Thermal Paste Comparison, Part Two: 39 Products Get Tested

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Calculatron

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"pump out" ? - http://www.nordsonefd.com/images/comp300.jpg

 

maestintaolius

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Conductivity is a bulk property that is not pressure dependent. However, the overall thermal resistance in application is going to be pressure dependent as it will be effected by the final bondline thickness and the interfacial resistances. It doesn't surprise me that it's not readily available as there's no official standard, usually a D5470 capable machine is used in a pressure control mode and the resulting interfacial resistance is recorded. We will typically run a pressure vs thermal resistance spectrum starting at 10 psi and ending at 500 psi.

I'm also not suggesting they're nonnewtonian, I'm flat out saying it. The silicones used in TIC greases are newtonian and not typically crosslinked, but the filler level is so high that they rapidly lose their newtonian behavior, particularly once you get to bondline. Highly filled materials have very large wall slip issues (which may give the appearance of newtonian behavior in capillary or parallel plate rheometers and makes for nice data sheet values) and once your gap becomes on the order of 10x the largest filler particle size, particle-particle interaction comes into play causing a further deviation from newtonian behavior. Below a gap of 5x your max filler size, particle-particle becomes a dominating contributor to rheological behavior and typically pressures become extreme at 2-3x which ultimately limit your minimum bondline thickness.

Usually, when you see a viscosity quoted on a data sheet is a value taken off a brookfield using a particular spindle at a particular RPM (T-F @ 20 RPM is pretty popular), its should never be assumed that the visocosity is newtownian.
 

maestintaolius

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You don't even have to go that far, once you start getting over 10 volume percent filler newtonian models start to break down depending on filler geometry.
 

maestintaolius

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Actually, its not correct to say they don't evaporate, depending on the type of silicone used there can be a substantial volatile portion. Vapor phase migration of silicones is a major concern for a lot of customers, particularly ones with optical connections and hard drive manufacturers. One of the ways to improve performance of a grease is to increase filler loading, but that increases viscosity, which usually prompts using a lower molecular weight silicone with a lower base viscosity to make the grease usable. I've seen greases that used silicones that were 8% volatile by mass, any silicones below D20 or L20 can, and will, undergo vapor phase migration. Silicones can be stripped of these lower molecular weights using distillation methods, but that makes them much more expensive and they're not available to retail consumers.

Liquid phase migration takes many forms, settling/separation and bleed are two dominate forms. Bleed is typically what you'll see when you dispense some grease on a surface and you can come back a day later and see a hazy halo surrounding the bead. Separation and settling can occur based more on filler loading, geometry and types of filler used. Settling happens a lot in greases because bondline is what dominates grease performance which means small fillers, which means low filling ratios (to hit a target usable viscosity) which means there will be settling. If you have a lot of fillers (like you do in gels and pastes) the fillers will interact with each other and slow or stop settling. Also, the lower the visocity of the resin, the more likely separation can occur.

Bleed, well, bleed happens with everything, pads, gels, greases, all of them bleed to various degrees and for various reasons. Bleed has been something I've been working for about 7 years now and could end up writing a book concerning it.

Pump-out is a kind of phenomena that occurs commonly with thin bondline applications and can be affected by liquid and vapor phase migrations. Generally, what happens is the TIM starts to separate (but separation isn't necessary for pumpout to happen), creating regions of higher and lower viscosities, then the system turns on and the gap changes shape due to thermal expansion, then, as a result, the TIM moves and some parts move more than others due to the different viscosities, then the system turns off and things change again. If the TIM was perfectly elastic, it'd return to its start point, but it's not, there's a viscoelastic behavior that basically prevents that from happening. So, what you end up having happen is things with low viscosity (like separated silicones) move more than others and gradually migrate out of the gap, causing a gradual decrease in thermal performance or a 'drying out' of the material. Movement can be from the center outwards, or from thinner gap regions to thicker gap regions. Sometimes to mitigate this people will make greases that harden in the gap (either by curing over time or vapor phase migration) to prevent pumpout, but it does create the risk of increased stresses on solder joints (which are less tolerant to stresses now that everything is lead free and keep getting smaller and smaller) or, the ultimate risk, loss of surface contact, which can result in device failure due to failure of the thermal solution.
 

