Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Treating process fluid by means other than agitation or...
Patent
1998-06-18
2000-07-04
Gorgos, Kathryn
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Treating process fluid by means other than agitation or...
205 82, 205335, 205641, 205673, 205687, C25D 2114
Patent
active
060833742
DESCRIPTION:
BRIEF SUMMARY
SPECIFICATION
The invention relates to a method for maintaining constant concentrations of substances contained in an electrolytic treatment bath, preferably in baths with aqueous solutions. The method is universally applicable. A preferred area of application is represented by the metering of chemicals in electrolytic baths and other wet-chemical baths for producing circuit boards, preferably in horizontal throughput units.
The chemicals contained in the bath are constantly depleted in an electrolytic processing bath because of the treatment of the item to be treated. A depletion of this type can also result in an exclusively time-dependent way, for example in a treatment bath for electroless copper plating. In this case, strongly alkaline solutions are used at high temperatures, in which solutions the caustic alkali reacts to caustic alkali in a reaction with carbon dioxide in the air which is introduced into the treatment solution to stabilise the bath and is depleted in this way. The depletion of the process-specific substances must be regenerated in such a way that the respective chemical concentration in the processing bath is maintained within preset limits. The same is true also of the decomposition products of the substances arising during the treatment, said products frequently interfering with the treatment. Their concentrations must be maintained as far as possible beneath certain concentration limits.
The substances are normally regenerated automatically. For this purpose, two methods are known, namely the addition of concentrated solutions (concentrates) to the treatment bath and also continuous replacement of the liquid in the bath by providing a constant volume flow of fresh liquids and corresponding overflow of the bath.
When adding concentrates to the treatment bath the volume of measured quantities is set very small naturally enough since, in order to maintain concentrations of substances in the bath, only small supplements of concentrates suffice in comparison with the entire quantity in the bath. Hence the change in volume of the treatment liquid in the bath caused by these supplements need not be considered. Usually a portion of the treatment solution is evaporated also, especially at high treatment temperatures so that the loss of liquid by evaporation loss is compensated for by regenerating with concentrates. In this case therefore, only small amounts of liquid need to be handled. Furthermore, entrainment losses also occur in the bath, since the item to be treated removes a portion of the treatment solution when being removed from the treatment bath. Corresponding addition of the substances is counteracted, since the item to be treated is either inserted into the bath dry or is already moistened with another treatment solution or water from a rinsing bath, so that even in this case the substances lost through removal are not regenerated by a corresponding supplement.
Apart from depletion caused by the chemical reactions taking place in the treatment liquid and entrainment losses, all the substances remain in the processing bath upon regeneration with the treatment concentrates since the overflowing of the bath caused by a rapid increase in volume does not occur. This has the advantage that no fairly large quantities from the bath need to be disposed of. However it is disadvantageous that, when chemical concentrates are added, the concentration of the substances in the processing bath are constantly increased (build up). Baths, in which the composition for the treatment must be kept within narrow concentration limits, can hence only be pre-set in an insufficiently stable manner. An added complication may then occur when these baths are operated with a small bath volume and with a large throughput of items for treatment. This is the case in electrolytic production methods of circuit boards in horizontal throughput units for example. Because of the substances accumulating in the treatment solution and also because of the progressive ageing of the bath, baths of this type must repeated
REFERENCES:
patent: 5352350 (1994-10-01), Andricacos et al.
patent: 5376256 (1994-12-01), Leutwyler
patent: 5858196 (1999-01-01), Ikenaga
Galvanotechnisches Fachwissen, Von einem Autorenkollektiv, Federfuhrung dr.-Ing. Alexander Strauch 1982 month of publication not available, pp. 436-441.
Atotech Deutschland GmbH
Gorgos Kathryn
Leader William T.
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