Heat Spreaders Made from Molybdenum and Molybdenum Alloys

In the electronics industry, aluminum and copper are widely employed as contacts and heat sinks since they are good conductors of heat. However, these materials exhibit high coefficient of thermal expansion, which is a major drawback. Owing to this factor, they cannot be used as a base plate material for semiconductors that are subjected to considerable thermal loads.

Refractory Metals: Tungsten and Molybdenum

Tungsten and molybdenum are refractory metals that can be used as the base material as they have low coefficients of thermal expansion. In fact, these materials have been utilized in power transistors for a number of years. Moreover, copper, tungsten and molybdenum-based composite materials have been designed for applications that require high thermal conductivity. These composite materials have copper content that can be modified to adapt the base plate’s thermal properties to the entire assembly. Since molybdenum-copper composites are lightweight, they are ideal for those applications where every gram is important. In the automotive industry, for instance, the composites are utilized as carrier plates in the IGBT modules. These modules function as inverters in electric drives.

When compared to pure molybdenum, copper-molybdenum composites can significantly increase the thermal conductivity of base plates. This sort of laminates can be used as base plates for high-frequency amplifiers employed in mobile radio base stations.

Composite Materials

Laminates made of WCu, MoCu, Cu-Mo-Cu and Cu-MoCu-Cu are capable of dissipating heat in electrical components and also aid in cooling LED chips, RF packages , IGBT modules etc. Composite materials from PLANSEE combine the superior thermal conductivity of copper and the low thermal expansion of tungsten and molybdenum. The composition of these materials has been optimally designed to fulfil the needs of GaAs, silicon and GaN-based semiconductor materials.

The Cu-MoCu-Cu laminates from PLANSEE are suitable for applications requiring high performance. The 3-layer composite, Cu-MoCu-Cu, is manufactured from MoCu and is plated with pure copper. The Cu-MoCu-Cu laminate is prepared with a thickness ratio of 1:4:1 between layers. Therefore, superior heat spreading and dissipation can be realized in LDMOS transistors and other applications having high power densities.

The coefficient of thermal expansion in PLANSEE’s thermal management products is equal to that of semiconductor materials. When the carrier material and semiconductor exhibit different thermal expansion behaviours, mechanical stresses can arise during operation or during the manufacture of semiconductor modules. This can impair the semiconductor and result in device failure.

Material
(wt%)

Density at 20°C
(g/cm3)

Thermal coefficient of expansion
(ppm/K)

Thermal conductivity at 20°C
(W/mK)

Mo

10.2

5.5

142

W

19.3

4.5

165

Mo-15Cu

9.9

6.7

170

Mo-30Cu

9.7

7.5

195

Mo-40Cu

9.6

8.7

215

Mo-50Cu

9.5

9.9

250

W-10Cu

17.1

6.4

195

W-15Cu

16.4

7.3

215

W-20Cu

15.5

8.3

235

Cu/MoCu/Cu laminates

~ 9.4

7.0-10.0

170-280

For the electronics industry, PLANSEE provides heat spreaders with a wide range of coatings. These coatings help in protecting the materials from corrosion and act as an ideal interface between the heat sink and the semiconductor. With Molibdenos y Metales (Molymet) and Global Tungsten & Powders (GTP), the PLANSEE Group covers all stages of tungsten and molybdenum processing, ranging from powder production and powder-metallurgical procedures to serving clients with customized and semi-finished components.

This information has been sourced, reviewed and adapted from materials provided by PLANSEE.

For more information on this source, please visit PLANSEE.

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