Liquid Metal TIM Solidifies on Copper Over Time, Not Drying Out

Liquid Metal TIM Behavior Over Time

Hardware enthusiast der8auer conducted a two-year study on liquid metal thermal interface material (TIM) using an electron microscope. The study found that the TIM, an alloy of gallium and indium, does not dry out as commonly believed. Instead, the gallium reacts with copper to form a solid compound, CuGa2.

Impact on Thermal Conductivity

The formation of CuGa2 significantly alters the TIM's performance. While copper has a thermal conductivity of approximately 400 W/mK, CuGa2 is rated at about 100 W/mK, roughly one-quarter of copper's conductivity. This reduction in heat transfer capability can affect the long-term cooling efficiency of components where liquid metal TIM is applied to copper surfaces.

Reaction Mechanism and Material Compatibility

The reaction involves gallium bonding with copper in a 1:2 ratio (one copper atom to two gallium atoms), with leftover indium and tin forming other solid areas. This solid layer grows approximately 1 micrometer per day until it reaches 50 to 100 micrometers. The study also highlighted that liquid metal reacts differently with other materials; for instance, it quickly makes aluminum brittle by traveling along grain boundaries once the oxide layer is compromised. Nickel plating on copper can reduce the thickness of the reaction layer by about 10 times.

Implications for High-Performance Hardware

As heat density in components like GPUs (e.g., RTX 5090 and RTX 5080) continues to increase, the long-term stability and performance of TIMs become more critical. The solidification of liquid metal TIM on copper suggests that while it offers initial superior thermal performance, its effectiveness can degrade over time due to the formation of less conductive compounds. Once formed, CuGa2 remains solid up to 254 degrees Celsius and cannot be re-melted.