In a message dated 09/25/00 20:23:40, [log in to unmask] writes:
>If I understand correctly, you are re-flowing the solder joint a second time
>(when it goes through the wave solder). Doesn't that raise a concern
>regarding increased intermetalic layer?

Hi,
The issue of "a concern regarding increased intermetalic layer" is totally
overblown--I wished I knew how it ever got started. I have never seen a
failed solder joint because of a increased intermetalic layer resulting from
multiple normal soldering operations. I have seen plenty of failed solder
joints  because of non-wetting (actually, they are not solder joints at all,
if think about it, since no metalurgical connection was ever formed). In an
assembly with a mix of components with widely differing thermal masses, the
SJs of the smaller components will always have thicker IMC layers
necessitated by the thermal need to properly wet the SJs of the larger
components which act as heat sinks during the reflow process.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com

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