GB2237818A

GB2237818A - Apparatus for the electrolytic regeneration of etching solutions

Info

Publication number: GB2237818A
Application number: GB9024439A
Authority: GB
Inventors: R Bernd Hartmann
Original assignee: Hans Kolbe and Co
Current assignee: Hans Kolbe and Co
Priority date: 1989-11-10
Filing date: 1990-11-09
Publication date: 1991-05-15
Also published as: IT1241008B; IT9067884A1; GB9024439D0; IT9067884A0; DE3937391A1

Abstract

Apparatuses for the regeneration of etching solutions which are associated directly with an etching system are known. The disadvantage of these is the fluctuating need of the etching system over a period of time in connection with the quasi-continuous working methods of the known apparatus, which essentially consists of an electrolytic cell which is used for the anodic re-oxidation of the etching solution reduced as a consequence of the etching process, and which thus leads to the known apparatus having to be dimensioned to cope with the peak needs of the etching system. In order to avoid this disadvantage, in accordance with the invention, a buffer tank (8) is provided which forms a circuit with the associated cell (2) and with pipework (9) connecting the cell and tank, the buffer tank serving as an intermediate store for regenerated etching solution, so that regenerated etching solution in the buffer tank (8) can be introduced into the anolyte circuit between the cell (2) and the etching system (1) according to need. In terms of capacity the buffer tank (8) is adaptable in the simplest manner and introduces a large degree of flexibility, particularly if additional etching systems are added. <IMAGE>

Description

1.

APPARATUS FOR THE REGENERATION OF ETCHING SOLUTIONS is This invention relates to apparatus for the regeneration of used etching solution laden with dissolved metal from an etching process, the apparatus comprising an electrolytic cell arranged for the anodic oxidation of the components of the etching solution which determine the etching reaction as well as for the cathodic removal of the metal, and wherein the cell is designed and arranged for interaction with an etching system or systems.

An electro-chemical removal or etching of metal is used in numerous manufacturing processes, inter alia in the manufacture of boards for printed circuits. In this particular case selectively defined surface area sections are removed from a layer of copper for example, in order to prepare a network of electrical conductors predetermined by the circuit to be manufactured.

I For the etching process, in many cases an aqueous acid solution of salts of the particular metal to be etched is used, wherein as a consequence of the etching process there is an increasing reduction of the metal ions as compared with the starting solution as well as an increasing content of the metal in solution. In order to restore and maintain the possibility for etching, the solution consequently needs to be regenerated.

From EP 0018848 BI there is known a method and an apparatus for the regeneration of used etching solution in which an etching system is associated with such an apparatus. The apparatus consists essentially of an electrolytic cell which is designed and arranged for the anodic oxidation of the said metal ions with the object of establishing a sufficient redox potential, as well as for the cathodic rempval of the is dissolved metal. Between the aforesaid cell, especially its anode chamber, and the etching system, is a supply circuit for the etching means, wherein the redox potential in this anolyte circuit is continuously monitored and the cell is switched off when an upper threshold value is achieved. A circulation of the etching medium occurs in the cathode chamber also of the cell, wherein, with regard to the metal separation process, def ined conditions can be maintained by the introduction of regenerated and used etching solution.

For example, the content of metal ions in solution in the catholyte circuit or circuits is supervised by monitoring the optical density. A disadvantage of this known concept of a coupling of etching system and electrolytic cell lies in the variations with time of the quantitative needs of the etching system for regenerated and sufficient regenerated solution on the one hand and the amounts of regenerated solution which can be supplied by the cell on the other hand, which has the result that the electrolytic cell has to be sized in terms of its capacity to meet the peak demand of the etching system. The average need of the etching systemr considered over a working period, amounts frequently to only 50% of the aforesaid peak demand.

This leads in many cases to an excessive dimensioning of the cell.

Also, in the case of a production plant, one often has several etching systems in use, so that according to this known concept, each etching system would have to have associated therewith a separate cell serving for the regeneration of etching solution, which results in a high investment cost.

