Inline Vs. Batch Cleaning Print E-mail
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Written by Ravi Parthasarathy   
Friday, 29 February 2008 19:00

Low volumes support batches; high volumes favor inline.

Process Doctor Processes in the precision cleaning industries are driven by customer requirements and economical efficiency. Published studies have concluded that overall process cost, with all its individual contributors, is essential in calculating the latter. Cleanliness requirements, on the other hand, depend largely on the cleaning agent technology and equipment employed. And it is here where industry opinions differ, especially when one is deciding whether to purchase conveyorized inline or batch cleaning equipment. OEMs will showcase benefits and disadvantages of both process technologies in an attempt to provide a sound platform to facilitate decision-making. (It is worth mentioning that during the past few years, significant improvements have been made to both technologies.)

To effectively analyze and compare different cleaning processes, the user has to take into account all the elements of pure cost associated with cleaning and rinsing agents, including associated costs for disposal, electricity, compatibility, labor and equipment maintenance. Earlier studies suggest costs per cleaned board range from $0.20 to more than $1, depending on the situation (Figure 1). The determinant, then, will be the number of boards used. In other words, the variable cost aspects for inline processes vary as the number of cleaned assemblies increases. Fixed costs will remain steady. Last, the user should consider future production requirements. A smaller machine might be sufficient at present, but not so much if production requirements were to increase.

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Conveyorized equipment can give specific attention to each and every board that enters the process. This minimizes process risks, as changes can be implemented per board, and also leads to a high degree of process control. Recent research on nozzle technologies shows promising results, further permitting individualization. Clearly, a fully automated process is designed for high throughput operations, and it is here where such cleaning equipment will be most economical overall.

One oft-cited limitation is the larger footprint. Some recent advances in cleaning nozzle efficiency have provided shorter, more compact inline machines. Another concern is the rinse and wastewater generation. Bigger machines generate up to 2 gpm or more of wastewater. Depending on local requirements, effluent flow must be addressed. Recent cleaning agent technologies include fully biodegradable products that minimize the environmental effect. Studies also suggest the organic content found from chemical isolation effluents is significantly below 1% by volume.

Pb-free solder’s emergence brought about an interesting trend that affects inline cleaning. In the past, the use of OA fluxes coincided with the use of DI water to clean. Such machines rely on cascading DI water systems and do not run effectively with a cleaning agent, because of the lack of a chemical isolation section. The increase in soldering temperatures due to Pb-free operations now makes the removal of OA flux significantly harder. Because of equipment limitations, chemical assistance is not possible, resulting in additional capital expenditures. As a result, a chemical isolation section as a simple fallback should be considered (thus providing long-term cost savings).

With respect to other mechanical considerations, the authors have established that with all professional process installations currently available, residues can be cleaned successfully, even under most demanding standoff heights or geometries. The same holds true to batch cleaning operations, as their average cycle times are three to five times longer than that of inline cleaning. Despite historically lower pressure settings, the prolonged cycle times are ample compensation.

Spray pressure innovations have further helped batch systems compete with conveyorized machines. Such advancements, for instance, address operating pressures and mechanisms to minimize spray shadowing; the latter an often-cited customer concern.

Naturally, batch cleaners require somewhat more laborious interaction, and typically process boards as a group, not individually. Throughput is beginning to be addressed, but at the cost of a larger footprint.

Noteworthy general advantages of batch cleaning equipment include the smaller footprint as well as significantly smaller volumes of wastewater generation.

Cleaning remains an important part of manufacturing. Associated costs are quantifiable and an optimal process solution can be found. Each process’s complexity becomes quickly apparent; however, with professional help, this challenge can be overcome. As a result, each user should define their specific performance envelope first, and take time to ask all necessary questions.

With batch and inline equipment capable of acceptable cleaning results, the final equipment choice depends on the number of assemblies cleaned. At volumes lower than 450 to 550 boards a day, batch cleaning will pose a more economical solution per cleaned assembly. At higher volumes, inline processes are more cost-efficient.

Ravi Parthasarathy
is a senior process engineer at Zestron America (zestron.com); This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

 

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