Fred,
Here are various techniques that I've done to address this as I've had to address this on boards that I've inherited from other designers/programs over the years.
Solder-mask plugging is one method. But I'm not a big fan of the solder plugging, one because of the volcano effect mentioned earlier, but also because it can leave a pocket on the solder source side that flux, such as water-soluble flux could get trapped in. This isn't ideal because most water-soluble flux don't deactivate and it will be corrosive and is an electrolytic. I've had the most issues with this one over the years.
One quick/easy fix I've done that the pwb vendor recommended is just do a non-conductive epoxy fill, no need for the wrap and cap. It's just a filled via and seems to work reasonably well. It does add an additional drill and panelize. I've used this on boards that I don't really need any via-in-pad, but I have thermal pads. Not as cost effective as the solder-mask, but I feel much more comfortable living with it. It's been pretty robust thus far. Pick a material with a similar Tg to the pwb material you're using.
The top of the line method (in my opinion) is the via fill, wrap and plate it sealed. You benefit by increasing your solder able surface for the thermal pad and you can use it for via-in-pad if you are hurting for real estate. But this will cost the most because of the planarization, additional plate/drill cycles and you have to watch your trace thickness on the outside layers.
Hope this helps,
-Jeffrey
Jeffrey A. Jenkins CID+,CIT
Senior PCB Staff Designer || L-3 Linkabit || Ph: 858-552-9832 || [log in to unmask]
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Fred Dark
Sent: Thursday, April 24, 2014 12:58 PM
To: [log in to unmask]
Subject: [DC] IC's with a "ground slug" with vias...
Hello all - we have been adding a solder-mask dot on the same side as the IC's with a "GND-SLUG"... no issue... however if a "SLUG" has a large quantity of vias due to the requirement to dissipate heat here is where I have a issue... not enough area for paste and proper solder percentage to the area... so in this case I was suggesting to tent the opposite side that the IC resides on... filling, capping and planarized is the way to go, however would tenting the opposite side be a issue..? note via hole size is 10mils... anyone aware of the IPC standard and or requirement..?
Regard's, Frederick Dark Jr.
Manager Senior PCB Designer
Crestron Electronics, Inc.
22 Link Drive Rockleigh N.J. 07647
P:201.750.7004 ext.11320
F:210.767.5772
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