Closed loop feedback for continuous mode materials jetting [solder/adhesives]

This paper presents a continuous mode materials jetting process that is being developed for solder and adhesive application in electronic and opto-electronic packaging. Specifically, the paper addresses closed loop feedback techniques applied to continuous mode materials jetting which work by measuring an increased number of smaller droplets both more accurately and more quickly than previously reported methods. Both of these process metrics are essential to the adaptation of the process in the target production environments. Several computer vision techniques are presented, each of which continue to perform satisfactorily as the ball size diminishes. This method allows control of the droplet diameter to within 2.5% of the target value throughout a wider range of sizes than has been reported to date. The paper also discusses the advantages of using differential pressure variation in the control loop to adjust droplet size as opposed to altering the frequency of the mechanical vibration.