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Scalable dispensing solutions, what does this mean? It’s a new concept in dispensing system design. Asymtek frequently interviews customers to better understand their future dispensing requirements and associated equipment configurations needed in the next 10 years. One recurring theme has been the ability to upgrade equipment at a future date and to buy only what is needed for today’s application requirements. Why should a company purchase a large machine when their boards/part carriers are often no larger than 300 x 200mm, approximately the size of sheet of paper? No one wants to pay for features that they won’t use. Instead, customers want the ability to upgrade in the future to include more heat stations and higher levels of feedback and control of the dispensing process as process requirements dictate. From this feedback was born the idea of scalable dispensing solutions, enabling customers to purchase what they needtoday and upgrade later. Some may say this is not a new idea, you can always add more features. While this may be true, add-on features have often had the appearance of a last-minute design. If a new option is simply bolted to the dispense head, there can be problems with the weight of the new option being off-axis and cantilevered from the original robot motion. Often the added option protrudes from the z-head and vibrates, impacting process accuracy and repeatability. If dot placement accuracy is crucial, a longer settling time must be added to the dispensing program to allow time for the vibrations to stop. Throughput is impacted. Yes, you can add new features to any system, but if they are not anticipated during the initial system design, these new features may still work, but not with optimum speed and accuracy. The automated dispensing system that customers asked for would not only be scalable, but would offer precision, accuracy, and high throughput. Low cost of ownership was another key desire. Such a system would offer functionality in the base platform, creating a flexible architecture that allows for future upgradeability, without losing the benefits of process control, ease of use, and other features they were used to. System size
First impressions are striking. A scalable system is much narrower than most in-line dispensing systems on the market today. Factory space costs money, particularly if the system is operating in a cleanroom environment. Today, many companies cannot add more space to cleanrooms that are at full capacity. Equipment size is important. An ultrasleek equipment design is accomplished by having a central dispense area with an optional single heater. If a customer is dispensing silver epoxy or ultra violet cured edge bond material that does not require heat, they do not need to buy a heater module. However, if they need heat to aid fluid flow characteristics, a heater module can be added. A no-heat or single-heater dispensing system has a working dispense area of 300 x 415mm, and the system is only 600mm wide. A laptop computer used to control the system is only 300mm wide so the entire dispensing system is only as wide as two laptop computers. Factories in Asia typically allocate a 750mm wide work space per employee, so an automated dispensing system could fit in that same amount of space. Two of the most popular dispensing applications are encapsulation and underfill. The standard dispensing system configuration for these applications includes a preheat and dispense heat station. A preheat module is simply mounted to the system with conveyor extension rails. If a post-heat station is required for flow-out after dispensing, it can be added. Each additional heater adds to the width of the system, but a two-heater configuration is still only 850mm wide compared to the typical threestation systems on the market today that measure 1100 to 1300mm wide. Heaters
Dispensing system heater designs have changed very little in the past 20 years. Most heaters are constructed with a lot of metal and cartridge heaters blasting heat into the system, and ultimately, the factory. It’s difficult to control the temperature in a cleanroom if the heat from a dispensing system is pumping up to three kilowatts (typical) of heat into the room. To solve this problem, it was determined that a more rapid heat response could be achieved if the heaters were a low mass design with all generated heat directed into heating impingement air used to heat the parts. The resultant rapid response heaters are able to bring parts to temperature more quickly than traditional large mass heaters, enabling a production line to come up to speed much faster. The converse is also true. If a number of part changes per day are required, the heaters’ low mass of material enable them to cool down much faster, allowing for quick line changes. Since most companies have made a significant investment in conventional part heaters, any new system should provide the ability to use existing heaters. The physical heater design is only one part of the heating equation. New control features are also needed. Through system sensors, a line stoppage can be detected and if that stoppage is greater than the programmed time in the dispense recipe, the heaters can be programmed to revert to a standby state or be turned off completely. The goal is to get the heater settings and control under recipe control, rather than rely on manual adjustment by the operators. Rapid response impingement heaters under controlled process heating (CpH) control can heat parts to temperature faster than conventional heaters, saving energy and time. Recipe controls
