Magnetic-assisted self-assembly of rectangular-shaped parts

A method for self-assembly of millimeter-sized, magnetized, rectangular-shaped parts floating on a molten solder–air interface under a rotating external magnetic field is developed. Rotating magnetic field produces a torque to rotate the magnetized parts into their specific in-plane orientations. The surface tension of the molten solder keeps the parts in these orientations. Experiments are carried out on glass substrates with patterned copper foil. Rectangular binding sites are the only hydrophilic areas on the substrate. By a simple coating process, molten solders wet only the binding sites on the substrate. The parts with orientation angles up to 90° can be rotated and translated to align with the binding sites by the magnetic torque and surface tension. Before the assembly, the solder is reflowed by heating to 80 °C. The alignment completed within 27 s with an orientation angle of 90°. The integrity of the bonding is confirmed by a static debonding test.