Failure modes and FEM analysis of Conductive Anodic Filament resistance during high-frequency electromagnetic of PCB

In the multilayered printed circuit board (PCB), the signal transmission between different layers occurs by way of through hole structure. The geometry of a through hole consists of traces, pads and a perfectly conducting hollow cylinder. Conductive Anodic Filament (CAF) generated easily in PCB when board size is decreased. CAF produced will lead to leakages or short circuit. Many reasons cause the phenomenon of the CAF, one of them is the voltage. In these situations, the signal transmission integrity is concerned. The excessive capacitance is generated near the through hole structure. Such capacitance influences the signal transmission between different layers. A number of factors can cause excessive capacitance, for example: geometry of transmission line, pad of through hole and the interaction of different layers. However, recent application of the multilayered printed circuit board such as cell phones and note books, have decreased the broad size for easy to carry or load more equipment. Decreasing the size of PCB, the excessive capacitance near the through hole structure is inevitable. It is more important to design the complexity of the layout and the geometry of structure. The quick and efficient prediction of the performance is concerned when manufacturing process become more complicated. The simulation model and problem discussion are the subject of this paper. In this study, we demonstrate that the geometry of the transmission line near the through hole may affect the transmission of the signal by excessive capacitance. By using ANSYS 12 to simulate the high frequency electromagnetism, and simulate the transmission line with different shapes near the through hole and extract the Scattering-parameters from the simulation results. Scattering-parameters are used to describe the electrical behavior of linear electrical network. The parameters are helpful for us to design electrical engineering, electronics engineering, and communication systems, and especially for microwave engineering. By comparing Scattering-parameters of different structures, we can understand the signal transmission and reflectivity between two layers. We also analyze the electric field and magnetic field of the structure, and use a method based on the quasi-static approximation to compute the excessive capacitance of the through hole structure. Using the concept of equivalent circuit to convert the original model into the RLC circuit. Equivalent circuit is divided into multiple series parts. Many parameters such as resistance, capacitance, inductance and characteristic impedance will be discussed, then compare these value changes between different shapes of the transmission line near the through hole. The ANSYS model is proposed to simulate the high-frequency electromagnetic of the structure. By these model, we want to predict the signal transmission performance of the through hole structure.