Scott,

Acid (pH=4.2-5.2) hypophosphite-based EN baths normally yield mid to high 7 --
12%P deposits.
Slightly acidic ones (pH=6.0-6.6) are "ultra-low" phos -- 2-3%.
Alkaline baths are low temperature, produce low phos deposits 3 -- 5%.
Consistent 12%P would be probably pushing it, since %P depends on a number of
variables (most notably pH) that normally fluctuate within their operating
windows.  Mid-phos EN followed by Immersion Au is considered best for
solderability.

Eric Yakobson
Alpha PC Fab





"CaranoMichael" <[log in to unmask]> on 08/25/99 12:33:35
PM

To:   [log in to unmask]
cc:    (bcc: Eric Yakobson/AlphaPCFabUS/Cookson)
Subject:  Re: [TN] E Ni/I Au




Dear Scott,

There was a very interesting paper presented at IPC Expo 99 by Nicholas
Biunno of HADCO. The paper details research into the failure mechanism for
solder joints of Electroless Nickel/immersion gold surface finishes. The
paper sheds light on the "Black Pad" phenomenon leading to poor or no
wetting of the solder to the nickel surface due to high phos content. The
high phos content was caused not by the elnic process itself (according to
the information presented) but by the hyperactive corrosion effect of the
immersion gold process on the nickel.

To answer you other question, most electroless nickel processes I am
familiar with (acid based pH) generally deposit as is 3-6% by weight P in
the deposit. The alkaline based Elnic processes can deposit a much higher
content of phosporous as is.

        -----Original Message-----
        From:   Severson, Scott M. [SMTP:[log in to unmask]]
        Sent:   Wednesday, August 25, 1999 2:23 PM
        To:     [log in to unmask]
        Subject:        [TN] E Ni/I Au

         All,

        Here's a theoretical question...What percentage of phosphorous can
be plated
        up with nickel in the electroless nickel immersion gold process?  I
have a
        vendor telling me its impossible to have 12% phosphorous in the bulk
nickel
        plating.

        More questions...At what point do you see problems with
solderability of the
        nickel?  Do repetitive reflows exaggerate the problem by locally
depleting
        the nickel at the surface of the board (by transformation into
Intermetallic
        compounds)?

        Thanks
        Scott


****************************************************************************
        *************************
        Scott M. Severson
        QA/FA Lab Manager                                            "Space
and Time
                                                                      are
not
        conditions in which we live,
        Benchmark Electronics Inc.                         but modes in
which we
        think."
        4155 Theurer Blvd.
        Winona, MN 55987
        ---Albert Einstein
        (507)452-8932

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################