Hi, TechNettlers,
I would like to test, additionally, this one:

We have had the classical one-or-two-disrupting-ball syndrom too. We found
some organic (polymeric) wet stuff in some PTHs which gave us the idea that
the PWB maker can have 'forgotten' something in the vias that disturbs
wetting. Imagine now the board with printed solder and put-on BGAs, and also
adjacent vias with mystic stuff. The assembly goes into ramp in oven, all
heats up, passes 50 degrees Celcius, flux activator begins to remove oxides
and wets the goldplated pad. At the same time the wet stuff tries to bubble
in the via and spread around. Temperature goes higher, passes 100C and flux
activator is on its max efficiency, soon we pass melting temperature and
solder begins to wet the gold pad.

Now, magicians of TechNet, what do you think? Imagine the wet stuff that
spreads from the via and tries to push away the flux and stop coming solder
wetting, is it likely to happen? I have my opinion in our own magicians
club, but I don't tell you what until I get some answers.

The stuff? Seems to be  a polyglycol or bisfenol or natriumbensoat. FTIR
does not give certain result because it's so little material to investigate.

Adieu...no...I mean > see you later

Ingemar Hernefjord
Ericsson Microsystems

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