Hi Wayne,
We assemble a little different, but same metallurgy.
Substrates are pre-printed with Sn63 solder, reflowed, and coined (flattened). Then, we use a tacky flux for the flip chip, reflow at around 220C, underfill, and go.
Just completed 1000 temperature cycles, -40 to +125C with no failures.
Of course, there are other design aspects such as size, thickness, underfill, etc.
Glenn
-----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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