No response to this message I am surprised that my fellow technet's haven't
came through.

Scott Lefebvre

-----Original Message-----
From:   Scott Lefebvre
Sent:   Monday, November 29, 1999 8:09 AM
Subject:        Help with Gold Plating

The following is what I know about gold plating processes on PCBs.  It is
the result of conversations with two Engineering Managers at a PCB FAB shop,
and with other, less knowledgeable people.  These conversations were at
times contradictory and were certainly confusing.  I have bullets by the
items I believe are absolutely true.
Do you have other sources? Can we bounce this between the three of us to
'fill out' the holes?  We need a quick reference guide to understand these
differences.
I believe we (as a manufacturing group) require less then 20 mincroiniches
of gold to maintain reasonable solderability.
Flash (Immersion) Plating
*       Most common in the industry.
*       Limited to 3-5 microinches in thickness.
*       Soft in nature ("Dead-Soft") less then 80 on a hardness scale.
*       The plating is a substitution process where nickel is replaced by
gold.
*       When the nickel is gone, the process stops.
*       Most baths are in the thinner side of spec.
        Possible to cheat and apply higher levels (8 or even 10 is
possible).
                Gold cell structure is incoherent.
                Plating is laminar in nature
        Electro-less Plating
*       Rarely done.
*       Unstable process, gold suspended in plating liquid can "fall"
easily.
                        Same as flash, (seems likely)?
                        Less predictable result.
                        Possible to reach 10 microinches in thickness.
                        Gold structure is incoherent.
        Electro-Plating
*       Still fairly common.
*       Required to reach higher gold thickness (10- unlimited?)
*       Slightly less controllable then flash.  Generally has a variation of
10 microinches.
*       Plating is based on an electrical current, and so requires a single
electrode, thus
*       cannot be applied after etching.
*       Etching requirements change and require an ammonium etchant.
*       Cobalt is used in this process.
*       Plating is columnar in nature.
*       Gold hardness is either a soft gold (82 on hardness scale) or a hard
gold, though
*       hard gold is the default.

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