Q:

What is the maximum distance for thermal paste to be effective?

Note the image and marked distance from one surface to the other on the heat sink assembly and the size of the thermal pad from the laptop I dis-assembled today. I want to use Thermaltake TG-7 paste when I replace the fan but don't know if it will break down prematurely that thick or if it will even conduct heat properly as intended. Are thermal pastes rated differently for situations like this as well? 

A:

I got an interesting and unsolicited answer from posting the image to imgur for use elsewhere. It was pointed out that, in addition to the rather large space between the heatsink and chip, if there is no positive form such as screws or a clip securing the heatsink to the chip as is the case here it would be wise to use the thermal pad. So that's my answer.
EDIT:  "You can't fill a void with paste, it's meant to join 2 surfaces that would otherwise make contact." from next to last or so post from someone that I would say is qualified at https://discuss.howtogeek.com/t/is-it-safe-to-replace-the-thermal-pad-on-this-board-with-grease/62082/18    That certainly answers the question @KronoS though it still only supports my original answer which is relevant in the process.

