Craig

It depends on the definition of first pass yields.  I've heard and seen
it defined many ways.  You can report a first pass yield through an
imaging sequence (IL and OL) where you're looking at the amount of
product produced with no defects (opens, shorts, etc).  At electrical
test, I've seen it reported on a piece-by-piece basis or a lot-by-lot
basis.  I've seen the same metrics at a Final Audit operation, also,
measuring escapes from previous processes.  Sometimes, first-pass will
refer to the first-time build of part.  Can you provide a clearer
definition of "first-pass"?  Otherwise it's hard to assess if 50-75% is
"typical".

        ----------
        From:  Craig Patterson [SMTP:[log in to unmask]]
        Sent:  Friday, August 27, 1999 3:15 AM
        To:  [log in to unmask]
        Subject:  [TN] First Pass Yields

        Recently our bare board manufacturer indicated that his first
pass yields
        from his electrical test for our six layer board (FR4, couple of
BGA, some
        20mil QFPs, 7" x 11") was about 70%. We were concerned that this
may mean
        his process is not under control. He said that 50 to 75% first
pass yield
        was typical in the industry. The failures were for various
reasons from
        opens to mask on pads.

        Does anyone have an opinion regarding 75% reflecting the first
pass yield
        as a benchmark of the board fab industry?

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