Platform forum

Via in SMD!

JohnsonMiller , 12-27-2018, 02:15 AM
Hi Guys,

I was wondering which problem placing VIA in SMD pad can cause?

robertferanec , 12-28-2018, 04:17 AM
Depends where it is placed and how it is done. For example, if not done properly, solder can flow out through the VIA (you may want to fill up the VIAs), or if not flat enough, soldering BGA can be problem ... it can also cause air trap and air can expand during soldering and can cause a weak or bad soldering (at least that is what I heard). But I do not use VIAs in pad much - we used it only once under BGA and had problems with soldering, so I do not really use it much.
Paul van Avesaath , 12-29-2018, 01:19 PM
I have used them a lot. There can be issues with larger via's, but 8/18 mil will fit nicely in a 0402.. Haven't had any problems with it.. You might need to tweak your rules a bit to make it function properly.. Normally it will see it as a clearance issue I believe.. Good luck..
robertferanec , 12-30-2018, 07:38 AM
@Paul van Avesaath how it increases price of PCB (comparing to same/similar PCB but without VIAs in pads)?
Paul van Avesaath , 12-30-2018, 01:59 PM
Good question, I don't really know, but in my experience it's about 10% or at least that's what the pcb manufacturer says
JohnsonMiller , 01-02-2019, 12:26 PM
I guess VIA in SMD PAD should not affect PCB manufacturing, only PCB assembly and probably testing. Any comment?
Paul van Avesaath , 01-02-2019, 12:32 PM
It does set the limits a bit tighter with drilling I believe, but it used to be more expensive. Now a days I Don't think it should make that much of a difference. It does impact the manufacturing a bit. Your right there! But again today's machines a much more capable with more heat zones, to prevent thomb stoning. Also manufacturing has A.O.I. so most cases will be cought before it lands on your doorstep. I do notice when hands soldering a 0402 on a gnd connection it takes more heat than the other pin.. But that's only in prototyping phases..
mairomaster , 01-07-2019, 03:31 AM
I've never had problems with via in pad, but I've used either micro vias, or mechanical vias in thermal pads only. Using mechanical vias in small pads doesn't feel like a good idea. Some manufacturers/assemblers I've worked with even recommend avoiding mechanical thermal pad vias, which sounds a bit too strict to me.
Paul van Avesaath , 01-08-2019, 05:59 AM
never had a problem with them .. full through hole drilled 18/8 via
JohnsonMiller , 01-22-2019, 12:47 PM
Hi Guys,

Thank you very much for your comments.

Regarding via in the PAD which are mostly for IC with thermal PAD, what type of connection we should use, direct plane connection or connection with thermal relief?

Paul van Avesaath , 01-24-2019, 06:13 AM

just checked a few designs, I can suggest direct connect in all cases...
Paul van Avesaath , 01-24-2019, 06:15 AM
see images, all direct connect.
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