Thermal management of a C4/CBGA interconnect technology for a high-performance RISC microprocessor: the Motorola PowerPC 620/sup TM/ microprocessor

Abstract

This paper presents various thermal management options for a high-performance RISC microprocessor available for controlled-collapse-chip-connection (C4) die attached to a ceramic-ball-grid-array substrate (CBGA), as they apply to air-cooled systems. Computational-fluid dynamics (CFD) methods are used to solve the conjugate heat transfer problems and a thermal test vehicle mounted to a printed-circuit board was used to validate the models. The internal package's contribution is typically less than 18% of the overall junction-to-ambient temperature rise. Of this 18%, approximately 85% is associated with the thermal paste internally sealed; while, the lid and the silicon chip account for the other 15% (approximately equal). For moderate airflow applications in the 1 to 4 m/s, the PowerPC 620 microprocessor will require a relatively large heat sink, approximately 20 times that of the C4/CBGA package, to maintain its die-junction temperature. The proper selection of a thermal interface material is critical in minimizing the thermal contact resistance between the package and the heat sink. Considering, the low interface pressure, the synthetic grease offers the best performance.