Question Acer Aspire 5735 GPU Thermal Pad/Paste

Aug 24, 2020

I am in the process of installing a new fan+heatsink into an old Acer Aspire 5735 laptop. Originally, there was a small wafer-thin square covering what is presumably the GPU. Unfortunately, while removing the old heatsink, this square tore and I threw it away. I am assuming that it is some kind of alternative to thermal paste for laptops? When I installed the new heatsink, I used "normal" thermal paste (NT-H1 to be exact) in place of the square. However, now after about 10 minutes of use, the screen of the laptop goes white and flickers (and rebooting immediately fixes the screen for about 30s, until it returns to going white). I am presuming that the thermal paste I used is not suitable, and the GPU is now overheating and failing, hence the white screen.

Firstly, am I correct in thinking the square is probably some type of thermal pad?
Secondly, what would be a good replacement for it? Since I threw it away, I do not know its measurements, and cannot find this information online. Through research, I have found some recommendations pointing towards a more viscous thermal paste, namely K5 Pro. Is this a good substitute for the original square? If not, can anyone recommend a suitable alternative?

Thank you for any help