Thick Film Materials (Substrate)

The majority of substrates are ceramic for their mechanical strength, electrical resistivity over broad range, thermal conductivity and chemical inertness.  Alumina has become the most widely used because it to has an excellent combination of all these properties.  The 96% Al₂O₃ composition has become an industry standard and is used in 90% of all circuits.  The 4% impurities are selected to accomplish complete densification without grain growth and to maximize electrical properties.  The most common additives are magnesia and silica.  Magnesia inhibits grain growth of alumina crystals and silica is used to form a glassy matrix with alumina that binds the system together.


For high frequency application, ultralow-loss alumina substrate is made by eliminating the glassy phase. This is accomplished by sintering 99.5% pure Al₂O₃ at 1800-1900°C to form high-purity dense substrate.

New substrate materials continue to appear, including ‘porcelainised steel’ (vitreous-enameled steel), organic materials such as epoxies, flexible substrates, and even synthetic diamond.

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