Phil,

 From what I have read and seen the conducting of heat into additional
layers and the bottom side is best done with a large number of tiny vias.
The vias should be under the part tab or all around the leads.

My understanding is that thin layers of copper foil (even 2oz) just does not
conduct well. Getting the heat down to additional internal layers helps
spread the heat using those layers. And getting heat down to the bottom
layer is important as the bottom side is exposed to convection currents.

I have a design with a DPAK device  and a large array of vias giving me
about 1C/watt. This design has a 50mil think 4 layer board on an aluminum
base. By getting the heat down to the bottom side of the board it was then
very close to the aluminum (1.5 mm thick) plate which really spread out the
heat.

Some of the best info I have seen in this area has been from the makers of
high power LEDs.

Bob Kondner.


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Nutting, Phil
Sent: Monday, December 19, 2016 1:35 PM
To: [log in to unmask]
Subject: [TN] PTH component lead to copper etch "heat sink"

Hi All,

We have several designs in which we use the thru-hole pad and surrounding
etch to act as a heat sink for device heat being transmitted via the
component leads.  Typically 2 ounce copper and often on 0.090" thick FR-4
boards.  With the added copper thickness and larger pad area for better
"heat sinking" we now introduce greater difficulty in getting a quality
solder joint and don't get me started on the increased difficulty in
removing a bad component.

So my questions are:
Is this a common practice?
Does it really provide effective device heat sinking?

Phil Nutting  |  HVP Development Engineer   |  Excelitas Technologies Corp

Lab: +1 978.224.4332   |  Office: +1 978.224.4152
35 Congress St, Salem, MA  01970 USA
[log in to unmask]<mailto:[log in to unmask]>
www.excelitas.com<http://www.excelitas.com/>


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