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November 2010

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From:
Grunde Gjertsen <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
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]> 
Sent by: TechNet <[log in to unmask]>
23.11.2010 16:01
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TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Chris Mahanna <[log in to unmask]>


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Subject
[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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