Research Of FPC Quality Detection Optical Probe Based On Differential Astigmatic Principle

Recent years, with the rapid development of civilian equipment, such as mobile telephone, digital camera and thin TV, the market of FPC (Flexible Printed Circuit), which meets high density, small and flexible, grows apace. During the progress of FPC quality detection, most measurements focus on electric parameters, but the detection of parameters involved in product life, such as tiny cracks and creases, is manual work, which is time-consuming, inefficient and fatigue. Compared to mature production technology, inefficient quality detection has become a major bottleneck to the FPC production efficiency.In the progress of FPC (Flexible Printed Circuit) quality detection, the major measurements are: profile measurement, geometric shape dimension measurement and roughness (or mivrotopoghaphy) measurement. During these progresses, non-contact measurement of surface microdimension is a nodus. Even though the interference microscopy and the optical heterodyne profilemeter have high resolution, they can be only used in measuring very smooth and continuous surfaces. On the other hand, the mechanical stylus transducer has a large measurement range, but it can damage the surface, so, it is not fit for measuring the soft, fragile surface and the one taking information. Therefore, it is imperative to provide a non-contact measurement system to measure not only non-continuous surface, but also surface topography and small dimension.The purpose of the project 'Research of FPC Quality Detection Optical Probe based on Differential Astigmatic Principle' is to develop a new measurement system with high resolution, non-contact and real-time measurement. The paper mainly includes the following contents:1. This paper starts with the overall design of the measurement system, determines the design of the system's main components: focus error detection, photoelectric conversion and the test system software platform, and then research the expansion of the measurement range.2. Sets up the mathematic model based on laser beam optics of differential astigmatic optical system, which is more accurate than the model derived from geometric optics and much closer to the real measurement situation. According to the mathematic model, influences of different optical path parameters on the focus-error signal (FES) are analyzed. Parameters of the optical system are optimized.3. Design the system hardware and software. Based on the analyses of sources and suppression methods, the hardware system includes the design of photoelectric conversion circuit; the establishment of voice coil motor (VCM) mathematical model, which makes a solid theoretical foundation for the focusing actuator; the details analyses of the data acquisition card. The software includes the choice of software platform; the presentation of the system function; the software system optimization, which includes function optimization and performance optimization.4. Debug the system in detail to improve the system accuracy and stability. Use the system to do static characteristic measurement. The experimental results show that the detection method is correct and meets the basic requirements.