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| Reply To: | Leadfree Electronics Assembly E-Mail Forum. |
| Date: | Wed, 7 Jul 1999 14:11:19 -0500 |
| Content-Type: | multipart/mixed |
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Hi Andy - zinc embrittles solder joints! There have been several cases of
soldering to brass substrates where the zinc then migrated into the solder
joint causing failure - this is sometimes called "dezincification".
Interactions between a zinc containing solder alloy and the board have been
shown to be an area of concern too. The use of zinc also causes an
assembler to address some pretty serious oxidation and flux activity
problems when using a zinc containing solder alloy. These issue can be
solved but the solutions are not simple (e.g. total, complete, low ppm O2
level solder process inert atmosphere is needed or you will have pounds (or
kilograms!) of dross). The NCMS Lead free project report addressed some
aspects of the Sn/Zn solder alloys.
Dave Hillman
Rockwell Collins
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Andy Mackie <[log in to unmask]> on 07/07/99 07:40:09 AM
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Subject: [LF] Tin / Zinc
Just from its melting point (198.5°C), the approximately 91Sn/9Zn eutectic
seems
to be an ideal alloy for soldering, although the zinc seems to make the
alloy
prone to corrosion (much like the lead-phase in Sn/Pb) in solder pastes,
and it
gives excessive drossing in wavesoldering.
I've heard that the zinc phase is a problem AFTER processing, too, but have
never seen any actual documentation of this: is this a technomyth, or does
someone out there have evidence of post-assembly corrosion?
Toodle pip,
Andy Mackie
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