Location means everything when you’re buying or selling a house. Location is also important in critical cleaning, especially with line-of-sight cleaning. In line-of-sight cleaning, the cleaning force is directionally-aimed at the part or component. Do you use line-of-sight cleaning? Most electronics assemblers remove flux and other residual soils using in-line systems. If you remove metalworking fluids using cabinet washers or spray cabinets, you face related problems. If there is not a clear line-of-sight between the water or aqueous cleaning chemistry and the soil to be removed, it is more than likely that cleaning will be sub-par. Read on to learn why electronics assemblers ought to revisit in-line cleaning for removing flux and other soils. Then learn the benefits of optimizing:
It’s all about location!
Why clean electronics assemblies?
Some assembly houses respond – “we don’t clean; we don’t have to,” or “we just deflux with water.” The reason is that while RMA fluxes are used for some applications, “no-clean” or water soluble organic acid (OA) fluxes are the norm. “No-clean” fluxes don’t magically disappear; a better term would be low-residue fluxes; they were developed to avoid the need for cleaning. OA flux is soluble in water; but residues are relatively active; so OA fluxes have to be removed thoroughly. However, assemblies have become more densely-populated, components have a lower standoff (the space between the board and the component), customer expectations can be higher, performance requirements are sometimes higher, and expected lifetime may be longer. The end result is that more assemblies need to be cleaned – and that includes both a wash step to remove fluxes and other contaminants and a rinse step to remove residual cleaning chemistry.
Electronics assemblies are commonly cleaned/defluxed using an in-line cleaning system. To use in-line cleaning systems effectively, you have to be very precise about the location of the parts relative to the spray. Achieving good assembly location during production requires strategic planning: test clean before you buy, re-evaluate during production scale-up, then be on the lookout for changes – monitor and reevaluate the process. Let’s consider how an in-line cleaning system works. Assemblies are placed on the conveyor belt of the in-line cleaner; as the belt moves along, the parts are washed and then rinsed. In the washing step (sometimes called the cleaning step to confuse matters) either water, an aqueous cleaning agent, or a semi-aqueous cleaning agent is sprayed on the parts. Next comes the rinse step where water is sprayed on the parts, removing cleaning agent residue. Of course, you dry the parts where appropriate; but let’s focus on washing and rinsing. What can go wrong? How can you avoid or fix the problem?
In an iconic “I Love Lucy Show,” (episode 4 of season 2, 1952), Lucy and Ethel go to work in an assembly plant; the product is chocolate, the process is wrapping the piece as it comes down the line. At the start, all goes well – a piece of chocolate comes down the conveyor belt and Lucy or Ethel pick it up and wrap it. Gradually, the conveyor belt speeds up; the process becomes hit or miss; they eat the chocolate to mask process problems. It’s hilarious on a sitcom; it’s not as funny in your manufacturing plant. The spray system has to have time to do the job of removing soil. With low standoff (below about 5 mil) and tight spacing, a conveyor belt speed of about 6 inches per minute is generally recommended.
Six inches per minute – that’s S-L-O-W. Place a ruler in front of you. Try moving, say, the point of a pen along the ruler for one minute. Try it right now. I’m waiting. Ok. I’ll trust you actually did it! That was deadly dull, wasn’t it? Even 1 foot per minute is pretty slow; and in-line systems can be 30 feet or so long (that means it takes 1 hour to get from one end to the other).
So, even if the written instructions call for a slow speed, imagine what happens when business is good. If you’ve purchased a system that barely meets capacity, you’ll be tempted to increase the speed and you’ll probably be faced with poor cleaning. Size the cleaning system realistically. Educate the operators and supervisors; monitor practices and performance.
In line-of-sight cleaning, if electronics assemblies have to be positioned perfectly, the cleaning chemistry may not reach the areas with sufficient force to remove the soil.
Invest time in choosing the correct fixtures. With new product lines, reevaluate the fixtures. Monitor performance; it may be time to replace the fixtures. Fixtures have a tough life; they have repeated long-term exposure to chemicals, forces, and heat. Degraded fixtures may not hold the parts in the correct location relative to the spray system.
For more ideas, read “Picturing Fixturing” in “Product Finishing Magazine.”
Even with the right fixture, does the spray actually reach the soils? During selection of new equipment, in addition to the force, consider the location of nozzles. Even with recently-purchased equipment, if you suspect poor cleaning performance due to incorrect nozzle location, a little detective work may show that fixtures are not pointing toward the part. If so, take corrective action.
Cleaning systems that are validated for one product line may not perform well for other designs. Did you evaluate the new product in the existing cleaning line?
Even with no changes in the product line, always monitor and maintain the cleaning equipment, notably the spray nozzles. Nozzles can be knocked out of position; or they can become clogged.
The bottom line
In any cleaning system involving chemicals, the cleaning solution must be in contact with the surface that needs to be cleaned with sufficient force, at an adequate temperature, and for enough time to remove the soil. Unless you can get away with solvency alone (and usually you can’t!) this is true for aqueous, semi-aqueous, and solvent cleaning processes. Because spray systems are line-of-sight (unidirectional), keep thinking about location. You’ll cut down on rework; and the acceptance rate will be higher. This adds up to higher quality and profitability.