[LG V20 Questions & Answers] Descent2:
On V20, the CPU is just like on PC, is attached to the board, but touching a metal heatsink (which is the internal frame) with a healp from some pink glob of crappy looking thermo paste. Actually, the CPU itself is covered tightly with a memory chip soldered right on top of the CPU, and the roof of that is sticky-glued to a copper foil, and then that copper foil is covered with the paste glob and that is stuck to the frame.

Few points to note right here:

- the reason that V20 has thermal issues, I think, is due to poor thermal design: three interfaces (CPU --> memory chip --> copper foil --> metal frame heatsink), and each has some less than 100% efficiency in thermal energy conductivity. There might even be a fourth interface if the CPU has a lid, like that on PC, but unlikely so, most probably it's an exposed one like on the graphics cards.

- each of these thermal interfaces has it's own expiration date. At this point in time, you don't know how many of them are expired.

- hardware guys already are doubtful about the goofy looking "thermal solution" paste that is applied between copper film and the frame. How efficient was it to begin with?

- if you had removed the board before, or if you had dropped the phone when this paste was already dried up, it is very likely that it has de-touched from the frame and there is an air gap. Typically this is not how a phone is designed and this is a surprise to some folks.

What ideally needs to be done is the memory chip needs to be removed, the interface conduction layer renewed, and chip needs to be soldered back. Then the renewal needs to be carried out with respect to the second and third interface as well.

Without having to solder anything, you can relatively easily replace / thinker with the second and especially the third interface. The second will require the copper foil to be peeled off. On the phone I ruined, I threw that foil away, intending to go directly from memory chip roof to the frame, but alas, I didn't get to try that. I think that the high efficiency thermal conductive solutions such as liquid metal or diamond pastes are not good here, because there is the reason the LG used the glob of chewing gum it seems - because the interface between the roof of the memory chip and the frame lacks the close tolerance required for a high efficiency conduit to work. Plus the phone has some flex to it, so even if yours happen to be aligned extremely tightly, this would keep changing. For this reason, I think the thermal conduit needs to be a high volume / flexible one, like that again, on the graphics cards. This could be a thick paste or a sticky pad.

The reason they used the copper foil and not a direct connection between the chip and the frame, I think was because the interface between the roof of the memory chip and the copper foil is more precise and is much more flex stable, so, by using a higher efficiency / thinner conduit there they were aiming to help the total efficiency at least a little bit.

I wanted to clean the roof of the memory chip and use some good video card thermal paste / goo / glue / pad directly connecting it to the frame during re-assembly.

I think this is what you can try to do as well. You can leave the copper foil there for now, and try just the third interface. If your results are not significant, then try and remove the foil as well. None of this will require soldering or a high magnification equipment. Just some patience, alcohol, a steady hand and at least a PC experience with the same.

Be careful with the screws. The screws are all different length, and when I opened mine I was following a guidance that there are two groups, but found it to be wrong as my phone seemed to have at least four groups of different screws. It was too late, however, because mine were already mixed within two groups I created. So, I would advise to create a diagram of screw location and keeping track of which screw goes where. I think that many times this phone is taken apart and put together, without this tracking, some screws end up too long for where they were placed and holding parts loosely, thus adding to the flex that might be cracking the older brittle thermal interface.