Chosen Solution
I’ve noticed that my iPad Pro 12.9 is noticeably more cool/cold to the touch than most of my other devices. More recently it put me into thought mode, where I’m now wondering if the large surface area of the back casing acts as a heatsink in any meaningful way? I notice in this image that the batteries appear to touch. https://d3nevzfk7ii3be.cloudfront.net/ig… Similarly, it looks like the chipset does, too? https://d3nevzfk7ii3be.cloudfront.net/ig… I’m assuming it would also add to the longevity of the device, or at least the batteries.
Surprisingly No! The SoC chip is not mounted in a way to leverage the bottom case for heat dissipation. There is EMI foam which meets up with the bottom case (in your image the silver areas are raw metal unlike the gold anodized finish which are touched). The black square just under the SoC chip is to insulate the small components on the bottom side of the logic board. What you are seeing is good engineering here within both the hardware & software so excessive heat is not created. As to lifespan of either the SoC or the batteries use is more a factor here.
Actually it is the display. The EMI shielding and thermal pad/stickers are at the front side of the board. There is a huge metal backplate behind the display to spread the heat evenly, then the heat is dissipated through the huge screen.
