After 5 years of production with Immersion Gold, I would like to answer 
your questions.  See below.

     Solderability is excellent!  5 assemble houses have all been doubtful, 
but when they tried it all was well with no variability and no change in 
soldering process from that used with HAL.

     Phosphorus content, must have varied, but I am not aware of how much 
variation.  The chemical suppliers furnishing the materials for this plating 
line must have done their homework and have this under control!
     
     Reflow profiles have not been changed, typically not exceeding 220 deg. 
C.

     Have been using press-fit connectors in boards for 3 years with no 
problems.  The immersion gold provides a slick surface of very low 
resistance.  Hole dia. are easier to control than with solder finish. 
 Mating leads should be specified on the connector as gold plated,  as small 
a amount as you can get.  Typically 15 micro-inch..

     Our spec on the finish of PCB's is 5 micro inch Au., Min..  50 micro 
inch Electroless Nickel Min.  (usually get 100-200)
 ----------
From: TechNet-request
To: TechNet
Subject: SOLDERABILITY  OF IMMERSION GOLD
Date: Wednesday, June 18, 1997 3:15PM

Hi,Technetters!

Could anybody comment on solderablity of immersion gold on electroless
nickel ?
What is the influence of the phosphorus content on the solder joint
reliability?
Some people say that phosphorus content up to 8% is beneficial for the
solderability.I heard  the opposite too.
What about having to change the reflow profile to a peak of 240
degrees in order to enhance its dissolution in solder?
And about press fit connectors in immersion gold plated holes:
Are there specifications from vendors concerning hole diameters,nickel
thickness,immersion force,aso?
Thank you,
Gaby

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