....talk of many things. Of sealing wax and thermal dings

I see several threads discussing Lilly the Pink and thermal compounds, perhaps the time has come, the walrus said to devote the subject a thread of its own.

Firstly
ALL thermal compounds are poorer conductors of heat than pure metal.
The problem lies in the fact that at the microscopic level even polished metal surfaces are not truly flat and only meet at a few points of contact. The gaps are filled with air, which is a good insulator. One purpose of the compound is to fill in the gaps thereby greatly increasing the contact area between the solid surfaces with something that is solid or semisolid. this greatly assists the heat transfer from component to heatsink. Incidentally it is not only processors that require heatsinking and annointing with thermal goo.

Secondly
In some instances the thermal interface material is required to also be an electrical insulator and electrically isolate the component from the heatsink. this is a difficult requirement because both heat and electricity are carried by electrons in solids and good thermal insulators are also good electrical insulators and vice versa. The usual solution to this dilemma is a very thin sheet of mica, although there are now some plastic materials that are also used.
Sometimes the reverse is true i.e. a good electrical contact is required then usually a thin sheet (foil)inium or copper is used of a 'squashy' metal such as aluminium or berillium -copper is used. This is of specially softer grade than the heatsink material.
Sometimes, as with most computer processors, electrical contact is not relevant. Here the manufaturer's decision is based on the total cost of material and assembly line costs. Some products such as the pads are dearer but easier to handle and fit so overall cheaper.

As to the difference between paste and grease, some assemblies are not designed to be disassembled for servicing. (Does Windows fall into this category?). Would you buy such a product from preference? These use the paste or wax which are designed to set and as one geek aptly described cement the parts together. Grease on the other hand dose not set and it remains easy to separate parts. Many a time have I released the processor heatsink to remove it and withdrawn the processor as well from the socket although the lever is still down. This problem does not arise with grease, properly applied. Of course excess grease causes to much 'stiction' and the problem can happen anyway.

Thirdly
So for two reasons, thermal efficiency and future service ease, it is essential to put on the minimum compound (guess which I favour?). I still use a tub of Repoint I bought from Jermyn Industries in 1974.

Fourthly
Amateurs are able to undertake proceedures not available industrially, and vice-versa. For instance the most efficient way possible is to use no compound an hand'wring' the surfaces as is done in a metrology lab, but this is very labour intensive.
Amateurs can also use petrol (yanks call it gas) as a solvent. this is a really marvellous stuff so long as you take sensible precautions, not only for heatsink compounds various but also label glue, evostick, greasy marks etc etc. If you don't want to use this neat either white spirit or the builder's paint brush cleaner which is a mix are both far better grease solvents than any alcohol. And they evaporate very quickly. I also use these to scrub recalcitrant sunstances from circuit boards as they do not damage electrical components, except natural rubber.

Any comments?
This is a hardware forum right?

Studio T