Alan:

     There are some advantages to gold that you might consider:

        1) Solder joints don't become brittle until the gold content
        reaches ~3% by volume.  With 5 microinches of gold on the board,
        any solder paste thickness > 200 microinches in a surface mount
        process will not generate brittle joints due to gold content.
        Since this is a wave solder process, you would have to process a
        VERY large number of boards before the solder pot reaches 3% Au by
        volume.

        2) If gold is used instead of HASL for copper coating, the board is
        subjected to one less thermal cycle.  Thus, there is one less
        chance for yield loss at the fabricator due to board warpage,
        especially if the board is thin.  With higher yields, could the
        board cost be reduced?

        3) Gold will not oxidize and create solderability problems if the
        bare boards remain on the storage shelf for a relatively long
        period of time before assembly.  HASL boards will tend to develop
        surface oxidation over time and can cause assembly problems
        downline.

        4) If I am not mistaken, the carbon ink solution for switch
        contacts has a shorter MTTF than gold contacts.  Wouldn't your end
        product have a better reliability with gold?

     In my opinion and given the choices between HASL and flash gold, I
     would GO FOR THE GOLD!

     Bill Fabry
     Plantronics, Inc.
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Subject: [TN] Gold Flash benefits over HAL
Author:  "TechNet Mail Forum." <[log in to unmask]> at INTERNET