It is therefore an object of the invention to provide an apparatus for the regeneration of etching solution which, with relatively low investment cost, makes possible a better matched working operation, i.e. with better matching to the demands for regenerated etching solution.

In accordance with the invention this is achieved by an apparatus of the type first referred to above in which the cell is connected to at least one buffer tank, and wherein said at least one buffer tank, over a working period of the at least one associated etching system, is dimensioned to hold sufficient regenerated etching medium to be able to achieve as even a charging of the etching system or systems as possible taking into account the material conversion of the cell.

It is essential to the invention that the electrolytic cell is associated with at least one buffer tank which in terms of capacity, in combination with the cell, considered over a working period, is sufficient to cover the needs of the etching system. Thus, one starts from the premise that byisuitable measuring and control means in the anolyte circuit of the cell, one can feed in a greater or lesser proportion of regenerated etching solution received from the buffer tank for the purpose of maintaining the required redox potential, for example to be able to cope with the needs for etching solution in the peak load region, while at times of a lesser need for etching solution the proportion of regenerated solution located in the buffer tank can be built up again. In order to equip an electrolytic cell which is known per se in the sense required by the invention it is only necessary therefore to provide a correspondingly dimensioned buffer tank in accordance with the timewise average need, together with associated pipework and measuring and control means. A dimensioning of the electrolytic cell in accordance with the peak demand of is the etching system is therefore no longer necessary.

The f eatur.es of claims 2 and 3 are preferred features which among other things concern the operational working. Thus, the cell together with the buffer tank can constitute a comparable anolyte circuit between the cell on the one hand and the at least one etching system on the other hand, wherein this lastmentioned circuit is independent of the first-mentioned circuit. However, the buffer tank can alternatively be connected directly to an etching system bypassing the electrolytic cell, and furthermore, additional etching systems can be connected to this having regard to its needs and to the capacity of the buffer tank. The provision of a buf f er tank of f ers great f lexibility of working, especially if one wishes to extend a system.

The measurement of redox potential and density of the etching solution can, according to the f eatures of claim 4. be used as measurements f or the control of the admixture of regenerated etching solution received from the buffer tank to the anolyte circuit.

The features of claim 5 are only directed to a supplementary measure for the correcting of the redox potential. For this, hydrogen peroxide can be used for example as the oxidation means.

The apparatus of the invention can be varied in very many ways. Thus, instead of one buffer tank, one could provide a group of buffer tanks in which at least partially used etching solution is stored which is regenerated electrolytically in the following period and is transferred to other buffer tanks. In this manner, existing systems can be extended in the simplest manner and existing electrolytic cells can be better utilised in enlarged systems.

The invention will now be more fully is 1 described with reference to the schematically illustrated diagrammatic representations of the accompanying drawings. In the drawings:

Fig. 1 shows a f irst embodiment by way of example of a recycling system according to the invention; Fig. 2 shows a second embodiment of an enlarged recycling system.

In Fig. 1, reference numeral 1 indicates an etching system whose actual format can be of essentially any type. It can for example be a system used in the manufacture of printed circuits and can be configured and adapted for the selective electrochemical removal of copper layers on circuit boards.

At 2 is indicated an electrolytic cell which is known per se and which is intended for the regeneration of the used etching medium introduced thereto as well as for the separation of the electrochemically removed metal, here copper. This cell comprises a series of receiving chambers for anodes 4 and cathodes 5 which are arranged in alternating manner adjacent to one another and which are separated from one another by porous walls 3 or diaphragms. Each of the anodes and cathodes is made of a material which is inert in relation to the electrolytic reactions.

The electrodes 4, 5 are connected to a suitable dc voltage source which is not shown in the drawings.

