Controlled fluid dispensing can remove the variability from manual dispensing manufacturing processes by using microprocessor circuitry, controlled air pressure, and digital displays to assure consistent deposits of various materials. Precise control of the various dispensing parameters will dramatically reduce the time required for operator training and eliminate operator inconsistencies. As a result, the dispensing process becomes less operator-dependent, material application is more consistent and new operators quickly learn to produce compliant assemblies.

Pneumatic dispensers use a combination of air pressure, dispense time, and tip size to determine the amount of fluid applied. Of these three parameters, dispense time is the most accurate way to control deposit size. Adjusting one or more of these parameters allows the user to fine-tune the deposit size for different fluids and applications. Thick materials like epoxies, solder pastes and adhesives require higher pressures, longer dispense times and larger tips than do thinner materials such as adhesives and conformal coatings.

Setup and operation of a timed-pulse dispenser system is simple and straightforward. The compact dispensing console is placed on the bench top, plugged into a power outlet and connected to a source of compressed air.

The material to be dispensed is contained in a disposable syringe reservoir that can either be purchased pre-filled from a supplier or loaded on site. The top of the reservoir is connected to the dispenser console by a flexible airline, and a precision dispense tip attached to the front end completes the assembly. To the user, the overall effect is similar to hand dispensing using a syringe, but with controlled air pressure regulating the amount of material dispensed.

A dispenser with a "Teach" function and digital display like the Model 1500XL from EFD, makes it easy to quickly determine the optimal amount of material to use for a given application. In Teach mode, the timer is temporarily bypassed and the dispenser's electric foot pedal is pressed to allow air pressure to move material through the barrel and tip and onto the part. As soon as the correct amount has been applied, the pedal is released and the dispense time stored in memory. Dispense time can also be set manually and fine-tuned with the microprocessor-based timer. Consistent deposits as small 0.006 inches in diameter can be attained with either method.

If dispense time needs to be increased or decreased after the initial deposit size has been established, the user can simply scroll up or down in 0.1, 0.01, or 0.001 second increments. Once the desired open time is known, it can be entered directly the next time that product is produced. To apply material, the operator simply holds the barrel like a pen, places the tip in position on the component, and taps the foot pedal to actuate the timer and dispense the predetermined amount of material. Tapping the pedal again applies an identical amount of material. For materials that are prone to changes in viscosity, the Teach function can also be used to quickly bring the size of the deposit back to original tolerance.

The EMPF's three EFD 1500 bench top dispensing units are being integrated into a robotic work cell. As part of the Power Electronics Teaching Factory (PETF), the work cell is being designed to assemble high power semiconductor modules. A programmable Logic Controller is controlling all of the dispensing functions for the three pumps.

Each dispensing unit will dispense a specific material:

• Pump one - Paste Flux will be dispensed to a base plate copper assembly before a module is placed.
• Pump two - An adhesive will be dispensed to seal the subassembly to the module housing. This dispensing pump will place a small bead of adhesive around the bottom side of the module housing before mating with the subassembly. Thermal curing will be used to finish off this process step.
• Pump three - Once the module is assembled, a two-part dielectric Gel will be injected through the top of the module.

The robotic work cell is being designed and built by Cyclone Industries working in conjunction with EFD and EMPF engineering support staff, incorporating EFD technology into the overall robotic cell capability. If you would like to see a demonstration of the EFD dispensing pumps, please contact Jeff Stong at the EMPF at 610-362-1200, extension 224 or jstong@aciusa.org . Jeff will gladly answer any questions regarding controlled fluid dispensing and assist you in any way possible.