Keywords

Au in, die attach, diffusion, high temperature, packaging, power module, power semiconductor, silicon carbide (sic), shear strength, solid liquid interdiffusion (slid), reliability, resistivity, transient liquid phase (tlp) die attach, thermal cycling, wide bandgap

Abstract

Advances in wide-bandgap semiconductor devices have increased the allowable operating temperature of power electronic systems. High-temperature devices can benefit applications such as renewable energy, electric vehicles, and space-based power electronics that currently require bulky cooling systems for silicon power devices. Cooling systems can typically be reduced in size or removed by adopting wide-bandgap semiconductor devices, such as silicon carbide. However, to do this, semiconductor device packaging with high reliability at high temperatures is necessary. Transient liquid phase (TLP) die-attach has shown in literature to be a promising bonding technique for this packaging need. In this work TLP has been comprehensively investigated and characterized to assess its viability for high-temperature power electronics applications. The reliability and durability of TLP die-attach was extensively investigated utilizing electrical resistivity measurement as an indicator of material diffusion in gold-indium TLP samples. Criteria of ensuring diffusive stability were also developed. Samples were fabricated by material deposition on glass substrates with variant Au–In compositions but identical barrier layers. They were stressed with thermal cycling to simulate their operating conditions then characterized and compared. Excess indium content in the die-attach was shown to have poor reliability due to material diffusion through barrier layers while samples containing suitable indium content proved reliable throughout the thermal cycling process. This was confirmed by electrical resistivity measurement, EDS, FIB, and SEM characterization. Thermal and mechanical characterization of TLP die-attached samples was also performed to gain a newfound understanding of the relationship between TLP design parameters and die-attach properties. Samples with a SiC diode chip TLP bonded to a copper metalized silicon nitride iv substrate were made using several different values of fabrication parameters such as gold and indium thickness, Au–In ratio, and bonding pressure. The TLP bonds were then characterized for die-attach voiding, shear strength, and thermal impedance. It was found that TLP die-attach offers high average shear force strength of 22.0 kgf and a low average thermal impedance of 0.35 K/W from the device junction to the substrate. The influence of various fabrication parameters on the bond characteristics were also compared, providing information necessary for implementing TLP die-attach into power electronic modules for high-temperature applications. The outcome of the investigation on TLP bonding techniques was incorporated into a new power module design utilizing TLP bonding. A full half-bridge inverter power module for low-power space applications has been designed and analyzed with extensive finite element thermomechanical modeling. In summary, TLP die-attach has investigated to confirm its reliability and to understand how to design effective TLP bonds, this information has been used to design a new high-temperature power electronic module.

Notes

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Graduation Date

2012

Semester

Fall

Advisor

Shen, Zheng (John)

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Electrical Engineering and Computer Science

Degree Program

Electrical Engineering

Format

application/pdf

Identifier

CFE0004499

URL

http://purl.fcla.edu/fcla/etd/CFE0004499

Language

English

Release Date

December 2013

Length of Campus-only Access

3 years

Access Status

Doctoral Dissertation (Open Access)

Subjects

Dissertations, Academic -- Engineering and Computer Science, Engineering and Computer Science -- Dissertations, Academic

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