Electrical Breakdown of Thermal Spray Alumina Ceramic Applied to AlSiC Baseplates Used in Power Module Packaging
Mossor, Charles W.
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Thermal spray coatings offer new alternatives in the production of electronic power modules that use alumina ceramic as an isolation layer. Current processes use direct bond copper (DBC) soldered to a nickel plated copper heat spreader. A coefficient of thermal expansion (CTE) mismatch exists between copper and alumina and leads to reliability issues that arise due to product failure during thermal cycling and lifetime operation. The substitution of an AlSiC metal matrix composite (MMC) heat spreader baseplate addresses the problem of CTE mismatch and will reduce the number of product failures related to cracking and delamination caused by this pronounced mismatch in the thermal expansion coefficient.. The substitution of an AlSiC (MMC) heat spreader baseplate also allows the production process to be achieved with a fewer number of metallization layers. Thermal spray can apply alumina ceramic coatings directly to the AlSiC (MMC) baseplates. A reduction in process steps will lead to a reduction in manufacturing costs, the main driving objective in Microelectronics Industries. Thermal spray coatings have a major problem since they have a porous microstructure which can trap undesired moisture. The moisture basically causes the coatings to have a lower dielectric breakdown voltage and a higher leakage current at normal operating voltages. This problem can be eliminated by manufacturing the electronic power modules in a controlled environment and packaging the devices in a hermetically sealed package. This thesis analyzes the data obtained from direct-voltage dielectric breakdown and direct-voltage leakage current tests conducted on coupons manufactured using the thermal plasma spray coating process and the thermal high-velocity oxyfuel (HVOF) coating process. ASTM specifications defining appropriate testing procedures are used in testing the dielectric strength of these coupons. Issues relating to the dielectric strength and dielectric leakage current are evaluated and validated at the Microelectronics Laboratory at Virginia Polytechnic Institute & State University. The objective to conduct this research study using plasma and HVOF alumina coatings as dielectric isolation layers is to support the Microelectronics Industries in developing a product with increased reliability at a lower manufacturing cost.
- Masters Theses