[PCB_FORUM] Re: Thermal Pad vias-to-gnd plugged?

  • From: "Macindoe, Gary" <Gary.Macindoe@xxxxxxxxxxxx>
  • To: "icu-pcb-forum@xxxxxxxxxxxxx" <icu-pcb-forum@xxxxxxxxxxxxx>
  • Date: Thu, 26 Jan 2012 16:26:48 +0000

Thanks for the reply Doug.

Your option 1 below would solve the issue for sure, but add quite a bit of cost.

I'm not sure your option 2 below would solve the issue. If there are 
protrusions on the Bottom from the vias wicking paste, the Bottom stencil would 
not be flat to the board.

Anyhow, thanks again.

Regards,

Gary MacIndoe
Senior PCB Design Engineer
EbD R&D Hardware
Surgical Solutions Group
Covidien
5920 Longbow Drive
M/S A20
Boulder, CO 80301

303.476.7458
www.covidien.com

From: icu-pcb-forum-bounce@xxxxxxxxxxxxx 
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Douglas Stanley
Sent: Wednesday, January 25, 2012 5:38 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Thermal Pad vias-to-gnd plugged?

Yes, we are concerned about this issue. The more vias you have in your heat 
slug, the more paste gets sucked in. It can cause a soldering problem due to 
the lack of paste that remains on the pad.

We have two ways to approach it:


1.       Have the PCB shop plug the vias with epoxy and then overplate them 
with copper. All of the vias are then completely closed.

2.       Add a matching copper pad to the bottom side of the board along with 
corresponding mask and paste features. This won't stop the wicking, but we hope 
it mitigates it to some degree since we're adding a big dollop of paste on the 
opposite side.

I'm in the process of writing a Skill program to find these issues on boards. 
Fab houses have a real problem with this, not only with heat sinks, but vias 
that fall into any mask opening that exist on only one side of the board.



Douglas G. Stanley
PC Board Designer, Principal
Broadcom Corporation<http://www.broadcom.com/> - Irvine, CA
dstanley@xxxxxxxxxxxx
(949) 926-5889





From: icu-pcb-forum-bounce@xxxxxxxxxxxxx 
[mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Macindoe, Gary
Sent: Wednesday, January 25, 2012 2:50 PM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Thermal Pad vias-to-gnd plugged?

Hey guys,

When you have an IC with a thermal pad (e.g. A/D), the typical requirement is 
to put vias in the center pad that is connected to the gnd plane for heat 
wicking.

Do you worry about the solder paste going down the vias, even with a 10 mil 
drill? My coworker is concerned that this will happen.

I haven't had this concern, have never "plugged" etc. the vias with no negative 
feedback.

Regards,

Gary MacIndoe
Senior PCB Design Engineer
EbD R&D Hardware
Surgical Solutions Group
Covidien
5920 Longbow Drive
M/S A20
Boulder, CO 80301

303.476.7458
www.covidien.com

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