Hi Pearl
As any delamination may be in a localized small area, it may be missed
when trying to do a series of hand soldering tests. You may be
interested in the method that I have adopted to check full panels that
involves passing them through a reflow oven having a temperature profile
that provides a thermal shock of sorts. The settings that work for me
provide a temperature gradient of 80 degrees C per minute to reach a
maximum temperature of 290 degrees in just under 4 minutes with a
similar cooling curve. I find that good boards will survive a double
pass and defective boards will fail on one pass. It also gives you a
good idea of how good your immersion silver finish is ~ a good finish
will dull down slightly after one pass and become slightly
tarnished/yellow after 2 passes.
 
Regards

Alistair Murray
Artetch Circuits Ltd
England UK


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of pearl petras
Sent: 28 November 2006 16:59
To: [log in to unmask]
Subject: Re: [TN] More delam

This is standard FR4 with immersion silver finish.
  The standard soldermask colour we spec is clear, not green.  Allows us
to better see the copper, and often some inner layer features as well,
but if you aren't used to working with FR4 with clear soldermask, it can
definitely look a little strange, at first.
  The dark colour seen is due to an inner layer that is primarily ground
plane.
  I'm pretty sure that it isn't soldermask bubbling
  We have not yet done any microsectioning.  So far we have only seen
this on fully populated boards that have experienced some
hand-soldering, and we are reluctant to sacrifice one, if it can be
saved for production.
  I have a blank two-up panel available from each manufacturer we've
used.  We are planning to run some hand-soldering tests.  Vary
temperatures, one unbaked and one baked from each panel, etc.  Any other
ideas?


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