On Mon, 31 Jul 2006 07:34:50 -0500, Roger wrote:

Wel,, it depends on which Pb-Free alloy is chosen. There is no
industry-agreed standard composition.

In general there are two competing systems:

Tin-Silver (Sn-Ag) and Tin-Bismith (Sn-Bi).

If Sn-Ag is used, then mixing standard Lead-Tin (Pb-Sn)with it is OK.
If Sn-Bi is used, however, there is a low-melting ternary Pb-Sn-Bi compound
that can cause you problems. Not all electronic component manufacturers
have decided against Sn-Bi (it costs less than Sn-Ag).

So the key is determining you have Sn-Ag solder on your Pb-Free component
(or in some cases, no solder on the component).
Thanks for that - I haven't encountered anything with Bismuth yet. Plain
tin plating seems most common amongst what I handle.

Steve