Hi - I get this sometimes too, it seems to happen more often when the=20
'print' thru the stencil isn't sharp, i.e. the little rectangles of=20
solder paste are 'blurry'.  My guess is that some of the paste is off=20
the pad, and doesn't necessarily automagically recombine with the paste=20
that is on the pad.  So, because of the solder mask, it kind of balls up.

Spraying with flux remover and scrub with toothbrush helps, but does not=20
solve it.

The cleaner the 'print' (I use a prototype grade metal stencil) the=20
better the results.  There is something to the angle of the squeegie=20
blade, the speed moving it, how much paste on the stencil your smearing,=20
downward force, alignment of stencil, ... all have an effect on results.

Practice and fiddle!
Cheers
J


Josh Koffman wrote:
> Hi all. Just as an update, I have been experimenting (as I have had
> time), and so far I'm doing fairly well. I had a stencil cut locally
> out of mylar, which works nicely. I'm running the toaster manually as
> I don't have a fancy temperature control yet.
>
> The boards are coming out quite nice. The only thing going a bit weird
> is that I often end up with a sort of ring or halo of solder balls
> around some of my pads. I have read that this could be caused by dried
> out paste, but mine is fresh. Has anyone else ever run across this?
> What did you do to fix it?
>
> Thanks!
>
> Josh
--=20
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