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

  • From: "Douglas Stanley" <dstanley@xxxxxxxxxxxx>
  • To: "icu-pcb-forum@xxxxxxxxxxxxx" <icu-pcb-forum@xxxxxxxxxxxxx>
  • Date: Thu, 26 Jan 2012 10:01:02 -0800

Having vias that are tented with mask on one side creates problems in fab and 
from a reliability standpoint. Since the hole is not completely clear, various 
post-mask fabrication solutions can accumulate inside the hole and lead to 
degradation of the hole wall. Speak with your fab shop for more information.

Tenting both sides of the hole with LPI mask is common, but it's not 100% 
reliable either.


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: Thursday, January 26, 2012 9:05 AM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Thermal Pad vias-to-gnd plugged?

Thanks Alan. Mask over the vias on Top only, then they can't "pop off" when 
they're under the thermal pad of the part.

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 Ritter, Alan
Sent: Thursday, January 26, 2012 8:03 AM
To: icu-pcb-forum@xxxxxxxxxxxxx
Subject: [PCB_FORUM] Re: Thermal Pad vias-to-gnd plugged?

Gary noted:

So Cypress is suggestion that the vias to ground be masked over on the Top. It 
seems like that would keep the part up off of the pads.

Gary:

That was my initial reaction as well but it seems the theory is that you lay 
down a layer of solder paste that is thicker than the soldermask thickness, so 
the thermal pad makes contact with the paste.  We have built several thousand 
boards like this and haven't seen an appreciable failure rate due to poor 
thermal contact, so it seems the Cypress technique works reasonably well.  (and 
I guarantee you that this particular USB hub will overheat if it doesn't have a 
good thermal contact...our prototype boards didn't have the recommended thermal 
pad layout and half of them would overheat and shut down the USB hub pretty 
quickly.)


Alan Ritter
Surgical Equipment Design & Development
Engineering Fellow

(636) 226-3364 (Office)
(636) 226-3552 (FAX)
(314) 488-1139 (Mobile)

Bausch + Lomb
3365 Treecourt Ind. Blvd.
St. Louis, MO  63122
www.bausch.com<http://www.bausch.com/>
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