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May 2009

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Subject:
From:
Lee parker <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Lee parker <[log in to unmask]>
Date:
Thu, 7 May 2009 17:29:38 -0400
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Joe 

I assume the board finish is HASL. I saw this phenomena many years ago immediately after installing one of the first HASL systems. It was determined that the impurities came from flux entrapped in the soldermask during HASL. A very aggressive  cleaning process was installed immediately after HASL which resolved the issue.

Best regards
Lee
J. L. Parker Ph. D.
JLP Consultants LLC
804 779 3389
  ----- Original Message ----- 
  From: Kane, Joseph E (US SSA)<mailto:[log in to unmask]> 
  To: [log in to unmask]<mailto:[log in to unmask]> 
  Sent: Thursday, May 07, 2009 9:12 AM
  Subject: [TN] PB Surface Contamination


  A cleaned bare PB is exposed to bake or reflow, and comes out with
  measurable ionic contamination.  The board is dirtier at the surface
  after 
  a heat excursion.

  The contamination isn't coming from the oven, handling, or anything
  external.
  Heat causes something to move from the inside of the board to the
  outside.

  We haven't done any ion chromatography or other testing yet to
  run this down, but has anyone heard of or experienced anything similar?

  In our normal process, we clean everything multiple times, but if the 
  contaminant builds up under solder mask, or in other areas that are 
  difficult to clean, we could have SIR or corrosion problems around fine 
  surface features or in high voltage areas.

  And if this ionic contamination doesn't just move up to the surface,
  but is somehow moving around inside the board, could it collect in 
  some places and lead to CAF or other problems?

  Joe Kane
  BAE Systems
  Johnson City, NY 


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