SMT007 Magazine

SMT-Jan2016

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20 SMT Magazine • January 2016 Contact vs. non-contact Dispensing Two methods are commonly employed to dispense process fluids: contact dispensing, in which fluids are dispensed using a dispens- ing tip, and non-contact dispensing, in which fluids are commonly jetted. A manufacturer should choose one or the other depending on the viscosity and consistency of the fluid and the application requirements. While contact dispensing produces much smaller deposit sizes than non-contact dispens- ing, the dispensing tip must be placed close enough to the part so that the fluid can make contact with the tip and part at the same time, as illustrated in Figure 1. In automated dispens- ing processes, this method is more time-con- suming than the non-contact method because the tip must be lowered onto the dispensing area and retracted before it is moved to the next dispensing point. In contrast, non-contact dispensing ac- celerates the process because the jetting ac- tion does not require automation to lower and raise the tip along the z-axis. Thus, the cycling of the jetting valve—which is usu- ally piezoelectric—is performed at much faster speeds and higher cycle rates than tip dispensing can achieve, allowing for greater cycle time savings. An example of how a non- contact jetting valve dispenses fluid is shown in Figure 2. In automated non-contact dispensing sys- tems, some valves dispense fluids in volumes down to 0.2 nl with diameters as small as 50 µm. They can also handle fluids with water- like viscosities ranging from 1 to 5 cPs or thick pastes with viscosities up to 1,000,000 cPs at continuous dispense speeds up to 500 Hz. Pre- cision automated dispensers are accurate sys- tems which can deposit fluids at the desired location, including hard-to-reach places and device edges. WHy MEDTECH ManuFaCTurErS SHOuLD auTOMaTE FLuID DISPEnSInG OPEraTIOnS figure 1: While contact dispensing produces much smaller deposit sizes than non-contact dis- pensing, the dispensing tip must be placed close enough to the part so that the fluid can make contact with the tip and part at the same time. figure 2: in noncontact dispensing, the cycling of the jetting valve—which is usually piezoelectric— is performed at much faster speeds and higher cycle rates than tip dispensing can achieve, allow- ing for greater cycle-time savings. FEATurE

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