"PCB platforms" for thermal management of hot chips

[Faringdon]

Hi,
We use Innoswitch, which has an internal FET, and we use lots of SMD power FETs....so now we want to mount them on a small piece of 1mm thick PCB...and have 2oz copper top and bottom with plated over thermal vias......then we will put "legs" on this...turn upside down, solder it to PCB, and then put a heatsink on top of this, with mounting for the heatsink on the little bit of PCB.
Do any such "PCB platforms" exist offTheShelf?

[Smokey]

That sounds like a lot of assembly trouble.
How about aluminum substrate?
https://www.pcbway.com/pcb_prototype/General_introduction_of_Aluminum_PCB.html

[wraper]

Do any such "PCB platforms" exist offTheShelf?

Because it's a cost inflating garbage made for no good reason? Normal practice when heatsink mounted over the parts through a thermal pad will likely work better than this and without complicating anything. Not to say you can put a heatsink on opposite side of a regular PCB as well, or use metal chassis as a heatsink. BTW multilayer PCB with copper polygons in internal layers is much better at transferring the heat away that trying to use vias to transfer the heat to opposite side.

[DavidAlfa]

Those ICs have been designed to be mounted in PCB, if overheating then it's a pcb design flaw, not the IC's fault.
Do proper thermal design, placing large copper areas, using lots of thermal vias. You can place the heatsink at the other side of the pcb, or in both sides.
With proper design you might be able to attach the chassis through some thermal pads, thus saving the heatsink.

https://electronics.stackexchange.com/questions/243989/optimize-heat-sink-design-connect-cooling-pad-on-pcb-backside-by-vias

[Faringdon]

Thanks, Often the PCB rests some 4mm above the heatsink...then somehow you have to find ways of filling that gap between the innoswitch and the heatsink.

[DavidAlfa]

How do you know the existence of the metric system?
You can get all kind of aluminum parts, 4mm-thick plates should be easy to source, maybe premade blocks exist, or just getting them cut to size in a nearby machining workshop.
A bit of thermal paste, insulation pad if required, and some clamping device like screws, clips... Shouldn't be that hard!

[wraper]

Thanks, Often the PCB rests some 4mm above the heatsink...then somehow you have to find ways of filling that gap between the innoswitch and the heatsink.

Never heard about thermal pads (thick and soft stuff like used in desktop GPUs and laptops)? Also there are putty like "thermal pads" such as Laird Tputty.

[coppercone2]

I actually like this idea if you can manage with the impedance of the standoffs and stuff in a good circuit. I think its worth experimenting on. I appreciate a solution that is not someone trying to jam putty in something. Actually serviceable.

What I would try is header connectors (perhaps a row of fine pin pitch ones in parallel, like a 2x or even 3x row, to make a low impedance connector between the riser board.

For the stand offs, I would use 4x solder mount threaded standoffs from Keystone or something like that. You could try to use them for ground too I guess.

You can look at Mac8 for PCB hardware too to make stuff like this possible.

https://mac8usa.com/products/spacer-for-smt/
https://mac8usa.com/products/conthrough/

Mounting a power section on interconnects is not as crazy as you think, its done with big IGBT like SKIIP series for welding machines. They do this so you can have a board mount IGBT that is bolted to a heat sink.

If that PCB thermal pad idea works, then I think maybe it might really give the transistors some breathing room for heat, and isolate the adjacent parts.

I recommend connectors for all pins though, don't rely on the spacers for a good electrical connection IMO, because its still a screw on a PCB, not going to be as nice as a connector.

For really high currents they have offset connectors too, that is a board to board connector that allows for horizontal motion between the two boards while maintaining full connection (200 amp range). Easier to install and it handles thermal, or so they say.

And a assembly feature for this is to solder some pins on the PCB to work as alignment pins that are taller then the connectors, so you don't mess up your pins trying to socket it.

I just don't recommend putting parts under the raised section. I feel like that area will be compromised for parts if there is power electronics on top of it.