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Virginia Tech

1. Gao, Shan. Two-dimensional Mapping of Interface Thermal Resistance by Transient Thermal Impedance Measurement.

Degree: PhD, Materials Science and Engineering, 2019, Virginia Tech

Interconnects in power module result in thermal interfaces. The thermal interfaces degrade under thermal cycling, or chemical loading. Moreover, the reliability of thermal interfaces can be especially problematic when the interconnecting area is large, which increases its predisposition to generate defects (voids, delamination, or nonuniform quality) during processing. In order to improve the quality of the bonding process, as well as to be able to accurately assess interface reliability, it would be desirable to have a simple, reliable, and nondestructive measurement technique that would produce a 2-d map of the interface thermal resistance across a large bonded area. Based on the transient thermal method of JEDEC standard 51-14, we developed a measurement technique that involves moving a thermal sensor discretely across a large-area bonded substrate and acquiring the interface thermal resistance at each location. As detailed herein, the sensor was fabricated by packaging an IGBT bare die. An analytical thermal model was built to investigate the effects of thermal sensor packaging materials and structural parameters on the sensitivity of the measurement technique. Based on this model, we increased the detection sensitivity of the sensor by modifying the size of the sensor substrate, the material of the sensor substrate, the size of the IGBT bare die, the size of the heat sink, and the thermal resistance between sample and the heat sink. The prototype of the thermal sensor was fabricated by mounting Si IGBT on copper substrate, after which the Al wires were ultrasonic bonded to connect the terminals to the electrodes. The sensor was also well protected with a 3-d printed fixture. Then the edge effect was investigated, indicating the application of the thermal sensor is suitable for samples thinner than the value in TABLE 2 3. The working principle of the movable thermal sensor – Zth measurement and its structure function analysis – was then evaluated by sequence. The Zth measurement was evaluated by measuring the Zth change of devices induced by degradation in sintered silver die-attach layer during temperature cycling. At the end of the temperature cycling, failure modes of the sintered silver layer were investigated by scanning electron microscope (SEM) and X-ray scanning, to construct a thermal model for FEA simulation. The simulation results showed good agreement with the measured Zth result, which verified the accuracy of the test setup. The sensitivity of structure function analysis was then evaluated by measuring thermal resistance (Rth) of interface layers with different thermal properties. The structure function analysis approach successfully detected the Rth change in the thermal interface layer. The movable thermal sensor was then applied for 2d-mapping of the interface Rth of a large-area bonded substrate. Examining the test coupons bonded by sintered silver showed good and uniform bonding quality. The standard deviation of Rth is about 0.005 K/W, indicating the 95% confidence interval is about 0.01… Advisors/Committee Members: Lu, Guo Quan (committeechair), Tallon Galdeano, Carolina (committee member), Huxtable, Scott T. (committee member), Ngo, Khai D. (committee member).

Subjects/Keywords: Thermal interface material; thermal resistance; movable thermal sensor; 2-d mapping; sintered silver; analytical thermal model; reliability

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Gao, S. (2019). Two-dimensional Mapping of Interface Thermal Resistance by Transient Thermal Impedance Measurement. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/90770

Chicago Manual of Style (16th Edition):

Gao, Shan. “Two-dimensional Mapping of Interface Thermal Resistance by Transient Thermal Impedance Measurement.” 2019. Doctoral Dissertation, Virginia Tech. Accessed July 20, 2019. http://hdl.handle.net/10919/90770.

MLA Handbook (7th Edition):

Gao, Shan. “Two-dimensional Mapping of Interface Thermal Resistance by Transient Thermal Impedance Measurement.” 2019. Web. 20 Jul 2019.

Vancouver:

Gao S. Two-dimensional Mapping of Interface Thermal Resistance by Transient Thermal Impedance Measurement. [Internet] [Doctoral dissertation]. Virginia Tech; 2019. [cited 2019 Jul 20]. Available from: http://hdl.handle.net/10919/90770.

Council of Science Editors:

Gao S. Two-dimensional Mapping of Interface Thermal Resistance by Transient Thermal Impedance Measurement. [Doctoral Dissertation]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/90770

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