WO1997015704A2 - Electroplating plant - Google Patents

Abstract

The invention concerns an electroplating plant comprising an electroplating container and a supply container between which the electrolyte circulates. In the supply container the metal content of the electrolyte is supplemented by a soluble anode which is associated with an auxiliary cathode located in an auxiliary catholyte which is separated from the electrolyte by a diaphragm which is impermeable to metallic ions. The insoluble anodes of the electroplating container are located in an auxiliary anolyte separated from the electrolyte by diaphragms which are impermeable to anions. The essential advantage of the invention is that insoluble anodes and necessary organic additives for the production of precision coatings, for example in the field of printed circuit boards, can also be used. According to a particularly advantageous development, the auxiliary catholyte and the auxiliary anolyte are guided in a common circuit such that opposed shifts in the pH value of the auxiliary catholyte and auxiliary anolyte are largely compensated as a result of their being continually mixed.

Description

 description

Electroplating system.

The invention relates to a galvanic system according to the preamble of patent claim 1.

State of the art

Such an electroplating system is known from DE 44 05 741 Cl.

The use of insoluble anodes in the previously known continuous electroplating system requires that the electrolyte be enriched with the metal ions provided for coating the electroplating material. In the solution according to the prior art, when using insoluble anodes, this is to be done by using a redox agent whose oxidized stage is present in the regeneration chamber and there causes the dissolution of the metal and thus the metal accumulation of the electrolyte. The metal is thus dissolved outside the electrolytic cell by adding a special electrochemical reagent that is not specified in detail.

In the previously known solution, decomposition products of the process organics used there arise, inter alia, at two points: on the insoluble anodes of the electrolytic cell and on account of the additive used for the anode solution. Both oxidation steps are not completely to electrochemically inert substances and, moreover, the extent is not predictable and can only be determined analytically with great effort. For this reason, both the decomposition products and the non-destroyed ones still have to be used with a complex activated carbon filter existing process organics are removed and then the process organics are adjusted again via a defined addition.

On the other hand, the use of the process organics in the electrolyte (at least in the vicinity of the cathode) explained in the generic document is essential in order to be able to produce high-quality metal layers with defined properties and constant quality in the object to be coated.

US Pat. No. 5,100,517 also shows a galvanic system, which involves the production of coatings on steel reinforcements, for example in tires or drive belts. Such coatings can in particular also consist of copper or zinc, it also being possible for several layers to be superimposed. The basic idea of the new process proposed in this document is to avoid the consumption of the copper anode customary in standard copper coating processes by using an insoluble anode in the electroplating bath, whereas the necessary provision of copper ions for coating the object takes place in a regeneration room. In this regeneration space, a basket with copper balls is provided as an anode and a cathode 27, with a membrane 26 being held between the two, which prevents the released copper ions from being deposited on the cathode 27 again, instead of via the circuit in the electroplating bath object to be coated.

In this respect, this solution is an alternative to the solution to this problem indicated in the generic DE 44 05 741 Cl by a purely electrochemical route and also enables the use of insoluble anodes in the electroplating cell (in the example, a titanium grid coated with iridium oxide) .

In the US patent mentioned, an alkaline electroplating bath is used for coating, in which the copper ion is present in a copper pyrophosphate solution, ie the positive copper ions are shielded by the ligands and the overall complex has a negative charge and thus a certain movement characteristic; this is also expressed in the design of the membrane 26 in the regeneration space, which prevents the flow of such molecular complexes.

With such an electroplating bath, for example, a copper layer with a thickness of 1 +/- 0.5 μ can be applied to a steel wire.

For the application purposes mentioned in the American patent specification, this layer is not subject to any gloss or leveling requirements, since the steel wires coated in this way are only intended as reinforcements for further components (tires).

In contrast, the use of electroplating in the printed circuit board industry requires significantly greater layer thicknesses (up to more than 30μ), to which the qualitative requirements mentioned at the beginning in connection with the generic document are made, which make it particularly necessary to add organic additives as process organics. However, the use of such process organics (with a possibly modified electroplating chemistry) in an electroplating plant in accordance with US Pat. No. 5,100,517 would have the immediate consequence, for example, that in the selection of the process chemistry and electrode materials provided there, amounts of oxidizing substances such as oxygen or Chlorine is formed, with the oxygen in particular leading to uncontrolled oxidation processes on such organic additives, some of which are attacked by intermediates and depending on parameters such as flow conditions, the amount of current that is enforced, in particular the usual organic brighteners and are oxidatively destroyed in an uncontrollable manner .

