Development of ultra dense edge interconnects for die to die connections based on immersion solder bridging

A high density 2-D integration process that involves linking multiple die along their edges using a linear array of solder bridges was explored. Solder bridging is a versatile approach that is compatible with a range of interconnect geometries and metallizations. We have demonstrated this approach using copper plated nodules that were fabricated on the surface of the die and extend beyond the edge of the die. These nodules were 25 microns (μm) thick with 10, 20, and 50 μm widths. The formation of solder bridges was accomplished using immersion soldering, where the entire part was dipped into a molten solder bath. Due to surface energy effects, the solder selectively wets and flows along all wettable metal surfaces to form a strong solder bond. The solder can even flow across gaps (15 microns).