Hybrid 3D printing of conductive bulk metal and dielectric polymer for sustainable and smart 3D electronics

Electronics are the dispensable element in the current modern society and new era of industrial 4.0, Internet of things (IoT), smart homes, wearable electronics as well as modern health solutions. However, the current electrical circuits manufacturing such as printed circuit boards (PCB) are mainly relying on the complex factories with a series of expensive instruments, consuming large amounts of etching chemicals and producing toxic wastewaters [1,2]. Moreover, the electronics are also limited to 2D rigid FR4 boards, which highly hinder it for individualized smart systems. Printed electronics offers high potential in integrating sustainable electronics on flexible and large area surfaces. It has advantages of high resource efficiency, miniaturized usage of energy in both fabrication and utilization, reduce the usage of the hazardous chemicals, higher potential in recyclability and usage of the biodegradable materials. However, it still faces some critical challenges: a) usage of chemicals and solvents; b) required of post-treatment; c) expensive particle-based ink d) high restriction on 3D printing In this talk, we introduce a hybrid printing system where the polymer/dielectric substrates can be directly printed from FFF technology. The StarJet technology is directly integrated into the 3D printing system as the 2nd extruder which prints the bulk metal (e.g. SAC305 solder) through digital and non-contact deposition of the molten metal droplets or Jet. Compared to current printed electronic technologies, the StarJet technology provides advantages of bulk electrical conductivity, conform printing, no pre- and post-treatment, high compatibility on flexible substrates due to solvent-free printing. Furthermore, when the bulk solder (e.g. Tin silver copper alloy) is used for the molten metal printing, the SMD components can be directly soldered and bonded onto the large-area flexible substrates. It eliminates the troublesome solder reflow process and simplifies the fabrication process. In the contrary to the high temperature of the StarJet printhead (e.g. 320 °C for soldering printing), the printed molten metal structure has high adhesion, high flexibility and no damage to the temperature sensitive polymer foils, textiles, and 3D-printed plastics. The high flexibility has been also shown on foldable polymer foils, where the printed circuits can be folded into a small part and stay fully functional after unfolded. A highly simplified workflow is also introduced where non-experts can make electrical designs and generate hybrid 3D electronic models. Then the hybrid 3D printing system will take care of the rest of printing. With this hybrid-printing platform, it provides high potential to direct prototype 3D electronics and integration of smart sensors with highly conductive traces, direct soldering, and without any post-processing (e.g drying, sintering).