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The Total Cost of Ownership Equation
December 31, 1969 |Estimated reading time: 10 minutes
Automated selective conformal coating systems can increase production throughput and reduce wasted materials, which are factors that need to be considered when determining total cost of ownership.
Chris Havlik
Conformal coating has become a critical step in the manufacturing process for the growing number of electronics products that must provide a high degree of ruggedness, reliability and survivability within harsh operating environments. Properly applied conformal coatings can effectively protect electronic assemblies from exposure to solvents, moisture, dust or other contaminants. In addition, by eliminating atmospheric exposure, coatings can prevent the growth of oxides that can create short circuits between electronic components.
Just as all electronic manufacturing processes have evolved to accommodate smaller, denser and more complex product designs, conformal coating processes have matured from early dipping and spraying methods into sophisticated automated coating systems. Along the way, the ability to selectively apply conformal coating in very precise locations and thicknesses has become critical to achieving consistently reliable production results.
Unlike manual dipping, brushing or spraying methods, selective conformal coating systems can dramatically increase production throughput while reducing wasted material and improving product consistency. However, as with any significant investment in automation, it is important to look at more than the purchase price to carefully evaluate all aspects of the total cost of ownership (TCO) equation (Figure 1).
When evaluating overall TCO for a selective conformal coating system, the key performance criteria to be addressed are:
- Sustained throughput speeds
- Quality
- Maintainability
- Flexibility
- Safety
- Support and service.
This article will take an in-depth look at each area.
Sustained Throughput Speeds
When investing in any type of automation, most manufacturers look for the degree to which it increases the speed of the operation that it is replacing. While this is obviously a key part of the TCO evaluation, it is equally important to look beyond raw speed issues to develop a clear understanding of the system`s overall sustained throughput capabilities.
For example, while the raw speed of an automated dipping process can appear attractive in comparison to selective application techniques, a full TCO evaluation should take into account the time required to mask the printed circuit boards (PCB) prior to dipping and mask removal after the dip process. Unless the assembly has been stringently designed to avoid sensitive areas that could be contaminated by coating materials, some degree of "watertight" tape masking will be required before submersion in the dip vat. Even some selective application methods, such as atomized spraying, will require a pre-masking step to avoid contamination from overspray. While prevention of overspray contamination can typically be accomplished with a simpler "boot-masking" technique that does not have to be watertight, putting the boot-mask in place and removing it still constitute additional steps that slow down the throughput of the overall process. Because most of today`s high-density electronics designs involve risk of overspray contamination to adjacent components, application methods such as needle dispensing, non-atomized dispensing or curtain coating are ideal. The sharp, well-defined edge that they provide is key to eliminating the overhead associated with masking, improving overall sustained throughput levels.
When evaluating the speed of a conformal coating system, it is also important to understand the differences between the system`s robotics raw speed and the actual speed at which the coating can effectively be applied. While some system specifications might indicate robotic speeds of 25" per second (ips) or more, in reality, the robotics raw speed plays a very small role. The actual system "coating velocity" is typically limited by the fluid characteristics coupled with the highest controllable speed of the dispensing head. For example, if high-speed robotics must be slowed to a coating velocity of 1 to 2 ips to maintain dispensing accuracy, the raw speed robotic specifications are essentially irrelevant to the TCO evaluation. Currently, a good target for achievable coating velocities under real-world conditions would be in the 5 to 20 ips range.
Another consideration that should be taken into account when evaluating overall throughput is the time required for setup and changeover. For example, the availability of an easy-to-use programming environment and menu-driven setup screens can be a major factor in getting the system up and running for each new assembly, as well as switching between assemblies on the production floor. Dedicated software that is written specifically for conformally coating PCBs incorporates commands specific to the applicator used to dispense the materials and offers flexibility beyond generic motion control/dispensing packages. Likewise, the mechanics of changing over fixtures and conveyor widths can play a significant role in maintaining a high level of machine utilization and throughput. While important for all manufacturers, these setup and changeover considerations can be critical for high-mix production environments such as contract manufacturers.
Quality
The movement from manual dipping, brushing and spraying to automated application methods has been a major factor in improving quality, with a marked improvement in the consistency and repeatability of the conformal coating results. However, significant quality trade-offs still exist between today`s selective coating systems. Among these are the ability to accurately deposit the desired coating thickness in the required locations, the avoidance of contamination to adjacent areas, and the minimization of dripping, stringing or overspray (Figure 2).
With today`s dense product designs and tight manufacturing tolerances, edge definition has become the most critical factor in conformal coating quality. As previously mentioned, atomized methods can exhibit a tendency for some of the material to "drift" because the process requires the conformal fluid to be broken into very fine droplets carried within an air spray stream. Most particles in the center of the spray tend to land in the required area, but a certain percentage drift to the outside, resulting in a ragged or nonuniform edge. Air-spray technology has a typical transfer efficiency of about 70 to 80 percent, depending on the applicator type chosen. This means that 20 to 30 percent of the material falls outside the target area, resulting in waste or contamination.
While needle-based systems can reduce the risk of overspray, dripping can become a concern. If the dispensing process does not include a positive shut-off mechanism that precludes dripping, excess material can easily fall on undesirable areas on the PCB, causing contamination to connectors or other non-coated areas. By placing the shut-off valve as close to the dispensing tip as possible, so-called reduced cavity or zero-cavity dispensers can effectively control dripping.
