Thanks for the info.
  ----- Original Message ----- 
  From: paul reid<mailto:[log in to unmask]> 
  To: [log in to unmask]<mailto:[log in to unmask]> 
  Sent: Monday, September 13, 2004 10:29 AM
  Subject: Re: [TN] PWB Conductive Contamination Under Solder Mask; What Can Cause ...


  Ref: Conductive Contamination Under S/M - Cause

  I have seen this phenomenon many times.  It is copper slivers from the edge
  of the traces breaking off as long metal threads and being captured under
  the solder mask.  In the process of copper etching, after pattern plating,
  the enchant will etch down and, at the same time, under the etch resist.
  This creates a cross section of the trace that looks like an hourglass.  The
  tip of the hourglass breaks off in long threads.  These copper threads are
  solder coated and they have a silver appearance.  This can also be cause by
  over-plating copper on the surface of the pattern plated board.

  To prove they are not solder or tin whiskers try to melt them with a
  soldering iron or reflow them in your oven.  They are an order of magnitude
  larger than dendritic growth. I have sent a picture I drew demonstrating the
  broken copper edge type defect to Steve's website and have asked him to post
  it for your review.

  Paul Reid



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