Apply Optical Coherence Tomography To Non-destructive Detection On Coating Quality Of Automotive Electronics

Optical coherence tomography(OCT)is an optical imaging technology what realized by interference of low coherence light,and can do the three dimensional imaging for the scattering structure of material by the method of un-contact and high-resolution.Currently,the OCT included two types,one is spectral domain OCT and other one is sweep source OCT.But swept source OCT is being concerned and adopted more and more because of faster processing speed and less calculation load from signal's input.As for the scanning imaging speed,sensitivity and resolution,swept source OCT can meet the requirements of non-destructive examination in electronic manufacturing industry.Conformal coating is a transparent or semi-transparent material which is frequently used in automotive electronics industry,and it can lock the water molecules of printed circuit board and air interface layer,cut off infiltration of water vapor,and reduce the possibility of ion migration and corrosion on surface of the board.However,if conformal coating of circuit board has any quality problems,it would accelerate the ion migration on surface of the board,and then cause the circuit shortage on printed circuit board.Currently there's still no effective way to well control the quality of conformal coating,thus it often occurs that ECU(Electronic Control Unit)cannot meet the requirements of design,production and use.In this paper,system performance of swept source OCT and characteristics of conformal coating are combined,to build a Swept source OCT test system platform.Its vertical resolution is 13.48?m,and the imaging depth in conformal coating is up to 2.68 mm,which fully meets the analysis requirement of conformal coating.Meanwhile,this paper also proposes an OCT analysis method of bubble,stratification,uneven thickness and incomplete curing of conformal coating.For bubble and stratification,to obtain irregular interface shape by edge detection and boundary tracing;for uneven thickness,to act longitudinal depth measurement by using OCT;for incomplete curing,to show curing state by utilizing signal attenuation coefficient in depth direction.Based on above,we have done some experiments and comparative analysis,and prove that Swept OCT has the potentiality to do nondestructive examination for the quality of conformal coating.