EP0878561B1 - Process and apparatus for the regeneration of tin plating solutions - Google Patents

Description

The invention relates to a method and an apparatus for regenerating used tinning solutions.

The external tinning of copper workpieces using an aqueous tinning solution is a common process in surface coating technology. It is used, for example, for the internal tinning of copper pipes or tinning of circuit boards for integrated circuits application.

The tinning solution contains aqueous dissolved tin ions which, due to a chemical reduction using a suitable reducing agent on the copper be deposited. This takes place on the surface of the copper workpieces Exchange between the metals takes place through one in the tinning solution contained complexing agent is made possible. Hypophosphite is the main reducing agent used, thiourea is mostly used as a complexing agent.

By reducing the redox potential of copper in the complex-bound Form, copper goes into solution and tin separates on the surface of the copper workpiece from. Since there are no free electrons in chemical reactions the oxidation of one reactant is always accompanied by the reduction of another.

With the process of electroless tinning is therefore an enrichment of Copper and a depletion of tin in the tinning solution. in the conventional operation must therefore be replenished with tin and complexing agents, until a copper limit concentration is reached at which the solution is unusable and needs to be replaced. Furthermore, reducing agents must be used from time to time can be replenished, as this is used up if after reaching one additional metal is to be deposited over the complete tin layer.

The used tinning solution then contains tin and copper ions, free and complexing agent bound to the copper ions, used and unused Reducing agents and, if appropriate, further constituents or in terms of process technology conditional contamination.

For the regeneration of a galvanic tinning electrolyte, the DE 27 42 718 A1 proposed to first remove the tin ions by means of electrolysis and then the foreign metal ions in a cation exchanger remove.

DE 43 10 366 C1 counts a method and a device for regeneration from aqueous, external currentless coating solutions for metal coating using metal ions and a reducing agent to the prior art Technology. Here a combination of an ion exchange process with the Electrode reactions of the electrolysis made.

The process takes place in an at least four-chamber electrolysis cell. It electrolytic regeneration is achieved by reducing the amount generated in the process Orthophosphite in a cathode chamber to hypophosphite and through Electrodialytic provision of counter ion-free resharpening chemicals.

An electrolytic regeneration of tinning solutions that operate without external current could not be practiced successfully because the thermodynamic Potentials of complex-bound copper and tin against one Speak copper deposition.

This is where the present invention comes in, the object of which is a method and to show a device that allow the accumulating interference component Separate copper by cathodic deposition and at the same time to supply the consumable component tin, so that the Service life or service life of tinning solutions that operate without external power for copper workpieces can be significantly extended.

The solution to the procedural part of this task consists in the features of claim 1.

The solution to the objective part of this task is in the characteristics of Claim 8 to see.

Advantageous developments of the method according to the invention are in the dependent Claims 2 to 7 characterized. Advantageous embodiments of the invention Device form the subject of dependent claims 9 until 12.

The essence of the invention is the measure of tinning solution used regenerate strong dilution. According to the invention, a combination of Electrode reactions of electrolysis with transport processes in ion exchange membranes performed. Here, copper is depleted by cathodic deposition from a dilution of the tinning solution and Enrichment of tin by anodic dissolution and transport through a cation exchange membrane.

The invention adopts the knowledge that in a regeneration solution, in which the tinning solution used in the tinning process is strong is present diluted, the separation ratios compared to the original concentrated Reverse tinning solution and prefer copper from the thermodynamic deposits disadvantaged copper complex. This can cause the interference component Copper depleted and the tin component required for the process can be supplied by anodic dissolution.

The regeneration solution is fed to an electrolysis cell, which has a cathode chamber with an inserted cathode, a middle chamber and one with a Anolyte-filled anode chamber with anode incorporated. The cathode chamber is separated from the middle chamber by an anion exchange membrane, whereas a cation exchange membrane between the anode chamber and the middle chamber is incorporated. There is an electrical one between the anode and the cathode Potential difference created.

In the electrolysis cell, the regeneration solution first reaches the cathode chamber and remains there with the deposition of copper on the cathode. The dwell time depends on the total amount of metal supplied. Then will the copper-depleted regeneration solution is directed into the middle chamber, where a tin enrichment from the anolyte of the anode chamber through the cathode exchange membrane penetrated tin ions.