Reference numeral 6 indicates tubular pipes which constitute a circulation path for the etching medium between the etching system 1 on the one hand and a receiving chamber of the cell 2 which contains an anode 4 on the other hand. In referring to the aforesaid receiving chamber, it is naturally to be understood that in practice this could be a group of k.

such receiving chambers. Although not shown in the drawingst there are provided in the pipe runs 6 which define the anolyte circuit, pumps and valve members by means of which the flow of the etching medium in the pipes 6 can be controlled.

Reference numeral 7 indicates pipes or pipe systemsf each of which is associated with a receiving chamber or group of such receiving chambers containing a cathode S. The pipes 7 together with the aforesaid receiving chambers again define circulation paths. These circuits for their part, in a manner not shown in the drawings, are connected either to the pipes 6, to the etching system 1 or to receiving chambers for anodes 4, and in this manner are charged with a defined quantity of etching medium. Also, within the framework of these circuits defined by the pipes 7 and their connecting pumps to other parts of the overall system, there are provided pipes and/or valve members by means of which the flow of etching medium flowing in these circuits can be controlled.

Finally, at 8, is indicated a buf f er tank which for its part is connected by means of pipes 9 to a receiving chamber or group of receiving chambers for anodes 4. The pipes 9, together with the aforesaid receiving chamber or receiving chambers, again define a circulation path and are likewise equipped with pumps and valves which are not shown in the drawings.

The buffer tank 8 serves, in a manner which will be described in more detail hereinafter, to match the performance of the electrolytic cell 2 to the needs of the etching system 1.

In the following illustration of the manner of operation of the recycling system according to the invention, one starts f rom, the premise that the acid etching medium is an aqueous solution based upon cupric i is chloride and hydrochloric acid which is introduced f or the electro- chemical removal of copper. The actual etching process itself, starting with a fresh. i.e. regenerated etching medium, is represented as a reduction of the copper (II)-ions to copper (I)-ionst where the copper being removed passes into solution likewise in the form of copper (I)- ions. In the course of the etching process. the strength of the etching means in terms of copper (II)-ions consequently falls, and the consequently falling redox potential is brought about by anodic reoxidation of the copper (I)-ions to copper (II)-ions in the cell 2. The circulation path of the etching medium through the pipes 6 between the cell 2 and the etching system 1 serves this purpose. By means of devices not shown in the drawings the redox potential of the etching medium circulating in the pipes 6 as well as in the associated anode chamber is continuously monitored in relation to upper and lower threshold values, and if thelupper threshold value is reached then the electrolysing process should be switched off in order to avoid the formation of chlorine gas.

Simultaneously, in the chambers of the cell 2 which are associated with the cathodes St there occurs a reduction of the dissolved copper to metallic copper which, in a manner not shown in the drawings, is removed from these chambers, as is indicated by the arrows 10. Subject to this metallic separation process, there is a limit value for the maximum permissible concentration of copper (I1)-ions. The porous walls 3, in combination with a dosed introduction of regenerated or used etching medium in the circuits definable by the pipes 7, serve for the setting of these boundary conditions which distinguish themselves from those of the anode chambers. The buf f er tank 8 serves f or the storage of regenerated, i.e. reoxidised etching medium, which is fed in dosed quantities into the anolyte circuit in such manner that one does not fall below a predetermined redox potential.even at times of peak demand of the etching system 1. The introduction can be effected at any position in the anolyte circuit. In the reverse sense, the cooperation of the electrolytic cell 2 with the buffer tank 8 is designed such that the circuit defined by the pipes 9 and separated or separable from the circuit of the pipes 6 for the purpose of regenerating used, i.e. reduced, etching medium is maintained at least until the etching medium stored in the buffer tank 8 has a predetermined redox potential.

The amount of the regenerated etching medium to be fed from the buffer tank 8 into the anolyte circuit can be regulated for example by means of density sensors.

1 Overall. the system of electrolytic cell and buffer tank 8 is quantitatively designed so that, taken over a working period, in any phase the needs of the etching system 1 can be covered by adequate suitable etching medium.

