thermal paste on flip chip BGA

[justis]

I got curious and pulled the heat sink off of a flip chip BGA on my motherboard that wasn't the CPU itself. I think it's the memory controller hub. After doing this, I realized that I was all out of thermal paste. How critical do you think it is to have the paste? The heatsink is clipped pretty tightly to it, with anchors that are firmly part of the PCB. I got the heatsink locked back into the anchors. I'm curious if it will run too hot and how I might measure this. Does anyone have pointers for me? It would be nice to be able to run this without waiting for a shipment of thermal paste or a trip to the store.

Kind regards,
Justis

[mjc]

Thermal paste is used to mate the surface of the heatsink to the surface of the chip, filling in any voids or spaces between the two surfaces. If the surfaces were extremely flat and 'polished' the need for paste would be almost nonexistent. But, since most chips aren't milled flat and most heatsinks are even worse, short of lapping them on you own, you will need some paste.

Chipset heatsinks, by nature are smaller/thinner than CPU heatsinks, so lapping them is not an easy chore and still may not provide enough contact to dramatically improve things. But, a light lapping and paste probably will and since you have it a part, now would be a good time to think about it...

[Whyzman]

Lapping: http://www.overclockersclub.com/guides/lapping/

[saphalline]

Unless you want a crispy Northbridge as soon as you hit the power button, I would suggest waiting until you can properly install that heatsink. The extra cooling is there for a reason. Modern NB's run in excess of 500 MHz, and you'd never do that to a 500MHz CPU, would you? ;)

[justis]

Thanks for the tips, mjc, Whyzman, and saphalline. For this particular motherboard, I'm not motivated enough to lap my heatsinks, but the technique looks interesting. Perhaps I'll try it when I buy something worth overclocking.

I installed lm-sensors under Linux to see if I could monitor its temperature, but I don't think there's a sensor on that chip. I guess I'll wait.

Thanks again for the help.

Kind regards,
Justis

[justis]

Unless you want a crispy Northbridge as soon as you hit the power button, I would suggest waiting until you can properly install that heatsink. The extra cooling is there for a reason. Modern NB's run in excess of 500 MHz, and you'd never do that to a 500MHz CPU, would you? ;)

I'm not quite sure whether it's running at 100MHz or 133MHz, but it's a pretty old board. The Northbridge itself is an Intel 82845 and it claims that it runs at 100MHz, "quad pumped". The RAM itself is PC133, and that's the only flavor it will accept.

Curiosity got the better of me before I saw your post. It ran just fine and there is no (apparent) damage. It passed 2 runs on memtest86. I'm still going to reapply the thermal compound when I get some and will largely leave the box off until then.

Thanks again for the help.

Kind regards,
Justis

[Whyzman]

I'm still going to reapply the thermal compound when I get some and will largely leave the box off until then.If you leave a box fan or something similar blowing gently on the innards that might provide some safety. However, if you simply leave the cover off the case you negate the proper flow of air over and across the internal components.

[saphalline]

I'm not quite sure whether it's running at 100MHz or 133MHz, but it's a pretty old board. The Northbridge itself is an Intel 82845 and it claims that it runs at 100MHz, "quad pumped". The RAM itself is PC133, and that's the only flavor it will accept.That would be the i845 Northbridge chip, and yes, the FSB runs at 100/133MHz quad-pumped. That means it can transfer 4 bits per clock, similar to the way DDR RAM works.

But for the purposes of clock straps and signal listening, the Northbridge runs much faster than a mere 133MHz!! If it only ran that fast, it wouldn't even be able to crest 50% RAM bandwidth efficiency! :p It's gotta be at least 266MHz to support the GMCH graphics engine! If you look at the docs, however, you'll see it's an asynchronous MCH with some parts of the chip running at only 48MHz while the fastest runs at 400MHz.

So essentially, it's a 400MHz Northbridge processor for the sake of heat dissipation. Don't run it without adequate cooling.

[justis]

So essentially, it's a 400MHz Northbridge processor for the sake of heat dissipation. Don't run it without adequate cooling.

Thanks, guys. When I said "I'll leave the box off until then", I meant that I was going to leave the power disconnected until I replace the thermal paste. Hopefully, I didn't do any damage during the time that it was running with just the heatsink and the disturbed thermal paste. It was still running fine when I turned it off.

Kind regards,
Justis