Then the prepared, tin-enriched regeneration solution can be removed from the Middle chamber are fed for further use.

The prepared regeneration solution is expediently used in the tinning process returned where they also the water losses occurring there through evaporation balances.

According to the features of claim 2, the regeneration solution consists of a 5 to 50% dilution of the tinning solution. Being particularly advantageous considered a concentration range between 10 to 15%.

Even if it is basically possible to withdraw the regeneration solution of tinning solution from the coating process and admixing one accordingly Getting high amounts of water is a particularly beneficial one Further development of the method according to the invention in the features of the claim 3 to see. The regeneration solution then becomes a rinsing process for the copper workpieces won.

The rinsing water concentrated by a suitable rinsing technique, the electrolyte concentration preferably has 10 to 15% of the process solution then passed into the cathode chamber of the electrolytic cell.

The dilution of the tinning solution that results automatically during the rinsing process and through suitable flushing techniques to the required concentration range brought, the cathodic deposition of copper from the complex compared to tin, even though the thermodynamic redox potentials do not expect this.

The copper ions contained in the regeneration solution are deposited cathodically. To a small extent, they are also in the regeneration solution contained tin ions cathodically deposited with. The ions of the reducing agent can diffuse through the ion exchange membranes into the middle chamber, in which the regeneration solution of the previous regeneration cycle is located. This is already depleted in copper.

After the copper enrichment in the cathode chamber, the regeneration solution transferred to the central chamber in which the tin enrichment takes place.

Here tin ions, which are anodically dissolved in the anode chamber, by diffusion from the anode chamber through the cation exchange membrane in the middle chamber. The anions of the reducing agent are through the cation exchange membrane prevented from passing into the anode chamber, so that they remain in the middle chamber.

The combination of electrode reactions of electrolysis with transport processes In ion exchange membranes, selective deposition is possible according to the invention the interfering component copper from a regeneration solution in the form of diluted tinning solution.

Following the tin enrichment, the regenerated solution is used in the tinning process returned and refreshes the tinning solution. This will the service life and useful life of the tinning solution are significantly extended.

As an anolyte, which is carried out in a separate circuit (claim 4) Sulfuric acid for use, preferably in a concentration between 3% and 6% (claim 5). Here, an anodic dissolution of the tin takes place without a polarization effect with almost 100% current efficiency.

Alternatively, tetrafluoroboric acid or methanesulfonic acid can also be used as the anolyte be, as provided for in claim 6.

According to the features of claim 7, the temperature in the electrolytic cell between 10 ° C and 60 ° C. Cathodic depletion starts best Copper and tin enrichment in a temperature range between 30 ° C and 40 ° C.

The regeneration solution is moved in the electrolysis cell as claimed in claim 9 provides. This can be done, for example, by pumping from chamber to chamber take place or by stirring in the chambers. This causes polarization effects avoided in the chambers, especially on the membrane surfaces.

To ensure optimal regeneration conditions, the temperature of the Electrolysis cell can be controlled (claim 10).

The method according to the invention can be used both in continuous cycle operation as well as in batch operation.

The regeneration solution can either run quasi continuously in two cycles the cathode chamber or middle chamber of the three-chamber membrane electrolysis led or there may be a portion of the tinning solution diluted in the batch Cell regenerated and then returned to the tinning solution.

The cathode material preferably consists of copper or stainless steel 11). The anode material consists of tin. This is a requirement for that Tin enrichment during the regeneration process.

Since a tinning process usually takes place at temperatures between 70 ° C and 80 ° C is carried out, correspondingly high evaporation losses occur in the Tinning solution. The prepared regeneration solution is the same this out. If necessary, a needs-based process-dependent correction can be made or adjustment of the regeneration solution. In this way is also a cheaper water cycle management by the inventive method reached.

According to the features of claim 12, two or more Electrolytic cells in stacks one after the other (series connection) or in parallel next to each other (Parallel connection). This creates a high capacity provided for the processing of used tinning solutions.

The invention is explained in more detail below by an example and an illustration.

The example concerns a tinning electrolyte for tinning without external current the fluoroborate-based with the complexing agent thiourea and the reducing agent Hypophosphite is built up.

