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By Harald Wack, Zestron
Cleaning processes bring upfront and hidden costs. The cleaning agent technology, vapor recovery, and bath monitoring are all elements of electronics assembly cleaning that can be optimized to keep costs low and performance high.
Economic news could not be bleaker at present. By the end of Q'01 2009, jobless claims reached alarming levels around the world. Companies are on a mission to survive, reverting to payroll cuts and line items reductions in an effort to meet these unprecedented challenges.
Not surprisingly, cleaning processes at the electronics manufacturer are also under investigation, and purchasing or engineering departments are tasked to verify whether the current solution is the best one available.
Internal task groups must ensure that cleanliness requirements are still met or exceeded regardless of changes made to the process.
Then, these groups have to compare apples to apples. In other words, they must take into account all the elements of overall cost associated with cleaning and rinsing agent usage, as well as associated hidden costs for disposal, power usage, compatibility, and equipment maintenance. Recent studies have demonstrated that for any in-line cost breakdown, the chemistry drag-out and evaporative losses are deemed most significant.
Top Cost DriversCleaning agent technology. Comparing cleaning products by price per gallon is a mistake that many of us still make. Most "cheaper by the drum" products have severe drawbacks and at the end of the year are more costly overall. For example, a product that can be used at half the concentration will provide 50% annual savings. This is the difference between running at 7.5% versus 15%. Another commonly overlooked cost driver is "work arounds" devised to make a product work. These redundant and costly additions are not needed as modern products can easily eliminate them. For example, manually pre-cleaning assemblies to ensure the product in the equipment was actually cleaning well enough. Other examples include waste water collection and disposal, as the product in use is hazardous to the environment and cannot be drained into the regular waste water system. New generations of cleaning products can be operated at as low as 510% and include pH-neutral versions for easier material compatibility and disposal. Product choice is the biggest potential cost driver for conveyorized cleaning processes, as operating concentration directly affects drag-out losses. Take the time to investigate all viable options thoroughly.
Vapor recovery. This is a peripheral, yet noticeable cost driver. As we now know, evaporative loss doubles with every 18°F increase in operating temperature. These losses truly add up, especially with exhaust rates of 800 to 1500 cfm. Modern cleaning solutions can reduce as much as 85% of the evaporative loss. Active and passive cooling systems allow for the evaporated cleaning agent to be returned to the wash tank to be reused for future cleaning cycles.
Bath monitoring. Proper bath control has been overlooked as a potential cost-reduction area. Determining concentration by refractive index has many drawbacks. All cleaning agents used are affected by the contamination (i.e. flux) they remove. In extreme cases, the difference between the perceived concentration and the actual concentration deviates by over 15%, as the contamination distorts the refractive index reading. For example, the operator might be reading a 10% concentration solution, which seems fairly close to his specified bath concentration of 12%. The operator now adds a concentrated cleaning solution to make up the difference. He cannot afford inaccuracy at this crucial point of the production process. Given that the operator was not using a freshly prepared cleaning agent in his cleaning equipment, there is a high possibility that this 10% concentration is more likely to be at 5%. This means that the cleaning agent might not be capable of cleaning at its full strength. The result could be board failure due to contamination-induced electrochemical migration. Furthermore, the contamination can also artificially decrease the operator's reading. In other words, if you are actually using a 20% concentration, but the contaminated solution makes you believe that you are at 14%, you are running significantly higher concentrations and increasing your chemistry cost. Again, any contamination added to the cleaning agent has a different effect on the refractive index and cumulatively it will affect the accuracy of the actual bath concentration. However, confirming the concentration is difficult unless the operator sends the contaminated sample to the cleaning agent manufacturer and allows them to perform more elaborate analytical tests, such as gas chromatograph (GC) measurements. Owning a GC is too costly for regular bath maintenance purposes. Therefore, alternative methods are required. New bath concentration measurement tools overcome this issue to allow operators to verify bath concentrations against the specified value.
ConclusionCleaning is a tremendously important value-added part of the electronic manufacturing process. This does not imply though that one should simply accept status quo. To the contrary, take the time to talk to your cleaning service provider and investigate process savings together. Hidden costs can be eliminated, but only without compromising the cleaning process effectiveness. Remember, board failures usually cost 100× the cost of the board.
Harald Wack, Ph.D., an SMT Editorial Advisory Board member, is president of ZESTRON worldwide. Wack has authored and published several scientific articles, and has provided technical information for various publications. He received his doctoral degree in organic chemistry from Johns Hopkins University. He may be contacted at (703) 393-9880 or via e-mail at firstname.lastname@example.org.
Dr. Wack recently wrote IPA-Water (75/25): Ineffective for Cleanliness Test with Modern Contaminations,Alkalinity, Defluxing, and Materials Compatibility, The Importance of Global Technical Support, and Material Compatibility Worldwide.