Power Inductors in Ceramic Multilayer Circuit Boards

Power electronic inductors, with values of several μH, have been integrated into thermally stable ceramic multilayer circuit boards by the use of NiZnCu and MnZn ferrite tapes in low temperature cofired ceramic (LTCC) technology. These ferrites are particularly attractive for switched mode power supplies in automation, drives, and consumer applications, where the miniaturization of modules is triggered by advances in transistor technology and switching frequencies. The small signal analysis of embedded individual inductors and coupled transformer coils reveals the generic design rules for these components and additional materials properties beyond those accessible by ring core measurements. In the process of adapting the materials to LTCC, the distinct differences between the two materials become blurred, for example, they can be engineered to exhibit similar cutoff frequencies. NiZnCu ferrite, which is sinterable in air, may even achieve higher permeability than MnZn ferrite. The latter, however, shows higher saturation flux density and current capacity of buried inductors for power line filters. The coupled inductor design in a transformer is particularly ruled by the shunt capacitance inside the coils and by the fact that Maxwell equations preclude strong magnetic coupling between ferrite-embedded conductor lines. While parasitic capacitances remain tolerable for standard dielectric layer material up to several MHz, the need for magnetic coupling requires a fabrication process for magnetic vias.

Two-Dimensional Modeling of Multilayer Multimaterial Circuit Boards by Using an EQLAM Multilayer Model

The materials used in the field of printed circuit boards are becoming increasingly complex as they are common to make use of numerous combination of metallic and composite plies. The potential for utilization of circuit boards is generally verified through the numerical simulation, especially for the multilayer printed circuit boards with high electronic density. This paper provides a numerical model intended to describe numerically the behavior of multilayer multimaterial circuit boards. Two parts are considered in the developed model: one is elastic-plastic damaging model that is presented to describe the metallic ply in the multilayer circuit boards; another is degenerated bi-phase model that is presented to describe composite ply. With the combination of equivalent laminate (EQLAM) method, the degenerated bi-phase successfully models the woven glass-fiber/epoxy-resin composite ply. These two plies are the basic components of multilayer circuit boards. Meanwhile, with the verification of static tests and dynamic tests, the reliability of presented model is confirmed.