Thermal Performance of Ball Grid Arrays and Thin Interface Materials
Type of DegreeDissertation
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Current electronic packages exhibit very high and ever increasing power densities. That trend mandates the need for enhanced thermal performance. This study introduces a state of the art apparatus to measure thermal resistance of electronic packages. The apparatus was designed to minimize human interaction and to maximize measurement accuracy through the use of a computer automated data acquisition and control system. The developed apparatus was used to measure thermal performance of Ball Grid Array packages. The impacts of different package configurations and board and assembly parameters on thermal performance were investigated. The parameters under investigation were die size, use of thermal balls, number of perimeter balls, use of underfill, and PCB heat spreader and thermal via design. By comparing the thermal performances of different packages, it was observed that utilization of larger die, use of thermal balls, use of underfill and rich copper PCB thermal vias can reduce thermal resistance by up to 60%. The number of perimeter balls did not have a notable impact on thermal performance due to their remote location from the die surface. Numerical thermal simulations of all test parameters combination were developed and were found to be in good agreement with the experimental measurements. The impact of thermal cycling on thermal performance was also investigated experimentally. Packages expected to be least reliable (with large die and no underfill), showed initial increase of thermal resistance after 750 thermal cycles. Further increases in thermal resistance were observed with continuous thermal cycling until solder joint failure occurred at 1250 cycles, preventing additional measurements. The correlation between thermal cycling and thermal resistance was then analyzed using a numerical structural simulation model that predicted crack initiation in the solder joints. A second apparatus based on the ASTM 5470D standard was developed to measure thermal resistance of thin components and interface materials used in electronic packaging. Thermal contact resistance versus applied force at the aluminum metering block surfaces was evaluated by testing 2 copper samples of different thicknesses. The established correlation can be used to correct future thermal resistance measurements. A new RTD Assembly was proposed to overcome current bare RTD fragility problems. The new proposed temperature probe dimensions and material were selected based on a numerical optimization study using a design variable sweep technique.