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October 1999

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Subject:
From:
Charles Pitarys <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 14 Oct 1999 13:29:51 -0400
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Stephen,
Here is a response to your question from one of my Kyzen co-workers, Bill Vuono in TX;

Charlie,

In general, you wouldn't expect the gold plating to affect the board performance, providing that the plating salts have been adequately removed before mask application.  This is a very expensive board, however.

The thickness of the gold on the pads could be a problem, however.  For years, NASA and the military have required that gold be removed from component leads before soldering.  Typically, thicknesses of >50 (.000050 in)  microinches will not cause problems.  Between 50-100 microinches, a tinning operation s necessary, and above 100 microinches, a double tinning is required.  The HASL process should have acted as a single tinning operation.

Gold does act as a contaminent within a soldered connection.  According to the MIL-HNBK-2000 (July 1990, but is now out of print) Gold (tin and lead) intermetallics will cause the solder joints to become dull gray and grainy.  Above 0.340 percent gold contamination in the solder may cause embrittlement  of the solder connection.

I believe that the EMPF also has a tech paper on this.  They are now located in Philly, and the author is now the Tech Director, Mike Frederickson.

Bill

>>> "Stephen R. Gregory" <[log in to unmask]> 10/11/99 06:58pm >>>
Hi All!

Remember my little problem with dry-film mask flaking off after multiple
washes in Kyzen? Well, it's not that problem this time.

We went to a different vendor and they used a DuPont dry-film...passed all
the tests I through at it (thermal excursion through reflow, and multiple
cleanings) passed without so much as a scratch.

BUT I discovered another little problem now. We got our first batch of boards
and they matched the drawing which called out SMOBC. We got some boards
delivered a little later that were needed to complete the lot, and I noticed
a lighter color over the traces and vias than the boards we got sent to us
earlier. Me being a little "gun-shy" about masks, I looked at things a little
closer and removed some mask over one of the vias, and discovered that the
whole board had been gold plated. (there's PCI fingers on the board that need
the gold)

The big thing is that they didn't follow the drawing and give us SMOBC like
the drawing states, but is there any real performance problems that I should
be worried about? (Cripes! Can't things run smooth once inna while?)

-Steve Gregory-

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