A fluid dynamic analysis in the chamber and nozzle for a jetting dispenser design

Electronic packaging industry widely uses a dispensing technology to deliver adhesive materials on substrates through a dispensing system. The cured adhesives can encapsulate and connect chips and substrates to provide mechanical, physical and chemical protections. For the high density packaging, a jet dispensing is regarded as the next generation adhesive delivery technology due to its features of non-contact, high precision and high efficiency. We developed a jet dispensing system including a jetting dispenser, a 3-axis movement platform, a substrate carrier, a power module, motion control hardware and software, supplementary modules, etc. The jetting dispenser is the most part since it affects the accuracy and quality during the dispensing process. Before its structure design and prototype manufacturing some important physical parameters can be determined by the fluid dynamics analysis. In the jetting dispenser, a piston drives a needle to move downwards and push the fluid flowing in the chamber and dispensing out of the nozzle. A simplified physical model has been set up to promote discussing the dynamic properties of the fluid. The results of dynamics analysis reveals that there are a back flow and a jetting flow existing in the chamber and an unsteady flow existing in the nozzle. The flow rate and volume are the most key parameters for the dispenser design. They are dependent on the nozzle length and diameter, the chamber length and diameter, the dynamic viscosity, the coefficient of the on-way resistance, the needle speed and the initial pressure on adhesive.