Title page for ETD etd-08192008-160519

Type of Document Master's Thesis
Author Kardak, Ajay Ashok
Author's Email Address akarda1@lsu.edu
URN etd-08192008-160519
Title Fabrication of Micro Bumps for Micro Scale Thermal Management
Degree Master of Science in Mechanical Engineering (M.S.M.E.)
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
Ram V. Devireddy Committee Chair
Michael C. Murphy Committee Member
Sunggook Park Committee Member
  • Microfabrication
  • Thermoelectric cooler
  • Thermocouple
Date of Defense 2008-05-15
Availability unrestricted
Cryopreservation is storage of biological systems at ultra low temperatures for a prolonged duration; such that they can be thawed and restored to the same living state. It is important to understand the behavior of cells when they are subjected to subzero temperatures. Research in this area has shown the occurrence of two main biophysical events; cellular dehydration and intracellular ice formation. Current techniques for characterizing the dehydration in cells as part of a tissue are not adequate for studying intracellular ice formation in tissues. An integrated device consisting of an array of thermal sensors (microthermocouples) and actuators (microthermoelectric coolers) would help to detect intracellular ice formation by measuring and modulating the heat release of individual cells during freezing. This requires a dense wiring layer below the devices which can act as a heat sink in turn affecting the performance of the device. To alleviate this problem fabrication of bump structures was proposed to isolate the dense wiring layer from the array.

Modeling was used to assess the effect of the bumps on the performance of the thermoelectric cooler. Bismuth telluride posts of 10 m diameter and 20 m height yielded optimal cooling with a bump radius of 5 m. A maximum effective change in temperature of 3.47 K was achieved for an applied current of 23.7 mA and Joules breakdown was found to occur at 47.7 mA.

To avoid the complexities in the measurements due to the presence of second junction, copper and constantan were chosen as bump material. Electrodeposition along with UV-LIGA microfabrication technique was used to fabricate the bumps. Copper and constantan micro bumps, with mean diameters of 6.5 & 27.76 m and heights of 7.81 and 12.04 m were fabricated with dimensional variation of 0.5 m with a 95% confidence interval.

A custom printed circuit board was fabricated on FR4 laminate using lithography and liftoff technique. The mean length and width of the structures were found to be 4151.98 1.86 m and 1003.21 0.55 m, respectively with 95% confidence interval. There is a need for future work to precisely fabricate metal features on FR4 laminate.

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