Hi,

I'm fairly sure that flux activity plays an important role in this also. In
other words as the flux activity increases so does the wetting action. As
the wetting action increases so does the force with which the solder pulls
itself ....to itself.
Thus reducing the incidence of isolated balls remaining unattached to the
bulk of the joint.
This is why we see solder balling with no-clean pastes (with lower flux
activities) and not with water soluble (washable) fluxes which have high
flux activities. Of course some of the new no clean pastes are on the edge
of IPC class 3 (only just) with reasonable flux activity levels, and this
means they are less likely to leave solderballs.

Regards


At 10:08 06/02/98 PST, you wrote:
>Hello TechNetters:
>
>I am looking for literature on the effect of overprinting solder paste
>onto solder mask and its effect on solder balling. I guess the critical
>parameters in this process would be
>
>* solder particle size in the paste
>* finish of the solder mask - matte/glossy, etc.
>* oven profile, and
>* length of overprint, and
>* surface energy at the solder-solder mask interface.
>
>I welcome all suggestions. And, thanks for your interest.
>
>Krishna Kalyan
>
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