Fabrication and characterization of embedded active and passive device for wireless application

Abstract

In this study, the research of embedded active and passive package is carried out for miniaturized wireless module. We fabricated very small RF module which one bare chip (0.3mm × 0.5mm, SPDT switch IC) and three 0603(0.6mm × 0.3mm, MLCC) passive devices were buried into within 1.85mm × 1.5mm substrate. Used materials were compatible with PCB process such as polymer laminating, dry film patterning, electroless-electrolytic copper plating and atmospheric plasma treatment. We studied low pressure bonding process using rheology dependence of polymer on temperature to prevent fracture or crack from embedding chips into PCB. The embedded chip and passives were electrically interconnected by small laser via(30μm) and Cu pattern plating process after atmospheric pressure plasma treatment, which revealed an effect on filling of micro via and shape of fine pattern. The interconnection between chip pad and Cu were evaluated by SEM image, which shows Cu pattern of PCB and pad of passive was interconnected without intermetallic formation. However, intermetallic, Cu-Sn-Ni, formed between passive electrode and plated Cu layer, and molten Sn is segregated along the wall of via hole after reflow. DSC (Differenntial Scanning Calorimetry) analysis was employed to calculate and optimize the amount of curing. Polymer showed maximum 90o peel strength (∼0.7kgf/cm) with Cu pattern when Cu is plated on polymer after pre-curing was 80∼90% completed. The RF characterization of embedded chip PCB was evaluated by measuring s-parameters (S11; return loss and S21; insertion loss). Return loss was below 20dB up to 4GHz. As a results, the embedded chip module is able to be applied for 2∼5 GHz frequency application (Bluetooth and WiFi) with small size and good performance.