Is it OK to use toothpaste instead of thermal paste when fitting a CPU?
This is the standard "saran-wrap-in-place-of-condom" question. While some toothpastes may provide the correct type of thermal conductivity, "toothpaste" is too big a category to answer the question accurately. Worse, unless you want to make it a fun science project, nobody is going to be testing different types of toothpastes for thermal conductivity.
That said, the answer is probably "yes." Toothpaste is definitely better than nothing, because air (i.e., nothing) is a terrible heat conductor. That said, there are other properties to consider. From Wikipedia
- How well it fills the gaps and conforms to the component's uneven surfaces and the heat sink
- How well it adheres to those surfaces
- How well it maintains its consistency over the required temperature range
- How well it resists drying out or flaking over time
- How well it insulates electrically
- Whether it degrades with oxidation or breaks down over time
I think that toothpaste might work for the thermal part, but you might have other problems in the short- or long-run.
On A Different Note: That said, if you need to stick a note to the wall, you can definitely use chewing gum (after chewing a bit). Sometimes it's hard to get off when your lease is over, though :)
I remember hearing about this at Dan's Data a while back, and he went back and forth with Arctic Silver's Nevin on the issue.
I think the basic idea was that toothpaste will dry up faster than true thermal paste, perhaps leaving you a lot worse off than if there was nothing at all. So, if you like removing your heatsink as much as I do, then no, it's not ok.
It might be better than nothing, but unless toothpaste has unsuspected thermal conductivity, I'd say it's a bad idea.
You also have to consider what the ingredients of the toothpaste might do in contact with your CPU. I suspect it would be pretty conductive in an electrical sense. You don't want electrical conductivity.
Better get some real thermal paste. It's more expensive than toothpaste, but worth it.