Been a while since I thought about C4.
From memory I don't think it's necessary to completely melt the 5/95 column,
as the 5/95 will dissolve in the Sn63. Using Sn63 with 5/95 does not make a
sharp interface, more of a zone. Soldering at normal temperatures produces a
conventional joint which tends to transition into the flexible high lead
column.
IBM, who invented this process, has some good explanations on how it works
with reliability data.
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne
Sent: Tuesday, January 27, 2009 7:26 AM
To: [log in to unmask]
Subject: [TN] C4 attach to organic laminate material
I've been provided with a C4 bumped die, peripheral contact pads, 200 micron
pitch, and the alloy is Sn5Pb95 (classic C4, melting point approx 290C).
Someone suggested attaching this to a BGA carrier substrate (core with low
elastic modulus SLC layers to absorb the CTE mismatch) using Sn63 solder
paste. Tough printing job, but possible. However, I don't believe we can
get this laminate material up to 290C, so the alloy mix will be incomplete,
meaning a likely brittle zone in the attach.
Only thought I have is using LTCC or HTCC instead of the organic laminate.
Any other ideas out there? Anyone do reliability studies with this type of
attach? Any input would be appreciated!
Wayne Thayer
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