An Intelligent Error Compensation Method for Height Measurement of Bump Package

The coplanarity of the bump height is the guarantee of packaging quality. Optical triangulation is a widely used method to measure the bump height. However, it is not easy to accurately measure the bump height due to its small size, curved and highly reflective surface. In order to solve the problem of poor stability in triangulation measurement when using light strip center extraction, we analyzed the error reasons in a white light triangulation based bump height measurement. Then, an improved gray centroid method was applied to extract the light strip center on the base wafer and the light spot on the bump top. Next, the calibration results was combined to calculate the initial bump height. Finally, two features of the light strip and light spot were detected to train a multilayer perceptron to obtain an intelligent compensation for the bump height. It was proved that the standard deviation and the extreme difference of bump height are reduced to at least 1/2 after using our compensation method. The average standard deviation was reduced from 0.651um to 0.281um, as well as the average extreme difference was reduced from 1.790um to 0.689um. The result can meet the requirements of most of the bump package.