“All things are poison, and nothing is without poison; only the dose permits something not to be poisonous.”
This 16th Century statement by Paracelsus states that at some level there can be too much, even of a good thing. Here are 8 examples where “more” is not better for critical cleaning; where “more” can waste money and compromise product quality.
1. More Cleaning
More cleaning is not necessarily better. More cleaning costs more money. There is always a balance involving effective soil removal, undesirable surface modification, and even product deformation.
2. Cleaning agent concentration
If cleaning is not effective, there is the temptation to throw more and more of the concentrated cleaning solution into the bath. Resist the impulse. Sometimes a dilute solution can show greater cleaning efficacy than a concentrated one.
Adding more and more cleaning concentrate can mask other problems with the cleaning process – like non-optimal temperature, time, or cleaning force. Or, the cleaning chemistry may be the wrong one for the soils to be removed.
The more cleaning agent in the wash tank, the more rinsing is required, and the more chance that residue remains on the part.
3. Aggressive solvency
In solvent cleaning, there is the temptation to use very aggressive solvents. The more aggressive the solvent, the more likely there is to be substrate damage (damage to the part you are trying to clean). Also, as a general principle, chemicals and mixtures that are aggressive as cleaners tend to be aggressive toward workers and/or the environment.
Higher temperatures can melt soils, assist in solubilizing the soils, and promote reactivity. However, high temperatures can damage the substrate. High temperatures can modify the soil so that it becomes more adherent.
Sometimes it’s not exactly an issue of the dose making the poison, it can be more the case that there is an optimum. Especially with ultrasonics, each chemical has an optimal temperature for effective cavitation. At lower temperatures, the density of the liquid does not allow optimal cavitation. At higher temperatures, dissolved gasses make the cavitation bubbles to “cushy” to cavitate effectively.
The temptation is to toss the part into the tank, then walk away, maybe go to lunch. Longer ultrasonic times are not necessarily better – they may be worse. Ultrasonic cleaning, cleaning by the cavitation associated with passing high frequency sound through a liquid, involves small, very transient implosions. These implosions blast the soil off of the part.
However, the same implosions, if uncontrolled, can damage the substrate. Another effect of long ultrasonic times, particularly in smaller tanks, is that the temperature tends to increase and may exceed the temperature for optimal cavitation.
6. Planning, Process Selection
In modifying a cleaning process, in selecting cleaning equipment, there is a learning curve. Understanding process requirements and cleaning standards is useful. Planning for future product modifications and anticipating likely changes in regulations is good.
Planning is good, but there is a point of diminishing returns. There will always be uncertainty. At some point, you have to come to a decision. With paralysis by analysis, nothing moves forward.
7. Not cleaning
The mantra of “not cleaning” can be taken to toxic levels.
Given that there is always a tradeoff between soil removal and product damage, don’t clean if you don’t have to. Sometimes, you can save money by not cleaning. At the other extreme, some companies refuse to do any cleaning on principle; and never cleaning can be as bad as always cleaning.
There’s the profit motive. Many electronics assemblers have embraced “no-clean” flux (actually fluxes that leave lower residue) as a way to avoid cleaning. The motivation to not clean may also involve regulatory concerns.
If “not cleaning” under any circumstance results in lost business, or unacceptable product quality, a paradigm shift might be productive.
The principle of not cleaning may be related to “green” company policy. Consider the impact of that policy. For example, by not cleaning in-house, are you pushing the problem back along the supply chain? Sure, cleaning early-on is important; but pushing the requirements to clean back onto smaller job shops may not be the most green approach.
8. Greener processes
Greener is better – all other things being equal. All other things are never equal.
Companies may select only officially “green” chemicals. We have to look at what green actually means. In our humble (or maybe not so humble) opinion, a green chemical that does not clean effectively is not green. Switching to a green chemical that generates three times the hazardous waste (or even non-hazardous waste) may not be truly green. As a society, we need to define truly green processes – and that means cradle to cradle process control, and it means negotiating the rocky path of political chemistry of industry and the perhaps politically correct path of some regulators. Data from peer-reviewed studies would help, too.
More is not necessarily better. There is usually an optimum cleaning process – not too hot, not too cold, just right. Not too little, not too much, just right.
We’ve helped lots of manufacturers choose the “just right” process. It involves evaluation, documentation, and some tough decisions – it’s worth it!
More about Pasacelsus
Paracelsus (b. 1493, d. 1541) was an important figure in the development of modern toxicology and pharmacology. He was considered to be an alchemist, but was not seeking to turn lead into gold. His primary interest was medical, combining spiritual with medicinal factors. He pursued the “Holy Grail” of cleaning engineers, the universal solvent, called alkahest. He countered the perennial argument about a universal solvent of ‘in what can you store it?’ by a belief that it did not dissolve elements, but reduced any compound into its elemental constituents. Of course, given the use of alloys, plastics, and composites, such a solvent, even if discovered, might have limited utility in contemporary manufacturing.