Pro/Forums - View Single Post - Making CU -and AL shiny. How?!

N8 · 10-11-2002, 06:48 PM

I thought about mentioning the contaminants issue, but like I said, "I haven't thought hard enough about the viabililty of doing that to give an opinion at this time."

Now that I have thought about it some more, here is a long-winded response.

It would depend on what suface you were doing the final polishing with. If you were using SiC sandpaper, 600/800/1000/1500/2000 grit, you would certainly be contaminating the AS3 with copper dust, which might not be a bad thing, except you may be increasing the electrical conductivity of the AS3. You would be taking a chance of some of the SiC grit detaching from the paper and getting mixed in as well - not a good thing unless it is one of the very fine grit specs. 1000 grit and finer 'may' not cause any interface problems. The SiC grit doesn't come off very easily unless the paper is very used or old, in which case the bonding adhesive is old and worn out.

If you are just doing the AS3 'polish' on a clean cloth, I don't think that would do anything unless there are some other particles in the AS3 that are harder than copper. I suppose it wouldn't hurt anything if this were done AFTER final cleaning, if you wanted to charge any pores and surface imperfections with AS3. However, you stand the likely chance of getting cloth fuzz and particles on the surface and mixed in with the AS3, which is not good.

If you are finished lapping/polishing your surface, I would clean it with soap and water first, then water, then isopropanol (you can buy 91% stuff pretty easily at the grocery/drug store). Around here you can buy 50%, 70% and 91% isopropanol, the other percentage is usually just distilled water. The higher the concentration of actual isopropanol, the better. If you have acetone, then you can use that as well, BUT I would still do the final cleaning with the isopropanol as it leaves the least amount of surface residue. Acetone evaporates so quickly, it usually leaves behind some spotty residue of what it has dissolved - unless you use a lot of it to ensure removal of all contaminants. It will also leach all the oils and dirt out of your skin and redeposit that onto the surface of what you are holding, so nitrile gloves are useful for copious acetone washing.

You can buy nitrile gloves at almost any drug store/pharmacy these days. They are thin and strong, and pretty damn chemical resistant (you can also use them for cleaning around the bathroom, using bleach, changing the oil in the car, etc.) Acetone will eat through them over time, depends on the quality and thickness of the glove.

You can blow the surface dry with canned air, or a blow dryer as BB2K mentioned. I would not try to blow dry it with your mouth, as you will just be breathing moisture onto the surface.

I usually apply the AS3 with my finger (inside a nitrile glove). I like to put on the nitrile glove(s) and then wash my hands like normal with water and soap (with the gloves on), then dump a bunch of isopropanol on them to clean them off some more, and then let them air dry for a minute or use canned air. They are then very clean and you will not contaminate the AS3 application.

*An important consideration - I know my pieces are very flat, so I only put on a translucent smear of the AS3, so I don't follow the 'AS3 application guide' that they provide. Unless you know for sure, you might not want to follow my AS3 application technique (using the glove/finger.)

I have put things together without any TIM (AS3), and find that since the metal surfaces are so flat and polished, they like to surface weld together. The big problem in doing this that I have found is that I must get the surfaces in the correct and final orientation the very first time I put them together, because if I need to shift them a bit, the surfaces stick together and gall, and I need to repolish or sometimes relap them. If they do stick and gall, they are not flat together across the whole surface anymore, and heat transfer is not as good. I have found that a very very thin layer of TIM (AS3) prevents this. It is somewhat difficult to line every mounting hole up properly and never move/shift the heatsink/waterblock/coldplate around, and a very thin layer of AS3 prevents the galling of the metals during slight alignment changes.

One of these days when I have time to do it, I would like to provide some results of direct interface, super polished and flattened surfaces with TIM vs no TIM. It will take some time.....

10-11-2002, 06:48 PM	#18
N8 Cooling Neophyte Join Date: Sep 2002 Location: Pullman, WA Posts: 91	I thought about mentioning the contaminants issue, but like I said, "I haven't thought hard enough about the viabililty of doing that to give an opinion at this time." Now that I have thought about it some more, here is a long-winded response. It would depend on what suface you were doing the final polishing with. If you were using SiC sandpaper, 600/800/1000/1500/2000 grit, you would certainly be contaminating the AS3 with copper dust, which might not be a bad thing, except you may be increasing the electrical conductivity of the AS3. You would be taking a chance of some of the SiC grit detaching from the paper and getting mixed in as well - not a good thing unless it is one of the very fine grit specs. 1000 grit and finer 'may' not cause any interface problems. The SiC grit doesn't come off very easily unless the paper is very used or old, in which case the bonding adhesive is old and worn out. If you are just doing the AS3 'polish' on a clean cloth, I don't think that would do anything unless there are some other particles in the AS3 that are harder than copper. I suppose it wouldn't hurt anything if this were done AFTER final cleaning, if you wanted to charge any pores and surface imperfections with AS3. However, you stand the likely chance of getting cloth fuzz and particles on the surface and mixed in with the AS3, which is not good. If you are finished lapping/polishing your surface, I would clean it with soap and water first, then water, then isopropanol (you can buy 91% stuff pretty easily at the grocery/drug store). Around here you can buy 50%, 70% and 91% isopropanol, the other percentage is usually just distilled water. The higher the concentration of actual isopropanol, the better. If you have acetone, then you can use that as well, BUT I would still do the final cleaning with the isopropanol as it leaves the least amount of surface residue. Acetone evaporates so quickly, it usually leaves behind some spotty residue of what it has dissolved - unless you use a lot of it to ensure removal of all contaminants. It will also leach all the oils and dirt out of your skin and redeposit that onto the surface of what you are holding, so nitrile gloves are useful for copious acetone washing. You can buy nitrile gloves at almost any drug store/pharmacy these days. They are thin and strong, and pretty damn chemical resistant (you can also use them for cleaning around the bathroom, using bleach, changing the oil in the car, etc.) Acetone will eat through them over time, depends on the quality and thickness of the glove. You can blow the surface dry with canned air, or a blow dryer as BB2K mentioned. I would not try to blow dry it with your mouth, as you will just be breathing moisture onto the surface. I usually apply the AS3 with my finger (inside a nitrile glove). I like to put on the nitrile glove(s) and then wash my hands like normal with water and soap (with the gloves on), then dump a bunch of isopropanol on them to clean them off some more, and then let them air dry for a minute or use canned air. They are then very clean and you will not contaminate the AS3 application. *An important consideration - I know my pieces are very flat, so I only put on a translucent smear of the AS3, so I don't follow the 'AS3 application guide' that they provide. Unless you know for sure, you might not want to follow my AS3 application technique (using the glove/finger.) I have put things together without any TIM (AS3), and find that since the metal surfaces are so flat and polished, they like to surface weld together. The big problem in doing this that I have found is that I must get the surfaces in the correct and final orientation the very first time I put them together, because if I need to shift them a bit, the surfaces stick together and gall, and I need to repolish or sometimes relap them. If they do stick and gall, they are not flat together across the whole surface anymore, and heat transfer is not as good. I have found that a very very thin layer of TIM (AS3) prevents this. It is somewhat difficult to line every mounting hole up properly and never move/shift the heatsink/waterblock/coldplate around, and a very thin layer of AS3 prevents the galling of the metals during slight alignment changes. One of these days when I have time to do it, I would like to provide some results of direct interface, super polished and flattened surfaces with TIM vs no TIM. It will take some time.....