Date of Graduation

8-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Mechanical Engineering

Advisor/Mentor

Huitink, David

Committee Member

Mantooth, Alan

Second Committee Member

Zou, Min

Third Committee Member

Meng, Xiangbo

Keywords

Diffusion Bonding; Electronics Packaging; High Temperature; Interconnect; Thermal Management; Transient Liquid Phase Bonding (TLPB)

Abstract

Growing applications in transportation make power density a key optimization target in the power electronics industry. More power in a shrinking environment leads to high heat flux and junction temperatures that damage silicon-based switching devices. Temperatures approaching 175℃ can result in false triggering of the device’s activated state, resulting in short circuits. Developing wide bandgap semi-conductors, such as gallium nitride and silicon carbide, are less susceptible to this complication as the energy from elevated temperature is a smaller fraction of what would be required to trigger the device. These devices are projected to function reliably in environments of up to 800℃. Thus far, such applications have been held back by packaging and passives technology. This work seeks to advance the knowledge and applicability of copper-tin transient liquid phase bonding technology by accelerating, simplifying and enhancing the process. Transient liquid phase bonding is a diffusion-based technology, highly dependent on length for processing speed. In electronics, thin bond lines lead to reliability concerns and process complications. Utilizing patterned copper substrates, the effective bond length can be maintained while the bond line thickness increases. Such a structure resembles a unidirectional lamina as defined by composite theory, affording the opportunity to tune bond properties by controlling the shape and density of substrate patterns. In this work copper-tin transient liquid phase bonding is demonstrated in atmosphere, using SAC305 solder on nanowire populated substrates. Demonstrations show up to 99.78% acceleration in the rate of bonding compared to a substrate without any surface structures. The bonding prosses is then refined for repeatability. Thermal and electrical conductivities are examined, and bond stability is evaluated using high temperature storage testing. Results show an average shear strength of 29.4 MPa that does not change with any statistical significance over 72 hours at 175℃. Additionally, thermal conductivity measurements demonstrate thermal conductivity up to 89.9 W/mK.

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