Versatile Electrochemical Plating Process Development for Heterogeneous WLP Structures

Newly developed electrochemical plating baths with the capability of plating features with a wide range of dimensions and ARs will be discussed in this paper. The bath consists of conventional copper sulfate electrolyte and the typical organic additives: accelerator, suppressor and leveler. The features being plated include RDL, vias, lines, and UBM with 1:1 to 1:10 aspect ratio, with and without recess, having widths ranging from 10 to 250 micrometers and depths from 5 to 50 micrometers. This chemistry design can overcome the barrier of balancing fill performance, i.e., bottom-up plating (via fill), and conformal plating (RDL, Pads, Lines), while achieving good coplanarity and bump shape for all the different features across the panel. Thus, the goal of plating multiple, heterogeneous features with a single plating electrolyte system has been demonstrated. To understand the impact of these factors, nucleation density measurement, linear sweep voltammetry (LSV) and convection dependent absorption (CDA) methods have been used to evaluate electrochemical plating bath performance. An example of this bath plating on several particular WLP panels with different feature dimensions and aspect ratios will be presented in details with satisfactory results of coplanarity and flatness. This successful approach can lead to wide range of applications for WLP substrates with different features, not only the structures evaluated here.