Optimal iterative learning feedforward control of wafer temperature uniformity in vacuum reflow soldering

Abstract

As device dimensions shrinks to submicrometer range, wafer level vacuum packaging and integration is an emerging method to resolve the requirements from industries. Addressing this issue and in consideration of nearly identical environmental conditions of each soldering process and difficulties in measuring temperature of wafer in real soldering process, in this paper, an optimal run-to-run iterative learning gain scheduled feedforward control of wafer temperature uniformity in vacuum reflow soldering process has been investigated. The proposed technique has been applied to a vacuum reflow soldering equipment for 8-in wafer. Along with run-to-run sequential experiments, gradual improvement of temperature uniformity across a wafer surface has been shown. The wafer was heated to desired temperature recipe and the temperature uniformity was maintained as desired level by applying the proposed control.