Automation of Wearable Thermoelectric Devices

Background:

Thermoelectric devices (TEDs) are small, portable devices that transfer heat between surfaces when supplied with electricity. When configured correctly, these TEDs can be worn as a personal heating or cooling device. This has several important implications, as TEDs have the potential to supersede the HVAC systems present in in most buildings. The per capita HVAC consumption rate is about 1.5KW while the human metabolic rate is about 150 W, indicating human body thermoregulation is 10x more efficient than modern HVAC systems; TEDs localize a heating or cooling device to a specific person, reducing climate control energy consumption as compared to modern HVAC units. TEDs can also serve as a protective device for workers operating in harsh environmental conditions, specifically those involving extreme heat or cold.

Professor Renkun Chen and the members of his lab, Thermal Energy Materials and Physics (TEMP) Lab, have successfully built a thermoelectric device that uses the Peltier effect to cool and heat specific parts of the body. The device is able to achieve this without the use of a heat sink and can maintain a comfortable body temperature with a range of 10 - 38 C. However, the current manufacturing process is 100% manual, necessitating close to 300 precise (millimeter-scale) soldering operations; this process takes up to 40 hours per unit and is prone to errors, resulting in a fairly high device failure/rejection rate.

Objectives:

The objective of this project is to redesign aspects of the manufacturing process for these devices for the following outcomes:

1. Reduced manual labor/labor cost

2. Significantly faster manufacturing time - from 40 hours to 2 hours

3. Higher process accuracy and reduced device rejection rate - Failure rate < 0.003%

The soldering process should be completely automated and all thermoelectric pillars should be soldered at once.

Final Design:

The automated soldering fixture (Figure 1) holds the thermoelectric components in place during the soldering process. The fixture frame components are machined from 6061-T6 aluminum stock, while the alignment combs are cut from Kovar nickel sheets. Precision-machined ceramic plates are used as carrier substrates for laser-cut copper foil electrodes; solder paste is applied to precise points on each electrode via a solder stencil. The assembly is heated via an oven until the pillars are soldered to the electrodes in the desired configuration. After the soldering is complete, the combs are removed and the soldered thermoelectric assembly is extracted from the fixture frame (Figure 2). The video shown below showcases the procedure of building one thermoelectric device.