The shims and thermal grease were delivered last evening so I decided to go ahead and perform the heatsink mod on my March z8750 device as quick post-midnight project.
I used a 15x15x0.5mm and some regular quality thermal grease-- nothing fancy.
Compared to some other teardown videos that I've seen, it does appear that there is a lot of inconsistency in the nature of ZIF plugs, tapes, fasteners that they use in different batches-- the fastener for the analogs was particularly non-intuitive and I accidentally lifted the right bit open-- had I not, I would've definitely broken it by trying to lift up the wrong end. The fan is also fixed in place with a fairly tacky tape (the foam variety-- don't know what they're called) but I think this is a good move to seal any gaps between the heatsink and the fan's holder.
The heatsink itself has a much neater application of the insulation tape (to a point where when I had opened up the device the last time, I had thought there was not tape being used at all). Where you see I've placed the copper pad, a neat gap was already present in the tape and a generous amount of thermal grease came pre-applied from factory. I performed a quick clean up with some q-tips and tissue before applying the shim.
I only used a very small amount of the grease and subsequent to taking the above picture, I evened it out a little more to get a thin but consistent layer on the chip. You can see the white stains from the grease that came with the unit still present on the sides over the package.
Outcome: putting everything back together was not exactly a breeze- I might have tightened some screws a tad too much and after I got it all put back together, the plastic clip under the lid makes a noticeable cracking sound.
There is also a fairly prominent bump on the region above the keyboard (where the GPD branding is).
Performance is really not much better-- the device idles at much lower temperatures but under continuous load for about 30 minutes I still hit 75-76 on at least 2 of the 4 cores. Earlier, the cores would reach these temperatures in somewhat less time.
Throttling begins in earnest as the temperatures rise and I can't seem to do anything about this. The BIOS settings don't seem to matter and it is still impossible to go past 2 GHz for heavy games-- perhaps, those games don't require a faster CPU and the bottleneck is the GPU. Either way, I DO NOT recommend performing the heatsink mod on the latest batch of z8750s. GPD have clearly rectified the glaring design flaws in certain areas, the CPU seems very well coupled to the heat sink by default (I say this because even a 0.5mm shim is proving to be too tall) and the fan is almost integrated into the heatsink making it much more efficient.
I do not feel the potential risk of chipping off a diode somewhere is worth a device that runs cooler by 5 degrees.
