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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