Even if the paste is fresh, if you let the stencil dirty with paste for
some minutes between printings, small portions of paste may get dry and
ruin your work.

Isaac


Em 18/5/2011 23:15, Jesse Lackey escreveu:
> 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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