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STEP 8 : Cleaning
December 31, 1969 |Estimated reading time: 6 minutes
What does low cost of ownership mean? Too many define it as outsourcing production to China. This article offers a checklist for establishing the lowest cost of ownership in batch cleaning systems.
By Tom Forsythe
What does low cost of ownership mean? Many agree with U.S. astronaut Alan Shepard who, when asked about his thoughts as he prepared for takeoff, stated, “…that everything on the spacecraft was built by the lowest bidder.” This précis is based on a body of data and analysis focused on identifying the critical parameters that drive the cost of owning and operating a cleaning process. Those parameters make a convenient checklist for determining the process with the lowest cost of ownership.
Operating Concentration
While we have heard creative constructs, the fastest way to lower cost of ownership is by lowering operating concentrations. New technologies that operate at 50% lower concentration should save money.
The primary consumption “operation” in a cleaning process, particularly a batch process, is known as drag out. Drag out is the wash solution that leaves the wash tank with your manufactured parts and is rinsed off in the second stage of the cleaning process. The constituents of drag out, a combination of the cleaning agent, water and soils that have been introduced, correlate 100% with the targeted operating concentration of the wash tank. Run at 20% and the drag out is 20%; run at 10% and the drag out is 10%. While the quantity of drag out will vary due to the nature of the assemblies, the design of the pallets or baskets and the basic design of the cleaning machine, the constituents of drag out are 100% the same as the constituents of the wash tank. Higher concentration means higher cost, given equal cost of the cleaning agents.
Operating Temperature
Most popular batch systems fall into two categories: cabinet/dishwasher-type designs and immersion/ultrasonic-type designs. Cabinet/dishwasher style features technology that has advanced in the past years, making it attractive to low-rate production operations pervasive in Europe and North America. Of particular importance is how these machines have evolved and become more cost efficient.
Modern cabinet or dishwasher-style machines are routinely rated to run at temperatures up to 158°F/70°C. Why would sophisticated equipment designers incur the expense and design challenges associated with such high temperatures? After all, the case has been made that higher temperatures create a significantly higher-cost cleaning operation.
Higher temperatures often enhance (or speed up) cleaning, adhesives often being a key exception. While new, modern cleaning agents are quite effective at low temperatures, overall process enhancements can be achieved if they are run at higher temperatures.¹ Likewise, it is known that this “temperature equals cost” concept is more accurately described as “high ventilation at high temperature equals high cost.” Therefore, cabinet/washer designers have focused on key design criteria to eliminate the need for significant ventilation. This design goal is standard in the industry.
But why was minimizing ventilation the proper design goal? There are several benefits:
- Less ventilation allows better chemistry containment;
- Few worker-exposure concerns (liquid or vapor);
- All but eliminating chemical consumption from exhaust;
- Better heat containment;
- Efficient use of higher operating temperatures, potentially shorter cleaning cycles and lower chemistry concentrations (lower drag-out costs);
- Lower heating energy costs;
- Better process control.
There is another reason why temperature is a key operating parameter. Certain soils, including a high percentage of lead-free soldering materials, are responsive to temperature. Because increasing temperature has little to no affect on batch-cleaning cost of ownership, evaluating the effect high temperatures will have on cleaning results is important. Figure 1 shows post-reflow cleaning results for one difficult lead-free soldering material. With less-effective cleaning materials such as products “A” and “C”, high temperatures allow them to provide a reasonably effective, but higher-cost solution. Product “B” performed poorly with this particular soil. We have run over 25,000 test boards through a standardized cleaning-evaluation program. The data in Figure 1 reflect what laboratory tests show: many lead-free materials respond favorable to high temperatures in the cleaning process. The solid execution on the operating temperature critical-design criterion provides an opportunity for batch systems to clean lead-free material effectively without a cost of ownership penalty.
Figure 1. Cleaning data for one of more than 60 lead-free solders.
Console equipment systems feature many cleaning-design elements that are dramatically different. Cleaning materials are not atomized or “sprayed-in-air,” but rather the process is run in a liquid volume with some sort of agitation beneath the surface. The agitation can be ultrasonic energy or a simple circulating pump system.
Science tells us that if we are considering the effects of temperature on the process losses associated with a relatively static volume of fluid, one must understand the physical properties of the materials on the surface of that fluid volume. Is this why you can find cleaning chemistry providers offering products specifically tailored for these immersion processes? Parts must pass through the surface of the fluid volume upon entering and exiting the cleaning process.
A review of more than ten leading materials designed for ultrasonic applications reveals most with reported boiling points of 100°C, with others in a range of 100° to 110°C. All materials evaluated for their boiling points are designed to mix with substantial amounts of water (routinely 80 to 90% water mixed with 10 to 20% cleaning chemistry). Therefore, it is logical that the boiling points of these mostly water-based solutions are close to the boiling point of water. With comparable boiling points, losses due to fluid evaporation will be comparable across the range of materials and suppliers. With process temperatures in the 123°F/50°C range, evaporative losses are restricted to the water added to dilute the product. Little active ingredient is lost to evaporation.
For processes other than immersion, there are many technologies offered for aqueous cleaning that are designed to split or separate. These often leave materials floating on the surface of the wash tank - rarely a good choice for immersion processes. Cleaning technology providers often have specialty materials (noted with a ‘US’ for ultrasonic) for these immersion processes. These materials minimize evaporation losses of the water component; however, this separation characteristic is a fatal flaw for immersion applications.
Process Mechanical Energy and Process Time
There are many mechanical energy options for use in a cleaning process. All use pumps or, in the case of ultrasonics, transducers as the energy source for their equipment.
Time is the process variable that all manufacturing operations understand. As with the operating concentration of the cleaning material, it is a case of less is more 100% of the time. This returns us to the temperature parameter. If higher temperature has no affect on the cost of ownership, and high temperatures can help accelerate cleaning at low concentrations, then high temperatures will allow for shorter cleaning cycle times.
Figure 2. One of more than 100 lead-free soldering materials.
Figure 2 shows solid cleaning effectiveness at low temperatures and concentrations allows for further testing at shorter cleaning process times. Products “A”, “B” and “C” have no prospects for cleaning at 10%, 110°F/43°C at less exposure time.
This is the payoff for using new technology. Faster cleaning process time allows higher throughput rates, which reduces the amortized cost of capital for each device cleaned and helps the operation avoid capital outlays by increasing throughputs in existing equipment.
Conclusion
A modern batch system can yield the lowest cost-of-ownership cleaning process. Select the cleaning chemistry that allows you to run at the lowest operating concentration. Avoid those that offer half the concentration for double the price. Temperature can help speed up the process (unless cleaning adhesives). Various options for mechanical energy tend not to be significant cost-of-ownership drivers. A faster cleaning process can clean more parts per manufacturing hour. That faster process has a lower cost of ownership.
REFERENCES
For references please contact the author.
Tom Forsythe, vice president, Kyzen Corp. may be contacted at (615) 831-0888; e-mail: Tom_Forsythe@kyzen.com.