Batch transfer of microstructures using flip-chip solder bonding

This paper describes a novel method for transfer and assembly of microstruc tures using sacrificial-layer micromachining and flip-chip bonding. The tec hnique is performed at room temperature (cold weld) and at the back end of the process how and may thus provide a commercially viable alternative to m onolithic integration and costly hybrid packages. The transfer is achieved using break-away tethers and by cold melding (compression bonding) electrop lated indium solder bumps to electroplated copper pads. Both high-aspect-ra tio MEMS devices as well as surface-micromachined devices have been success fully transferred using this method with no observable misalignment between moving and stationary parts. The maximum tensile and shear stress the sold er bond can withstand before failure is measured to be 11 +/- 3 MPa and 9 /- 1 MPa, respectively, The contact resistance is measured to be of the ord er of 1.5 m Omega for a 65 mu m x 65 mu m x 4-mu m indium bump. [317].