Is heatsink necessary for using Penta SATA Hat?

In the product description for the Penta SATA Hat on allnetchina, it says:

PLEASE NOTE: You need to order the heat-sink with Rock 4, otherwise the Penta HAT can not be mounted on top. For use with Rock 3A please purchase the base plate for proper installation.

Do I really need this heatsink to use the Penta SATA Hat?

The title of this item leaves out the 4A+, will the same heatsink also work for the 4A+?

The picture in Section 4.2 of this PDF shows the Penta SATA Hat on a Rock 4 with no heatsink, so it looks like it works without a heatsink:

Please inform if the heatsink is truly necessary for mounting.

Thank you

The Penta Hat screws need some “bed” to be mounded. That’s the reason for the “can not be mounted on top” half-sentence. I.e., the screws fit “naturally” in the headsink. Of course the Penta Hat itself works without the headsink. However, Rock 4s do not really work without any headsink or fan, so for a reliable setup your Rock 4 should have a headsink. The massive heat sink from Allnet works very well and keeps the Rk3399 typically <50°C.

For the second part of the question, yes the headsink should also work on an 4A+. To my knowledge, only the 4C need s slightly different one (and the 4C+ / 4SE of course).

Thank you for the swift reply!

Did you see the picture in the linked PDF at Section 4.2? It looks fine without a heatsink in the image with the metal bolts looking fastened below the primary Rock 4 PCB.

I did not know the RK3399 ran so hot, so I might get one anyway!

Thanks again