A cooler isn’t one blob of grey goo. The CPU or GPU die sits higher than the memory chips, the power stages, the SSD. The factory fills those gaps with a pad or putty of a chosen thickness so one metal plate can touch all of it. Paste goes on the high spot. Pads go in the gaps. Treat every surface like a CPU and you’ll either crush a chip or leave it sitting in air. I’ve done the post-mortem on both.
What each material is for
| Material | Where it belongs | What it is not for |
|---|---|---|
| Thermal paste (grease) | CPU / GPU die, or a desktop CPU heat spreader (IHS) | Filling a 1mm air gap over VRAM or a VRM. It will squeeze out and the plate will not sit on those chips. |
| Thermal pad (sheet) | VRAM, VRM/MOSFET, chipset, some NVMe plates, some RAM heat spreaders | The CPU die. A pad on a die is a blanket. Temps go up. |
| Thermal putty | Mixed-height VRAM and VRM on a GPU or laptop plate | A substitute for mounting pressure. Putty still needs the cooler screwed down evenly. |
| Liquid metal | A known die with a compatible cooler, by people who will clean a spill | VRAM, aluminum plates, a first laptop job, anything you cannot keep level. |
| Phase-change sheet (PTM-style) | Some laptop CPU/GPU dies as a factory or enthusiast swap | VRAM gaps. It is a thin die interface, not a pad. |
Those “12.8 W/mK” numbers on Amazon are often fiction. I buy a known paste and a pad with the thickness printed on the pack. Thickness is what actually kills chips. Softness next. Color doesn’t matter.
Where you will actually find this stuff
- Laptop CPU and GPU: paste (or a thin factory pad/PTM) on the silicon. One heatsink usually covers both.
- Around that die, on the same plate: pads on VRAM (especially discrete GPU laptops) and on VRM power stages.
- Desktop CPU: paste on the metal heat spreader. You are not putting paste on the motherboard.
- Desktop GPU: paste on the GPU die. Pads or putty on VRAM and VRMs. Some cards also pad chips on the back of the board, under a backplate.
- NVMe SSD: a pad or a copper sticker between the NAND/controller and a motherboard heatsink or the laptop shield. Some drives already have a pad on the label side.
- Chipset / PCH: a small pad under a motherboard or laptop shield.
- Laptop memory: SODIMMs almost never get paste. A few machines put a pad on the module under a plate. Do not grease a stick of RAM.
- Power supply: there are pads inside. You do not open a PSU to “repaste” it.
Memory (VRAM) is the one people ruin
VRAM sits lower than the GPU die. Factory cooler: thin paste on the die, thicker pad on the memory (often 1.0 / 1.5 / 2.0 mm, sometimes putty). Scrape the pads and paste the memory and the plate bottoms out on the die. Never touches the chips. GPU looks “fine” in a screenshot. Memory cooks. Then artifacts, crashes, dead card. I’ve seen that one more than once.
Other way around happens too. Pad so thick on the VRAM that the plate can’t sit on the die. CPU/GPU temps go stupid and you blame the paste. Peel the extra. Die has to make contact first, thin film of compound. Everything else is just filling gaps around it.
- Match the old pad’s thickness. If the old pad is ruined, measure the gap with the cooler mock-fitted, or read the thickness printed on the leftover pad.
- Do not stack three random scraps to “make 1.5 mm.” Stacks shift and dry into a step.
- Cut pads so they cover the chip, not the tiny resistors and solder balls next to it. Overhang onto a power stage the factory left bare is how you get a short if the pad is even slightly conductive — and some cheap “carbon” pads are.
- Putty is allowed on mixed-height VRAM/VRM if you use a non-conductive product and keep it off connectors. It is not toothpaste.
VRMs, chipsets, and the SSD plate
Power stages (those square MOSFET blocks near the CPU or GPU) dump heat into the same plate through pads. Machine throttles only under CPU+GPU load, fan’s clean? Sometimes it’s a dried VRM pad, not “the paste dried.” Same thickness, same spots. Don’t paste a VRM and hope. The gap is too big.
