Quality inspection of optical lens in IC Packaging Equipment based on MTF

As IC packaging equipment has higher and higher requirements for vision module, high quality optical lenses play a key role in the image quality. As an important index, the modulation transfer function (MTF) is widely used in qualitative and quantitative expression of an optical imaging system performance. The improved slanted edge method is used to calculate the MTF of the imaging system in the study of the imaging quality. A method of canny operator combined with cubic function fitting is proposed to track the edge, and the accurate sub-pixel edge points are obtained. The five-point linear filter is used to de-noise the sample points, and the improved Hyperbolic function is used to fit the ESF curve. The influences of the angle of edge and noise on the accuracy of MTF measurement are analyzed. Experiments suggested that Edge angle and noise have a great influence on the accuracy of MTF test and the modulation transfer function area (MTFA) method has high efficiency in determining the quality of the lens. Compared with the previous method, the proposed method has higher test accuracy, better test repeatability and stronger noise resistance.