All
We who work with these things have varied success with the
elctroless/immersion combinations of Nickel/ Palladium/Gold.  On the other  hand the
electrolytic nickel/palladium/gold has had very good success in the  downhole oil well
drilling tool industry. The electronic units that go down the  hole with the
drilling tools have an environment up to 175oC and sometimes up to  200oC for
many hundreds of hours.  I have seen results of many hours of  testing on many
test and operational unit's after aging at these  temperatures and have never
seen a case of black pad. The solder or the  component lead is the major cause
of failure and not board plating.  For  the application it is difficult to
find a solder that will melt at reasonable  temperatures and still withstand
aging at the operational temperatures.
Component lead plaring/coating is also a problem as not many suppliers  will
do the electrolytic Ni/PdAu.  For most applications the board should  be
electrolytically plated with Ni-100 to 200 microinches, Pd 10 to 20  microinches
and Au 5 to 10 microinches.  This plating is then used as an  etch resist when
manufacturing the board.  Soldrability is good for and  extended length of time
since the Pd seems to be a good barrier

Phil Hinton  .

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