Thinking obout the environment and all, a solder paste that can be cleaned
after reflow using (DEMI)water is a beautiful thing. However, when i'm 
thinking about using it, questions bubble up...

Water-washable fluxes in solder pastes are always? non-rosin (for example 
organic acids). Because my fab produces many militairy PB's, this is 
unaccceptable. Only R and RMA are conform the the good old MIL-STD-2000. 
(Or you may only solder sealed devices etc. and still meet some conditions) 
OK, flux activity of these paste are higher, but the modern OA flux-types are
comparable with RMA? 

An other problem is that "Flux residue or foreign material" is a defect
(acc. to the 2000). Cleaning SMT, even with low residue/no clean flux becomes 
very difficult that way. Especially when i consider that ionic contamination 
test equipment for THT is not adequate for SMT. And when coating the PB's, 
the less residue the better. Mixed THT/SMT products are also food for 
thought. 

Can someone help me see the light? Any statement, suggestion or experiences
using "aqua" pastes and cleaning/coating them after reflow FOR MILITAIRY USE
are welcome! (MIL-STD-2000 is still our guideline)


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 Ivo de Rooij                                       Process Engineer SMT/THT
 Fokker Elmo BV (Fokker Aviation)                         [log in to unmask]
                                                                            .