Is there a pattern to where you see the Tin/Lead etching off?  Is it perhaps
in the high current density areas?   The Tin to Lead ratio will vary on the
board, with the low CD areas giving high Lead, and the high CD areas giving
high Tin.  Tin is much more readily attacked than Lead.

Another possibility is that the Tin/Lead is being deposited on an oxide, not
on to bare metal.  This can be caused by leaving the board in the acid dip
between the Copper plating, and the Tin/Lead plating too long, or else, having
too much dissolved Copper in the acid dip.   When this happens, some (nearly
invisible) Cuprous oxide can form, and if plating occurs on top of this oxide,
it could be liable to much easier removal than plating on to bare metal.

Hope this helps,

Rudy Sedlak
RD Chemical Company

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information.
For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311
################################################################