Maybe the people that sold the sockets which made them leaded will make a
comeback too? (It helps to have a sense of humour when thinking about this)
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Sunday, October 17, 2004 4:00 PM
To: [log in to unmask]
Subject: Re: [TN] LCC process and manufacturing recommendations
Hi Jorge and all,
CLCCs have a large CTE mismatch with resin-based PCBs which translate to
large expansion mismatches for larger-sized CLCCs and larger delta-T's. This
does
not create higher stresses in solder joints--those are limited by the yield
strength of solder--but larger displacement strains in the SJs and thus
larger
plastic deformation. On a cyclic basis, these larger strains lead to much
earlier creep-fatigue failure.
Having thicker solder joints [balls, columns] or compliant leads [QFPs]
reduces the strains in the solder for a given displacement.
PLCCs are quite different, because they lack the large CTE-mismatch with
PCBs.
If you need more information, get a copy of IPC-D-279 and/or IPC-SM-785--or
you could take one of my workshops.
If CLCCs are indeed coming back, people simply have forgotten history, will
be condemned to repeat it, and my consulting business will increase.
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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