Hi Michael! I don't have an specific information in my files that covers
the impact of Zn as a solder alloy constituent in relation to long term
reliability - most of the documentation covers the diffusion/migration
aspects of zinc within copper based systems. I would guess (and I have no
data to support this statement) that there is a Zn level that will result
in the same embrittlement issues when Zn becomes a major portion of the
solder joint alloy. Most of the Zn solder alloy information details the
problems of manufacturing electronic assemblies and is silent in the solder
alloy reliability area.


Dave Hillman
Rockwell Collins
[log in to unmask]




Michael Fenner <[log in to unmask]> on 07/07/99 05:43:12 PM

Please respond to Michael Fenner <[log in to unmask]>

To:   [log in to unmask]
cc:
Subject:  Re: [LF] Tin / Zinc




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]
>
>
>
>
>

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