Hello,

I would like deposit solder bumps on 100um-by-100um aluminum pads; I
also have other exposed metals (Cr, Au) on my chip.

I came across a technique where the chip is dipped into a hot solution
in which a low melting temperature alloy (Field's metal, Cerrolow 136,
etc.) is melted; the metals are selectively deposited on the exposed
aluminum pads. These alloys usually contain Bismuth, Indium, Tin and Lead.

Does anybody have experience with this? Any ideas on selectivity of
deposition onto different materials (Cr, Au)?. Any recipes that I can use?

Thanks,

Emre

--

Mustafa Emre Karagozler
Graduate Student
Carnegie Mellon University
Department of Electrical & Computer Engineering
5000 Forbes Avenue
Pittsburgh, PA 15213