No abstract

Numerous applications exist where electronics must operate reliably in moist environments, and often for long periods of time. In these environments, the circuit board assemblies may experience moisture ingress, which can deleteriously affect the operation and life span of these systems. Detecting moisture ingress is therefore useful for improving system design, assembly techniques, packaging technologies and maintenance scheduling. Capacitive fringing field sensors are useful for measuring the moisture content of materials. Therefore, a capacitive fringing field sensor, implemented in printed circuit board technology with a CMOS relaxation oscillator interface circuit, is proposed for detecting moisture ingress into the printed circuit board assembly. A set of instrumented sensors was designed, fabricated and tested. The results demonstrated that when the test articles experienced prolonged exposure to moisture, the instrumented sensors experienced an 18.42% change in output value, indicating a satisfactory sensitivity to moisture ingress.

Most circuit boards operate in environments that have the potential to be exposed to moisture, either in vapor or liquid form. Because low-cost circuit boards can readily absorb moisture, this can lead to performance issues, reliability issues, and even catastrophic failure. However, it is difficult to detect if moisture absorption has occurred before the circuit board suffers a complete failure. To alleviate this issue, a fringing field capacitor was implemented in printed circuit board (PCB) technology and used to detect the absorption of moisture in the circuit board through the accompanying increase in capacitance. Prototype sensors were fabricated and immersed for 42 d, demonstrating an increase in capacitance of between 14% and 29%. This sensor technology can easily be added to circuit board designs because they use the standard materials and fabrication processes used in commercial PCB construction.