Versatile Selective Soldering via Molten Metal Printing for Heat-Sensitive 3D Electronics and Smart Wearables

A novel and versatile soldering method is presented using non-contact direct printing of molten metal for 3D electronics, printed electronics, and smart wearables. The solder joints can be created selectively by the StarJet technology in a non-contact manner at room temperature on substrates with 3D topology. The interconnections exhibit minimal void content and a microstructure comparable to traditional solder joints, indicating high electrical and thermal conductivity. They show a robust shear strength (≈30 N with 0805 SMDs on a 3D-printed polymer substrate). The approach enables the soldering of sensors, microchips, and electronic components on standard PCBs as well as heat-sensitive substrates, offering a sustainable alternative to industry-standard conductive adhesives. Electronic components are selectively soldered onto a biodegradable polymer (PLA), a heat-sensitive textile (polyester), and hybrid 3D-printed flexible circuits to highlight the versatility of the molten metal selective soldering technology.