Hello.  This is the first time I have used IPC TechNet, so please forgive
me if this question has been asked before.

Our company has built some SEM Modules (Standard Electronic Modules) for a
customer who recently reported failures in the field with these Modules.
These types of Modules have Leadless Chip Carrier ICs with castellated
terminations on them.  The solder pads are underneath the IC packages.  As
part of the failure analysis performed by the customer, some of these LCCs
were removed, and they noticed an off-yellow coating on the bottom of the
LCCs which they feel is solder flux.  They theorize that the solder flux
has hardened over time and has become conductive.

Our Production Manager thinks that this problem is caused by the fact that
these LCCs sit flat on the substrate and therefore the solder flux gets
trapped under the LCC during reflow and cannot be cleaned out.  He proposes
two possible solutions:

 - put adhesive under the LCC

 - put a spacer under the LCC which is dissolvable in water (i.e. during
cleaning)

I was wondering if anyone had experienced a similar problem and knew of
an "industry standard" solution, or any solution.  Thank you in advance.

Best regards,


Paul Baine
Q.A. Manager
C-Tech Ltd., Cornwall, Ontario, Canada

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