RDL Copper Plating Process for Panel Level Packaging Application

Abstract

Advanced packaging suppliers are having two primary challenges during IC substrate fabrication, meeting the requirements on copper plating performance and reducing the cost from manufacturing process. The requirements on plating performance include high resolution and strict height uniformity within a die (WID) and within a panel (WIP), consistent deposit grain structure, and robust physical properties to meet reliability requirements. The plated features include fine lines, trenches, and vias, whose top shape and coplanarity are critical to the product quality. A non-planar surface could result in signal transmission loss and introduce weak points in the connections. Therefore, copper plating solutions providing uniform, planar structures, without any special post treatment are highly desirable features from RDL plating processes. The copper plating solution can also reduce cost by plating two or three types of features in a single electrolyte, this flexibility allows fabricators to save on space and equipmentIn this paper, an electroplating package, Systek UVF 200, is introduced to plate RDL under different current densities in vertical continuous platers (VCP) and a high-speed panel plater. The plating uniformity was evaluated on a panel level in a high-speed plater, AMSPT NEXX P500.The Systek UVF 200 package offered excellent coplanarity within a pattern unit or die for RDL plating. The variation in the plated height (or thickness) between fine lines (as low as 9 μm in width) and pads, was below 2.0 μm when using a current density below 5.0 ASD to obtain the plated copper thickness around 12 μm. For 14 μm wide lines, the plated copper thickness variation can be below 1.2 μm. The variation of plated thickness across 510 mm x 515 mm panels was below 5%. The tops of the fine lines have defined, slightly domed shapes, these types of profiles have excellent conductivity.Physical properties of the plated copper deposit are essential for the reliability of the finished product. A few key physical properties are tensile strength, elongation %, and internal stress. These properties show the tolerance of the deposit to withstand thermal stress and warpage. The additives (wetter, brightener, and leveler) strongly influence the physical properties of the deposit. Copper deposited with the Systek UVF 200 package has tensile strength above 40,000 psi, elongation % above 18%, and internal stress below 1.0 Kg/mm2. The physical properties of the deposited copper did not change under different current density, showing that the package has stable performance.