Novel multiple compartments shielding for high performance RF design — LTE modem SiP

This paper describes a compartment shielding process which is suitable for a system module which needs multiple shielded areas to reduce the interference among digital, analog and RF circuits. The process to implement this compartment shielding is ideal for integrating die or wafer level package, and results in miniaturized form factory both in area and in height. The compartment shielding structure is seamlessly connected to the grounding of the substrate, hence has superior isolation performance. The shielding wall which isolates the compartments is made by laser scribing and trench filling. Therefore, the isolation wall can be straight line, L, U or zigzag shape. In addition, the process is flexible to design change, high in shielding effectiveness, and low in cost. A test vehicle was built to verify the performance and shielding effectiveness can be as high as 60dB in up to at least 6 GHz range. Simulation is used to analyze and predict the shielding effect for various filling material, thickness, and over frequency. Moreover, an LTE modem is implemented using this shielding structure. This single mode/dual bands LTE modem module with size 23×26×1.9 mm is target to be the smallest SiP module in this product category. It consists of more than 370 components which were populated by high density SMT. One time MUF (molded under fill) was applied and two shielding trenches were made to separate this module into three compartments. Finally, sputtering is used to form a conformai shielding layer on the surface of the SiP module for EMI shielding.