Research On Key Problems Of Micro Coating Detection For High Power White LED Phosphors

High-power white LED is considered as the mainstream light source in the future lighting field due to its advantages of high power,high brightness,environmental protection,energy saving and high efficiency.In order to seize the market dividend,manufacturers at home and abroad have vigorously developed LED manufacturing technologies.Phosphor coating is a key part of LED packaging process,and the coating effect has a great relationship with the coating method.The micro-coating method is an efficient phosphor coating method,which has the advantages of high coating speed,high coating accuracy,large coating coverage,and the like.However,in the micro coating process,defects such as incomplete coating surface,offset coating position,and poor coating thickness may also occur,so that coating inspection is very important.In addition,since the micro coating method has a thin coating thickness and the object to be coated is a large number of small-size LED chips on the substrate,the coating inspection needs to meet the requirements of rapid and high precision.However,the manual detection methods commonly used in industry have low detection efficiency and accuracy and cannot meet the requirements of micro-coating detection.In view of the above situation,this article will use the automatic detection method to detect the surface defects and coating thickness of the coating area,the main work is as follows:(1)According to the characteristics of the micro-coating method and its coating object,and combining with the industrial production requirements,the applicability of commonly used detection methods is analyzed,and a reasonable coating inspection program is finally determined.The detection scheme is mainly composed of two parts,the surface defect detection and coating thickness detection in the coating area.(2)According to the detection scheme and requirement analysis,this paper designs the hardware and software system structure,and makes rational selection of hardware components such as camera and light source.(3)In order to achieve the purpose of surface defect detection in the coating area,this paper first segmented the coated area on the tested substrate,and then obtained the information of the scale lines on the substrate frame through a certain detection algorithm,and used the information of the scale lines and the chip design specifications to locate the area to be coated.The coverage area is compared with the area to be coated.Finally,the defect type is identified according to the comparison results of the coating area and the area to be coated and the set criteria.Considering that coating area segmentation is the focus and difficulty of surface defect detection,this paper also specifically proposes a segmentation algorithm based on the combination of threshold method and region growing method.This algorithm can effectively avoid the interference of discrete phosphor particles and pin oxidation on the segmentation effect,and has the advantages of fast segmentation and high precision.(4)The oblique laser triangle method was used to detect the coating thickness.In order to obtain high-precision detection results,this paper puts forward a centering algorithm of laser spot center extraction based on iterative fitting of center of gravity scanning.The algorithm has changed the traditional gravity center method,and can avoid the interference of spot edge nicks,burrs and noise in the image on the spot center extraction,and has strong robustness.