Tungsten Heat Sink Solutions for Advanced Thermal Management

A tungsten heat sink is the thermal management solution for applications where the combination of extremely high heat flux, precise thermal expansion matching to semiconductor materials, and dimensional stability at operating temperature pushes copper and aluminium heat sinks beyond their capability. Tungsten, and particularly tungsten-copper composites, occupies a specific niche in advanced thermal management where these property combinations are required simultaneously.

Why Tungsten for Thermal Management

Pure tungsten has a thermal conductivity of approximately 170 W/mK, lower than copper’s 400 W/mK, but its other properties make it valuable in thermal management applications where copper’s thermal expansion coefficient is a limitation.

Tungsten’s coefficient of thermal expansion (CTE) is approximately 4-5 ppm/K, close to the CTE of gallium arsenide (GaAs), indium phosphide (InP), and silicon carbide (SiC) semiconductors. Copper’s CTE of 17 ppm/K is far higher than these materials. When a heat sink is bonded to a semiconductor die, the CTE mismatch between the heat sink and the semiconductor generates thermal stresses during temperature cycling. If the mismatch is large, these stresses can cause cracking of the die or failure of the bond interface over time.

For compound semiconductors used in high-power RF applications, laser diodes, and power electronics, tungsten heat sinks and tungsten-copper composites provide better CTE match to the semiconductor material than copper, extending device lifetime and improving reliability.

Tungsten-Copper Composites

Tungsten-copper (W-Cu) composites are the more common commercial form for heat sink applications. These composites, typically in the range 70-90% tungsten by weight, are produced by infiltrating a porous tungsten skeleton with liquid copper. The resulting material combines the low CTE of the tungsten skeleton with a thermal conductivity significantly higher than tungsten alone, due to the copper filling the pore spaces.

W-Cu composites can be tailored in composition to adjust the balance between CTE and thermal conductivity, allowing the designer to optimise the thermal management solution for a specific semiconductor package.

“Precision thermal management is the discipline that allows high-power devices to operate reliably at their design limits,” said EDB’s director of electronics manufacturing at an advanced packaging forum. Tungsten heat sinks and W-Cu composites are the materials that deliver that precision in the most demanding applications.

Applications

Tungsten heat sink components are used in:

• High-power RF transistor and amplifier packages, where GaAs or GaN on SiC semiconductors produce heat fluxes that require efficient removal and where CTE matching to the semiconductor substrate is essential for reliability.
• Laser diode packages, where the thermal resistance of the mounting determines the operating temperature and lifetime of the laser diode and where CTE mismatch can cause facet damage over thermal cycling.
• Power electronics modules, where wide-bandgap semiconductors including SiC and GaN operate at higher power densities than silicon and require effective thermal management with matched CTE.
• Microwave module packaging in defence and aerospace applications, where operating environment temperatures span a wide range and reliability over thermal cycling is a design requirement.

Manufacturing Tungsten Heat Sinks

Precision tungsten heat sinks are manufactured by powder metallurgy methods, including pressing and sintering of tungsten powder, or through MIM for complex geometries. W-Cu composites are typically produced by infiltration of a sintered tungsten skeleton. Finished heat sinks are machined to final dimensions and flatness specifications required for reliable bonding to the semiconductor package.

AMT Tungsten Heat Sink Manufacturing

AMT produces tungsten and tungsten-copper heat sink components for high-power semiconductor packaging applications through its powder metallurgy and precision machining capabilities. Their manufacturing quality systems support the dimensional and material specifications required for reliable advanced thermal management components.