Flux

[J. Larry Hendry]

> You must have got some really bad soldermask; usually this stuff is
> TOUGH. The brush is not absolutely required, but it does give an idea of
> how clean the board is---if you get some foam when you use the brush,
> keep cleaning. 
> John Blacet

Exactly what I have found in my limited experience.  The toothbrush is fine
(unless you are the tinman from The Wizard of Oz and have one with wire
bristles).  HAHA.

Larry Hendry  :)