The transfer of the concept of an external regeneration bath according to US Pat. No. 5,100,517 to electroplating baths in which process organics are indispensable has not been successful in finding a reaction principle with insoluble anodes for the deposition of copper from acidic electrolytes on printed circuit boards. The continuous addition of the components of the process organic destroyed in this process by the oxidation mentioned is also unsatisfactory, since this is caused by non-analysis. sierability of the still partially galvanotechnically effective degradation products leads to fluctuating inhibition by fluctuating sums of the process organics, which in turn questions the quality of the coating. A considerable additional consumption of expensive process organics would be necessary, which makes such a process appear economically not very promising. In addition, the lifespan of the electrolyte would be significantly reduced or expensive regeneration methods would be necessary, which further reduces the economic efficiency.

Description of the invention

It is therefore an object of the invention to develop a generic electroplating system so that on the one hand insoluble anodes can be used, but on the other hand chemical processes such as e.g. the addition of the redox agent mentioned can be dispensed with, it being possible to dispense at least largely with addition of process organics beyond that which is part of the normal continuous addition of electrolytic consumption.

This object is achieved according to the characterizing part of patent claim 1.

The basic idea of the invention is thus, based on US Pat. No. 5,100,517, also to provide an external regeneration space for electroplating baths, as are typically used for the coating of printed circuit boards with copper, for the subsequent delivery of the copper ions consumed during the coating, but on the other hand the unsolvable one Lichen anodes of the electrolytic cell to protect the process organics of the electroplating bath and thus to protect them from decomposition, so that they are fully available for their actual goal, the production of high-quality metal layers with defined properties on the circuit board to be coated, and not in more or less uncontrollable way permanently replaced and their decay products have to be disposed of consuming. Compared to the use of soluble anodes, however, disadvantageous effects of the use of insoluble anodes which can occur can be avoided, since this can prevent the degradation processes of the process organic, such as, for example, brightening additive and wetting agent, which normally take place in the anode reaction of an insoluble anode in the working electrolyte Whose defined replacement is the main subject of the measures in the generic solution. The principle reduction in degradation reactions of the process organics makes the process as it is carried out in the electroplating system according to the invention more economical and process-technically easier to control, since neither oxidized process organics are disposed of by complex measures in the electrolyte circuit, nor does uncontrolled oxidized process organics have to be supplemented .

It is known in principle (DE 42 21 970 C2) to provide cation exchange membranes in the case of problems with the use of insoluble anodes in halogen-containing electrolytes in order to at least reduce the deposition of harmful halogen gases at the anode, but the anion-impermeable ones have this purpose Diagrams for separating the auxiliary anolyte from the electrolyte are not, since in the usual baths for coating printed circuit boards only low chloride concentrations occur in the electrolytes used and therefore no significant chlorine development takes place at the anode anyway.

A further embodiment of the electroplating system according to the invention provides that methods such as those described in electroplating baths with soluble anodes, for example in GB-22 14 520 A, are used to operate the circuit of the electroplating bath, in particular the so-called "pulse plating" -Procedure or "periodic reverse plating", or any combination of these processes with the desired specification of the positive and negative voltages independently of one another. The coating results can thus be improved, the use of this method also enables the use of high current intensities, which in turn has an advantageous effect on the deposition rate or the duration of the electroplating bath. Further advantageous embodiments, in particular of the diaphragms used, can be found in the subclaims.

Brief description of the drawings

An embodiment of the solution according to the invention is explained in more detail with reference to the drawing, in which:

FIG. 1: a schematic representation of the first exemplary embodiment of the electroplating system,

Figure 2 is a schematic representation of the second embodiment of the electroplating system.

Description of the first embodiment:

In a galvanizing container A there is a cathode 1, which is formed by the object to be coated with metal, for example a circuit board to be copper-plated. The metal ions symbolically marked with circled plus signs are deposited on its surface (copper ions Cu ^ ⁺ in the example) and separate as metal.

The associated insoluble anodes 3 are not in the metal salt electrolyte 9 (in the example an acidic copper bath), but in an auxiliary anolyte 4. An anode diaphragm 2, which is designed to be impermeable to anions, is used to separate the electrolyte 9 from the auxiliary anolyte 4.

