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Increased Accuracy and Speed with Piezo Dispensing
PICO jet dispensing system is a non-contact dispensing system that uses piezoelectric technology.

As today's mobile devices continue to get smaller and thinner, the amount of space available for securing components and subassemblies is steadily decreasing. In response, many

manufacturers are turning to adhesives and other assembly fluids as alternatives to mechanical fasteners in their assembly processes.

Traditional fluid application methods include handheld syringes, air-powered benchtop dispensers, and precision dispense valves. While these technologies are viable for many processes, today's smaller mobile device packages have made consistent size and placement of the adhesives, coatings and other materials used to build them more critical than ever before. Piezoelectric dispense valves provide a way for companies seeking faster production speeds or greater accuracy in this challenging environment a way to achieve these objectives.

Piezo is Greek for "pressure." When pressure is applied to certain crystalline materials, such as quartz, it creates voltage. Conversely, when voltage is applied to a crystal, the crystal changes shape.
Piezoelectric jet valve in closed position.

Piezoelectric valve systems typically consist of three components: the valve (styles include jet valves, needle valves, and slider valves), a valve driver, and a valve controller. Nordson EFD's PICO piezoelectric dispensing systems are a good example of a three-component setup.

Jet Valves. Jet valves incorporate two piezoelectric actuators comprised of stacked ceramic coins that expand and contract in response to changes in voltage supplied from the valve driver. Both actuators are connected to a vertical rod that has a ceramic sealing ball attached to its lower end. When the valve is in the closed position, the ball is seated in the valve nozzle. When voltage is applied to the actuators, the rod and sealing ball are raised so that the pressurized dispensing fluid can flow to the nozzle. When the voltage is changed, the rod and sealing ball descend rapidly to force or "jet" the fluid out of the nozzle and onto the substrate. Depending on the application, deposits can be in the form of dots or lines.

Extremely Fast Action
The extremely fast action of the piezoelectric actuators makes it possible to dispense fluid continuously at speeds of up to 150 cycles per second. Depending on the fluid being dispensed, the system can produce consistent shot volumes as small as 2 nanoliters, and the high resolution (0.01 milliseconds) of the valve controller makes it possible to adjust the size of the fluid deposit with exceptional precision.
Piezoelectric jet valve in open position.

PICO jet valves are available in several different configurations to handle fluids ranging from 50 to 500,000 cps. The LV configuration is designed for use with low-viscosity fluids from 50 to 1,000 cps; the MV configuration covers a wide range of viscosities from 50 to 200,000 cps; and the HV configuration is specifically designed for fluids with high viscosities of 1,000 to 500,000 cps. Nozzles are available with 150, 200, 300 and 400µm orifice diameters to accommodate a wide range of dot sizes.

Because the valve nozzle does not contact the substrate, piezoelectric jet dispensing systems are also a good choice for applications where controlled amounts of fluid must be applied on surfaces that are not perfectly flat, such as printed circuit boards. Eliminating contact with the substrate also eliminates the need for vertical Z-axis movement and precise height positioning, which can significantly increase production speeds. The typical dispense height for a piezoelectric jet valve is 3 to 5mm from the substrate.

Built-In Heater
Most PICO jet valves incorporate a heater near the fluid channel to maintain optimum jetting viscosity. While jet valves are capable of dispensing a wide variety of fluids, they are not suitable for use with anaerobics or fluids with a pot life of less than four hours, because of the risk of these materials curing inside the valve. Piezoelectric jet valve applications include bonding LCD panels to transparent touch screens, attaching keypads to silicone membranes and encapsulation of components on flexible circuits.

Needle Valves Piezoelectric needle valves also use a horizontal actuator, but have a dispensing needle instead of a nozzle.

Needle valves are a good choice for applying stringy fluids that cannot be jetted. Because they permit the use of higher fluid pressures while maintaining the highest accuracy, they can dispense at a more rapid rate than conventional dispense valves, resulting in faster production speeds with fewer bottlenecks.

Typical Applications
Typical needle valve applications include bonding camera lens covers and bonding LCDs to frames on mobile devices.

Slider Valves. Piezoelectric slider valves are capable of producing very small, very repeatable deposits of solder paste and other highly filled materials such as electrically conductive adhesives, making them especially suitable for mobile device electronics assembly.

With this design, the actuators are mounted vertically and the solder paste or electrically conductive adhesive is kept in a vertical fluid path under steady pressure. When the voltage is applied, the actuators cause the components of the dispensing orifice to rapidly slide open and closed to produce the deposit. Compared to the conventional auger valves often used in electronics assembly, piezoelectric slider valves can produce much smaller deposits at a much faster rate, with less stress on the fluids or its fillers.

Valve Driver. Piezoelectric dispense valves are powered by valve drivers that use an amplifier to generate the signal for the piezoelectric actuators.

Valve drivers usually contain a temperature controller for the integrated heater in the valve. Temperature adjustment affects the temperature of the valve body, which in turn affects the temperature of the fluid being dispensed. The maximum temperature attainable is 100°C (212°F) or 180°C (356°F), depending on the driver model. Temperature can be adjusted with the potentiometer on the valve driver, with the valve controller, or with a CAN BUS interface connected to the valve controller.

Valve Controller. PICO valve controllers are used to set the fluid application parameters for each valve. Graphical displays and user-friendly menus make it simple to create complex jetting processes on a PC, and then download them to the controller through an integrated SD card slot. A password protection feature ensures that standard procedures are not changed accidentally, helping to ensure accurate and repeatable results.

{X]Contact: Nordson EFD LLC, 40 Catamore Blvd., East Providence, RI 02914 401-431-7000 E-mail: info@nordsonefd.com Web:

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