Hi Paul,
I certainly concur with you technical assessments--the reliability bottleneck
for LF-soldering will be in the PWB as well as in the component areas, and
less though with the solder joints, where most of the efforts are concentrated.
There are people that understand these issues--there is you and PWB
Solutions, there is Hans Danielsson in Europe and I give workshops on these issues. But
you are correct, that the industry has not yet grasped the importance of
these issues. Thermal excursions to SnPb soldering processes cost between 12 and
14% of the life of the PTHs/vias--going to LF-solders and a 30C increase raises
the cost to 18 to 20% of the life--no wonder you saw what you reported.
The slash sheets for laminate/prepreg materials given in IPC-4101 are so wide
open in the ranges of properties that they are in fact useless. New slash
sheets IPC-4101B/99, /101, /121, and /124 have been proposed for use for
LF-soldering--again, the property ranges are much too wide to be useful for any
designer. I proposed a "Soldering Tempreature Impact Index [STII]" for these slash
sheets and was promplty shot down by the committee consisting of lots of
suppliers. The STII incorporates the 3 most important properties in this context,
Tg, Td, and CTE.
Yes, there are people out there that understand the issues, the rest of the
industry will have to learn the hard way.
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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