The uniform droplet spray (UDS) process produces solder spheres by controlling the breakup of a continuous laminar jet into uniform droplets, which are then rapidly solidified in a liquid bath or an inert gas. Although the spheres have a narrow size distribution (+/-9% from mean size), still greater size accuracy is required (+/-3% from mean size) for the use of these spheres by the electronics industry, particularly for ball grid array (BOA) chip interconnection technology. This article discusses the production of highly size-accurate solder microspheres (75-1000 mu m in diameter) by the UDS process. An on-line droplet size control system was developed to achieve the size distribution requirements. Droplet size control is accomplished by performing a real-time measurement of the droplet size, and then compensating for the difference between actual and target sizes by adjusting the breakup frequency. The control system is effective irt controlling sphere size, enabling the UDS process to accurately determine and control solder sphere size within +/-2.5% of the target size. While this article focuses on the production of large solder spheres (250-800 mu m), the control system can be applied to spheres of any size produced try the controlled breakup of a liquid jet.