Only as a supplementary procedure. for the purpose of adjusting the redox potential of the etching medium, can an additional oxidation means, f or example hydrogen peroxide, be introduced into the etching medium at a suitable point. On cost grounds. the latter should however only be regarded as a correcting measure.

With regard to the technicalities of the pipe connections, particularly the feeding in of regenerated etching medium from the buffer tank 8 into the etching system 1, there are numerous possible variations. Instead of one buffer tank 8 one could have a plurality 1 i i 1 -g- of tanks which each serve for the transitory storage of used or regenerated etching medium, so that easy capacity matchings are possible.

In Fig. 2, where the functional elements which correspond to those of Fig. 1 are shown by the corresponding same reference numerals, a development of the system shown in Fig. 1 is illustrated. According to this, the buffer tank 8 is connected by way of additional pipes 11 to a further etching system 12, with these pipes 11 again defining a circuit, here the catholyte circuit of the etching system 12. In terms of its capacity the buffer tank 8 is dimensioned such that both etching systems 1 and 12, which can be spatially separated from one another, in combination with the electrolytic cell 2 can be supplied with a" sufficient quantity of suitable etching medium.

Here also, several further connecting possibilities are available for the pipe connections between the etching systems, the cell 2 and the buffer tank 8. As is indicated by the dotted lines 13, the etching system 1 for example can then be fed with regenerated etching medium directly from the buffer tank 8. In addition to this, each of the two etching systems 1 and 12 can be fed simultaneously from the cell 2 as well as the buffer tank 8 in accordance with controllable mixture ratios.

If needed. for the correction of the redox potential of the etching medium, a supplementary oxidation means, such as for example hydrogen peroxide. can be introduced again at a suitable point.

The system shown in Fig. 2, basically because of the buffer tank 8, can be used also forthe loading of transportable tanks. in order to be able to provide small, remotely located etching systems for example which are not connected by way of a fixed pipe system to the recycling plant shown in Fig. 2 with a suitable etching medium.

The concept shown in Fig. 2 can be used for the supply of f urther etching systems depending upon the design data of the cell 2 as well as of the buffer tank or tanks 8.

Overall, the design of a recycling system according to the invention opens up the achievement of a more economical utilisation of an electrolytic cell, especially a flexible matching to different system requirements, and is characterised by a relatively small investment cost.

1 0.

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Claims

CLAIMS:

1. Apparatus f or the regeneration of used etching solution laden with dissolved metal from an etching process,, the apparatus comprising an electrolytic cell arranged for the anodic oxidation of the components of the etching solution which determine the etching reaction as well as for the cathodic removal of the metal, wherein the cell is designed and arranged for interaction with an etching system or systems, wherein the cell is connected to at least one buffer tank, and wherein said at least one buffer tank, over a working period of said at least one associated etching system, is dimensioned to hold sufficient regenerated etching medium to be able to achieve as even a charging of the etching system or systems as possible taking into account the material conversion of the cell.

2. Apparatus according to claim 1, in which the cell with the buffer tank and pipe means connecting these together constitute a circuit for the etching medium.

3. Apparatus according to claim 1 or 2, in which the buffer tank is connectable directly to at least one etching system.

4. Apparatus acc ording to any preceding claim, which includes additional measuring means f or the continuous determination of for example the redox potential and/or the density of the withdrawn etching solution intended to be introduced into the etching system or systems, and also including control means for the admixture of regenerated etching medium stored in the buffer tank according to a sufficient suitable redox potential.

5. Apparatus according to any preceding claim, which includes means f or the introduction of an oxidation means into the etching solution intended to be introduced into the etching system or systems.

6. Apparatus f or the regeneration of used etching solutionf substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.

1 is 114kl,,d 1991 atilbe Patent Office state H 66171 High Holbom. LA)ndonWC1R41?. Further copies rnay be obtained from 3 Branclk Unit 6. Him M& Paint Cwmfehnfach. Cros, Keys. Ncwport NPI 7HZ. Printed by Muluplex techniques ltd. St Mary Cray. Kent.