Phil Bavaro wrote:
> 
> 1)  Has the question posed by Tom Olafsson below ever been answered?  I
> could not find any follow up in the archive.
> 
> 2)  Has anyone published a report on SMT solderballing, such as causes and
> cures?  I have seen a lot of correspondence on the wavesolder generated
> solderballs, but I am looking for a cure to what we call "squeezeballs"
> (usually found on the sides of 1206 chip caps and resistors.  We are about
> to initiate a DOE to solve the problem by varying the solderpaste print
> shapes (home plate shapes, etc), stencil thickness, as well as three other
> parameters.
> 
> 3)  How is the J-STD-001 defect for solderballs supposed to be
> interpreted........anotherwards if the solderball is encapsulated and
> doesn't reduce the minimum design electrical clearance, can it be larger
> than .005"?
> 
> 4)  We have run a no clean process for five years without ever having a
> failure related to solderballs, but we have been asked to eliminate
> solderballs entirely.  Is this too much to ask from a no clean process?
> 
> 5)  Does anyone have a good method for removing solderballs from the sides
> of chip caps without running the risk of losing it under some other
> component?  Use of a vacuum desoldering device has been suggested but the
> tips aren't small enough to reach in between a lot of the components.
> 
> All suggestions or responses will be appreciated.
> 
> Regards,
> 
> Phillip A. Bavaro
> Senior Manufacturing Engineer
> [log in to unmask]
> (619) 658-2542
> 
> _______________________________
> 
> At 5:51 PM -0000 10/16/96, [log in to unmask] wrote:
> >Do any of you know of or have a checklist (at a high level) of what should
> >be investigated if solder balls left on PCB assemblies after reflow?  What
> >is typically the most common cause that should be investigated first?
> >
> >Thanks,
> >
> >Tom Olafsson
> >Teradyne Inc.
> >[log in to unmask]
> >
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Philip, I hope the following helps.

Solder Balling during SMT Reflow

SMT solder ball formation is affected by - Solder Paste, SMT component,
Pre-dry and Reflow process variables. The main cause of solder ball
formation on SMT boards are the fineness of oxidized solder particles
and paste volume. Care should be taken to minimize the oxide formation
on the surface of the solder particles during pre-dry process. Too long
or too short can encourage solder balling. Also the wait time after
pre-dry prior to reflow can adversely affect the solder ball formation
in SMT assembly.

The metal content and the particle size in the paste are also
significant in solder ball formation. If you have solder balls , try
higher metal paste and or with next larger particle size taking care to
see that your printing process is not disturbed bt these changes.

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