In a supply container B there is also electrolyte liquid 9, which is held by means of a pump 10 in a continuous electrolyte circuit K1A, K1B between galvanizing container A and supply container B. In the supply container B, the "loss" of metal ions which are deposited on the cathode for coating is at least partially replaced, with the help of a soluble anode 5, which is shown in the drawing as an anode basket with copper balls. An auxiliary cathode 7, which is surrounded by an auxiliary catholyte 8, is also located in the supply container B. A metal ion-impermeable diaphragm 6 serves to separate the auxiliary catholyte 8 from the metal salt electrolyte 9, which prevents the metal ions from attaching to the auxiliary cathode 7, which is symbolized by the reversing arrow.

It is thereby achieved overall that the metal ions provided by the soluble anode 5 almost completely enter the electroplating container A in order to be deposited there as a metallic coating on the object to be coated. This solution is particularly advantageous if instead of the vertical arrangement of cathode and auxiliary anode shown in the exemplary embodiment in the electroplating container A, a horizontal, layer-like arrangement of these components is also frequently used (as is also the case with the generic document), which has the unpleasant consequence that When using soluble anodes in the electroplating bath, complex measures are necessary (combined with considerable downtimes) to replace exhausted soluble anodes. Since such a replacement in the solution according to the invention can be carried out quickly and easily outside of the electroplating container by adding copper balls, the continuous operation of electroplating systems with horizontally arranged elements is also possible.

Typical examples of the components described above in terms of their effectiveness are as follows:

The auxiliary catholyte 8 used in the supply container B typically consists of an acid solution of the same acid that is used in the electrolyte 9 in the same concentration. As a rule, the auxiliary catholyte contains no process organics, apart from a small amount that can diffuse through the diaphragm 6. The auxiliary anolyte 4 in the electroplating tank A typically consists of the acid of the electrolyte 9 in approximately the same concentration; here too, practically no components of the process organics are contained. It is crucial that the auxiliary anolyte is thus compatible with the auxiliary anode and that the action of the diaphragm 2 prevents certain anions of the electrolyte 9 from being in the auxiliary anolyte and that there is an undesirable gas development, for example of chlorine gas, there through corresponding deposits.

In the case of copper electrolysis, as is preferably used for the coating of printed circuit boards, the following can be used, for example, as electrolyte 9:

10 - 35 g / l copper as copper sulfate, 150 - 300 g / l sulfuric acid,

30 - 150 mg / l chloride, as well as usual amounts of process organics consisting of surfactants, brighteners, smoothing additives, leveling, etc.

Plastic material can be used as material for the diaphragms 2 and 6, which are designed as an anion exchanger in the case of the metal ion-impermeable diaphragm 6 and as a cation exchanger in the case of the anion-impermeable diaphragm 2. In the former case, the effect is based on the fact that the current conduction is effected by anion transport and the migration of metal ions is excluded, in the latter case that only cations, in particular protons, are transported.

For the particularly important diaphragm 6, which serves the basic aim of keeping the metal ions of the electrolyte 9 away from the auxiliary cathode 7, a diaphragm made of porous ceramic can also be used, the effect of which is improved by adding suitable chemicals; in the case of an acidic copper bath as the electrolyte, this additive can be, for example, potassium hexacyanoferrate (yellow blood lye salt). The effect of this addition is that the interfering copper ions in the form of the corresponding copper salt (Copper hexacyanoferrate) in the pores of the diaphragm. This makes the diaphragm even more effective. In addition to the improved mechanical function of the diaphragm, any remaining copper ions are trapped.

In the case of tin / lead electrolytes 9, acids other than electrolytes are used, for example methanesulfonic acid or borofluorohydric acid. In this case, other acids can also be used as auxiliary catholyte or other acids of this electrolytic acid can be added, whereby in principle the same failure reaction takes place (sulfuric acid, the lead precipitates as lead sulfate, phosphoric acid, the tin IV as tin acid or similar compounds) .

With the solution according to the invention it is relatively easy to maintain a balance of metal ions in the electrolyte, i.e. an exact possible approximation of the dissolution rate in the area of the soluble anode 5 to the deposition rate at the cathode 1. For this purpose, either a common circuit for the electroplating container and the supply container can be provided, or alternatively a metal content measurement can be carried out, for example the electrolyte 9 can be colored with a suitable sensor (for example a photocell) can be determined and its signal used as a control signal of a control circuit, the control variable of which is, for example, the on-time of the power supply in the supply container B.

