I am doing some via-in-pad BGAs and need to figure out if there is a 
"good" way to provide the top solder and top paste masks while keeping 
the bottom solder mask and bottom paste masks off.

I defined the BGA pads as multilayer since I am doing via-in-pad (sort 
of like it was a PGA) except I do not want holes in solder mask on the 
bottom and I do want holes in the paste mask on the top.

I have tried several rules combinations without success, and so far the 
only way I can see to do it is to:
   1) set the solder mask for tenting (no openings top or bottom) in
      pad specification (advanced tab). This makes sure I have no
      openings in the bottom solder mask.
   2) draw arcs (donuts) on the top solder and top paste layers for
      each pad where the trace width of the arc is such that there is
      no hole in the donut and the outer edge matches the opening
      required in the masks.

Does anyone have a better solution?

David W. Gulley
Destiny Designs


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