I have found PSA materials tend to be hydroscopic and can blister during
the reflow process.  I have worked with two different assemblies that
required baking prior to the SMT process in order to avoid opens and
pillowing.

Regards,

Ted T.

 
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dan Skweres
Sent: Friday, November 20, 2009 9:22 AM
To: [log in to unmask]
Subject: Re: [TN] Stiffener on Flex Circuit

Depending on the type of adhesive process (thermal set or PSA tape) they
could be applied at different stages. Typically they're done in panel
form
using external tooling holes for registration. If however, PSA tape is
being
used to apply then they could be applied in pc form and aligned by eye.
As
far as the size of clearance in the stiffeners normally they're slightly
larger than the underlying pad that you plan on wicking solder to. If
you're
wanting a S/S flex without pads on the side your applying the stiffener
to,
then you could go smaller. It's best to contact the potential supplier
and
seeing what they recommend that will best fit their processes and get
you
what you need.
Dan S.

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