Doug -
Tg of resin does not necessarily mean better thermal performance at
temperatures above the Tg - Tg is an indication of the degree of cure
for that resin system based on an expected value. Lead-free soldering
excursions are well in excess of Tg and what condition is most important
is the decomposition temperature of the base material. We have seen
that some lower Tg materials actually have a higher decomp temperature
than higher Tg materials. This should be studied with your board house
to find the correct material that meets your specific temperature
cycling for lead-free. There are also base materials that are
specifically designed to have high decomp temperatures and maintain
adequate electrical performance also. The trade off with these
materials is cost - both in base materials and in processing.
Jeff
Jeffrey Bush
Director, Quality Assurance and Technical Support
76 Technology Drive - POB 1890
Brattleboro, Vermont 05302-1890
Tel. 802.257.4571.21 Fax. 802.257.0011
[log in to unmask]
http://www.vtcircuits.com
-----Original Message-----
From: McCall,Doug [mailto:[log in to unmask]]
Sent: Wednesday, May 19, 2004 3:02 AM
To: [log in to unmask]
Subject: [TN] Pb-free and laminate Tg requirements
Hi,
What is the general thinking on the glas transistion temp (Tg) for FR4
being used for Pb-free PCBAs. I guess that the 'standard' is 140 deg-C
and is it sensible (and required) to go for a higher Tg?? Is it a good
idea to use a higher spec laminate??
Any thoughts will be very interesting.
Thanks,
> Douglas I McCall
> Printed Circuit Board Assembly Engineer,
>
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