Talking about QFN's, they dont really sit flush. I use a 10X scope at work and can't see a gap but flushing with water cleans it out. There is the gap of solder between them that water can get to. It is easier to remove WS than NoClean (NC). Even hot tapwater will wash it out.
Brian
--- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan <stefan_trethan@...> wrote:
>
> I don't think mine is so conductive - I hope not.
>
> I can't imagine how anything can get the crud out from under a QFN
> package. Even a BGA seems relatively easy by comparision. Basically
> any component that sits flush against the board would seem pretty much
> impossible to me.... (Obviously there ought to be ways that I can't
> think of).
>
> ST
>
>
> On Sat, May 2, 2009 at 5:40 PM, DJ Delorie <dj@...> wrote:
> >
> > You folks aren't making this easy for me... ;-)
> >
> > One thing I noticed about my current no-clean is that the residue has
> > (relatively) low resistance. If I have a 25 mil gap between power and
> > ground, an inch of that results in 330k between them. I end up
> > scraping between traces to get the hardened residue off.
> >
> > I wonder if a waterpik would be enough to get those hard-to-reach
> > places that make people avoid water soluble flux? I do have some QFNs
> > in my current project...
> >
>