Varnish and rosin core solder

[UnionTech]

I just finished a repair on a power board and went to clean flux from new solder joint but board is varnished... My question is should I not clean flux from new solder joint so I dont distrub varnish? When I use my flux cleaner on clearcoat it always melts it off and makes a sticky mess (ruined a few brushes like that). If I leave the little bit of flux is it likely to damage my joint over time? Thanks for any tips or advice u guys may have.

 

[Harald Kapp]

Depends on the composition of the flux. If it is acidic it may slowly attack the PCB or components and therefore should be removed. If it is aresin based flux designated for use in electronic applications there should be no necessity to remove it.

Professional PCBs used to be washed after soldering to remove flux. But in many cases washing has been abandoned for environmental reasons.

By the way: I almost never use additional flux. Just solder wire with a flux core. That is enough in most cases.

 

[shrtrnd]

You'll have to experiment. I always wash-off the excess flux.
I try the spray contact cleaners first, a liitle on a corner of the board to see if it bothers
the conformal coating. (with a clean solder flux brush)
I've used a Q-tip with isopropyl alcohol, but it has a trendency to dissolve the coating,
so you have to be careful.