Wednesday, June 20, 2018
Publication Date: 09/1/2011
Archive >  September 2011 Issue >  Special Features: Assembly and Production > 

Tabletop Automation for Fluid Dispensing
A PICO piezoelectric jet valve applies UV adhesive on a keypad. PICO valves can apply a wide range of fluids at up to 150 cycles/second, with exceptional process control.

In the fast-paced world of wireless handset manufacturing, companies are continuing to pack more features and functionality into ever-smaller packages. Tabletop automation systems provide the flexibility and precision to quickly respond to rapidly changing product designs, and can also be a cost-effective way to increase throughput and reduce production costs by automating repetitive tasks.

While circuit board production is largely automated, many other processes require the application of precise amounts of UV-cure bonding adhesives or other assembly fluids. Examples of these processes include:

  • Camera modules. Bonding lenses to barrels and barrels to holders.
  • Microspeakers. Bonding membranes to coils and housings.
  • Displays. Exterior edge seals, chip on glass (COG), tab seals and interior filling.
  • Touch panels. Exterior bonding to displays or other components, interior bonding of panel layers.
  • Keypads. Bonding keys to pads.
  • Miscellaneous assembly. Bonding cover glass, trim, emblems.
  • Applying hydrophobic coatings, encapsulating materials, protective lubricants.

Tabletop dispensing systems are an efficient way to streamline these fluid application processes without making a large capital investment in a full-scale automated production line. Tabletop systems include an XYZ (right/left, forward/back, up/down) positioning platform, a dispensing valve and controller, and a fluid reservoir. Typical platform sizes range from 200 x 200mm to 510 x 510mm. Dispensing valve options include pneumatic and high-speed piezoelectric designs.

The fluid reservoir may be a syringe, a cartridge or a pressurized tank. With the dispensing valve mounted on the robot, the desired pattern — dots, lines, rectangles, circles, etc. — is programmed with the robot's menu-driven teaching pendant. The dispensing parameters that control the dot size or line width produced by the valve are then set with the dedicated valve controller.
The Nordson EFD MicroSpray valve produces uniform spray patterns as small as 3.3mm in diameter. Here, a hydrophobic material is applied for moisture protection.

Once the positioning pattern and dispensing parameters have been set, all that the operator needs to do to process a batch of parts is load them into a fixture, secure the fixture to the positioning platform, and press the start button. While the fluid is being automatically dispensed on each part, the operator can be freed up to load the next pallet or perform other value-added tasks.

Pneumatic Dispensing Valves
Pneumatic dispensing valves used in wireless handset assembly processes include needle valves like Nordson EFD's 741V and 741MD-SS, and precision spray valves like the 787MS-SS. With pneumatic valves, the amount of material applied is determined by a combination of the pressure at which fluid is supplied to the valve, the length of time the valve is opened, and the size or gauge of the dispensing tip.

With the 741V valve, a precisely timed air pulse is used to lift an internal piston attached to the top of needle and withdraw the needle a preset distance from its seat so that fluid can flow to the dispensing tip. At the end of each cycle the needle seats inside the valve body at the point where the dispensing tip is attached. This minimizes dead fluid volume between dispensing cycles, which prevents extra material from being deposited when the valve opens to make the next dot or line. The 741V valve is capable of cycling more than 400 times per minute.

For even greater control when making very fine lines or very small dots, the 741MD-SS valve seats the stainless steel needle in the hub of the dispensing tip rather than the valve body. By having the fluid cutoff occur as close as possible to the dispensing orifice (the opening of the dispense tip), this design reduces dead fluid volume even further. Because the needle seat is part of the disposable dispense tip, the needle seat can be easily renewed as necessary, simply by replacing the dispense tip.

Either of these valves is available with a BackPack Valve Actuator — a fast-acting, miniature solenoid that mounts on the valve's actuating air cylinder — instead of on a separate fixture. By maintaining constant pressure at the actuating air inlet, the BackPack minimizes the risk of process variations due to fluctuating plant air supplies. It also provides the capability to cycle the valves 2 to 3 times faster and achieve valve actuation speeds as short as 5 to 6 milliseconds, and cycle rates as high as 800 per minute. This contrasts with typical valve actuation speeds and cycle rates of 15 milliseconds and 400 cycles per minute.

A precision spray valve can be used for protective treatment applications, such as hydrophobic fluids that repel moisture. The 787MS-SS MicroSpray valve uses an innovative design that uses a small gauge — 0.013 to 0.004-in. (0.33 to 0.1mm) internal diameter — disposable dispensing tip in place of a standard spray nozzle. This approach concentrates the Low Volume Low Pressure (LVLP) air used to atomize the coating into uniform spray patterns as small as 0.130-in. (3.3mm) in diameter — over 60 percent smaller than a standard spray valve configuration.

Piezoelectric Valves
PICO piezoelectric valves are another option that is rapidly gaining in popularity for handset dispensing applications. Although they require a larger initial expenditure than pneumatic dispense valves, piezoelectric valves can provide a fast return on investment due to their extremely high speed. They are capable of continuous operation at up to 150 cycles/second, or bursts of 150 at a speed of 1000 cycles/second, with exceptional process control.

Piezoelectric needle valves use fast-acting ceramic actuators that make it possible to apply very well-defined lines with precise control of the beginning and end points. When making circles or rectangles, this capability eliminates "knit lines" where these two points meet, for a nearly invisible juncture.

Piezoelectric jet valves bring the same level of speed and process control to applications where small dots are required. Because the fluid is jetted from a nozzle rather than applied through a needle, these valves do not need to contact the substrate, making them especially suitable for applying fluids on uneven or delicate surfaces. This also eliminates need for vertical Z axis movement between fluid deposits, allowing faster process speeds.

Both types of piezoelectric valves are available with integrated heaters that keep the fluid being applied at optimal dispensing or jetting viscosity.

Contact: Nordson EFD, 40 Catamore Blvd., East Providence, RI 02914-1206 800-394-3484 or 401-431-7000 fax: 401-431-7079 E-mail: Web:

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