Many large global companies buy equipment to be used at multiple sites. Often they are building the same products in different parts of the world. The goal is to have the same process at all plants, producing consistent products with the same high yield. If operators or engineers are dialing in settings for fluid pressure, air pressure used with jets or valves, impingement air flow rates for heaters, or heater temperatures, mistakes can creep into the manufacturing process and yield will vary between plants. One way to avoid random setting changes and maintain process control is to have integrated sensors and regulators control fluid and air pressure and a mass flow controller coupled with the impingement heaters to ensure a consistent flow and air volume. Adding calibrated process jetting (CpJ) makes it a complete recipe-controlled system. With CpJ, the system is constantly monitoring itself and, provided it has sufficient air pressure, will continuously adjust to provide constant air pressure on fluid supplylines and air required to operate jets and valves. If the air pressure should fall below minimum acceptable values, thesystem will shut itself down and activate a system alarm. Motion control
As parts get smaller, the accuracy of underfill or adhesive dot placement becomes more demanding. In the past, 75-micron accuracy was an acceptable motion tolerance. However, higher accuracy machines are now required, typically 50 micron. Newer dispensing systems can achieve this 50 micron positional accuracy in all three axes, x, y, and z, and not have to sacrifice speed. Many factors contribute to higher accuracy motion control. One factor that cannot be overlooked is feedback to the control computer regarding z head position. This can be achieved through the use of linear encoders for all axes, including the z head. A built-in mechanical height sensor or laser height sensor can be mounted directly to the base of the z head, avoiding the cantilevering effect caused by a bolt-on height sensor. This is another example of the advantage of designing a scalable system. Range finding
Even when using a basic machine, speed is often still required. To increase speed, an alternative feedback mechanism to the height sensor, called range finding, uses the laser height sensor in a scanning motion. As the laser height sensor moves over the dispense area, the laser reports the z height position of the parts under the laser. Zposition data is captured for each part. This is significantly faster than using a mechanical height senor that moves into position, then moves vertically to trip a light sensor, and finally records the position of the head and infers the z height. Although jet dispensing has reduced the number of required height senses, range finding can significantly reduce throughput time. Conveyor motion
Conveyor motion transports boards into the dispensing system from the up-stream conveyor or releases them to the down-stream conveyor. This can significantly impact throughput. Throughput is increased if boards or parts move simultaneously, rather than in series. If a system has a multimove conveyor, no time is wasted waiting for one board to register before allowing another board to enter the system. Since boards come in a variety of sizes, weights, and with different surface finishes, a scalable solution includes a range of available conveyor belts from 3, 4, and 6mm flat belts and a chain conveyor option. Vision
You can move the dispense head quickly, but analog vision systems may not keep pace. New surfaces on circuit boards and smaller fiducial marks viewed at high speed can cause problems locating a board’s registration marks. Using a digital camera is faster and removes the need to have an analog-to-digital conversion. A digital vision system is more reliable when compared to today’s analog cameras. In addition, the camera works at a frame rate of 60 Hz compared to analog cameras which capture images at 30 frames per second. This improves throughput by speeding up the vision portion of the process. Conclusion
Technologies and their accompanying products change at a rapid pace. Scalable system architectures allow companies to meet their present requirements with the ability to adapt to future needs. Companies need to invest in capital equipment for the present, but should not overlook the potential manufacturing requirements of new or emerging technologies. Similarly, contract manufacturers must accommodate many different applications and often need to ramp up quickly. If a scalable dispensing system is purchased, companies can start with a small footprint, noheat system for UV corner bonding, or other applications. When new applications require heat, preheat and dispense and post-heat stations can be added. For high volume throughput, a single-lane system can be upgraded to dual-lane configuration. The ability to scale in capability and process control make today’s new dispensing systems suitable for tomorrow’s application or capacity requirements. Steven J Adamson, Asymtek Figure 1 Figure 2 Figure 3 About the author:
Steven J Adamson is the Market Manager at Asymtek. He is also the Presidentof the International Microelectronics and Packaging Society (IMAPS). Stevencan be reached at sadamson@asymtek.com | 
