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Clamping devices to enable concurrent mechanical and electrical connections of a power semiconductor




Shover, Michael Andrew, author
Collins, George J., advisor
Reising, Steven C., committee member
Chen, Thomas Wei, committee member
Sakurai, Hiroshi, committee member

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In response to the restrictions of lead bearing solders in the European Union Restriction of Hazardous Substances Directive of 2002, new strategies for solderless electrical connections are desired. In this work, such concepts are used in the simultaneous electrical connection of power semiconductor leads to a PCBA and mechanical attachment of the device package to a heat sink. These concepts are specifically designed for use in an industrial high power (kW to tens of kW) radio frequency generator. The many constraints of such a system, some of which are directly contradictory to each other, are considered throughout, including manufacturability, mechanical tolerances, system reliability, and cost. Theoretical models predict that in the expected usage environment, the transistor leads in the clamped connection under consideration will move 5.1 micrometers for a thermal excursion of 50°C. SEM micrographs showing that the size of z-axis asperities is on the order of 1 micrometers and calculations estimating adhesive junctions with surface energies on the order of 100 N/mm2 demonstrate that contact wear is likely. A survey of available materials has been conducted, with beryllium copper and polyetherimide being the favored options for clamp construction. Four concepts are modeled, noting the benefits and drawbacks of each. The preferred embodiment is found to be a clamping mechanism fabricated from electrically insulating material, specifically injection molded 30% fiberglass filled polyetherimide, incorporating cantilevered beams which deflect upon installment into the system with fasteners, thus forming the electrical connections. Test regimens have been performed, including room temperature aging, elevated temperature aging at 50°C and 80°C, thermal cycling, highly accelerated life testing, and thermal analysis in both the steady state and transient regimes. The results of the experiments show this clamping system to have a useful life in the intended environment of multiple years.


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