Maintainability
In addition to creating final assembly quality issues, uncontrolled dispensing accuracy can have significant impact on the maintainability of the conformal coating system itself, thereby further driving up the TCO. Dispensers that require frequent adjustment during production significantly slow the process, requiring more operator intervention to avoid process variations that can require costly rework.
Even if it does not contaminate the PCBs, overspray or dripping from the dispenser that lands on the surrounding work area or conveyors can necessitate frequent production flow stoppage to clean the machine. Also, premature fluid curing within dispensers that internally pre-mix air with the coating fluid results in higher maintenance requirements, work stoppages and increased cost of consumables. Here again, it is important to consider the total cost beyond the specific conformal coating operation. For example, frequent work stoppages to clean or maintain an in-line conformal coating workstation can have dramatic effects on the rest of the production line, bringing down the utilization levels of other machines and reducing overall production efficiency.
Flexibility
With today`s shorter product life cycles and relatively high-mix production environments, the configurability and flexibility of equipment is increasingly important in establishing TCO. The ability of a single conformal coating system to adapt to different fluids, dispensing patterns, throughput requirements and PCB configurations is crucial to extending the return on investment for optimal TCO.
Multi-function heads that accommodate different dispensing methods can significantly expand the flexibility of the base system. Attaching multiple dispensers to a single head can become cumbersome to program and maintain, whereas using dispensers that can dispense different fluid types and dispensing patterns can increase flexibility without undue complexity. Likewise, the ability to use either airless or air-assisted dispensing technologies provides an expanded range of options for balancing accuracy and throughput as dictated by specific assemblies. Availability of specialized board-handling mechanisms, such as inverters, to allow coating of both sides of a PCB, can also boost speed and flexibility.
The integration of a state-of-the-art curing oven with the conformal coating system can be one advantageous factor in optimizing the system`s overall effectiveness. Here again, the flexibility and programmability of oven parameters can be a crucial factor in quickly tuning the entire conformal coating process for optimal throughput and quality results. From an overall process standpoint, it does little good to invest in a sophisticated dispensing system for conformal coating and then harness it to a relatively inflexible "hobbyist"-type of curing oven. On the other hand, a professional oven that can store multiple curing profiles, allow for quick changeover of rail widths and accommodate a variety of PCB sizes will rapidly pay back the initial investment by enabling the entire conformal coating process cell to run at a higher utilization level.
Safety
Although safety should always be taken into account with any equipment purchase, it is frequently overlooked as a key component in TCO. Unsafe equipment can increase the TCO when one considers the economic impact of damage to equipment and product, production downtime, lost orders and delayed shipments. In addition, unsafe equipment poses a danger to plant and operating personnel.
With conformal coating systems that involve potential exposure to noxious fumes and the risk of combustion, a diligent safety evaluation must always look at the adequacy of ventilation methodologies, which become critical when dealing with solvent-based materials and certain 100-percent-solids materials.
The proper amount of airflow, in combination with well-designed flow paths, can eliminate the possibility of hazardous fume buildup. In addition, the accumulation of volatile conditions within the machine can be mitigated by minimizing the use of atomization techniques in the dispensing process because a non-atomized environment is less susceptible to combustion than an atomized one.
With respect to equipment safety, the key guidelines to consider are full conformance with National Fire Protection Association (NFPA) 33 design standards and NFPA 496 ventilation standards. For equipment destined for use in Europe, it is imperative that all applicable CE Directives are adhered to and use of the CE Mark is supported by a technical file.
Service and Support
Some final important considerations in the TCO evaluation are the ease with which the system can be brought up to full production, how long it is likely to operate before a failure (MTBF) and how quickly it can be returned to full production after a failure (MTTR). Generally, overall service and support factors can be assessed by carefully scrutinizing the vendors` historic performance, industry reputation, and the responsiveness and professionalism of their customer service organization.
Key considerations should include the depth and cost of training available for process engineers and production floor staff, the availability of 24-hour/7-day hotline support, and the vendors` applications engineering capabilities for assistance with process optimization. When assessing applications support, it is also important to find out what the vendors` policies are with regard to providing future assistance with setting up and qualifying subsequent applications after the initial installation and system buy-off has long passed. In today`s global manufacturing environments, it is often critical to consider the vendors` ability to provide direct service and support capabilities on a worldwide basis.
The Bottom Line
While conformal coating processes have significantly matured over the past decade, from crude manual processes to automated selective coating systems, there remain a number of key trade-offs in system selection. In today`s changing production environments, with shorter product life cycles, greater product variation and higher mix assembly demands, manufacturers need to carefully look at all facets of TCO equation to ensure maximum productivity and return on investment.
CHRIS HAVLIK is the product manager, Electronics Systems Group, at Nordson Corp., 300 Nordson Dr., Amherst, OH 44001-2422; (440) 985-4000; Fax: (440) 985-1122; Web site: www.nordson.com./electronics.
Figure 1. Determining TCO for an automated selective conformal coating system proves the importance in looking beyond purchase price when choosing capital equipment.
Figure 2. With edge definition becoming a more critical factor, finding a conformal coating system with high accuracy is crucial.