sorry if this repeats old news - our corporate link was not functional
inbound for several days.  Charlie's comment about not getting paste on
the board was right on the mark for us.  We were getting an unacceptable
number of balls near the outside center of passives.  This was caused by
paste on the inner side of the pad being squeezed to the board surface
underneath the part by the placement force.  When the flux volatilized
it blew the balls out to the side.  We started modifying pads for
passives to a baseball home base or plate shape with the points toward
the center.  This reduced the past volume at the center of the passive
and eliminated the squeeze balls.

> -----Original Message-----
> From: Charles Barker [SMTP:[log in to unmask]]
> Sent: Friday, August 20, 1999 10:42 AM
> To:   [log in to unmask]
> Subject:      Re: [TN] Solder/Flux/ICT Issue
>
> Hi Grant,
>
> FWIW, at an earlier job location, we had jsut about finished
> qualifying
> Interflux no-clean flux for wavs soldering. We couldn't detect visible
> residuye
> after wave. Their hand soldereing cored solder was a different matter.
> Thjis was
> about 4-5 years ago. I'm sure there have been many improvements on the
> part of
> all the flux makers.
>
> In the area of solderballs, one thing that will help reduce
> solderballs is being
> absolutly certain that all solder paste goes on the pads and NOT ON
> THE BOARD!
> For me, this mean getting slightly wider that "normal" pads on our
> .5mm pitch
> parts. It also means that any mis-printed boards need to be cleaned
> very
> thoroughly. You pretty much need a stencil cleaner with a board holder
> attachment. Even though some thing is "no-clean" it doesn't mean that
> cleaning
> goes completely away  : > {
>
> Good luck
>
> Charlie B.
>
>
>
>
> Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please
> respond to
>       Grant Emandien <[log in to unmask]>
>
>
>
>
>
>
>
>
>  To:      [log in to unmask]
>
>  cc:      (bcc: Charles Barker/US/I-O INC)
>
>
>
>  Subject: [TN] Solder/Flux/ICT Issue
>
>
>
>
>
>
>
>
> Hi again,
> Thanks for all the input as it has now directed me towards fluxes (and
> control thereof) and ICT.
> Leading from one of the members advice of low residue flux I stumbled
> across
> this Kester comment:
> 'Flux selection does have some play as to the occurrence of solder
> balls. A
> rule of thumb is that the lower the solids content of the flux is the
> more
> solder balls will be noted when all other parameters are held
> constant. This
> is sort of a dilemma for us as a flux manufacturer in that if we
> increase
> the solids content, we will more than likely have an adverse impact on
> probe
> testing of final soldered assemblies. The aesthetics of the final
> soldered
> assembly will also be affected as you can imagine.'  This was posted
> in 1993
> so any idea on what has since transpired and is this statement still
> valid
> wrt the solids content?
> Geez, my research thusfar has brought an array of variables to this
> party
> such as test pin profiles and type, gold plating vs gold alloy, pin
> base
> material hardness, spring force etc. on the ICT aside. Nevertheless it
> is
> now beginning to get interesting.
> As a comment, I hope my research drives me away from introducing
> another
> process i.e. cleaning of assemblies hence and control of flux effluent
> (we
> are coincidentally reviewing ISO14000) etc. and rather focus on
> improving
> the existing process i.e. flux residue reduction (without cleaning)
> and ICT
> issues.
> Thanks again to all,
> Grant
>
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