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Nickel Sulphamate won't plate on sharp edge

Q. I am investigating a plating failure that involves a non-plated region along the sharp edge at the end of a surface mount component. The underlying layer is gold which achieves good coverage around the edge.
It is a nickel sulphamate bath, and we have recently (last 2 months) started making-up the organic components based on the number of amp-hours of operation. The only other variation from our historical plating scheme is that the lead content went from the typical 1.5ppm to about 4ppm around the same time. Which is the most likely culprit, the lead or an imbalance in the organic components?

Neil Jones
passive components - Corpus Christi, Texas
2005

A. Organic contamination (or an excess of organic addition agent) can cause "skip" playing, ie, areas where there is no plating at all. Suggest you carbon treat to remove organics and start over with more discretion about organic adds. 4 ppm lead will not cause this problem.

Jeffrey Holmes, CEF
Spartanburg, South Carolina
2005

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Q. Thanks for your response. How much lead or organic contamination would it take before I began to see this issue? The most recent analysis (just before the bath was changed) indicates the lead content was 24ppm and the TOC (Total Organic Content) was 1500 ppm or 2.4 times that of a fresh bath. Also, the nickel finish was very bright with the problematic bath. Does this information change your diagnosis at all? Is it possible both contaminations were working in unison towards the same effect?

Neil Jones
passive components - Corpus Christi, Texas
2005

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A. Sharp edges are sources of high current densities and will be susceptible to the adverse effects of the same. Additives do their job by altering the way the metal is deposited; in some cases they can actually inhibit the deposition process. I suspect that the organics are being overdosed and this is affecting the deposition characteristics of the nickel in the high current density areas. I suggest you carbon treat the solution, as that should take out the more modern additives, although ones such as NTS are notoriously difficult to remove. If the carbon treatment doesn't work, try adding peroxide and then carbon treat and if that doesn't work, you will have to dump the bath and start again. It is not always a linear relationship between organic consumption and amp-hrs, so you may be overdosing if you use only coulombic derived additions. I suggest you recalibrate your SPC system.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2005