Question: We have been having problems adjusting our acidic copper electrolyte for weeks. After the new preparation, budding appears in the high current density range. This can be reproduced in the Hull cell, which is why we rule out the influence of the anodes. The plates are run for 10 minutes at 2 A. The buds appear up to approx. 5 mm from the left to the inside.
We also detect a lack of organic material in the Hull cell. After adding these, the defects disappeared, but reappear after a very short time.
According to the analysis, the copper and sulphuric acid content are OK. We cannot determine the chloride content analytically, but see no signs of a deviation. In the beginning, we were able to explain the organic problem because we accidentally had activated carbon cartridges in the filter pumps. These were removed, but the problem still occurs.
Answer: Your description of the problem as well as your analyses and Hull cell sheets allow us to draw several conclusions. Unfortunately, we do not know the purpose of the application or the reason for the new approach. It may be necessary to check whether the electrolyte is at all suitable for the application or the current density.
Organics at the limit
The obvious assumption on our part is that you are at the limit with the organics. As you have already described, you had activated carbon cartridges in the filter pump after the new batch and thus removed a considerable proportion of the organics. If you only check this via the Hull cell and therefore have no analysis values for the organic components, there is a risk that you will always add up to the lower value and therefore fall below it again after a few days of production.
With several additives, there is of course also the possibility that one of these additives is particularly low, while you concentrate the rest with each addition. This occurs when some of the additives only adhere slightly to activated carbon, while another additive has a very high affinity.
In our opinion, you should send a sample to the bath manufacturer to obtain a complete analysis. You can then adjust the bath completely and thus have a point in time x at which everything should be in order. From this point on, it is important to keep a close eye on all parameters, changes and influences so that you can intervene accordingly as soon as the error occurs again. It is also important to take another sample for the laboratory as soon as the error occurs so that it can be analyzed by the bath manufacturer. Then you can see which parameters are actually out of control.
You should have the sample checked for impurities - both foreign metals and anions as well as copper chloride particles - as early as the first analysis. You may already receive valuable information about the problem described here.
Current density
First of all, it must be noted that you have a local current density of 13 to 28 amperes in the described area of the Hull cell. Depending on the electrolyte, process technology and flow direction, the current density should be between 0.5 and 5 A/dm2, with the exception of strip electroplating and spot plating processes. Otherwise, defects in the high current density range in the Hull cell are to be expected.
The fact that budding also occurs in production and that you complain about a very high consumption of organic additives suggests that the current density in the cathodic and anodic range is too high. It is generally known that, in addition to the leveling effect of organic bath additives, e.g. when adding thiourea or polyethylene glycol, coexisting conditions can occur on the cathode under certain electrolysis conditions during copper deposition, which lead to roughening and budding [1].
The high current density can cause problems at both the cathode and anode. If the anodic current density is too high, the cathode can become passive, causing subsequent problems. This can also occur if the bath temperature is too low, there is insufficient bath movement and poor contacts, as well as if the chloride or sulphate content is too high.
If the problem occurs all over the cathode, you should significantly reduce the current density. If this only occurs at the tips and edges of rack parts, blanking would be a common method, whereby the current density should also be reconsidered here.
Literature
[1] Prof. Dr.-Ing. Roland Kammer, Uwe Landau and Manfred Mayer: Dissolution and deposition behavior of copper in sulfate electrolytes with organic bath additives, Galvanotechnik 09/1984 p. 1082