The data listed in the table below apply to the example:

redox potentials:

Stability constants:

K_s (Cu(TH)₂ ⁺)

= 2,0 x 10¹²

K_s (Cu(TH)₃ ⁺)

= 2,0 x 10¹⁴

K_s (Cu(TH)₄ ⁺)

= 3,4 x 10¹⁵ bzw. 2,4 x 10¹⁵

aus [Inorg. Chem., 15, 940, (1976)] und [J. Am. Chem. Soc., 72, 4724, (1950)]

K _s (Cu (TH) ₂ ⁺ )

= 2.0 x 10 ¹²

K _s (Cu (TH) ₃ ⁺ )

= 2.0 x 10 ¹⁴

K _s (Cu (TH) ₄ ⁺ )

= 3.4 x 10 ¹⁵ or 2.4 x 10 ¹⁵

from [Inorg. Chem., 15, 940, (1976)] and [J. At the. Chem. Soc., 72, 4724, (1950)]

In addition to the reaction equilibria for the tin ion system, complex-bound copper ions and anions of the reducing agent too those of chemical water decomposition, as these are used in membrane electrolysis, especially with very dilute solutions Need to become.

The data show that free copper, both as Cu (I) and as Cu (II) could preferably be deposited over tin. Since the copper Tin is only present as complex-bound copper. This is also the case in concentrated solutions.

The invention results in that in the regeneration solution in the tinning solution is present in the specified dilution, electrode kinetic effects (Breakdown reaction, exchange current density, overvoltage) an increasingly important Play role, so that preferred despite the unfavorable potential conditions Copper can be deposited.

The course of the regeneration process of a tinning solution is illustrated in FIG. 1. The reaction equilibria, redox potentials that are important for the system and complex stability constants can be found in the table above.

1 in FIG. 1 is a system for tinning copper workpieces without external current referred to by means of an aqueous tinning solution.

Following the tinning process, the copper workpieces are made in one Rinsing process cleaned. The flushing process is with SP, the water supply through the Arrow marked W. Here, the tinning solution is carried out by electrolyte extraction towed portion diluted by the rinse water. By a appropriate rinsing technology, the rinse water to a 10 to 15% dilution the process solution concentrated.

The regeneration solution produced in this way becomes a three-chamber electrolysis cell 2 forwarded. The electrolytic cell comprises a cathode chamber 3, one Middle chamber 4 and an anode chamber 5.

In the cathode chamber 3 there is a cathode 6 made of copper, in the anode chamber 5 is an anode 7 made of tin. Between anode 7 and cathode 6 a potential difference is created.

The cathode chamber 3 is through an anion exchange membrane 8 and the anode chamber 5 through a cation exchange membrane 9 from the middle chamber 4 Cut.

The regeneration solution is first fed into the cathode chamber 3 (arrow P1). The interfering component copper is then cathodically deposited from the thiourea complex at a current density of 0.4 to 0.6 A / dm ² and thus removed from the system. At the same time, anions such as the tetrafluoroborate anion and the hypophosphite anion can pass through the anion exchange membrane 8 into the middle chamber 4.

As a side reaction, tin co-deposition of less than 35%, the decomposition of water through the evolution of hydrogen and a reduction of Orthophosphite parts to hypophosphite occur via the hydrogen formed. In particular, the water decomposition due to the dilution leads to a lower current efficiency (approx. 40%) with regard to metal deposition.

After a dwell time corresponding to the amount of metal to be deposited, the Contents of the cathode chamber 3 pumped into the middle chamber 4 (see arrow P 2). Here a tin enrichment by tin ions takes place, which comes from the anode chamber 5 diffuse through the cation exchange membrane 9 The tetrafluoroborate and Hypophospitations can not because of the cation exchange membrane 9 in the Step through anode chamber 5.

Following the tin enrichment, the regenerated solution can be used in the tinning process be returned (arrow P3). This can also be used in the tinning process occurring evaporation losses can be compensated. The in Evaporation occurring during the tinning process is indicated by the arrows V. If a need correction (arrow BK) of the prepared diluted solution made to the process engineering requirements of the tinning solution become.

