Friday, May 27, 2016
VOLUME -25 NUMBER 9
Publication Date: 09/1/2010
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ARCHIVE >  September 2010 Issue >  Special Features: PCB and Assembly > 

Advances in Fluid Dispensing Save Time, Production Costs
Scalable dispensing system.

Automated fluid dispensing has been an integral part of the electronics assembly line for high-volume manufacturing for many years. Even jetting, which was introduced by Nordson ASYMTEK in 1994, is now an established technology. As electronic components become smaller and more complex, automated dispensing systems have evolved to meet the requirements for precision microelectronics manufacturing. Incorporating some of the newer innovations in dispensing can greatly improve quality, reliability, throughput, yield, and cost of ownership, and can be easily adapted to a broad array of new and emerging technologies.

"Adapt" is definitely an operative word for today's systems, as they have become scalable in both size and configuration — in the type of fluid delivery system, number of lanes, heat or no heat, and option offerings. With manufacturing floor space at a premium, the amount of real estate a system uses can make a tremendous difference in the cost of ownership. Today, a basic dispensing system can have a slim footprint of 600 x 1391mm (23.6 x 54.8-in.), which is just 1/2 the width of standard dispensers. Some companies have realized up to a 17 percent reduction in cycle-time with 26 percent smaller footprint than they had with their previous systems. A scalable system design allows companies to buy only the capability needed now and upgrade later as needs change — such as adding needed options for transition from lab to full production.

Dispensing systems can be used with a wide range of fluids, such as underfill, silicones, encapsulants, conformal coating, UV adhesives, conductive epoxies, and SMA (surface mount adhesive), for a vast array of markets and applications. Applications include printed circuit board assembly, semiconductors, LEDs, flat panel displays, medical, and automotive applications. For printed circuit board assembly, these systems are used to dispense SMA, solder pastes, CSP and BGA underfills, conductive adhesives, conformal coatings, and are used for corner and edge bonding of components.
Dual lane system.


The semiconductor industry uses precision dispensing for flip-chip on wafer-level packages, systems in package (SiPs), package-on-package (PoP), micro-electromechanical systems (MEMs), and other electronic component assembly. End products range from handheld devices such as mobile phones and PDAs, LEDs, automotive sensors and control systems, to medically implantable devices, optical displays, disk drives, and game systems.

Systems can be configured without heaters for dispensing applications that do not require substrate heat, or one to three heaters can be added with up to six heat stations for dual-lane systems for applications that do require it. Either contact or impingement heated tooling is available for quick ramp to target temperature to ensure part heating does not create a bottleneck. Today's systems support a wide variety of part handling

configurations, from JEDEC trays and Auer boats, to PCBs — organic and ceramic — and bare- or film-frame wafers. Pre- and post-queue stations can be added for higher throughput or as buffer stations or part pre-heating. Cleanroom versions with stainless steel exteriors are also available for Class 100 environments, required for applications that are extremely sensitive to contamination, such as wafer-level packaging.

Improving Speed & Accuracy
The speed and accuracy of dispensing has improved tremendously over the years with jetting technology and the ability to jet precise shot volumes as small as one nanoliter. However, increasing throughput involves more than just dispensing. It includes conveying and heating the parts, vision and/or imaging, and height sensing, and improvements are being made to these aspects of the dispensing process.
Dual simultaneous jetting.


When flow-out times are longer than the time to dispense all first-pass lines, a single lane dispenser loses valuable production time. Dual lane systems allow parallel processing on two lanes for continuous dispensing, eliminating lost time in non-dispensing activities such as material flow-out and substrate loading/unloading. Dual lanes are especially beneficial in applications with high heat requirements or long pre-heat cycles. Dispensing can be done in one lane while substrates reach temperature set-point in the second lane. This multi-tasking capability can provide a 60 to 85-percent increase in throughput over a single-lane system.

Dual simultaneous jetting uses two valves to jet fluid, reducing dispense time by 50 percent. When jetting simultaneously, it is critical that both jets deliver the same fluid mass. Dual simultaneous jetting, in conjunction with calibrated process jetting technology, ensures that flow rates for both jets deliver the same fluid mass per part for uniform deposition. The system automatically compensates for fluid viscosity changes over time as well as batch-to-batch variations to keep the process under machine control. CSP underfill, precise coating, and LED silicone encapsulation on multi-up panelized or patterned parts, or similar applications where precision, accuracy, reliability, and increased throughput are required, benefit from dual simultaneous jetting.

Advanced Process Control
Controlling the variables that cause process variation is critical to increasing yield and reducing both cost and cycle time. There is a cost benefit for using the correct amount of fluid and dispensing it accurately in the right location. More settings that are computer-controllable mean less process variability caused by operator interaction. Closed-loop software and hardware process controls for automatic fluid weight calibration, multi-state heat control, and fluid/valve pressure provide advanced process control for higher quality and improved yield.

Some of the process control features available are:

Laser Height Sensing. Non-contact and five times faster than mechanical height sensing, all height measurements are captured in a single pass without need for z-axis motion. According to user reports, LHS is faster and more robust than mechanical height sensing.

Fids-on-the-Fly. Locates fiducials up to 5.5 times faster than the traditional method of stop-and-capture and can increase UPH (units per hour) as much as 35 percent. In traditional stop-and-capture mode, the camera must pause to locate each fiducial; the more fiducials, the longer it takes. By way of contrast, with Fids-on-the-Fly, the camera is always in motion, snapping images on the fly. The more fiducials to capture, the greater the time savings.

Controlled Process Heat. Controlled Process Heat (CpH) provides software control of impingement air flow and temperature, eliminating operator interaction. System users can define temperature and air flow at different parts of the process, such as when a part is first loaded (process ramp), after it has reached set point (process steady), and when no part is present for a specified period of time. A separate "cool down" state provides the fastest method of cooling a tool when change-out is required.

Pre-Heating. A pre-heat station is beneficial for applications with long pre-heat cycles or when it's necessary to quickly ramp parts to temperature or to evaporate absorbed moisture on substrates prior to applying underfill. A post-heat station is available to aid in material flow-out prior to oven cure.

Programmable Fluid and Valve Pressure. Enables users to set pressure values in the software for closed-loop process control and better traceability with log file capture. Pressure gauges are removed from the front panel to eliminate errors associated with manual adjustments during operation. Complete processes (recipes that include conveyor, heater, and pressure settings) are easily copied to similar systems within a factory or in factories located around the world. This is especially beneficial to contract manufacturers or companies with a global footprint.

Calibrated Process Jetting (CpJ). CPJ maintains volumetric repeatability during long production runs improving process capability (CpK). By using the exact amount of fluid needed, some companies have reduced the amount of material they have to purchase by 20 to 40 percent, which also reduces waste byproducts.

A Safer Workplace
Operator safety and concern for the environment have become necessary considerations for every dispensing system. Emergency systems, ventilation and exhaust considerations, power saving features, and ergonomic configurations are available, while ease-of-use and serviceability have also been factored in.

As technology moves forward, more adaptations and innovations will occur. It is beneficial for designers and manufacturing engineers to work with a fluid dispensing equipment manufacturer and fluid formulator from the beginning of the design process to ensure the best success for their product's quality, reliability, throughput, and yield, with the lowest cost of ownership.

Contact: Nordson ASYMTEK 2762 Loker Ave. West, Carlsbad, CA 92010 800-279-6835 or 760-431-1919 fax: 760-431-2678 E-mail: info@nordsonasymtek.com Web:
http://www.nordsonasymtek.com

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