印制电路板板内阻抗测试关键操作点以及失效案例分析

Study on PCB impedance test method and failure cases analysis

随着数字时代的发展，高速、高频板上信号传输速率要求越来越快，对信号完整性的要求也越来越严格，客户对印制电路板（PCB）的传输线阻抗匹配性也越来越重视。传统的PCB阻抗测试主要以板边的测试COUPON为参考，但考虑到PCB板边阻抗Coupon自身的局限性，无法完全反映PCB板内真实走线的特性阻抗；随着大家对阻抗匹配性、信号完整性的影响等的加深认识，对于PCB板内阻抗测试的要求越来越受到PCB厂商、高速电路设计者的重视。同时阻抗的测试也受到操作、设备、参数选取、测试点选取等多方面的影响。文章主要是分析影响PCB板内阻抗测试结果的关键点，同时结合相关的测试失效案例分析，规范快速定位正确测试区域的方法，对PCB板内阻抗利用TDR方法测试具有参考意义。

With the development of digital era, the high speed and high frequency PCB signal transmission rate is more and more fast. And the requirement is more and more strict with signal integrity（SI）. At the same time, the customer pays more attention on the impedance consistency of PCB. As we know, most of the PCB impedance test is by the coupon near the board, but it can not reflect the perfect truth inside the board with its limitation. According to the understanding of the impedance consistency and SI, the PCB impedance testing on the units will be more and more importance for the PCB manufactory and the designer. And the impedance test may be affected by the operation, equipment, parameter, test position and so on. This paper studies on the test method of PCB by TDR with the failure cases analysis, and intend to give the guideline on how to choose the right test area quickly. It will be helpful to the PCB impedance test on the units by TDR.