Ceramic substrates are widely used in microelectronic techno logy and power systems. At present Cu/Al2O3/Cu bonded components are manufactured but the relatively poor thermal conductivity exhibited by this combination is restricting the development of power electronic systems. Two strategies are available to improve the thermal conductivity of the metal conductor/ceramic insulator/metal heat sink combination: to continue using Al2O3 but to reduce the thickness of this material to use alternative ceramic dielectrics exhibiting high thermal conductivities.
Metal ceramic assemblies with a low thermal resistance were manufactured by 2 routes. Thin films (1-25 um) of alumina and aluminium nitride were deposited by various methods onto copper substrates and their dielectric properties investigated. Radiofrequency sputtering was the most reliable method, but the safety requirement of 4500 V AC electrical insulation could not be attained within the range of thicknesses studied. The thermal oxidation of the aluminium nitride substrates prior to copper bonding gave good results for thermally grown aluminium oxide thicknesses higher than 5 um. Strong bonds were obtained with the use of an active braze. A new promising route, using a sol-gel deposited alumina silica glass was discovered, but not fully understood.
The objective of the project was to develop bonded metal conductor ceramic insulator metal heat systems with improved thermal conductivities and to ensure that the associated manufacturing costs are economically competitive.
Two main routes were tested to develop bonded metal ceramic components. Either to use the conventional Al203 but reducing its thickness or to use ceramic dielectrics showing high thermal conductivity (AIN, for instance). Regarding the first route, sputtering was the best technique to obtain thin ceramic films on metallic substrates among all techniques tested (chemical vapour deposition, metaloorganic decomposition, and mist pyrolysis methods). For the other alternative route, 3 techniques for joining oxide ceramics to metals were unsuccessfully tried (direct copper bonding, active brazing and glass bonding).
CERAMIC SUBSTRATES ARE WIDELY USED IN MICROELECTRONIC TECHNOLOGY AND POWER SYSTEMS. AT PRESENT CU/AL2O3/CU BONDED COMPONENTS ARE MANUFACTURED BUT THE RELATIVELY POOR THERMAL CONDUCTIVITY EXHIBITED BY THIS COMBINATION IS RESTRICTING THE DEVELOPMENT OF POWER ELECTRONIC SYSTEMS. TWO STRATEGIES ARE AVAILABLE TO IMPROVE THE THERMAL CONDUCTIVITY OF THE METAL CONDUCTOR-CERAMIC INSULATOR-METAL HEAT SINK COMBINATION.
1.- TO CONTINUE USING AL2O3 BUT TO REDUCE THE THICKNESS OF THIS MATERIAL.
2.- TO USE ALTERNATIVE CERAMIC DIELECTRICS EXHIBITING HIGHER THERMAL CONDUCTIVITIES.
IT IS INTENDED TO FOLLOW BOTH APPROACHES IN PARALLEL AND THEN TO CONCENTRATE ON THE OPTIMIZATION OF THE MOST PROMISING COMBINATION.
Funding SchemeCSC - Cost-sharing contracts