In many industries the failure of temperature devices such as resistance temperature detectors (RTDs) are of significance to process control. Therefore, a study was instituted to evaluate these failures. RTDs from various manufacturers were monitored and periodically calibrated until failure. Sensors that developed open circuits were then examined. Upon examination of the sensors, it was found that failures were occurring at or near the solder connection between the platinum lead-out and copper wire. A two-dimensional (2-D) finite element analysis of this joint was then developed.
Finite element models were created to evaluate stresses at 100, 200, and 300°C. The thermal expansion mismatch between the wires joined by the solder results in high-stress gradients at the corners of the solder joint. Photomicrographs were produced of the joint failures with a scanning electron microscope to study the crack nucleation and propagation. Aging of the solder due to long-term temperature exposure may also play a key role in the fracture behavior. The need for improved joint design and special coating materials is of primary importance to improve the life of the solder joints in many applications. This will improve the reliability of the components.