There are two schools of thought on the effect matte surface finish has
on solderballs.

1. The matte surface typically has a lower surface tension,  allowing
better wetting of no-clean flux to the mask surface. The no-clean flux
forms an insulation barrier,  preventing solder from sticking  to the mask.

2. Because of the irregular surface, typically produced by a matte solder
mask, there is less surface area for solder balls to adhere to.  

Your second question requires input from your solder mask vendor.
Your solder mask vendor should have a list of compatible conformal
coatings.

Bob Metcalf
Morton Electronic Materials
>>> JIM ENNIS <[log in to unmask]> 08/20/96 08:27am >>>

We are beginning to see more PCB suppliers offering matte finish LPI. 
We  have heard that this finish reduces the adherence of solderballs.  Is
this  true?  If so, at which process, reflow or wave?  What is the
science behind  this lessening of solderballs?

2nd Question: We are also starting a project that will require conformal 
coating. Is there a preference in solder mask type/finish? The coatings
we  are leaning towards are silicone-based.

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