A flow substrate mounting structure comprising a fastener aperture and an alignment feature, wherein the alignment feature comprises at least one of an alignment pin removably coupled with the flow substrate mounting structure, an alignment slot, and an alignment step. A structure for coupling a plurality of flow substrates comprising a flow substrate mounting structure comprising a first fastener aperture, and a second fastener aperture, wherein the first fastener aperture is configured to couple with a first fastener and the second fastener aperture is configured to couple with a second fastener, wherein an alignment fixture is used to align the flow substrate mounting structure with the plurality of flow substrates.