A back plate for rapid and fluid-assisted assembly of micro light emitting elements thereon includes a substrate with a driving circuit, and blocking walls made to protrude from a top surface of the substrate. The top surface of the substrate defines grooves for accommodating and powering micro light emitting elements. Each of the blocking walls semi-surrounds one groove and defines a notch. The notches defined by each blocking wall all face a single direction and the blocking walls and notches impede and gather micro light emitting elements which are made to flow in a fluid suspension and render them much more likely to tumble into the groove. A method for fluid-assisted assembly is also disclosed.