Improving CPU and GPU Cooling Efficiency: From Thermal Paste and Phase-Change Materials to the Classic 1mm Copper Shim Mod for Laptop GPUs

Whether building a desktop PC or using a laptop long-term for heavy computing, 3D gaming, and video editing, the nightmare most PC enthusiasts fear is the fan howling at full speed, the processor hitting the thermal wall and throttling (thermal throttling), or even an unexpected blue screen or instant black screen — the “thermal crash.”

When a computer shows poor cooling, most people’s first reaction is: “Is the thermal paste dried out? Just take it apart and reapply!” Then they squeeze out a big blob of thermal paste and spread it over the entire heat spreader like butter on toast.

However, many people don’t know: thermal paste is by no means “the more the better,” nor is it the main contributor to CPU cooling. Applying it incorrectly, or mistakenly using a conductive medium, will at best halve cooling performance and at worst directly burn out the motherboard and graphics card core!

This article starts from the physics of heat conduction, walks you through the characteristics of various thermal interface materials, and revisits the most classic “GPU-failure copper shim mod miracle” in laptop repair history.

Debunking the Myth: Thermal Paste’s Real Job Is to “Squeeze Out Microscopic Air,” Not to Cool Actively

Thermal interface materials from various brands have many colloquial names: thermal paste, thermal grease, thermal glue, and so on. Many beginners mistakenly believe thermal paste itself has powerful cooling ability, or even think that removing the heatsink and relying on thermal paste alone can dissipate heat.

This is a serious physical misunderstanding! A metal heatsink’s heat conduction is dozens of times stronger than any top-tier thermal paste!

Let’s look at the thermal conductivity (in W/m·K) of common materials at room temperature:

• Pure copper (heatsink fins and heat pipe base): about 390 ~ 401 W/m·K
• Pure aluminum (budget heatsinks): about 200 ~ 237 W/m·K
• Commercial high-end thermal grease: usually only about 5 ~ 14 W/m·K
• Still air (an extremely poor thermal insulator): only about 0.026 W/m·K

From the data it’s clear that a pure copper base conducts heat dozens of times more efficiently than top-tier thermal paste. So why not just press the CPU’s metal heat spreader directly against the heatsink’s metal base, instead of applying a layer of thermal grease?

The reason is: the air insulation barrier at the microscopic contact surface.

No matter how precisely metal is machined, the integrated heat spreader (IHS) on top of the CPU and the copper base of the heatsink are, under an electron microscope, actually covered with countless invisible pits, tiny gaps, and metal burrs. If pressed together dry, the actual physical contact area between the two metal surfaces is often less than 10%–20%, and the rest is filled with “air microbubbles” with a conductivity of only 0.026, forming a solid insulating layer.

At this point, the sole mission of thermal grease is: to use its flowability to fill all the microscopic pits, squeeze out the air molecules that block heat dissipation, and build a heat-conduction bridge between metal and metal.

The iron rule of application: the thinner the better, even and bubble-free! As long as the microscopic depressions are filled, the thinner the thermal paste layer, the shorter the heat conduction path. If you apply a thick layer (say over 0.5mm), you’re effectively inserting a poorly conducting insulating layer between the CPU and heatsink, and the temperature will surely soar!

Common Thermal Interface Types and the Deadly Short-Circuit Landmine

When choosing and replacing thermal materials, the market commonly offers the following media, whose physical properties and dangers differ greatly:

1. Traditional Silicone Thermal Grease

Silicone oil-based, mixed with fine powders such as zinc oxide, aluminum oxide, or boron nitride.

• Pros: excellent insulation, completely non-conductive, high tolerance for application errors — even if excess overflows onto nearby circuit boards, no short circuit occurs. The first choice for DIY beginners.
• Cons: under repeated severe thermal expansion and contraction at high temperatures, silicone oil separation and drying into powder easily occur after one to two years.

2. The Deadly Risk of Metal-Powder Grease and Liquid Metal

Some extreme-performance thermal pastes add metal particles such as silver powder, or even use gallium-indium alloy “liquid metal” (thermal conductivity up to 70+ W/m·K).

• Deadly short-circuit crisis: these media are highly conductive! If the amount applied isn’t precisely controlled, when the mounting bracket is tightened under high pressure, any overflowing paste that flows into contact with the exposed resistors and capacitors (SMD components) around the CPU/GPU die will trigger a violent arc short circuit the instant the machine powers on, directly burning through and destroying the motherboard chipset and graphics card core!
• Metal corrosiveness: liquid metal contains the metal “gallium,” which undergoes a violent gallium amalgamation reaction with the “aluminum” in heatsinks, and within days can completely corrode a hard aluminum heatsink base into loose powder. Therefore liquid metal must absolutely never be used with aluminum-based heatsinks.

3. Thermal Pad

Commonly found between graphics card VRAM, power-delivery MOSFET modules, and M.2 SSD heatsinks. Mainly used to fill larger physical gaps between components (usually