Carrie-
Assuming you are referring to "Immersion white tin" it
sounds like your supplier has not solidified their process.Immersion tin is
a very aggressive chemistry which just loves to attack soldermask unless
preventative measures are taken to insure good adhesion such as using oxide
or even oxide replacement chemistry prior to applying the mask. You
mentioned it is also peeling along the traces which sounds like the boards
may have been over copper plated which gives you a very high trace height
which in turn gives you a very thin coating of soldermask,(assuming they are
using LPI) probably less than .0003
at the knee of the trace.

Tony Steinke
AIT-Atlanta Inc.

----- Original Message -----
From: "Morse, Carrie" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, March 10, 2004 3:39 PM
Subject: [TN] The Sin of Tin -- Again


We have some unpopulated bare boards that are white tin plated with
SMOBC.  The boards are exhibiting peeling mask at the interface between
the tin pad (TH and SMT) and the mask along the circuit runs.  Per IPC
A610 , exposed copper is not acceptable in this case.  Can anyone
provide possible root causes to this phenomena?  The boards are date
coded from Oct 2003 as well as Feb 2004.  Both lots exhibit the exposed
copper/missing mask.  These boards were also stored in a Temp/RH of
about 70F/10-15%RH

TIA
-Carrie

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