Decoupling of Temperature and Strain Effects on Optical Fiber-Based Measurements of Thermomechanical Loaded Printed Circuit Board Assemblies
Author:
Leite Tiago Maurício1, Freitas Cláudia2, Magalhães Roberto1ORCID, Ferreira da Silva Alexandre3ORCID, Alves José R.1, Viana Júlio C.2, Delgado Isabel1
Affiliation:
1. BOSCH Car Multimedia, 4705-820 Braga, Portugal 2. IPC—Institute for Polymers and Composites/LASI, Department of Polymer Engineering, University of Minho, 4800-048 Guimaraes, Portugal 3. CMEMS-UMinho and LABBELS-Associate Laboratory, Department of Industrial Electronics, University of Minho, 4800-048 Guimaraes, Portugal
Abstract
This study investigated the use of distributed optical fiber sensing to measure temperature and strain during thermomechanical processes in printed circuit board (PCB) manufacturing. An optical fiber (OF) was bonded to a PCB for simultaneous measurement of temperature and strain. Optical frequency-domain reflectometry was used to interrogate the fiber optic sensor. As the optical fiber is sensitive to both temperature and strain, a demodulation technique is required to separate both effects. Several demodulation techniques were compared to find the best one, highlighting their main limitations. The importance of good estimations of the temperature sensitivity coefficient of the OF and the coefficient of thermal expansion of the PCB was highlighted for accurate results. Furthermore, the temperature sensitivity of the bonded OF should not be neglected for accurate estimations of strains. The two-sensor combination model provided the best results, with a 2.3% error of temperature values and expected strain values. Based on this decoupling model, a methodology for measuring strain and temperature variations in PCB thermomechanical processes using a single and simple OF was developed and tested, and then applied to a trial in an industrial environment using a dynamic oven with similar characteristics to those of a reflow oven. This approach allows the measurement of the temperature profile on the PCB during oven travel and its strain state (warpage).
Subject
Electrical and Electronic Engineering,Biochemistry,Instrumentation,Atomic and Molecular Physics, and Optics,Analytical Chemistry
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