Distributed Optical Fiber Sensors for PCB-Strain Analysis

Printed circuit board (PCB)-strain tests are part of the quality control processes to detect and identify predamages on manufactured products. Such tests are commonly performed by instrumenting a PCB, and subjecting it to the manufacturing conditions. Among the various parameters to evaluate on the production equipment, the induced strain on the PCB is one of them, enabling the assessment of the manufacturing equipment performance. PCB instrumentation with foil strain gauges is currently highly complex due to small size and over populated boards, limiting the overall number of monitoring points. This paper aims at outlining an alternative approach based on distributed optical fiber technology sensors. To prove its feasibility, optical fiber sensors based on optical frequency domain reflectometry are considered and benchmarked against conventional foil strain gauges. A PCB was instrumented with both sensor technologies and subjected to an in-circuit test machine. The strain results showed a match between both technologies, with a maximum deviation of 3.5%, a high precision level for multiple tests, and a high sensitivity for both high and low induced strains. Overall, the fiber optic solution proved to be a suitable alternative technology for foil strain gauges in PCB-strain measurement application.