Nick:
- You didn't mention who your customer is or what specification you are
working to or the technology (leaded SMT is presumed).  Par. 5.3.1.3 of
Mil-Std-2000A is pretty specific (using the same words that are found in
ANSI/J-STD-001B) that gold has to be removed from 95% of the to-be-soldered
surface.
- My advice would be to: a) sacrifice a couple of components and do a
destructive physical analysis to measure the thickness of the gold plating,
b) if plating on the components is less than 50 microinches, solder some
connections without tinning of the components and then perform a DPA of
connections soldered without gold removal to determine the quantity of gold
in the solder connection.  On leaded components where the leads have some
compliance, greater than 3% gold in the connection will cause you problems in
any environment unless the Tce of the components and pwb are closely matched
(less than 8 ppm/Deg. C differential).  If the gold content is less than 3%,
leads have some degree of compliance and your processes are tightly
controlled you should talk to your customer about discontinuing the (dual or
single) tinning process.  If the gold is greater than 50 microinches on the
(as received) leads then you probably need to continue tinning the components.
- The next alternative would be to develop an SPI (Single Process Initiative)
and convince your DOD customer(s) that your SPI would meet their technical
requirements, then effect a Block Change to transition all of your DOD
contracts to the SPI instead of Mil-Std-454, Mil-S-45743, DOD-STD-2000,
Mil-Std-2000, Mil-Std-2000A, or wherever they are presently.  Many recent
SPI's have been created using the ANSI/J-STD-001B as the foundation for
technical requirements.  Talk to your local DCMC Rep. about this, he can
provide you some valuable advice.
- Hope this helps, if not feel free to call me at 317/73-5570 or email direct
to <[log in to unmask]>.
Regards, Jim Moffitt, Technical Director, Electronics Training Advantage

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