I would guess that matte is thought to reduce solder balls because of the
high surface area. The uneven surface makes it harder for the solder balls
to stick.
This does not mean that solder balls are not formed, just that they will
stick to leads rather than to soldermask. Or if you are lucky they will be
removed by a post soldering process.
I am not sure if there is any definitive data on this issue. We have run
soldermask experiments with positive results at one site and the opposite at
another. The solderballs have not been seen for 3 years now and we use all
major brands (transparently) on the same lines.
I still have the experimental data, if you are interested.
Steve

One of our suppliers of PWBs has requested and accross the board process
deviation. They want (need?) to use gloss LPI instead of the matte finish
that we specify on all our drawings. They are having problems with the matte
mask peeling. I have no other details.

We specify matte because it reduces inspector fatigue and improves vapor
cleaning results (cosmetic).

I have also heard that matte finish solder mask reduces solder balls in the
SMT reflow process. I have no proof. Does any one know why this would be the
case?

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