Amol,
Here is Werner's formula, in case you missed it a few weeks ago.
Werner, thanks again.
Richard Stadem
[Hi Richard,
To some degree there is such a classification--it is the properties of
the
resins like Tg, Td, and thermal expansion.
I am also proposing a Soldering Temperature Impact Index, defined as
STII = [(Tg+Td)/2] - [% thermal expansion from 50 to 260C]x10
For LF-soldering, a STII>= 215 would be about right.]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Wednesday, December 28, 2005 9:11 PM
To: [log in to unmask]
Subject: Re: [TN] Lead Free Compatible Values
Hi Amol,
The rationale behind the STII is that the three properties,Tg, Td & TE
(thermal expansion), are independent of each other, but all three affect
the reliability potential of a PWB. Td, and to a lesser extent Tg,
affects the capability to withstand the soldering temperatures without
thermal degradation and lamination; Tg and TE (a combination of alpha 1
and alpha 2) directly affect the capability of PTHs and PTVs as well as
micro-vias to survice excursions to soldering temperatures.
The relationship of these three properties within the STII is simply
based on fitting the STII to my experience.
Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com
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