Reliability quantification of printed circuit boards subjected to thermal and vibration loads

Abstract

Reliability quantification is one of the most important tasks in Reliability Engineering. During the design, development, and operational phase, this information can be very valuable to the product's designers, and users. The designers can use it to guide their design, find the design's weak points. Users can use it to setup maintenance plans and schedule. PCBs, as the major building block of electronic equipment, have been widely used in modern complex systems, such as aircraft, automotives, laptop computers, etc. Its reliability plays a vital role in the whole system's reliability. Thus, effective and accurate quantification of PCB's reliability becomes very essential to the whole electronic system's reliability quantification. Random vibration and thermal cycling are two common environments experienced by PCB's. As a result, quantifying the reliability of a PCB under these two environments becomes necessary. Currently, in industry, the commonly used methods to quantify the reliability of a PCB are the MIL-HDBK-217 and Bellcore type methods. However, the lack of accuracy and slow pace of updating the databases have limited the usage of these methods. In this dissertation, a Modified Stress-Strength Interference (MSSI) method is proposed to quantify the reliability of a PCB. In this method, not only the stress and the strength are assumed to be distributed, but also is the mean value of the strength, so that both the initial designed-in reliability and the reliability at any time can be quantified. Based on this method, a reliability quantification model for the PCB is developed. In this model, a PCB is divided into three parts: i.e., board, interconnects, and parts and modules mounted on the board. Seven (7) failure modes related to the board and the interconnects, and one (1) failure mode related to the module have been investigated. The dependence between these failure modes is studied and incorporated into the reliability quantification model. A three-step popcorn effect reliability quantification model is also proposed by means of considering the failure mechanism of the popcorn effect. Finally, a comprehensive example is given to demonstrate the usage of the methodology proposed in this dissertation.