Novel Electrolytic Plating Solution for RDL in Advanced Packaging Applications

With the emerging development of high-tech applications such as consumer electronics, 5G, artificial intelligence, and internet of vehicles, the need for IC chips featuring higher functionality, performance, and reliability but smaller volume is pushing close to the limit of Moore's law. To keep extending the Moore's law, besides development of novel nano technology for transistors, technology in advanced packaging in 2.5D and 3D are evolving rapidly. Introduction of redistribution layer (RDL) in an integrated fan-out (InFO) package allows better integration capability and lower cost. Copper electrolytic plating is one of the important steps in the fabrication of RDL process. RDL features blind vias with diameter smaller than 50 um and fine lines with pitch ranging from 50 um to 20 um or even smaller. Both via-filling capability and uniformity have remained two major key challenges for this application. Proprietary design of organic additives provides good via-filling performance down to 30 um vias without voids. To improve uniformity, simulation on COMSOL Multiphysics predicts difference of electric field distribution from ground surface to unit edge. Along with the simulation of mass-transfer mechanism in fine-line areas, novel selection of organic additives demonstrates differential adsorption along the electric field, creating differential suppression levels on different features, leading to achieve superior uniformity within unit with various pattern features. Besides extraordinary via filling and uniformity performance, a wide range of operating conditions and stable reliability offers key features for easy bath maintenance with this unconventional electrolytic plating solution. In summary, this paper demonstrates an innovative electroplating solution with superior uniformity for advanced RDL applications.