James Edwards asked Could someone tell me the advantages of using
 Gold/NI vs HASL and what are the common (if any) process problems
 I may encounter when screening/placing parts/soldering to these type
 boards using 63/37 eutectic solder paste? Any wave solder issues?

Firstly, I would agree with Steve Gregory - why not go all the way
and convert to an OSP finish-
but if you want to go to ENAu you will have to change your wave solder
parameters to get good solder rise in the through holes. ENAu requires
more heat to get a Ni/Pb/Sn intermetallic and the gold dissolving in the
solder as it rises up the hole, slows down the rate of wetting. There are
some options to help this:
preheat 100 C +10-0, solder temp 235C, speed 1.2m/min, contact time with
wave 4 secs, spray fluxer but ensure that flux reaches the top of the
through holes.

Dougal Stewart,
Exacta Circuits Scotland

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