I do not want a "circular block in the center of the pad".

For this board using Via in Pad:
The board fabrication process drills a through hole through the board
and plates the holes (so far just like any other plated hole). Then they 
plug the hole in the BGA pads using a process that leaves the BGA pad flat.

If I use a though-hole pad, I do not get a hole in the paste mask (but I 
do get holes in both top and bottom solder masks). I still need a 
circular hole in the top paste mask. I was considering using an arc 
placed on the paste mask layer over each of the BGA pads. If the width 
of the trace used to create the arc is greater than 2x the radius, there 
will be no hole in the donut. Using the example of a 20mil wide track 
used for a full circle arc with a 5 mil radius (measured to the center 
of the track); the outside edge of the track makes a 30mil circle, the 
inner edge of the track covers (by 5mil) the center of the arc. Its a 
filled donut!

How would you place a circle on the paste mask layer?


Dwight Harm wrote:

> If I understand this, it still can't work.  The paste-mask stencil has an
> opening for the pad, and you want a circular block in the center of the
> pad -- but there's nothing to support it.
>>-----Original Message-----
>>From: David W. Gulley
>>Sent: Saturday, June 01, 2002 11:13 AM
>>Richard Sumner wrote:
>>>Talk to your assembler before you invest time in this. The paste mask
>>>becomes a metal stencil for applying the solder paste. So donuts will
>>>not work (the donut hole is unsupported).
>>Actually my idea was to make the width of the track greater than 2x the
>>radius of the arc so I would end up with a "filled donut". (For example
>>if I want a 30 mil opening in the paste mask, I could use a 20mil wide
>>arc with a radius of 5mil.)
>>However, what I have just tried that seems a bit simpler is to use a pad
>>and a via (gee a via in a pad!) where the pad is TopLayer only and the
>>via is set for tenting. Do an update free primitives after import to the
>>PCB and viola...

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