Summary for de-wetting in tin dip process Discussion
de-wetting of short leads in a tin dip process is described as a contamination-related problem. June Apolinar asked why short leads showed de-wetting while taller leads did not, and how to prevent it. Tess Molina explained that de-wetting usually happens when an unwettable material is present on or near the base metal surface, interrupting normal intermetallic growth; the solder then pulls back from those areas, leaving a very thin intermetallic layer with little or no solder. Her practical advice was to ensure a very clean, activated base-metal preparation before the final plate if the parts are plated in-house, with gold mentioned as a possible final plate. The thread does not give a specific reason why only short leads were affected, but it points first to surface contamination and preparation as the likely cause.
Q. Using a tin dip process we encountered de-wetting on short leads only and none at all at high leads, what do you think is the problem? how to avoid de-wetting?
June Apolinar
student – Makati City, Philippines
2004
A. de-wetting is generally caused by a contamination problem. An interruption occurs in the orderly growth of the intermetallic compound because of the presence of some unwettable material on or near the surface of the base metal. The base metal is covered by a layer of molten solder, which pulls back from the unwetted areas. The result is a thin <1 µm layer of intermetallic compound covered with little or no solder. If you are plating your own parts prior to solder process, make sure that you have a very clean, activated base metal preparation prior to final plate (gold?).
Tess Molina
– Hawthorne, California, USA
2004