Advantages and new development of direct bonded copper substrates

Direct bonded copper (DBC) substrates have become the most important electronic circuit boards for multichip power semiconductor modules. They are replacing complicated assemblies based on leadframes and refractory metallized substrates due to ease of assembly and the low temperature coefficient of expansion of DBC which matches silicon in spite of thick copper metallization. The DBC technology allows bonding of copper to alumina and aluminum nitride, fusing of copper to copper has been developed to establish efficient water cooling devices with sophisticated internal micro channel structures for cooling power laser diodes and other high power density electronics. Low weight, hermetically sealed DBC packages are replacing more and more heavy weight metal can packages. Increasing requirements for temperature cycling reliability and mechanical stability in automotive, avionics and space applications is the driving force for the development of a new type of DBC material with a 60% increase in flexural strength and more than 100% increase of temperature cycles: This new type of DBC allows 35% thicker copper layers on 20% thinner ceramic, for example 0.4 mm copper on 0.32 mm ceramic. By this the thermal resistance of multichip power modules can be reduced substantially without decreasing reliability. In many applications this will be an economic solution where the price of AlN and Si₃N₄ substrates would be too high.