These silver loaded epoxies (such as Epotek H20E) are designed for gold to
gold bonding.  They are optimized for electrical and thermal contact, not
strength, but there shouldn't be any problems.

The two epoxy vendors I mentioned have data on the maximum die size versus
CTE mismatch for each type of epoxy they sell.  It's either on the website
or available from talking to an applications engineer.  Epoxy has a lot more
"give" to it than solder.  If you peruse the options, there are different
epoxies depending on whether you are concerned most with thermal dissipation
or CTE mismatch.

Bonding GaAs chips with gold backsides to gold plated aluminum is an
industry standard process when making microwave assemblies, so I don't think
that will be a problem.

David Nemeth
Senior Engineer

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of Adamson, Steve
Sent: Friday, March 28, 2008 11:47 AM
To: General MEMS discussion
Subject: RE: [mems-talk] About Die Bonding

David, I have heard that epoxy does not stick to gold very well. If X.P.
Zhu uses solder I can understand the gold flash. But this may not be the
best backside coating if he uses epoxy. What do you think?

Also he is using copper. That is going to have a huge TCE compared to a
ceramic. Depending on the temperature excursion and his bonding method
he could run into die cracking problems. However I agree with you that
Epoxy is probably his best bet.