Low Temperature Solders for Energy-Efficient Electronics Manufacturing

Electronics manufacturing is an extremely energy-consuming process as a large amount of heat is required to melt the filler metal (solder) that connects the electronic components to the circuit boards. The solders form mechanical, electrical and thermal connections between the circuit boards and components in processes that typically involve heating the assembly to temperatures above the solder alloy melting point and holding at this temperature until a metallurgical bond is achieved. Therefore, the melting point of the solder alloy directly affects the process temperature.

Low-temperature solders (LTS) represent a solution that would allow the electronics industry to significantly reduce costs in the manufacturing of electronics. This project aims to develop new low-melting point solders, based on the tin-bismuth (Sn-Bi) system, that will lower not only the energy consumption required for assembly but also the potential thermal damage to circuit boards during manufacturing.

Despite the low costs and low-melting point, the alloys have an atypical change in thermal and electrical resistivity during temperature fluctuations which can be experienced by electronic devices during manufacturing and use. The project aims to understand the fundamental mechanisms related to the atypical electrical and thermal resistivity of these alloys through innovative analytical methods. Also, Sn-Bi solders have low ductility at high strain rates. Microstructure refinement is reported to enhance Sn-Bi alloys’ ductility as it promotes superplasticity. The project aims to achieve microstructure refinement via cooling rate control and ternary alloy additions.

This work is conducted in collaboration with industry partners, Masters & Young Pty. Ltd., a Brisbane-based designer and manufacturer specialised in defense, medical, and industrial devices; and Nihon Superior Co., Ltd., a global solder supplier to the electronics manufacturing industry. The student will have an opportunity to conduct research at the industry partners' sites in Brisbane and Japan. Test vehicles and solder pastes for the experiments will be supplied by the industry partners and validation of the new alloys will be conducted at the industry partners' sites.

In the context of the foregoing, the objectives of this project are:

1. Understand the complex relationship between the temperature-sensitive electrical and thermal resistivity of binary Sn-Bi alloys in relation to their compositions, microstructure and crystal structure.
2. Develop reliable advanced LTS via cooling rate control and ternary alloy additions.
3. Translate findings from Objectives 1 and 2 for industrial applications through validation tests.

The project will be based at the St Lucia campus at The University of Queensland (UQ).

The student will have access to a foundry for sample fabrication, a metallography laboratory, state-of-the-art electron microscopes, X-ray characterisation facilities, synchrotron facilities, 4-point electrical and thermal conductivity measurement instrument and specialist software required for the project. The UQ library also provides access to a list of generic software and journal database.

The student will also have access to solder characterisation instruments, software for test vehicle design and industry scale reflow soldering equipment at the industry partners’ sites.

Training for specialist and transferable skills relevant to the project is available.