Transfer of metal MEMS packages using a wafer-level solder sacrificial layer

This paper presents a modular, low profile, wafer-level encapsulation technology for 0-level MEMS packaging. Electroplated caps are formed on a carrier wafer then simultaneously transferred and bonded to a device wafer by a novel solder transfer method and transient liquid phase (TLP) bonding technology. The solder transfer method is enabled by the dewetting of the solder transfer layer from the carrier wafer, and TLP bonding of the cap to the device wafer during bonding. The nickel-tin TLP bond and transfer cycle has a maximum temperature of 300 °C and lasts about 2.5 hours. This approach has been demonstrated with nickel caps 5 microns thick, ranging in size from 200 μm 1 mm. They were transferred with a lead-tin transfer solder layer and bonded with nickel-tin TLP bonding with greater than 99% transfer yield across the wafer.