Detect curing extent of conformal coating using speckle variance optical coherence tomography

Xiwen Wang; Qian Wu; Jie Zhu; Jianing Dai; Jianhua Mo

doi:10.1117/12.2537491

18 November 2019 Detect curing extent of conformal coating using speckle variance optical coherence tomography

Xiwen Wang, Qian Wu, Jie Zhu, Jianing Dai, Jianhua Mo

Proceedings Volume 11189, Optical Metrology and Inspection for Industrial Applications VI; 111890C (2019) https://doi.org/10.1117/12.2537491
Event: SPIE/COS Photonics Asia, 2019, Hangzhou, China

Abstract

Conformal coating is a protective coating widely used in printed circuit boards (PCBs), protecting PCBs from harsh environmental conditions. Its curing extent and thickness are the key factors, determining its protection performance. At present, the traditional method to evaluate the curing extent is metallographic section, which cuts PCB and images its cross-section under a microscope. However, it is destructive. In this study, we proposed to use optical coherence tomography (OCT) to evaluate the coating curing extent. Note that Brownian motion inside the conformal coating gets slower during curing process, leading to a smaller OCT intensity variation over time. Therefore, speckle variance (SV) of OCT imaging, which actually measures the OCT intensity variation, is expected to become smaller during the curing process and can be used to evaluate the curing extent over the whole imaging depth. To demonstrate the capability of SVOCT in detecting the curing extent of conformal coating, multiple OCT images were acquired at each curing status for SV calculation. The results show that the speckle variance of OCT image will gradually decrease during the curing process of conformal coating and eventually stabilize after the coating cures completely. This can be utilized to assess the curing extent of the conformal coating.

Citation Download Citation

Xiwen Wang, Qian Wu, Jie Zhu, Jianing Dai, and Jianhua Mo "Detect curing extent of conformal coating using speckle variance optical coherence tomography", Proc. SPIE 11189, Optical Metrology and Inspection for Industrial Applications VI, 111890C (18 November 2019); https://doi.org/10.1117/12.2537491

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