Dramatically Lower Soldering Temperatures with Metastable Liquid Metal Particles
Supercooled liquid metal microcapsules are a transformational technology that simplifies circuit board assembly. Forming full-metal interconnects of lead-free solder alloys without high-heat processes avoids thermal damage to components and materials or quality issues caused by the coefficient of thermal expansion mismatch. The technology encapsulates RoHS compliant solder alloys inside a nanofilm that keeps the metal in a metastable supercooled liquid state at ambient temperatures. Metastability is maintained by a core-shell particle architecture. The thin oxide/organic shell can be mechanically broken or chemically dissolved to release the liquid metal that then rapidly solidifies all without requiring heat. Supercooled liquid metal microcapsules of ambient processable InBiSn and BiSn have been manufactured as well as prototypes of SAC305. We demonstrate applications of supercooled liquid metal microcapsules for the heat-free fabrication of electrically conductive interconnections. We demonstrate ambient temperature molding, sheet rolling for continuous films, and chemical sintering to create porous films. Shear (plane) stress allows fabrication of uniform thin films which can be further advanced into fabricating conductive traces with a tunable thickness on flexible or heat-sensitive substrates. As expected, when normal stress is applied to a packed bed of supercooled liquid metal microcapsules flow of the liquid metal occurs only at the point the stress is applied allowing for patterning of conductive pathways. The new technologies and substrates that are needed to bring many advances to the market in miniaturization, packaging, and flexible electronics create challenges for manufacturers especially when it comes to heat management. Multiple heat-free application pathways highlight the versatility of this approach, allowing a multitude of conductive products to be fabricated without damaging the base material.