As an alternative to this, the current consumption of the two circuits in the electroplating tank A and the supply tank B can also be measured and then an adjustment can be made via the duty cycle and / or the current strength.

As mentioned above, the metal ions required for the deposition process on the electroplating material 1 to be coated are preferably or at least partially obtained in the supply container B by the processes described; As a result of the configuration of the auxiliary anolyte 4 with the associated diaphragm 2 according to the invention, however, there is an additional or possibly also exclusive possibility of Introduce additional metal ions into the cathode compartment of the electroplating container A if this appears necessary, for example, to maintain a desired metal ion concentration:

The solution according to the invention is based on the idea that the anion-impermeable diaphragm 2, which shields the insoluble anodes 3, is by definition permeable to metal ions which are added to the auxiliary anolyte 4. In the drawing, this is shown schematically by a circuit K2A, K2B, in which the auxiliary anolyte 4 is fed via a regeneration chamber C via a pump 11. In this circuit, 4 metal cations can be added to the auxiliary anolyte, for example in the form of a salt, a hydroxide, an oxide or a carbonate of the desired metal of the electrolyte, the recycling being appropriate depending on the regeneration material used and the chemical-physical composition of the overall system of the anolyte for reasons of equilibrium in the recycle circuit to be carried out only partially, ie to withdraw part of the overflowing auxiliary anolyte from the circuit. This will be the case in particular if metal salts or solutions of those which could lead to an accumulation of anions in the auxiliary anolyte 4 are used for the intended supply of the metal cations (the return line from the auxiliary anolyte 4 arranged on the right to the regeneration container C is not for reasons of clarity shown).

The importance of this supplementary or predominantly used method for supplementing metal ion consumption is that the additives (metal salts, metal hydroxides, etc.) that can be used do not have to be obtained from raw materials or raw materials, but through well-known, simple chemical reactions (precipitation, crystallization) ) can be produced from substances that fall off, for example, in the processing of printed circuit boards, in particular in the case of etching processes, and whose use or disposal has hitherto been problematic. This solution thus opens up a way of returning at least some of these products, which were previously regarded as waste, to the coating process in the circuit board processing, thus showing a recycling path for the respective coating metal in the circuit board production.

With this additional "supply" of metal ions there are thus two largely independent "supply circuits" for feeding metal ions into the cathode compartment of the electroplating container A; depending on practical needs, for example the amount of recyclable waste products, these two supply circuits can be easily coordinated, for example by controlling and mutually adjusting the two pumps 10, 11, so that one circuit is selected as the "main supplier" for metal ions and the other Circulation then ensures the additional needs still required.

In the exemplary embodiment shown in FIG. 1, DC voltage sources Q are used for the voltage or power supply of the electroplating container A and the supply container B. The power supply to the cathode 1 and auxiliary anodes 3 can be provided via a control unit S, which can be constructed, for example, as in FIG 4a of GB 22 14 520 A mentioned at the outset, and which is used to generate a voltage profile at cathode 1 and auxiliary anodes 3 shown there under FIG. 4c, with the aforementioned aim of improving the coating quality, in particular in the case of profiled objects, such as printed circuit boards with holes. Even when this method is used for the current or voltage supply of insoluble anodes, the omission of the solution according to the invention of known chemical additives, such as the redox agents known from the generic publication for regenerating the electrolyte metal and minimizing the process organics, has a positive effect, since this does not result Predictable physical or electrochemical interactions between, for example, pulsed voltages of different polarity with the molecular structures of such additives and the process organics or their waste materials can at least be minimized. Description of the second embodiment:

FIG. 2 shows a second exemplary embodiment, which corresponds in its basic principle to the first exemplary embodiment explained in detail above, so that identical components have been provided with the same reference numerals.

In contrast to the first exemplary embodiment, in addition to the circuit K1A, K1B, a circuit K3A, K3B is established, which runs between the auxiliary anolyte 4 in the electrolytic cell A and the auxiliary catholyte 8 in the regeneration chamber B, for the maintenance of which a pump 12 is provided.

