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Evaluation of Ceramic Substrates for High Power and High Temperature Applications
Keywords: High Power, Ceramic Substartes, Reliability
Ceramic substrates with thin film and thick film conductor are widely used in microelectronic packages for high temperature operation. In high power applications where the maximum current in the package may be hundreds of amperes, much thicker conductive traces are normally required. For such applications, Direct Bonded Copper (DBC), Direct Bonded Aluminum (DBA) or Active Metal Brazed (AMB) substrates are good candidates. These substrates provide low electrical resistance and high ampacity, thereby enabling the design of high power circuits for high temperature operation. The most commonly observed failure mode in these substrates is the delamination of metal layer from the ceramic. The lifetime of a ceramic substrate can also be significantly reduced by the processing conditions such as maximum process temperature, and the process gases that the substrates are exposed to. It has been also been shown that the propagation of cracks in the ceramic can be abated by dimpling the metal layers along edges and corners. In order to evaluate the effectiveness of these types of substrates for power applications, substrates with various combinations of metal thicknesses and ceramic composition (Al2O3 and AlN) were eva-luated for delamination as a function of thermal shock cycles. These samples included both dimpled and non-dimpled metallization. The samples were thermally cycled between -40 °C and 200 °C. A few of these substrates were exposed to forming gas at 240 °C prior to thermal cycling to imitate process conditions. The sample randomization was performed to provide statistically significant data. After a certain number of thermal cycles, in the substrates delamination cracks were observed to nucleate and propagate. Data regarding the reliability of these substrates as a function of thermal shock cycles will be presented in this paper, along with failure mechanisms that are commonly observed. Computer simulations were performed to understand the conditions that lead to delamination cracks, and to estimate the crack growth rates in these substrates.
Srikanth Kulkarni, Student
University of Idaho
Moscow, ID
USA


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