[TowerTalk] re; Whiskers growing where you cannot shave them

[Jamesnf@aol.com]

In a message dated 4/2/2005 3:50:20 PM Central Standard Time, 
w8ji at contesting.com writes:
Apparently this is just a problem with a few metals used in
solder? Or is it the flux?
Tom:

I'm no chemist, that's for sure.  I was working as a manufacturing manager in 
a high volume electronics assembly plant at the time.  But I will say all our 
efforts were directed at removing flux residue after waveline or reflow 
soldering, so I guess the enabler was the flux.  At least proper cleaning of flux 
residue after soldering eliminated the dentrite growth problem. To test the 
cleaning process, a piece of test equipment was used that measured the 
conductivity of a container of deionized water and then measured it again after an 
assembled and washed board had been immersed and agitated.  If any flux residues 
washed off the board and caused the conductivity of the deionized water to rise 
beyond spec, we had to check the board washers, make corrections and re-wash 
and re-test that lot of boards.  

Because the freon used in the chemical-type board washers was banned and 
because maintaining a deionizing plant for the water-type washers was a big task, 
I was glad when no-clean fluxes were developed.  We adapted no-clean flux to 
the waveline flux fountains and solder paste manufacturers adapted it to their 
formulations of solder paste.  We were able to eliminate the board cleaning 
process and that was a happy day.

BTW, all this was going on in a plant manufacturing 2-way radios and cell 
phones.  We were using fine pitch smt ic's and close spacing on board traces.

Jim W9TM