The Study And Implementation Of Ultramicro Dispensing

In recent years, the higher requirements for the micro-dispensing is put forward to satisfythe miniaturization of products, the improvement of technical requirements precision and thecomplication of operating environment, which makes existing micro-dispensing technology isdifficult to adapt to the higher requirements.In this work, we put forward an ultra-micro dispensing approach based on the surfacetension of micro-droplet: a thin tungsten needle travel through a capillary equipped with fluidand a micro-droplet will be adhered to its tip (or end). When the needle’s tip closed to thetarget surface, dispensing can be achieved due to the interfacial tension between the adhereddroplet and the target surface. The dispensing volume can be easily controlled by means ofmatching the parameters of dispensing process. This approach can be used for high viscosityfluid and spatial arbitrary direction dispensing. The concrete contents and conclusions are asfollows.Firstly, the surface edge effect involved in the process of ultra-micro dispensing isdescribed, and the whole ultra-micro dispensing process is divided into several main stageswith choosing the “micro-droplet” as the study object and the surface force of each stage isanalyzed. Then, a device for ultra-micro dispensing is designed and the operating process isalso elaborated on this device.Secondly, according to the several stages, the control mechanism and quantitativedescription for the dispensing volume is theoretically analyzed with reasonable assumption.Theory analysis shows that the end diameter of tungsten needle, dispensing distance GAP, andthe movement velocity of tungsten needle play a critical role during the formation and ruptureprocess of the liquid bridge, which point out the direction for selecting which dispensingparameters will be considered in the simulation and experiment.Thirdly, the numerical simulation model of ultra-micro dispensing is established by jointingthe VOF model, CSF model, Dynamic Contact Angle model and Dynamic Grid Technique,etc with the traditional control fluid mechanics equation. Then, on basis of the simulationmodel, the dynamic process of ultra-micro dispensing is simulated and how the end diameterof tungsten needle, GAP as well as the movement velocity of tungsten needle affect thediameter of the dispensing dot are simulated respectively.The last but one, an ultra-micro dispensing experiment platform was built and theexperiments that micro-droplet adhered to the end of tungsten needle were conducted athorizontal and vertical direction respectively, the experimental results show that the two micro-droplet shapes are very similar that indicated the ultra-micro dispensing can be suitablefor spatial arbitrary direction dispensing. Corresponding to the simulation parameters, theexperiments that analyze how the end diameter of tungsten needle, the GAP and themovement velocity of tungsten needle affect the diameter of the dispensing dot were carriedout respectively. And then the contrastive analysis between experimental values andsimulation values verified the established numerical simulation model has certain validity bywhich the variation tendency of dispensing dots can be well predicted. With proper dispensingparameters, the ultra-micro dispensing with a volume of40fL,170fL and180fL when thefluid viscosity was971cP was achieved and the dispensing spot’s diameter of243.9um as wellwhen the viscosity was up to30000cP. To satisfy the requirement of ultra-micro volume withnot more than3pL (the diameter of dispensing dot not more than50um) for the used glueTRA-BOND2115dispensed on one special material in a micro-sealing engineering, thepreliminary experiments by using the tungsten needle with a diameter of30um wereconducted and the average experimental value of the diameter of dispensing glue dot is about44um which can satisfy the requirement.Finally, considering that there are bubbles may appear at the bottom of the liquid bridgeand the demand of the high speed dispensing, the preliminary optimization for motion law oftungsten needle has been experimentally conducted.