[sdiy] Lead-free DIY

[Magnus Danielson]

From: karl dalen <dalenkarl at yahoo.se>
Subject: Re: [sdiy] Lead-free DIY
Date: Tue, 5 Oct 2004 02:31:55 +0200 (CEST)
Message-ID: <20041005003155.58960.qmail at web53507.mail.yahoo.com>

>  --- Roman <modular at go2.pl> skrev: 
> > And how about mixing Pb/Sn and lead-free solder?
> > What bad is happening inside the solder joint when you solder leaded
> > component with lead-free solder? What if you use it on leaded PCB? 
> > Can someone please explain what's happening then, maybe some molecular level
> > explanation if someone dares?
> > Pretty plese?
> 
> every thing depends on what metals are used, as i said previous if
> Bi are a component of the solder and  platings or component legs
> contain Pb you will have termal problems, Pb amd Bi maks for 96deg c
> melt point.

Yes, but it is the amount of Pb in the final soldering-point which is of
interest. As with gold-plated, where the Au migrates into the solder, the Pb of
that surface will migrate all into the solder at the time of the soldering.
The concentration of Pb will be the critical part. Now, it is naturally easier
to say that you should stay of Pb altogether than say that you must ensure that
the Pb contamination stays below such and such limit. The interesting thing is
how certain mixtures of Sn, Pb and Bi creates melting points, becomes brittle,
generate whiskers etc. However, the Sn-Cu-Ag seems to be more in use when I
scan the world (let it be right or wrong), so it then becomes the Sn-Cu-Ag-Pb
mixtures which is of interest.

Where's my Metalurgy-DIY handbook when I need it?

Cheers,
Magnus