Phone Soft Board For Image Processing And Machine Vision-based Defect Detection

Nowadays, there are two key issues for most domestic mobile phone manufacturers to produce FPC (Flexible Printed Circuit) board, one is the low cost of FPC board and the high cost of the automatic measurement equipments of FPC board, and the other is the relatively laggard measuring means and the demand of high quality mobile phone. Therefore, it becomes more and more important to study the defects measurement system for mobile phone FPC board.As a typical multi-layer FPC board, the quality would be improved by measuring the defects on each layer before gluing. This measurement operation is arranged just following the single layer of FPC board process, and before the board being incised. For the defects on mobile phone FPC board are too tiny to measure by eyes and the defects do not need to be repaired, based on the AOI (Automatic Optical Inspector) technique and the theory of image process and machine vision, a new automatic measurement system is designed. For the dim, low contrast of the FPC board image, the double annular optical fiber source and CMOS (Complementary Metal Oxide Semiconductor) camera are used to get image. The single layer basic board of FPC board area is equal to A4 (297mm×210mm). To satisfy the requirement of resolution, it is divided into 4 sub-boards, whose image is obtained by camera which is with 3 million pixels. The median filter is used to suppress the real-time noise and the LOG (Laplacian of Gaussian) filter is adopt to enhance the edge, the threshold value is obtained by adaptive threshold method, then the binary images can be acquired. Its flaw is measured by the design judgment criteria; the slight defect disturbance will be wiped off by comparing with some CAD templates based on the method of multi-template reference comparison. Finally the whole and part defects are determined and the bad FPC board would be discovered, which will be rejected.It is showed by experiment that the defects measurement system for the mobile phone FPC board is with the characteristics of high speed and high precision, the common defects can be measured accurately in the single-layer basic board with the area of 297mm×210mm in which the width of the circuit is 0.2mm and the distance between circuits is 0.2mm, also the faults of the circuit and other defects could be measured accurately.