thermal pad Using Lead as a thermal pad?

[Bumblebeepee]

So in the 1990's I had a IBM (Cyrix) CPU which used a thin slice of lead / lead alloy (about 1/32" thick) as its thermal interface material against the rough surface of the heat-sink,

Manufacturers stopped using lead in consumer electronics due to requirements for products to be lead free, 

 

But how well would lead stand up against new thermal pads?

As thermal pads are just terrible compared to any average thermal paste, and that lead should have a thermal conductivity of around 34.7W/m K (depending on purity).

 

My best guess is that it was used to conform to the rough surface of the extruded aluminium heat-sink due to its softness, as most things did not need heatsinks back then.

I'd expect if you try to use it now you'd most likely need a high mounting pressure.

You'd need to avoid lead foil as it's just lead coated aluminium, but thin lead sheets can be gotten down to 1/64" thicknesses.

[Eigenvektor]

I suppose it should work, but since lead is poisonous I'd hesitate to use it.

 

Touching it should be fine in general, but e.g. if you have small amounts on your fingers you could get it into your food and ultimately into your body. The risk probably isn't that great, but why take it, when there's less harmful stuff available that's probably easier to source, too.

 

I agree about the mounting pressure etc. but ultimately I think paste is probably easier to work with (albeit a bit more messy).

[Bumblebeepee]

I'm more curious if a 90's cooling solution would still be effective in the current day, 

(i've also seen it used in vintage audio equipment from the 70's).

[Eigenvektor]

35 minutes ago, Bumblebeepee said:

I'm more curious if a 90's cooling solution would still be effective in the current day, 

(i've also seen it used in vintage audio equipment from the 70's).

Sure, 35 W/mK is still good. I'm sure we'd still be using it today, if it wasn't for the whole "poisonous" issue. People didn't stop using it because better stuff became available but rather because of health and environmental issues.

 

From what I can find most thermal pads are somewhere between 3-15 W/mK, though there are some that claim 35 and even 50 W/mK: AL20, AL50. Most paste is somewhere in the same ballpark.

 

~edit: I'd suggest watching this, there's a lot of info about thermal conductivity and paste vs pad

 

[Bumblebeepee]

Ive seen that video from GN, got some good info in there.
 

The biggest issue with any thermal pad is having consistent pressure across the entire pad, and ensuring a good surface contact with no gaps due to surface imperfections.

 

Though lead being used as a thermal interface was back when devices were not kicking out more than 50W of heat.  
 

[clandestiny]

That likely was not lead but rather Indium foil which is still used as an excellent interface to fill the potential rough surfaces and insure a better coupling between CPU, LED or laser diode array and the heatsink base plate.  I harvest it anytime dismantle any old mobos and I come across it for my project laser builds.