Generally we just make sure the opposite side of the board has soldermask "encroaching" onto the via pad, as close to the hole as the board fabricator can get it without leaving mask in the hole.

The result is usually acceptable for moderately sized mounting pads, but there will be a little variability in the solder joint due to an unpredictable amount of solder flowing into the hole. For the most critical work, fill and cap is the only option.

Wayne
________________________________________
From: TechNet [[log in to unmask]] on behalf of Richard Krug [[log in to unmask]]
Sent: Friday, August 08, 2014 10:03 AM
To: [log in to unmask]
Subject: Re: [TN] via in pad solder wicking Vs drill size

We've seen solder wicking through 12 mil vias on thin, ~25 mil, boards.

Dick Krug, CSSBB, CSMTPE
Lead Process Engineer
Sparton Brooksville, LLC
30167 Power Line Road
Brooksville, FL  34602-8299
p (352) 540-4012  (Internal Ext. 2012)
[log in to unmask]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Nagaraj Shanmugam
Sent: Friday, August 08, 2014 7:59 AM
To: [log in to unmask]
Subject: [TN] via in pad solder wicking Vs drill size

Hello All,

Bring back an old topic for clarification and seeking more details on this.

Few application note says that the solder wicking is not seen when the through hole via drill size is kept equal to 0.3mm(0.012") or less Few application note recommend to fill the vias used on Thermal pad on QFN devices - epoxy or capping  on all via sizes.

Please advise is solder wicking  do happen on through hole via drill size 0.3mm(0.012") or less? i.e. solder wicking Vs the via drill size Is this applicable to passive parts using Though via in pad? Because I see the pad area Vs solder quantity difference between a thermal pad and a passive component pad.

Appreciate any information on this topic.

Thanks,
Nagaraj.




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