Hi, Yuan,
There are some postings in the TechNet archives about 'Fatigue Resistant
Solders'. These are like normal solders, but have dopants added that make
their grain structure much finer. They have been developed specifically for
BGA and CLCC applications where solder joint inflexibility has caused creep
fatigue failures with substrate materials that have a significantly
different CTE. Look up "fatigue resistant solder" on the Net, and you'll
find what I found, which isn't a lot, but it is growing as research is
carried out and completed. The potential downside to FRS's is that they
have a lower melting point than 'normal' solders. If your assembly is
manufactured with an FRS and it subsequently goes through a wave soldering
process that uses normal solder, the chances are that your components will
move or even fall off. So be careful! Using a FRS may reduce the thermal
stresses on you BGA joints, or permit better solder joints at the lower
temperatures that BGA's seem to reach in the Convection Reflow pre-heat
stages, but as BGA balls are of normal eutectic solder, these may not be
compatible with FRS's - the FRS will melt and reflow, but the BGA balls may
only partially flow, and this could give you more trouble than started
with.
Take it carefully and do a full evaluation of whatever options you go for.
Peter
Yuan Li <[log in to unmask]> 06/08/2002 12:10 AM
Sent by: TechNet <[log in to unmask]>
Please respond to "TechNet E-Mail Forum."; Please respond to Yuan Li
To: [log in to unmask]
cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: [TN] Solder creeping
Hi,
Wondering anyone knows what additives can be added into the eutectic solder
system to slow down the creeping effect ?
Thx,
Yuan
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