This may be of some interest...  A paper was given at this year's IPC
Printed Circuits EXPO entitled "Effects on Surface Finish on High Frequency
Signal Loss Using Various Substrate Material".  OPS was one of the surface
finishes tested, along with HASL, ENIG and immersion silver.  The team
concluded that the surface finishes had less influence on loss
characteristics than expected.  All surface finishes were measured to within
0.1dB/inch even at 10 GHz.  The paper doesn't mention anything about
promoting oxidation growth, though.

Jim Marsico
Senior Engineer
Production Engineering
EDO Electronics Systems Group
[log in to unmask] <mailto:[log in to unmask]>


        -----Original Message-----
        From:   Ryan Grant [SMTP:[log in to unmask]]
        Sent:   Wednesday, May 23, 2001 10:49 AM
        To:     [log in to unmask]
        Subject:        Re: [TN] High Freq and OSP Coated Boards

        Hi Mike,

        I'm a little doubtful that much effect could be seen since the
copper is
        covered with soldermask and solder everywhere except vias.  However,
if you
        do verify the effect, will you let us know?  It seems like pretty
important
        information.

        Kind Regards

        Ryan Grant
        Advanced Technology Engineer
        MCMS
        (208) 898-1145
        [log in to unmask]


        > -----Original Message-----
        > From: Michael Forrester [SMTP:[log in to unmask]]
        > Sent: Friday, May 18, 2001 8:04 AM
        > To:   [log in to unmask]
        > Subject:      [TN] High Freq and OSP Coated Boards
        >
        > We are currently designing products that have signals in the 2GHz
range
        > and soon
        > 10 GHz.  The use of OSP
        > as a surface finish was rejected for the use in such products.
The reason
        > is
        > that when the copper oxidizes after
        > assembly the high frequency properties of the copper would change.
Does
        > anyone
        > have any idea at what frequency
        > this effect starts and actually how much effect it has on high
frequency
        > signals?  Thank you.
        >
        > Best Regards,
        >
        > Mike Forrester
        >
        >
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