Letter 34022

Plating Aluminum pads on an IC [California] 

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I am looking for a solution to mounting solder balls (SnPb or InPb) onto Aluminum pads on a silicon IC. The IC pads are Aluminum. As I understand it, the Aluminum pads will not bond well directly to a solder ball, and thus some form of pad treatment must precede the solder balling procedure.

Mechanically, the IC can be dipped in a bath, as the IC has a passivation layer (glass) over the necessary circuitry, and recesses in this passivation layer where the Al pads exist. The pads are 150um square and about 3um thick.

Would electroless nickel work for this? If so, what is the procedure? Can this be done on-site for low volumes, or does it need to be subcontracted to a shop?

Any other ideas for this problem?

Thank you for any responses.

Steve Chacko
Furaxa, Inc. - Orinda, CA, USA

Your problem could be solved by electroless nickel as you suggest, and then plated with copper and autocatalytic electroless silver.

Best regards,

Karl Lundahl
- Mölndal, Sweden

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