The respective electrolyte solutions in the three reaction chambers (cathode chamber 3, middle chamber 4, anode chamber 5) are moved so that polarization effects in the reaction chambers 3, 4, 5, in particular on the membrane surfaces, are avoided. The movement in the cathode chamber 3 and in the middle chamber 4 is indicated by the arrows B1 and B2. The movement B1, B2 can take place, for example, by stirring. The anolyte (H ₂ SO ₄ ) in the anode chamber 5 is conducted in a separate circuit. This is indicated by arrow B3.

The combination of electrode reactions of electrolysis with transport processes in ion exchange membranes thus enables a selective separation of the Interfering component copper from a diluted tinning solution with simultaneous Enrichment of tin via anodic dissolution and transport of the tin ions through the cation exchange membrane. The regenerated solution is in the tinning solution of the tinning process. This will make the Service life or the useful life of the tinning solution significantly extended.

According to the invention it is possible that two or more of the above Electrolytic cells 2 in stacks one after the other (series connection) or in parallel next to each other (Parallel connection) are connected. In this way, each Capacity designed for the processing of tinning solutions reached.

REFERENCE NUMBERS

1 -

tinning

2 -

electrolysis cell

3 -

cathode chamber

4 -

middle chamber

5 -

anode chamber

6 -

cathode

7 -

anode

8th -

anion exchange membrane

9 -

cation

B1 -

arrow

82 -

arrow

B3 -

arrow

BK -

needs correction

P1 -

arrow

P2 -

arrow

P3 -

arrow

SP -

flushing

V -

evaporation

Claims (12)

1. Method for regeneration of an aqueous copper workpiece tinning solution which works without external current and contains tin and copper ions, free complexing agents and complexing agents bound to the copper ions and used and unused reducing agent, characterised in that a regeneration solution with a solution exhibiting a lower tin content than the tinning solution working without external current is fed to an electrolysis cell (2) which comprises a cathode chamber (3) with an integral cathode (6), a middle chamber (4) and an anode chamber (5) filled with an anolyte with an integral tin anode (7), and a potential difference is applied between the tin anode (7) and the cathode (6) and the cathode chamber (3) is separated from the middle chamber (4) by an anion exchanger membrane (8) and the anode chamber (5) is separated from the middle chamber (4) by a cation exchanger membrane (9), and the regeneration solution is first passed into the cathode chamber (3) and retained there while depositing copper on the cathode (6), and in that after the retention time the regeneration solution depleted of copper is pumped into the middle chamber (4) where tin enrichment is carried out with tin ions which have passed out of the anode chamber (5) through the cation exchanger membrane (9).
2. Method according to claim 1, characterised in that the regeneration solution contains between 5% and 50%, preferably 10% to 15% of tinning solution.
3. Method according to claim 1 or 2, characterised in that the regeneration solution is recovered from a copper workpiece rinsing process (SP).
4. Method according to one of claims 1 to 3, characterised in that the anolyte is conveyed in a circuit (B3).
5. Method according to one of claims 1 to 4, characterised in that a 3 to 6% sulphuric acid is used as anolyte.
6. Method according to one of claims 1 to 4, characterised in that a tetrafluoroboric acid or a methane sulphonic acid is used as anolyte.
7. Method according to one of claims 1 to 6, characterised in that the temperature in the electrolysis cell (2) lies between 10°C and 60°C, preferably between 30°C and 40°C.
8. Device for implementing the method according to one or more of claims 1 to 7, consisting of an electrolysis cell (2) which comprises a cathode chamber (3) with an integral cathode (6), a middle chamber (4) and an anode chamber (5) with an integral tin anode (7), and the cathode chamber (3) is separated from the middle chamber (4) by an anion exchanger membrane (8) and the anode chamber (5) is separated from the middle chamber (4) by a cation exchanger membrane (9), and a potential difference can be applied between the tin anode (7) and the cathode (6).
9. Device according to claim 8, characterised in that the regeneration solution can be moved in the electrolysis cell (2).
10. Device according to claim 8 or 9, characterised in that the temperature of the electrolysis cell (2) can be controlled.
11. Device according to one of claims 8 to 10, characterised in that the cathode (6) is made of copper or special steel.
12. Device according to one of claims 8 to 11, characterised in that a plurality of electrolysis cells are connected in series and/or in parallel with one another.

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