.....
When the stakes are comparatively low and everything is sitting flat, you can get away without a mechanical means of securing the heatsink.
However, I do hope that Pi v5 has a pair of screw holes on opposite corners of the CPU, to support a mechanical restraint. I would prefer to do it "the right way", even if I think I could probably get away with something less.
I don't expect them to do it - it takes valuable, precious space. They're battling for every mm^2 of the board area. I've read that a prototype of Raspberry Pi 4 was 5mm longer (in the longer dimension) and the've been optimising itt for half a year to shorten it. The movement of an ethernet jack to the other side was necessary.
The RPI4 has a quadrature of holes, which can be used for heatsink attachment - exactly what we did with CooliPi 4B. But - given they're far away from the SoC - you need some mechanism to create force from the underside of the board against a heatsink. We've bet on the PCB rigidity and flexibility and it paid off. The heatsink is designed in a way in which it's fastened by four screws (hexagonal nuts) BUT the Aluminium island above the BCM chipset (and the two other chips) is 0.3mm closer to the PCB than it should nominally be. This distance is enough to exert a small force on all the chips. It makes a triangle of contacts (every one of the 3 chips), defining a plane - the PCB is bent a little bit between each corner and this middle triangle.
This strategy has paid off well. It's a good balance between the exerted force, PCB bending (not too much) without the necessity to create any support mechanism under the board to force it against the heatsink. Using thermal paste is highly recommended.
I've added a page to our support site here
https://www.coolipi.com/Direct_contact.html
Some users were keen to see it, so there it is.
Your idea would help only if it were useful to install a heatsink smaller than the board. That's not the case - any decent coolercase needs to cool by its chassis to gain surface area. Any small heatsink inside a case is worthless. And with the 3-8W power budget, you need something between this size (SilverStone case) and CooliPi on the upper side of the size spectrum.
Any future SoC will be either underclocked to fit into some rectricted power envelope, or running at full tilt but with higher power draw. And power users will demand more performance for desktop anyway. So, with any future process technology RPF could pay for, we power users will demand to get the most of it. And that means (again) the biggest heatsink money can buy.
And any big heatsink can be mounted as CooliPi 4B - using existing holes.
Facebook
Twitter
Instagram