Come again? Both thermal pads and thermal paste do the same thing, they transfer heat from the GPU or CPU die to the heat sink. I'm really not sure what you mean by the "memory on the board." The heat sink only makes contact with the die which a drop of thermal paste is good for that.
no on the laptop heatsink makes contact with the memory on the gpu. So i want to replace the thermal pads and i want to know which ones i want. is the 4.0 (W/m.K) better? I would assume so since its more expensive that it is the higher quality one. See my link to cooling mod for a picture of my heatsink
My guess is that higher numbers mean better heat transfer rate though i just used one from ebay on my gtx260m with a rating of 3.2w/m-K. I used a 1mm thickness pad. The pads are kind of color coded, the one i used is a light blue color kind of close to the thermal pads you find in hp dv series laptops. I would guess these will work fine as a replacement.
I just ordered this thermal pad
this is the best you can get on the market, I bought it for my Asus G73Jh and my HD 6990 , this is a perfect choice. this has the highest thermal transfer rate.
(don't use IC Diamond , it may damage your GPU die which causes lines on screen and many side effects)
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