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

Abstract 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.