Properties of Material Used In Electronics

Many materials are required for today's electronics and electronics systems.  In thermal management we need to consider how all these properties affect the system not only during power cycling during the service life, but also in the assembly and testing.

Thermal Conductivity and Coefficient of Thermal Expansion are the most common considered in power electronics.  But the careful design engineer must also consider the weight (density), strength and stiffness too as these have an influence in system reliability.  

Figure 1: CPS AlSiC Products Illustrating Design Functionality

Other considerations, that are not material properties, are what is the materials capability to be fabricated into something that is useful and design capabilities to hold the necessary dimensional tolerances.  These issues will be discussed in the applications in later posts.  Figure 1 shows a wide range of AlSiC products illustrating design functionality.

Figure 2 is a table of physical properties for common materials used in electronic assemblies and their material properties.


I have color coded this chart with the light blue for the packaging materials commonly used.  AlSiC-9 and AlSiC-12 are on top.  AlSiC-9 is applicable for direct mounting of die and ceramic substrates.  AlSiC-12 is good for microprocessor lid assemblies that are mounted on FR-4 boards.


Also included are materials like Copper and Aluminum.  Copper is used in Low power IGBTs.  I can be lower cost since the material is stamped.  Aluminum is used as a low cost heat sink. It also can be stamped but most commonly extruded to have fins for extended surface area for convective or forced air cooling.  The drawbacks of these materials is that both have very high CTE values which will not match that of the electronic die materials (Green) or the substrate materials that are used for electrical isolation.  

Figure 2:  Physical Properties of Materials used in Electronic Systems

Copper Molybdenum (CuMo) and Copper Tungsten (CuW) are considered thermal management materials because they have CTE values that are compatible with the electronic materials and substrate materials.  Both these materials have been used extensively in the military and aerospace industry in hermetic packaging because of the CTE thermal management reliability required in these systems.  The draw back of these materials is that the material is more expensive, it is expensive to machine (most parts are consequently flat) and they are heavy (high density).  They high density is not desirable in weight sensitive aerospace applications or where shock and vibration are a consideration.


In contrast AlSiC materials are thermal management materials having a good thermal dissipation and CTE that is compatible with the electronics and dielectric substrates.  Additionally these materials are light weight, and the fabrication technology allows for functional shapes to be considered. 

Electronic materials are in green contrast in this table.  The notable properties of these materials is that they have very low CTE values and that they have very low fracture strength.  The low strength means that the design engineer really needs to be cognizant of thermal stresses that may be induced during power cycling, and at operation temperatures.


In yellow are some common dielectric substrate materials.  These materials are used for electrical isolation the electronics to the rest of the world.  Their strength and CTE values are relatively low.  So choosing choosing compatible CTE values is necessary when considering heat sink attachment.  

Usually these dielectric materials are metallized with a very thin (~ 300 µm) Copper layer that provides electrical connection between devices and also a solder or braze Cu attachment surface on the side opposite to the electronics to integrate these substrates with a heat sink.  These copper layers are attached by an activated attachment process called Direct Bond Copper or DBC. DBC substrates are commonly used in IGBTs.   In IGBTs the CTE of the assembled materials is very important.


for more information please visit CPS at www.alsic.com.