are you sure you don't want the bottom pads untented?
a recent customer specifically wanted the bottom via fanouts to be
untented for test probing
(i realize yours are in pad)
your via in pad only goes to the layer below, right?

in my understanding this is the only way it can be small enough to not
louse up the paste reflow

what is the ball count and pitch of your chip and why exactly are you
doing via in pad?
what are the various dimensions you are using?
(just curious)

Dennis Saputelli


"David W. Gulley" wrote:
> 
> 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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