Large-scale, surface tension assisted Ball-in-Pit self population for chip-to-chip passive alignment

The Ball-in-Pit passive layer-to-layer self-alignment technique has previously been shown to achieve submicron alignment between stacked chips. This structure sandwiches a precision sapphire ball between inverse pyramidal pits etched on the faces of chips to be aligned. In this work, we present a universal and low-cost fluidic approach to self-populate balls into a large-scale array of etched pits. This population technique could be used to populate pits on a wafer, a multichip interposer, or individual chips.