Characterization of interconnects resulting from capillary die-to-substrate self-assembly

Capillary fluidic self-assembly (SA) intrinsically features massively-parallel, contactless die handling and allows for high-precision die placement. It may thus boost die-to-substrate assembly throughput and scalability. Here we characterize for the first time indium interconnects established between dummy dies and substrates as integral part of a capillary SA process. We present a simple way to keep the solder surface free of oxide during assembly, and we show that In/Au wetting and bonding is not prevented by hydrocarbons and self-assembled monolayers locally present during processing. Resulting solder joints are characterized by mechanical shear tests, SEM and SAM. We assess the electrical functionality of interconnects with a simple test structure. Finally, we discuss the effects of an external load applied on dies during bonding. Our results open interesting perspectives for adopting capillary SA for die integration over non-planar substrates.