Copper heat spreader info?

[VK2GOM]

I am collecting parts for an amplifier that requires the devices to be soldered to a Copper heat spreader.

In terms of Copper, this got me thinking... What are the requirements of a heat spreader? Thinking about the properties of Copper and its ability to both retain heat and conduct heat efficiently (ie. saucepan bases) would it be better to have a fairly thin heat spreader to conduct the heat quickly to the heatsink, or a thick one, which could retain more heat and the board could possibly run hotter than if it had a thin one?

Having said that, it doesn't look like my choice of Copper thickness from the supplier I have found is very varied; either 10mm thick or 12.7mm thick. Having said that, I can mill it down if required to a new thickness but it seems a bit of a waste given its high cost.

Any thoughts?

73 - Rob VK2GOM / GW0MOH

[VK3HZ]

What the copper plate is doing is spreading heat away from a very concentrated source (the RF devices) to the much larger area of the heatsink. Copper has about half the thermal resistance of aluminium (in the heatsink). However, it is still significant, so the farthest reaches of the heatsink will be cooler than the part directly under the devices due to this thermal resistance. A thicker copper plate has lower resistance, so will spread the heat more efficiently to the outer edges resulting in a cooler device.

As far as what thickness to use, the thicker the better thermally. However, going thicker has diminishing returns and other penalties like weight and cost. 12.7 mm sounds like a good compromise.

[VK2GOM]

Thanks for the info Dave. I am thinking about a heat spreader the same size as the amplifier board, rather than just a small spreader under the devices as some tend to run. In fact, I will make it a little longer than the board itself to allow the termination for the combiner to be mounted on the same piece of Copper.

73 - Rob VK2GOM / GW0MOH

[VK4GHZ]

Rob, after some great advice from Doug, VK4OE, I obtained a copper off cut ($20) from a local Copper/Bronze/Brass merchant, to help move the heat away from the active device in my Toshiba 3.4 GHz amp.
Drawing around 3A at idle, these linear amps run very hot!


This assembly sits vertically (note mount screws). The heatsnk then helps dissipate heat.
I also allowed for a small fan as well, but that has not been needed.
The copper and heatsink do a good enough job.

Can't quite remember, but comparing to the SMA, the copper bar looks like it's 1/4".
You can be lucky rummaging through the off cuts bin.

Be very careful when you are drilling thick copper.
Being soft, the drill bit will tend to grab, and the thicker the bar, the greater the chance of breaking the drill bit.
Take it very slowly, and regularly clean away the swarf.
Drilling these holes was the most nerve-racking job ever... and two of them required tapping.

I would hate to drill something twice as thick.

[VK2GOM]

Thanks for the info Adam, we have a 'Brass & Copper' outlet near us. I am hoping they have either offcuts or will cut a piece from stock without having to buy a full length (and probably sell my IC7600 to pay for it ).

I have done a bit of drilling/tapping of Copper before when I built my magnetic loop. I just used my usual Rocol RTD cutting lubricant and the drill bit didn't hang up at all. Having said that, with thicker material it might be a bit trickier as you mention.

73 - Rob VK2GOM / GW0MOH

[VK2XAX]

Thanks for the info Adam, we have a 'Brass & Copper' outlet near us. I am hoping they have either offcuts or will cut a piece from stock without having to buy a full length (and probably sell my IC7600 to pay for it ).

73 - Rob VK2GOM / GW0MOH

Hi Rob,

Did you get some offcuts for your project and if so where did you get it, I need some for my amp projects

regards

Tim