Electroplating of 3D Sn-rich solder for MEMS packaging applications

Abstract

Electroplating is a popular method to produce solders in microelectromechanical systems (MEMS) encapsulation and interconnection applications. In this work, a fabrication process is introduced for the generation of three-dimensional (3D) Sn solder microstructures. An aluminum membrane was employed as the conducting layer while electroplating. Based on the proposed method, Sn solders with different heights can be easily obtained after reflow. Taking advantage of these 3D structures, MEMS packaging, electrical interconnections, hermetic seals and metal-armoring can be formed simultaneously in one step. Metal-armoring provided by the solder–solder contact can be used at the extremes of the suspension travel, greatly increasing the capability of shock resistance. The helium leak rates of the packaged samples are lower than the reject limit (5 × 10−8 atm cc s−1 based on MIL-STD-883E standard). The bonding strength of samples is measured by a die shear strength tests with an average value of 7.4 MPa. In addition, the ohmic behavior of the Sn solder bonding is verified as well. These excellent results show an outstanding packaging quality in MEMS encapsulation applications.