Design for Manufacture - Ceramic Thick-Film Embedded Capacitors

摘要

Embedding discrete capacitors right into printed circuit boards (PWB), although not new, is part of a pivotal technology for the PWB industry. For example, the ability to locate decoupling capacitors within a couple hundred microns of semiconductor I/Os can greatly improve response time and signal integrity. One crucial packaging need, however, is high capacitance density. High capacitance density can only be readily achieved by ceramic capacitor technology. Therefore, the focus of this work has been to develop materials and methodologies to embed high capacitance ceramic capacitor layers inside the layers of the printed wiring board. Most research in embedding high capacitance ceramic capacitors layers directly into printed wiring boards has focused on forming capacitors on metal foil at high temperatures. It has generally been assumed that demonstration of good properties of these "fired-on-foil" capacitors is all that is necessary to be successful. However, in our experience, the greatest challenges to reliably embedding ceramic capacitor layers inside printed wiring boards reside in the design of the circuit containing embedded capacitors and the PWB embedding process. Not only does the PWB process have to contend with additional tolerance issues but, depending upon design, the capacitor may be subjected to aggressive processes and chemicals that may affect its mechanical or chemical integrity. It is, therefore, incumbent upon the designer to design circuits that can be reliably made by a PWB shop. This paper discusses these issues and gives some guidelines for design for manufacturing.