expensive regeneration processes.

Description

~833~4 The present invention relates to a process for separating undesirable reaction by-products from electroless copper plating .
bath solutions.
Electroless metal deposition bath solutions, especially "
of the type used for producing printed circuits, like alkaline reduction copper bath solutions, are different from electro-plating bath solutions, as electroless bath solutions are very 3ensitive with respect to their reaction to any kind of by-products.
Methods for controlling copper deposition from electroless copper baths on sensitized surfaces have been lately developed and respective problems have been overcome. However, up to now, many problems arising with respect to waste water and economic problams with respect to the use of expensive chemicals, are unso lved .
The present invention provides for a process for separating undesirable reaction by-products from electroless copper plating bath solutions, comprising submitting at least part of said solution to a continuous distillation process for concentrating it to a point where it is supersaturated with respect to the said undesirable by-products; and settling said by-products at tha bottom of a sedimentation tank; and separating the so formed precipitate from the remaining concentrated ba~h solution.
This way, the present invention provides for a simple and ine~pensive method for separating the waste products which interfere with the copper deposition from the bath solution, and at the same time the process suggested respects pollution control regulations.
In one particular aspect the present invention provides a process for separating undesirable reaction by-products from~

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electroless copper plating bath solutions comprising submitting at least part of a said solution to a continuous distillation process for concentrating it to a point where it is super-saturated with respect to said undesirable reaction by~products, thus precipitating the by-products; settling said by-products at the bottom of a sedimentation tank; and separating the formed precipitate from the remaining concentrated bath solution.
The inventive method is by far more economic than the regeneration processes conventionally used. In the conventionally used reclamation processes the copper complex in the bath solution is decomposed when the different bath components are precipitated by chemical reaction or chemical reaction and alactr~c energy. The reclaimed chemical compounds were almost al~ unuseable for replenishing the bath and had to be stored or ~ransported to places to be destroyed without violating pollution control regulations. This way, additional costs were incurred in addition to those for the reclamation process itself.
The inventive method comprises a relatively inexpensive and simple process to separate the waste products while the copper(II)-EDTA-complex remains unaffected. This is an important improvement compared to now used reclamation processes. `
It has been found to be especially advantageous to use for the distillation the bath overflow and to reuse the concentrated bath solution after separating the undesirable by-products.
The distillation process is preferably performed under reduced pressure of about 80 Torr and at about 50C and is continued until the volume is reduced by 80 to 85% of the original volume, i.e. a distillate-to-concentrate ratio of about 6:1 to 7:1.
By continuously evaporating water by distillation of the ~''' ' ' ~'' "'' ` , '." ''"'',,,~'",. "i",, ,, ~", .,` ` .', . . .

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OVerflow, the solution becomes supersaturated with respect to sodium sulfate, which precipitates and settles on the bottom of a sedimentation tank and subsequently can be easily separated - from the concentrated bath solution. The concentrated bath solution may be used for replenishing the copper deposition bath and the distillate, mainly consisting of water with traces of EDTA, is also usable for bath replenishing. The concentration of the bath concentrate may be ad~usted before adding it to the electroless plating bath.
Distilling the solution under reduced pressure of about 80 Torr has the advantage that the boiling point of the solution is about 50C which avoids decomposition of the other bath components like copper, EDTA, formaldehyde and sodium hydroxide.
The distillation device is preferably steam heated with stean~ of max. 3 bar pressure.
After removal of the sodium sulfate the concentrated bath solution consists approximately of:
EDTA 110 - 130 g/l Copper sulfate 20 - 22 g/l Formaldehyde (357~ 1.5 - 3.0 g/l and a very small amount of surfactant. With respect to the different original concentrations, the concentrations in the concentrate may vary respectively.
The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for separating undesirable reaction by-products from electroless copper plating bath solutions comprising sub-mitting at least part of a said solution to a continuous distillation process for concentrating it to a point where it is supersaturated with respect to said undesirable reaction by-products, thus precipitating the by-products; settling said by-products at the bottom of a sedimentation tank; and separating the formed precipitate from the remaining concentrated bath solution.

2. A process as claimed in Claim 1 wherein the reclaimed concentrated bath solution is adjusted to conform with the original electroless plating bath formulation used.

3. A process as claimed in Claim 1 wherein the distillation and separation process are performed by vacuum evaporation.

4. A process as claimed in Claim 3 wherein the vacuum evaporation is performed at a pressure of about 80 Torr.

5. The process of Claim 3 wherein the vacuum evaporation is performed at a temperature of about 50°C.

6. The process as claimed in Claim 1, 4 or 5 wherein the distillation is continued until the volume of the bath solution submitted to the process is reduced to 15 - 20% of the original volume.

7. The process of Claim 1 used in combination with the operation of an electroless plating bath which, from time to time or continuously, is replenished and wherein all the bath overflow caused by replenishing is submitted to the distillation process.

8. The process of Claim 7 wherein the remaining bath concentrate produced by the distillation process is circulated to the electroless plating bath.

9. The process of Claim 8 wherein the concentration of the bath concentrate may be adjusted before adding it to the electroless plating bath.