Hi Madhav,

You can electroplate different alloys of solder.
The exact minimum feature size really depends on the aspect ratio of your
bumps, but I think industry does <50micron bump pitch without problem.
The trend is to choose lead free solder for environmental reasons.
Search for wafer bumping, flip-chip bonding, solder electroplating vs. in
search engines.

Below paper can give you an introduction:

Deborah S. Patterson, Peter Elenius, James A. Leal,
"Wafer Bumping Technologies:
A Comparative Analysis
of Solder Deposition Processes
and Assembly Considerations"


http://www.suss.com/products/devicebonder/techpapers/04-WaferBumpingTechniqueUsi
ngElectroplating.pdf

Best,

Serhan Ardanuç
Cornell University


>From: madhav rao 
>Reply-To: General MEMS discussion 
>To: mems-talk@memsnet.org
>Subject: [mems-talk] minimum Solder paste width!!
>Date: Fri, 16 Mar 2007 16:54:10 +0000 (GMT)
>Hi All,
>        I wanted to put solder to the 2 copper faces
>which are separated at 10um apart. Can Anyone tell me
>how do I put solder pastes in that region. Solder
>should cover that 10um gap and it should be on copper
>faces for about 10um. Hence the overall solder width I
>want to put is 30um. Is it possible ?? or what is the
>minimum solder paste width, I can go about!!
>If anyone knows please let me know the process of
>that. I would appreciate, If you can pass on any
>technical paper to me.