Substrates and Packages for Integrated Circuits

Substrates and packages for integrated circuits (ICs) constitute the largest application for ceramic insulators. The following properties are required  

Three ceramics are usually used for this application  

Alumina ceramics dominate, but there are important reasons why BeO and AIN are used in certain applications. Table 30.11 compares the properties of these three 

AIN has a theoretical thermal conductivity of 320 W m K and values as high as 285 Wm K have been experimentally measured for single crystals. Commercial AIN substrates are available with a thermal conductivity up to about 200Wm K at room temperature. The thermal expansion of AIN (3.9 x 10 K ) from room temperature to 500 K is very similar to that of silicon (3 x 10 K ) over the same temperature interval, which helps to avoid cracking due to thermal misfit stresses between substrate and device. This consideration is particularly important for large silicon chips. AIN also does not have the inherent toxicity problems associated with BeO. 

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Alumina ceramics are widely used for thick-film circuit substrates and for integrated circuit packaging. This aspect is discussed in Section 5.5.5. 

Another important low-permittivity, low-loss ceramic is alumina. Alumina has such an excellent combination of good mechanical properties, high thermal conductivity, and ease of metallization that it is widely used today for thick-film circuit substrates and integrated electronic packaging. 

The method of deposition is what differentiates the hybrid circuit from other packaging technologies and may be one of two types thick film or thin film. Other methods of metallizing a ceramic substrate, such as direct bond copper, active metal brazing, and plated copper, may also be considered to be in the hybrid family, but do not have a means for directly fabricating resistors and are not considered here. Semiconductor technology provides the active components, such as integrated circuits, transistors, and diodes. The passive components, such as resistors, capacitors, and inductors, may also be fabricated by thick- or thin-film methods or may be added as separate components. 

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