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August 2008

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Subject:
From:
Werner Engelmaier /* <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Thu, 14 Aug 2008 15:24:00 EDT
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Hi Lenny,
Unless you make very simple, thin PCBs the change is highly recommended.
However, Tg is not the whole story, you also should choose a material with a 
Td(5%) of >= C and a thermal expansion TE(50<=>260C) of <=3.2% . Generally, 
you should pick a material with an STII>=215 [the STII combines the effects of 
Tg, Td and TE].
If you want to get some background and other suggestions, I would recommend 
you get my White Paper: "Recommendations for PCB FAB Notes and Specifications 
in Printed Circuit Board Drawings for SnPb and Lead-Free Soldering Assemblies, 
the Qualification of PCB Shops and Activities to Assure Continued Quality.



Werner
Future workshops:
Reliability Issues with Lead-Free Soldering Processes, September 22, 
Schaumburg
Failure Mode and Root Cause Analyses Reliability (Fatigue, Brittle Fracture, 
ENIG), September 22, Schaumburg
Solder Joint Reliability: Parts 1 & 4, Oct. 9, Moscow, Russia
Solder Joint Reliability: Part 4, Oct. 17, Timisoara, Rumania
Solder Joint Reliability: Parts 1 & 4, Oct. 22, Tallinn, Estonia



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