I recall from somewhere that Sn/Zn alloys are unsuitable long term because
of the electrochemical differential between Sn and Zn and that they also
suffer from oxidation probems in assembly, but don't know how I came to know
this, so an informed opinion would be good to have.
Also just to clarify understanding in this area: the need to immunise brass
with Ni when using Sn/Pb solders to prevent Zn becoming a problem as a low
level impurity in a Sn/Pb solder system is known as Dave reminds us. But
does it automatically follow that Zn would be a problem when present as an
alloy constituent? For example gold is a problem at low levels in Sn/Pb
systems, but 80Au/20Sn is an excellent solder.

BSP, OX15 4JQ, England
T:+44 1295 722 992
F: +44 1295 720 937
-----Original Message-----
From: David D Hillman <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 07 July 1999 20:52
Subject: Re: [LF] Tin / Zinc


>
>
>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
>[log in to unmask]
>
>
>
>
>
>Andy Mackie <[log in to unmask]> on 07/07/99 07:40:09 AM
>
>Please respond to "Leadfree Electronics Assembly E-Mail Forum."
>      <[log in to unmask]>; Please respond to [log in to unmask]
>
>To:   [log in to unmask]
>cc:
>Subject:  [LF] Tin / Zinc
>
>
>

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