Hi Carl,
Before you try all sorts of proces deviations, start with the
beginning: test the solder paste:

Stick two paper labels together (about 0.6 mm thick), punch a hole
with a diameter of  about 6 mm (2 inches) in it with a perforator,
stick the label stack on an alumina or non wetting substrate and fill
the punch hole with solder paste with the help of a spatula. Tip:
first stick the label on your skin before sticking on the substrate.
It will ease the release of the paper stack after the deposit of the
solder paste).
Remove the paper label and reflow the solder within 5 seconds on a
solder bath or hot plate.
The coagulated solder ball should have no satellites within the flux
residues around the ball.

If solder satellites are found outside that area, probably moisture is
in the paste.
If satellites are found in the flux residues, the flux has inadequate activity.
In both cases, use proper conditioned solder paste or ask another flux
formula from your paste supplier respectively.

If only the solder paste has the correct formulation, you can explore
the reflow behaviour that might result in unwanted satellites. See the
list from Richard Stadem.

Succes.


2006/7/7, Carl Beharry <[log in to unmask]>:
> Hello fellow Technetters,
>
> Would like some advise from the experts out there.
>
> We have always assembled pcb with minimal solder balls that usually gets
> washed away in the cleaning process, hence not creating any major problems.
> However, recently we have been getting involve with more complex boards that
> has alot of 1mm and .8mm low profile bga's.
> The problem that we are noticing is that the solder balls that never was a
> problem before are now getting stuck under the bga's, sometimes creating shorts.
> I am not sure if we can eliminate solder balls completely but would
> like to know how the experts are resolving a problem of this sort.
>
> Thanks in advance for your input.
> Regards,
> Carl Beharry
> Ectronics, Inc.
> 855 Industrial Hwy
> Cinnaminson, NJ 08077
> Phone : (856) 829-7161
> Fax : (856) 829-6950
> Email : [log in to unmask]

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