Abstract
We have developed a drop-on-demand printhead that can eject molten metal droplets. The capability of ejecting solder drops onto an X-Y stage controlled substrate makes this new technology ideal for fast prototyping of metallic traces on planar and three-dimensional (3D) objects. The ejection process uses the electromagnetic repulsion force between two parallel currents moving in opposite directions. One current path flows through the molten metal, such as solder, the other through a copper stripe. The electrical connection between the two conductors was accomplished by two Ni plated vias. By adding an appropriate nozzle in the solder channel, a current pulse can cause a drop to squirt out. The size of the ejected solder drop depends on the driving energy, which is controlled by both the pulse width and the drive voltage. For successful operation of the printhead, wettability of the solder to the printhead material needs to be taken into consideration. We have constructed the solder jet printhead in both a polyimide laminate stack and a ceramic form that can withstand a much high temperature. We have ejected molten PbSn eutectic solder as well as BiSn and InSn with precision on Si wafers, over substrates with different heights and connecting the traces on different levels, as well as creating freestanding 3D structures.
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