Analysis on mechanisms and performance of on-line angle correction in LED die sorting

All dies are required to keep consistent angles in LED chip sorting. It is a problem because all chips are adhesive to wafer tape, each is rotated, and locations of all other dies change. Usually, visual rectification is used for this. While, each correction needs several adjustments, it may decrease production efficiency greatly. To solve this problem, an on-line angle correction method is put forward. Techniques including fast fitting to rotating center with machine vision, reverse seeking angle offset and translation distance for correction, approach for over-quadrant are discussed in detail. In addition, SPN model of sorting is built to analyze its influence to production rate. With experimental results, it is proved to be effective for angle correction with little loss of sort efficiency even in not too good working conditions.