Hello to all,

I thought " tin whiskers" only occurred with electrolytic 
plated tin.   Is it not the stresses induced during plating that 
provide the energy to produce the whiskers?  In any case I
have used immersion tins on pcbs  for many years, both
as a short term finish in captive shops and as a rework  for
outdated HASL boards.  The new 1 part liquids make the 
process much easier.  You need only  about 20 mins at 
100 F to put down about 20 millionths.  thats millionths with
six zeroes, certainly not enough to sustain whisker growth.

As with all plating processes the base metal must be 
"meticuously"? well very clean.  Copper  will require a 
microetch , tin/lead may require a solder brightener step
if highly oxidized.   If the copper is not clean immersion 
tin will not take thus making inspection easy.  As always
the solderability time limit will depend storage conditions. 
I've seen them last for 6-8 weeks on the floor during a brutal 
South Carolina summer.  

     Remember, all the tin is doing is protecting that perfectly
clean  copper surface from the elements with something that
will help your solderpot ratios. Contact your supplier for the
processing details.  But try it you'll like it.  And if the project
gets hung up for some reason don't fret, just wrap them up like
Cristmas leftovers and keepem in the fridge.  
Robert E. Welch
Process Specialist
Email: [log in to unmask]
Modem: 804-239-9120
Fax:   804-237-3048

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