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May 2002

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Subject:
From:
"Sauer, Steven T." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 9 May 2002 07:32:09 -0400
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Good Morning Henry,
To answer your question, yes I have experienced non-wetting with Pd along
with Sn85Pb15 & Sn80Pb20 lead finishes.  The first question is, "where does
the non-wetting occur?"  Typically solder plated or solder dipped leads
during reflow experience mixing of the solder screened onto the substrate
and the lead itself providing a smooth transition from the solder to the
lead.  With alternate lead finishes such as Pd, the only solder available to
form the joint is that which is applied via printing, dispensing or wire
core.  This provides little or no solder on the top of the foot creating a
transition line along the lead outline.
The second question is, "does your solder joint exhibit good wetting at the
heel and the along the foot?"
The most casual observer will say the solder joint is a defect but under
heightened magnification and scrutiny, the joint is probably acceptable but
looks different.
TI used to have a user's manual on Pd lead finish available for download.  I
suggest that you get a copy of that document and also begin a training
exercise for your operators and inspectors regarding the differences in
solder joint wetting characteristics dependent on lead finish.

Steve Sauer
Mfg Engineer
Northrop Grumman, Xetron

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