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Plating contaminants

I have an AlN spacer that had Au plated over a layer of TiW. At a future assembly operation (braze), a large stain was found to form at elevated temperature, around the AlN spacer. It is suspected the stain came from the plating on the AlN. One suggestion was that these may be plating salts. What contaminants might come from these plating operations and how might I control them?

Mike Scherbarth
- Milpitas, California, USA
 

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The AlN should be inert and fully fused if procured from the standard reputable manufacturers. The Ti/W is an adhesion promoter as well as a diffusion blocker although diffusion should not be a problem. The only reliable way to up-plate Au on the Ti/W is with a seed layer of sputtered Au on top of the Ti/W. 2000-3000 Ang is sufficient. 1000 Ang might pass muster but be wary of 500 Ang or less. A contaminated Au bath (either cyanide or sulfite) can definitely give a stain, particularly on high temp brazes such as used for Au/Ge or Au/Sn. Have the plating bath analyzed. You may want to run a carbon filter on your bath and clean it up as I would tend to believe organic contaminants are the culprit (been there, done that).

Good luck.

Jeff Albom
- El Granada, California, USA