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Date: | Wed, 24 Nov 2010 13:58:44 +0100 |
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Hi
Depends on your supplier and the type of business you're into but
personally I'm very reluctant to ImmSn. In the world of hi mix and lo to
medium volume ImmSn is the devil, it's just too unreliable.
Only people I know using it sucessfully is running very high volumes on
not very complicated boards, with high stock turnover and from select
suppliers.
The J-STD-003 is pretty worthless to determine whether the boards will
work in your process, reflow simulation is marginally better but it
depends a lot on how it's carried out and is usually just an approximate
approach to simulate your actual process on a populated board.
It's pretty important, especially with ImmSn that the full process cycle
is carried out because solderability issues may not show up during the
first solder cycle.
Best regards
Grunde
Chris Mahanna <[log in to unmask]>
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23.11.2010 16:01
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[TN] ImSn finish, BGA solderability
Due to the holiday time crunch, I'm looking for some brainstorming on ImSn
solderability forensics.
I'm thinking that there may be some low hanging fruit that I'm missing
because we just have little experience with ImSn.
We've found random one-up Pb-free BGA balls not wetted to the lands.
Finish is ImSn. Basic question in my mind is Sn oxides, SnCu
intermetallics, or misprint.
Representative bare boards passed J-STD-003 solderability with flying
colors, but it is a double sided SMT. Haven't tried after reflow
simulation yet.
Both the assemblies and representative bare boards are now naturally aged,
so SERA wouldn't quantify the problem as it existed. Would it?
I've noted the coincidence of eggshell voids with the non-wet balls.
Doesn't that imply some paste/flux? Does it imply anything else? Are the
volatiles more likely to form eggshells when they are burning through Sn
oxides?
Here are some pics:
http://ipc-technet.groupsite.com/gallery/16789
Thanks!
Chris
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