Here are some thermal conductivity properties I once found in the IPC-D-279 Design standard, at least that is where I think I found them originally. I believe they are also listed separately within the IPC-4101B slash sheets also.
There are via fill materials that are designed specifically to aid in thermal conduction, I would start by looking at the Peters website.
Also, you may wish to look at Zymet TC 201 as a hard fill. It is also used as a thermal gap filler material and is very effective.
There are certain polyimides used as substrates that are much more thermally conductive than standard FR-4.
As you can see by the charts below, soldermask is a thermal insulator. If you can leave the copper exposed, you would have a conductivity of 392 W/m, but if soldermasked you are bringing it down considerably, as the masking thermal conductivity is only .245 W/m.
Here is a link to an invaluable paper on thermal conductivity and the proper methods of measurement and calculations in electronic designs. I have referred to it many times on various designs, especially high-power circuits and where guaranteed long service life are required (ultra harsh environments such as down-hole drilling controls, ultra-high-rel avionics, etc.).
http://focus.ti.com/download/trng/docs/seminar/Topic%2010%20-%20Thermal%20Design%20Consideration%20for%20Surface%20Mount%20Layouts%20.pdf?DCMP=mdrvblog&HQS=gma-indu-motr-mdrvblog-150422-thermal-mc-en
One particular item that stands out to me is the use of thinner dielectric layers (FR-4 or polyimide) coupled with thicker copper (1 oz or greater per layer). This has been a very effective way to provide better thermal performance, but you do need to consider the copper pour balance in order to avoid warpage or severe TCE travel and other unintended processing or thermal stress issues.
I hope this helps.
Odin
Thermal conductivity [W/m K]
Silver: 418
Aluminum: 403
Copper [rolled annealed]: 392
Copper [electrodeposited]: 392
Gold: 297
Nickel: 90.7
Tin: 73
SAC: 73
Castin: 57
Pb37Sn63: 51
Lead: 35
Epoxy, phenolic: 25-75
Conformal coating [AR, ER, UR]: 17-21
Epoxy, silicone: 13-26
Epoxy, conductive: 5
Molding compound: 0.63
FR4: 0.35
Solder mask: 0.245
BT resin: 0.17
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Dave Schaefer
Sent: Tuesday, August 16, 2016 12:13 PM
To: [log in to unmask]
Subject: [DC] Using PCB Features for Cooling Purposes
Can anyone point me to good technical resources on Using PCB Features for Cooling Purposes.
Some of the items I'm interested in summarizing are:
- Vias .. do filled vias provide better thermal "relief" than standard vias?
- Exposed copper vs copper with soldermask cover .. which is better for thermal "relief"?
- How effective is potting material at providing thermal "relief" and which specific materials are geared towards cooling?
- Is the effectiveness of potting material cooling better if it is applied over bare copper than soldermasked copper?
- How effective are internal copper areas at providing thermal relief?
- How does the thermal conductivity of the PCB features / materials I've listed compare to other cooling methods (standard metal heatsink, "tweak" heatsink, etc.)
Any other tips/resources are greatly appreciated, including information on non-PCB feature "tweak" type solutions to address thermal issues.
Thanks,
Dave
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