Study on the Effect of Moisture Stress on Printed Circuit Board of Numerical Control System

This paper studies the effect of moisture stress on insulation resistance (IR) failures of printed circuit board (PCB) for numerical control (NC) purpose under the temperature-humidity-bias conditions. A characteristic of the IR failures is a series of intermittent IR drops, which can severely affect the reliability of NC assemblies. In this paper, all the test multilayer PCBs for NC purpose are subjected to a humidity and heating experiment in a high and low temperature damp heat test chamber, maintained at 40°C throughout the test. Then the effect of moisture stress on NC finished boards is discussed and a relative humidity threshold is predicted from analyzing experimental data which can provide an basis for accelerated life testing of NC PCBs. Conductor spacing is observed to represent a factor in the electrochemical migration (ECM) process, indicating that further study on conductor spacing is required to predict reliability of today´s high-density PCBs. The study reveals that the effect of moisture stress on IR is investigated to decrease faults from humidity then improve the quality and reliability of NC circuit boards.