Yes, but a caution is advised if you are using flux that must be removed. 
It is practically impossible to get the material out of the reverse meniscus
that forms if the mask enters the via hole. When I worked in an FA lab, we
once documented this type of failure.

Now that I think of it. This would be a problem on blind vias too. There is
no way to clean in the void that invariably forms. 

-----Original Message-----
From: Dwight Mattix [mailto:[log in to unmask]] 
Sent: Tuesday, February 05, 2008 12:48 PM
To: TechNet E-Mail Forum; Guy Ramsey; [log in to unmask]
Subject: Re: [TN] Open via in pad - any success?

At 09:41 AM 2/5/2008, Guy Ramsey wrote:
>I am not party to the HP secrets for successful assembly with through hole
>via in pad. I can say we tried pre-filling them with solder here and it did
>not help.
>The condition is a function of hole size, wetting forces, gravity, surface
>tension, and reflow profile.
>
>We have done it successfully, the problem is the hole must be quite small
>and the aspect ratio of the PTH becomes difficult to produce if the boards
>are a standard thickness.

Key is to cheat the soldermask up to the via on the back side (so-called 
"tentbreaker" mask openings work well.). Doesn't take much s/m to keep the 
solder from wicking out.



>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Ryan Grant
>Sent: Tuesday, February 05, 2008 8:38 AM
>To: [log in to unmask]
>Subject: Re: [TN] Open via in pad - any success?
>
>Thanks Paul,
>
>If you and two others can do it, I guess it can be done...  I'm glad I
>asked before I made a fool out of myself.
>
>So now the question is, how did you do it (if you can tell me)?
>
>Whenever I've tried it, either gravity would cause the solder to sag out
>the bottom, or the via would suck solder away from the joint.
>
>Thanks,
>Ryan
>
>________________________________
>
>From: Paul Edwards [mailto:[log in to unmask]]
>Sent: Monday, February 04, 2008 6:43 PM
>To: TechNet E-Mail Forum; rgrant
>Subject: RE: Open via in pad - any success?
>
>
>Ryan,
>
>It really depends on the size and depth of the via, the via to pad
>diameter ratio....
>
>Q: has anyone been successful with a via in pad that is not plugged?..
>A: YES, both through and blind vias
>
>Q: If so, was it double sided?
>A: YES if you mean a double sided PCB, and YES if you mean it was a
>through via..
>
>Q: ...was one side connected to a BGA ball?
>A: YES
>
>Paul
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Ryan Grant
>Sent: Monday, February 04, 2008 4:55 PM
>To: [log in to unmask]
>Subject: [TN] Open via in pad - any success?
>
>Hi All,
>
>I just got told by a design engineer that LaserJet printers are built
>using via in pad where the via is NOT plugged.  He claims the via is
>filled with solder first, then goes through the normal SMT process.
>
>He intends to use this to connect a BGA ball on one side of the board to
>a cap on the other side using an mechanically drill via that is not
>plugged.
>
>Before I call BS on this, and tell him "do not pass go until that via is
>plugged, flattened and plated over", has anyone been successful with a
>via in pad that is not plugged?
>If so, was it double sided?
>And, was one side connected to a BGA ball?
>
>Thanks,
>Ryan
>
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