Best method to apply TIM (Artic Silver, etc) to GPU heatsink?

[DeathAndTaxes]

So while I wait to go to the inlaws for Turkey day I decided to replace a "noisy" fan on 5970 (reference design, 1st gen, ATI)
By "noisy" I mean periodically screaming like the fan shaft was binding.  

First observation is ATIs quality control sucks.  Two components (not RAM or GPU) had no thermal paste.

Second observation is the the heatsink surface is horrible.   Very very low quality.  Kinda hard to believe low quality when you consider this card is a fist gen reference so when it was built the selling price was $699.

Third observation is whatever generic garbage TIM (thermal interface material) AMD used for the GPU is crap.  Very thick, "pastey" and almost "chunky".  It appear to be overly thick and reducing conductivity between GPU and heatsink.  Granted it is now almost 3 years old but it was applied very sloppily (some dripped across PCB and onto RAM thermal pad). 

So I replaced the fan, cleanup the the heatsink, added missing thermal pads.

Got three questions for anyone who has replaced TIM on GPU.
1) Has you ever lapped a GPU heatsink.  I never lap CPU heatsinks because generally speaking the quality is pretty good and I think any sanding would be likely negligble improvement.  This heat sink is such a POS I am actually considering lapping it (and maybe all 15 5970s).

2) What TIM do you use?  I have always used Artic Silver for CPU.  Been using it since they started making it.  However not sure if it is the best for GPU?

3) What is the best way to apply TIM do you think.  Generally speaking there are 5 ways to apply TIM
   a) use credit card and try to apply an thin even layer
   b) same as a) but plastic bag on finger
   c) apply a thin line allow heat sink pressure to spread it out
   d) same as c) but a single dot in middle of CPU/GPU die (method advised by Artic Silver)
   e) same ad d) but 4 dots in square on the die.

[godofal]

there's this utube vid that really clearly shows that the center dot method is the best for a CPU
that being said, a GPU is different from a CPU in the sense that it doesnt have a heat-spreader
the dot method is best on a CPU becouse the actual die is alot smaller than the heat-spreader, so if you're missing some edge-room, its not a big deal

i wouldnt ever use the creditcard/plastig bag thin layer method though
maybe 4 smaller dots are the best in this case; more area affected is more important than wich area in this case

you could ofcourse try both methods, see how much you need and how it spreads. just take care when taking off the cooler

lapping the heatsink would be *very* hard i'd imagine, and if you screw up you're alot farther away from home than you are right now
personally i wouldn't do it

if you won't lap the cooler, AS is the way to go: after a burn-in period it cools alot better since it fills the tiny little gaps in the metal better
if you do lap it, arctic cooling might be better (don't know for sure though)
but even if there is any difference, i would imagine it being really small (<1 degree) so i'd go with whatever you have lying around

[RyNinDaCleM]

You can't lap the GPU heat sink if it has solid/rigid mount. Most I've seen are! If you do, and it is rigid mount, then you will have a gap between HSF and GPU die.

Arctic Silver is awesome, but do remember it is conductive. A ceramique TIM is often considered a better option for a GPU, since it is not conductive, and there are a lot of transistors around the die. The effectiveness between the two is negligible.

I always put a dot 1/3-1/2 the size you would do on a CPU, in the center of the die. Method d)
Don't use too much or it will insulate more than conduct heat.

[SlaveInDebt]

Lapping would be difficult and the gains not worth while.

TIM for non-IHS gpu's (ATI/AMD) I prefer a thin layer of AS5, OCZ freeze, or MX-2 and use a credit card to spread.

[vapourminer]

artic silver requires several warmup/cool down cycles to set properly. not something Id think you want to do with a mining rig; you just want to turn it back on and walk away.

I have used artic cooling MX2 the last few video cards. better temps than AS5, very easy to work with, no cure time.. just works. I applied in a "X" shape as it seemed to give the best coverage, the dot bit did not give 100% coverage (the occasional corners didnt get it) or it was too much and I had extra that pushed out the sides.

I wouldnt lap a GPU HS, the mounting mechanisms are different from CPUs. they look a lot less tolerant to height changes.

[jjshabadoo]

Never heard of anyone lapping a GPU on other overclocking forums I frequent. I'd advise against it as well. I use shin-etzu on GPU's and it works GREAT. I also use a + or X method as the poster above stated. When I've pulled the covers off after, it is usually spread fairly evenly. The shin-etzu typically gives me 2-3c better than the arctic brand, I've used silver and mx-5. I've heard MX-2 is the best of the arctic compounds for GPU's.

The credit card thing is just a great way to waste TIM in my opinion.

[plastic.elastic]

Actually against anyone's believe the application of TIM to a die core do requires manually thin layer of spreaded compound. The problem is its not easy to do and more than often ppl mess up hence they tend to believe its not a optimal method.

The dot method is not recommended at all for a bare die surface

Any method with multiple dots will allow bubble to be formed. As the heatsink base touches the die, the compound will be spreaded from multiple direction and air can be trapped.

I also advice against using AS5, its extremely hard to spread on a die, its thick and you will tend to over apply it.

The best TIM for die application is IC diamond. But for economical reason, AC MX-2 is very good.

[malevolent]

 I never lap CPU heatsinks because generally speaking the quality is pretty good and I think any sanding would be likely negligble improvement.  

Untrue.
Lapping cpu heatsinks can lower temperatures by 7-10 degrees, lapping IHS (especially if it's not flat) will lower temp. by another 5-10.
But you have to be very patient while doing this.