Maxx_Power

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That is a coherent piece. I think this makes a lot of logical sense. I do observe that silicone rim (only on some compounds I used to use), but not recently, so I must have forgotten about it. Now that you mention it, the pressing action is actually enough to drive the particles out of suspension. Thanks for chipping in! Much appreciated.
 

Maxx_Power

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I see what you are saying. I know that most of the data sheets I have come across states some amount of percentage based evaporation over an amount of time.

As for the Newtonian aspect of the thermal grease, I had no idea the contact zone depth is approaching within an order of magnitude of the average size of the particles suspended in the mixture. I would have guessed the fluid becomes highly non-Newtonian if I had suspected this; it is certainly not an aspect for someone not in the field to be able to easily accomplish by measurement. Although I suppose one could calculate, by measuring average applied drop sizes to estimate volume of paste used, then calculate the final surface area after press-fitting the surfaces, then estimate the thickness by dividing the volume by an average diameter of spread... I now have a better idea why the filler size and quality is an important aspect.

Long story short, thank you very much for chipping in, given that you seem to be in this field.
 

InvalidError

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Or simply use an automatic measurement microscope: spread a test sample on a glass plate, put the plate on the microscope and let the microscope count particles along with statistics about their size.
 

Maxx_Power

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That's a great idea. I actually do have access to some measuring microscopes, I think I'll try that on some samples and take some pictures!

Thanks again!
 

wdmfiber

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It's $6 on newegg.ca, 4 bucks more on the USA newegg.com
Prices at stores change weekly, sometimes daily. If the $4 bucks is killing you; I can help (PM me, I'll mail you some singles).
 
Sep 22, 2013
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Why would you use thermal *adhesive* in a situation where the heatsink has something else (like a bolted mount) to keep it in place?

It makes no sense to test this on a GPU with a cooler held down by screws.

It would make a lot more sense to test it on RAM or other ICs where you can't physically retain the cooler, mostly because this is the type of situation a real user is going to apply this type of solution.

Even Arctic Silver claims the performance of this adhesive vs. standard AS5 is the same.
 
Sep 22, 2013
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Also... I'm surprised you didn't try mayonnaise. Hardware Secrets' paste round-up landed mayo right in the middle on cooling ability. Margarine scored slightly worse than your toothpaste test.
I'm still waiting for the results of peanut butter vs. hemorrhoid cream.
 

InvalidError

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Getting numbers from a dry-run might be tougher than it sounds since the CPU might hit thermtrip during boot and shutdown.
 

youcanDUit

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ooohhh. thank you for being nice and answering as well.
 

shulkman

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I've considered swapping out the fans, but I don't think I'll go for Corsair fans... I was leaning more towards the BeQuiet! fans or Noctua. I'm a little turned off by Corsair. The majority of parts in my build are Corsair components (Case, RAM, Cooler, a couple others) and I believe that they should have included their better fans with their products to begin with, particularly when it comes to the case (600T White). It just seemed a little cruddy to sell items with basic components in order to get the customer to shell out more for quality.
 
Sep 22, 2013
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I'd still like a response to my question asking why you tested thermal ADHESIVE on a cooler that has a secure fastening method.

I'd really like to see it in real-world applications where it would actually be used, like sticking a heat sink somewhere where you CAN'T fasten it in place.
 

FormatC

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It is simple: comparison between adhesive and thermal grease. Normally I use adhesive only for VRM or RAM heatsinks. But it was interesting to know, how performs this adhesive :)

You also can mix the Arctic adhesive with ceramic grease to get a compromise.
 

Raghar

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Where are our favorites. IC Diamonds 7 - scratches your CPU clean. And Indigo Xtreme - would it be compatible with my heatsink and would a hairdryer suffice to force it to melt properly?
 

ITFT

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Can you also compare the Russian made one? It's dirt cheap and pretty decent, so I heard -) Here is the descriptionhttp://www.ulmart.ru/goods/158600#http://ru.wikipedia.org/wiki/%D0%9A%D0%9F%D0%A2-8Also could you add some cheap Chinese ones off the ebay, for the sake of comparison?
 
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