Very common for SnPb solder paste over here to be the 2% silver loaded
variety ("brighter joints", slightly lower melt point at 179C, etc, etc)

________________________________

From: John Burke [mailto:[log in to unmask]] 
Sent: 05 January 2007 18:28
To: 'TechNet E-Mail Forum'; Burtt, Nigel
Subject: RE: [TN] Qualification of ROHS Components with tin/lead Solder



Interesting  - I note in the conclusions in the opening paragraph that
they state on the QFP failures:

" Failures in Sn-plated QFP components were probably due to batch
related solderability issues."

If you look at the "batch" you will find that this was:

4.3.5 QFP Electrical Testing
No electrical test failures occurred in any of the following
combinations:
- Batch A (SAC solder with SnPb QFPs)
- Batch B (SnPbAg solder with SnPb QFPs)
- Batch D (SnPbAg solder with Sn QFPs)
- Batches E2, E3, E4 and E5 (Contaminated solder with Sn QFPs)
Electrical failures occurred only in the following batch between 1000
and 2000 thermal
cycles
- Batch E1, 4 failures (SAC solder with Sn QFPs)


Since in any experiment of this sort all other variables are removed,
such as component batch, reflow profile, solder batch et al to avoid
skewing the results I draw the conclusion by looking at this data that
the "batch" they are referring to is actually a tin finish component
with SAC alloy combination, and that anyone using this combo is in for
an interesting time unless he is right in the "sweet spot" of a reflow
profile.


I find it extraordinary and very Interesting that they actually did not
use any 63/37 for the BGA trials (or any of the other testing given it's
market share historically) - I wonder why that would have been - anyone
know??



John




John Burke

(408) 515 4992

-----Original Message-----
From: TechNet [mailto:[log in to unmask] <mailto:[log in to unmask]> ] On
Behalf Of N Burtt
Sent: Friday, January 05, 2007 8:01 AM
To: [log in to unmask]
Subject: Re: [TN] Qualification of ROHS Components with tin/lead Solder

THE NPL project report

"Measuring the reliability of electronics assemblies during the
transition period to lead-free soldering."

can be downloded free at

http://tinyurl.com/t6vlt <http://tinyurl.com/t6vlt> 

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