NVMe is the quiet one. Laptop shield or a motherboard heatsink often has a pad. Too thick and you bow the drive in the socket. Random disconnects. Drive “dies” after a CPU repaste. Too thin or missing and the controller hits 80°C+ on a long copy. Factory had a pad? Same thickness back. Drive already has a pad on it? Don’t add a second one on the shield unless you know the stack height.
Paste jobs that fail without the paste being “bad”
| What happened | What you will see | The actual fault |
|---|---|---|
| Rice-grain of paste on a big laptop die | Hot spots, throttle after a few minutes | Dry corners. The cooler never wet the whole silicon. |
| Painted a thick mosaic with a card | Mess, sometimes worse temps | The layer is too thick. The cooler is supposed to spread a pea or a thin line. |
| Forgot a standoff or a spring screw | Temps like the cooler is off | It is. Uneven pressure beats any compound. |
| Reused a dried pad | VRAM or VRM much hotter than before | Pads take a set. Once they have been crushed and cooled, they do not spring back. Replace them. |
| Liquid metal on an aluminum plate or a tilted laptop | Short, no boot, stained metal | Gallium eats aluminum and it moves. Do not. |
| Household toothpaste / “thermal paste” with metal flakes on a bare die next to components | Immediate failure or a short later | Conductive junk on a live board. Use a known non-conductive paste. |
| Pad on the CPU die “because thicker is better” | Immediate thermal throttle | You insulated the thing you meant to cool. |
| Heatsink packed with dust, then a full repaste | Same temps as before | Paste was never the job. Clean first. See the dusty-desktop guide for towers. |
How to put it back without making it worse
- Photo the plate before you wipe it. You want a map of which squares had pads.
- Clean paste with isopropyl 90%+ and a lint-free wipe. Do not scrape the die with a screwdriver. Old pads peel; leftover film gets IPA too.
- CPU/GPU: pea or thin line in the center. Laptop dies are small — less than you think. Desktop IHS can take a line across the spreader.
- Pads: cut to the chip, peel the film, one layer, factory thickness. The cooler’s screws compress them. If you have to force the plate down, the pad is too thick.
- Tighten in a cross pattern, a little at a time. A laptop cooler that clicks on one side first will pump paste out the other.
- First boot: watch CPU and GPU temps under a real load (a game, Cinebench, a long encode). If the die is 20°C hotter than before, you missed contact. Open it. Do not “let it bed in” for a week while VRAM fries.
On the bench
A known non-conductive paste (NT-H1 or MX-4 class)
This is the die stuff. Non-conductive, boring, doesn’t turn into epoxy. One small syringe lasts me years of laptops. You don’t need a no-name 12 W/mK tube.
- Skip liquid metal unless you already know the cooler and the lid metal.
- A 3–4g syringe is enough. A 30g tub is for a shop.
On the bench
Thermal pads with a printed thickness
Buy this after you know the thickness you pulled. A mixed sheet (0.5 / 1.0 / 1.5 mm) is useful on my bench. A “universal GPU pad kit” with no millimeters in the listing is how VRAM dies.
- The number on the packet is the spec. Match it to the old pad, not to a YouTube title.
- Soft silicone pads beat hard cheap foam. If it feels like a mousepad that does not compress, keep walking.
On the bench
Isopropyl 90% or higher
Cleaning is half the job. 70% leaves water on the die. Let 91 or 99 flash off before the cooler goes back on.
- No paper towel grit on a laptop die if you can use a real wipe.
- Power off, battery disconnected on a laptop, before you soak anything.
What not to buy
- Liquid metal as your first laptop compound.
- A 10mm-thick “cooling pad” meant for a hard drive, stuck on a GPU.
- Toothpaste, Arctic-style knockoffs with no datasheet, or “metal” paste for VRAM.
- A replacement GPU because temps were high and you have not seated the cooler yet.
Verdict
Paste on the die. Pads or putty in the gaps. Copy the thickness you pulled. VRAM and VRMs fail when you treat them like a CPU. If the plate doesn’t sit flat on the silicon first, nothing else you bought will matter.