If you just changed to an ENIG finish without changing the profile you
may need to go back and optimize the reflow profile for a slightly
longer TALT and try to achieve at least a 220C peak temp.
If your PWB material changed that can affect your profile as well.
Another possibility is black pad, or brittle interfacial fracture due to
soldering to nickel. Look at the pads that the parts broke off of under
high power magnification. Check for a distinctive "cracked mud"
appearance. 

-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of DeGenova, Jon R.
Sent: Friday, October 27, 2006 1:19 PM
To: [log in to unmask]
Subject: [LF] Lead free parts falling off boards

We have some PCB assemblies, measuring approximately 11x13 inches in
size, .062" thick, with very dense population on both sides.  They are
mostly SMT, including about 3 BGAs.  These ran fine on as leaded boards,
but in our first runs using a lead-free process and an ENIG board finish
we're seeing a strange problem.  Reports are that parts are 'falling
off', not in large numbers, but enough to raise an eyebrow.  Mostly
these are passives that are coming off after a double reflow process
(there was no wave soldering done on the boards at the point that this
was noticed).  And in some cases, the entire PAD was coming up off the
circuit board.  Has anyone seen similar issues? I'd like to give our
assembly personnel some advice on where to start investigating.
 
Thanks,
Jon DeGenova
 

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