cure time of thermal paste and lapping?

[smokewarlock]

i just got my artic thermal compound(ceramice).... and i noticed in a reveiw it says it needs about 12hrs of cure time to set in ...is the cure time the time the paste needs to dry set before running system or cure time before you overclock it or run system at all?

my temps are 40c now...should i lap the heatsink before applying compound? it does have some noticeable groves of swirls....and would this improve lowering temps...would i have to lap the cpu as well...since thermal compound has been applied to it previously?..

and can i clean it with rubbing alchol with out hurting the cpu..i have read that this is used to clean ...but would it hurt it to clean the not contact area(the green area on my cpu)?

thanks in advance to advice and input.

 

[jhurst]

The "cure time" refers to the time it takes for the compound to make the most contact with the CPU and HS. When you first the HS on, it is not making as good of contact as it will after a few times of heating/cooling/heating/cooling. Don't worry too much about this IMO, I think the set in time is a bit overrated. Overclock if you want.

Yes, you should lap the HS before applying compound. Then, when you are done lapping, apply a thin layer of compound, rub it around on it, and then wipe it all off. You may ask why do this, well when you rub it on there, you are filling in the microscopic pores in the metal (that didn't get lapped), and then you are wiping off the compound so that the maximum amound of surface area is touching the CPU.

Yes, you can clean the CPU without hurting it. I have even heard that it is safe to dip your CPU into soap/water, but I would just recommend using alcohol to clean it off. Alcohol also evaporates very quickly and cleanly, so don't worry about if you get it on the green silicon part.

 

[wkwong]

i dont know about wiping all your thermal compound off. specially after lapping it.

when you lap it manually, theres a good chance the the surface would be smooth, but not straight. wiping all the excess thermal compound might result in parts of the cpu not touching the base of the heatsink.

i am not saying put a giant glob of compound on your cpu, but u should rub it around with the tip of the tube, and make it as thin as possible that way. the pressure of the heatsink will push the remaing excess compound out of the way and into areas that arent lapped evenly.

 

[smokewarlock]

so if i lapp the heatsink it will not be flat..even if i use a flat surface to lap it i had planned on using a sheet of glass to lap it on figuring that it would be a relatively flat surface to avoid the sink becoming uneven.....

in using the glass surface ...you still reccomend leaving the thermal compound on the heatsink and the cpu?

 

[oldman420]

lapping will make it flat thats the whole idea flat and smooth. and yes a little dab on the hsf rub it in good and wipe off exess you will see the compound filling the micro grooves then a little dab on the center of the cpu spread it as evenly as you can then put on the hsf i always wiggle the whole assy gentlt to work the thermal paste evenly across the chip
i have never lapped my hsf and overclock like a fool with no heat problems so lap if you want . bottom line is a good cpu cooler will keep the chip cool without lapping. my cnps 7000 was as smooth as a babys butt.
have fun and watch those temps

 

[smokewarlock]

thanks old man...i see we have the same board...and that you are using three sticks...are you in dual channel...and are they 512 sticks?

 

[jhurst]

Originally posted by: oldman420
lapping will make it flat thats the whole idea flat and smooth. and yes a little dab on the hsf rub it in good and wipe off exess you will see the compound filling the micro grooves then a little dab on the center of the cpu spread it as evenly as you can then put on the hsf i always wiggle the whole assy gentlt to work the thermal paste evenly across the chip
i have never lapped my hsf and overclock like a fool with no heat problems so lap if you want . bottom line is a good cpu cooler will keep the chip cool without lapping. my cnps 7000 was as smooth as a babys butt.
have fun and watch those temps

I got the CNPS7000 and it was smoother than a baby's butt! Zalman does a good job lapping their heatsinks to a mirror finish.

WKWONG: I don't know where you have gotten your information, but everyone says to wipe off excess off the HS. You do not need to put a layer on the CPU, and a layer on the HS, all you are asking for is air getting trapped between the 2. The compound on the CPU ensures that there is no space in between the CPU and HS, it is VERY unnecessary to have two layers of compound.

 

[hifisoftware]

Does lapping help with temps? It seems illogical to me. Heat transfer is a functiono the surface area. Rough surfaces have larger surface area vs smooth areas (given same geometrical area). The difference would be very small of course, but it just seems to me that laping should slow down heat transfer from CPU to heatsink.

If you do not use termal combound of any sort, then lapping will be usefull. Yet in order not to use termal coumpund slopping on both CPU and heatsink has to be the same and it's probably almost impossible to achive.

 

[jhurst]

Originally posted by: hifisoftware
Does lapping help with temps? It seems illogical to me. Heat transfer is a functiono the surface area. Rough surfaces have larger surface area vs smooth areas (given same geometrical area). The difference would be very small of course, but it just seems to me that laping should slow down heat transfer from CPU to heatsink.

If you do not use termal combound of any sort, then lapping will be usefull. Yet in order not to use termal coumpund slopping on both CPU and heatsink has to be the same and it's probably almost impossible to achive.

You are correct about rougher surfaces having larger surface areas, and that larger surface area = more heat transfer. But, since both the CPU and HS are hard, flat surfaces, you get no advantage by having a rough surface. And actually what would happen if you had rough surfaces is that air would get trapped in between the CPU and HS, and air does not transfer heat worth a damn.

And as for compound application, you only put a small drop on the center of the die on the CPU. And that is done just to ensure that a) there are no air pockets trapped and b) maximum surface area touching. The compound should be removed from the HS after applying a thin layer, you just want to fill in the microscopic pores of the HS (which are almost all removed with good lapping).

 

[hifisoftware]

Thanks jhurst. When you metioned air it all made sense. Thanks