Back-drilling of high-speed printed circuit boards: a review

Back-drilling is a crucial technology for improving the signal integrity (SI) of high-speed printed circuit boards (PCBs) and plays a significant role in the growth of signal transmission to high frequencies and speeds. However, the performance of high-speed PCBs is greatly affected by hole plugging, the hole registration accuracy, and the via stub in back-drilling. Therefore, the key problems and technologies of back-drilling are investigated and summarized in this paper. First, the classification, the system components, and the features of back-drilling are presented. A summary of back-drilling effects on SI allows better understanding of the advantages of back-drilling in reducing the signal time delay, reflection, and resonance. The studies done by scholars to avoid plugged holes, to improve the hole registration accuracy, and to decrease the length of the via stub are also reviewed from the aspects of technological processes, machining parameters, back-drilling methods, and drilling machine accuracy. Finally, this paper provides some points of research that will help in the further study of the hole quality, hole registration accuracy, and stub control to enhance the performance of back-drilling.