Cu Termination Development Progress

摘要

In recent years, Ni electrode multilayer ceramic capacitors (MLCCs) have been adopted successfully in the marketplace. The termination material of choice with Ni electrodes is Cu, and much activity has been spent in the industry to develop suitable Cu terminations. The typical problems reported with commercial Cu materials are marginal dip cosmetics, poor fired film density, and poor adhesion. Our efforts on Cu materials have been focused on acrylic resin-based systems, which are shown to be relatively tacky and newtonian in character. Rheology modifiers are required in order to more closely simulate the shear response that is obtained with the better known ethyl cellulose-based systems. Also, the microstructure of the Cu over the electrode area is critical to obtaining a reliable MLCC. For instance, the coverage over the electrodes is controlled by the paste rheology, coupled with the solids loading in the paste. There can be a tendency with acrylic/Cu systems to deposit excessive material over the electrode area, resulting in at best a rounded chip contour (resulting in a capacitor with a less precise geometry), and at worst leading to cracks in the termination after firing. Blotting is a practice that can control the deposit volume, though is an inefficient method in high volume manufacturing. Another important area microstructurally is the Cu/Ni/ceramic interface, where Cu-Ni interdiffusion can lead to a type of electrode projection problem, and insufficient glass migration to the interface can result in poor adhesion over the electrode area.