This training is based on the following idea:

In the solution shown in FIG. 1 without this circuit K3A.K3B, the auxiliary catholyte 8 would increase its pH in static operation and a lower acid content or a higher alkali content would result compared to the starting solution. The auxiliary anolytes 4 would have the reverse development in static operation. This is avoided by the common circuit K3A.K3B of auxiliary anolyte 4 and auxiliary catholyte 8, since the mixing of these two substances eliminates the opposite shifts in pH, so that the circulation of these two auxiliary electrolytes is far greater than in static operation constant composition can be operated. In practical implementation, the auxiliary anolyte 4 can either flow back into the space of the auxiliary catholyte 8 in free fall via overflows (as shown in the drawing), or optionally via a further pump (not shown).

Claims

Expectations 1. Electroplating system with an electroplating tank (A) in which insoluble anodes and the cathode to be coated are arranged, the electrolyte containing organic additives (process organics) to achieve the desired properties and quality assurance of the layers deposited on the cathode, and with a supply tank (B ) outside the electroplating container (A), in which the metal content of the electrolyte (9) guided in a circuit (K1A, K1B) is continuously supplemented, characterized in that the metal content of the electrolyte (9) is supplemented, at least in part, by a soluble anode ( 5) takes place in the supply container (B), which is assigned an auxiliary cathode (7), which is located in an auxiliary catholyte (8), which is separated from the electrolyte (9) via a metal ion-impermeable diaphragm (6), and that the insoluble ones Anodes (3) of the electroplating container (A) are in an auxiliary anolyte (4) which is separated from the electrolyte (9) is separated via anion-impermeable diaphragms (2). 2. Galvanic system according to claim 1, characterized in that the auxiliary catholyte (8) consists of the same acid or contains this as the electrolyte (9). 3. Electroplating system according to claim 1, characterized in that the auxiliary anolyte (4) contains the acid of the electrolyte (9). 4. Electroplating system according to claim 1, characterized in that the auxiliary anolyte (4) contains metal cations to cover a need for metal ions in the electrolyte (9) of the electroplating container (A) which is not covered by the soluble anode (5). 5. Electroplating system according to claim 4, characterized in that the auxiliary anolyte (4) is guided in an at least partially closed auxiliary anolyte circuit (K2A.K2B) in which metal cations diffuse through the diaphragm (2) to the object to be coated (1) Need to be replaced. 6. Galvanic system according to claim 5, characterized in that the return of the overflowing auxiliary anolyte (4) to a regeneration container (C) does not take place completely if such metal compounds are added to supplement metal cations that enrich anions in the auxiliary anolyte (4). would lead. 7. A method of operating a galvanic system according to the preceding claims, characterized in that the metal ions added to the auxiliary anolyte originate from compounds of the coating metal, which in turn come from by-products or waste products, e.g. can be obtained in etching processes in printed circuit board production. 8. The method according to claim 7, characterized in that the metal compound is a copper salt of the acid used in the electrolyte or is formed by adding the corresponding acid, such as e.g. Copper sulfate and / or copper hydroxide and / or copper oxide and / or copper carbonate. 9. electroplating system according to claim 1, characterized in that the metal ion-impermeable diaphragm (6) is a plastic fabric. 10. Galvanic system according to claim 1, characterized in that the metal ion-impermeable diaphragm (6) consists of a porous ceramic material. 11. Electroplating system according to claim 10, characterized in that the auxiliary catholyte (8) contains chemical additives which precipitate the metal of the electrolyte as a sparingly soluble salt which seals the openings of the diaphragm (6) and intercepts metal ions. 12. Galvanic system according to claim 3, characterized in that the anion-impermeable diaphragm (2) is a plastic fabric which is designed as a cation exchanger. 13. Electroplating system according to claim 1, characterized in that the circuit - insoluble anode (3) - electrolyte (9) - object to be coated (1) is operated by alternating current, the positive and negative voltage values being set independently of one another (periodic reverse plating) and / or pulsed individually or together at high frequency (pulse plating). 14. Galvanic system according to claim 1, characterized in that the circuit auxiliary cathode (7) - electrolyte (9) - soluble anode (5) is DC-operated. 15. Electroplating system according to claim 13, characterized in that the ratio of the anode current to the cathode current is between 2 and 10. 16. Electroplating system according to claim 13, characterized in that the ratio of the duty cycle of the anode current to the duty cycle of the cathode current is between 0.3 and 0.01. 17. Electroplating system according to claim 1, characterized in that auxiliary catholyte (8) and auxiliary anolyte (4) are guided in a common circuit (K3A, K3B).