Modeling and control of dispensing processes for surface mount technology

Dispensing is a key process in surface mount technology (SMT), in which minute amounts of fluid materials (such as solder paste, adhesive) are delivered controllably onto printed circuit boards for the purpose of conducting, bonding, etc. Time-pressure dispensing by means of pressurized air is currently the most widely used approach in SMT. Due to air compressibility, the control of the time-pressure dispensing process has proven to be a challenging task in achieving a high degree of consistency in the amount of fluid dispensed. This paper presents the development of a model of the amount of fluid dispensed by taking air compressibility into account. Based on the model, a control strategy is then developed to improve the consistency in the amount of fluid dispensed. Experiments were conducted to verify the effectiveness of the control strategy.