Letter 18043

Zincating [Colorado] 

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I am currently work for a company (IC Interconnect) which plates electroless nickel and immersion gold on aluminum based semiconductors. We have been able to plate nickel on aluminum with 0.1% to 0.5% copper for the past four years with great success. However, we have not been able to plate on aluminum with silicon. The zincation process results in very spotty coverage over the aluminum/silicon pads. The resulting nickel adhesion is very poor. In addition, the plating quality is dependent on the potential of the pad, i.e. ground pads plate different than gate, drain, and power pads. This is only true for aluminum with silicon. When copper is added (AlSiCu or AlCu), all of these issues disappear.

Can anyone give me any advice?

Andrew Strandjord
- Colorado Springs, Colorado, USA

As a general plating statement, parts that contain silicon can be troublesome to process. To obtain good adhesion on silicon, it usually must be etched. To my knowledge, fluoride is the most commonly used etchant (there may be others). Hydrofluoric Acid can be used, but is extremely hazardous. A more benign, but still hazardous, compound is ammonium bifluoride. The time/temp/concentration factors would have to be determined by experimentation. Posting another (more specific) question on this website might result in more specifics.

Vic Waldman
- Naugatuck, CT

Use a dilute type zincate at about 30 to 45 seconds, rinse, rinse, 4 oz/gal Sodium Bicarbonate, rinse, ALKALINE electroless nickel, rinse, rinse in ammoniated water, then finally acid electroless nickel plate.

Robert H Probert Robert H Probert Technical Services Garner, NC, USA Editor's note:        Mr. Probert is the    author of Aluminum How-To

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