Green, environmentally-preferred, sustainable, biobased, safe — the terms are sometimes used interchangeably. However, their meaning and interpretation really depend on one’s viewpoint.
The following thoughts on green cleaning represent my viewpoint. I did, after all, volunteer to write this article; and, at this point I have been involved in precision and industrial cleaning activities for decades.
My own view of green cleaning has evolved; and will no doubt continue to change. About a generation ago, I became involved in (“was coerced into” might be a more apt description) industrial and precision cleaning as a consequence of the move away from ozone depleting chemicals, specifically CFC-113 (chlorofluorocarbon 113, popularly known under the trade names Freon or Genesolv) and TCA (1,1,1- trichloroethane). Both were considered relatively benign to workers; they were inexpensive, plentiful, and widely used in industry. Unfortunately, given their molecular stability, they reach the stratosphere, releasing chlorine free radicals that destroy the protective ozone layer.
Both were phased out of production under the Montreal Protocol; the phase-out presented an acute problem for industry. Typical precision or critical cleaning processes were straightforward; processes depended on repeated spraying, ultrasonic cleaning, and vapor phase degreasing with CFC-113 and/or TCA. Perhaps a bit of isopropyl alcohol might be used; a final rinse/drying step in acetone was popular. Aqueous cleaning was often consigned to industrial, rather than critical, cleaning applications.
As the availability of CFC-113 and TCA decreased and the costs increased, a wide variety of aqueous and solvent based cleaning chemistries became available. So-called “non-chemical” cleaning such as CO2 snow and plasma cleaning were considered. It gradually dawned on many in manufacturing that cleaning is not a chemical, it is a process. In electronics, water-washable and so-called “no-clean” fluxes were introduced. Cleaning processes were tested and validated; crucial customer requirements were met; irrelevant customer requirements were negotiated away. The manufacturing world did not wither and die; it thrived.
IT’S NOT EASY BEING GREEN
We helped to protect the ozone layer. In fact, the U.S. EPA “Stratospheric Ozone Protection” award is proudly displayed in my office. Protecting the ozone layer, while necessary, was not sufficient. The concept of green still eludes us. The stakes are higher; the pathway to success is more complex.
Many of the chemicals that were initially instituted as replacements for ozone-depleters have themselves come under fire by safety and/or environmental regulatory agencies. We protected the stratospheric ozone layer, but often adopted substitutes that impact tropo - spheric (smog producing) ozone. Aqueous processes were adopted; but the impact of waste streams were either not understood or not adequately dealt with. As more studies were performed, issues of worker safety and neighborhood safety increased. With increasing regulatory scrutiny and given the costs to develop new cleaning chemistries, finding appropriate cleaning agents has become a challenge.
Environmental and worker safety regulations are becoming increasingly stringent. The “regulatory distress” of a given cleaning agent depends on a complex blend of local, regional, and national regulations. A given chemical may be either favored or essentially banned, depending on where you alight on this planet. Effective cleaning agents that can be readily adopted are decreasing, and may be sitespecific.
At the same time, manufacturers are faced with increasingly tough performance requirements. Mini - ature and micro-components as well as nano-based products all involve surfaces with exacting qualities and properties. Critical or precision cleaning activities have increased.
Perhaps in response to this complexity, there is a growing trend in some regulatory and industrial groups toward a more holistic view. The concept of cleaning operations that utilize principles of pollution prevention has been supplanted by the concept of sustainable cleaning processes. The concept of “cradle to cradle” is supplanting that of “cradle to grave” to describe manufacturing operations.
MEETING THE REGULATIONS
The reality is that the “command and control” regulatory approach is still the norm. Given limited technical and economic resources, many companies struggle to understand, interpret, and meet a complex and perhaps conflicting set of safety and environmental regulations.
Certainly, meeting or exceeding the regulations is necessary, but it is not sufficient.
The regulations are complex and ever-changing. A company may adopt what appears to be a sustainable, environmentally-preferred cleaning process, only to discover within a few years that their efforts are insufficient or even counterproductive.
For many manufacturers, green cleaning has become using a specific chemical or group of cleaning agents, or avoiding a specific chemical or group of chemicals. For example, some manufacturers have adopted all aqueous processes; or they use acetone or some other VOC-exempt compound extensively.
Volatile Organic Compounds (VOCs) produce smog; but not all VOCs are created equal. While acetone has been declared “VOC-exempt” at the Federal level,1 the exemption does not mean that acetone does not contribute to smog. It does, but at a rate below a threshold set by the EPA.
As a result of the exemption, acetone has been adopted extensively in areas of poor air quality. In terms of air pollution, in some locales it is treated essentially like water, so people use a great deal of acetone. Aside from issues of materials compatibility and flammability, this means that a great deal of acetone is emitted to the air. It is, in a way, like a reduced, but not zero, calorie cookie. If you eat enough of them, you can still gain weight. Emit enough acetone, and you still produce smog. Given the lack of availability of other VOC exempt options that are cost effective, reasonably aggressive, and volatile, my colleagues and I have observed significant increases in acetone use in cleaning.
Other approaches to VOC reduction
Other scenarios might reduce the current dependence on acetone for cleaning. All have pros and cons. Using smaller amounts of non-exempt VOCs may result in more effective cleaning, with less solvent usage, and less smog production. However, many local regulatory agencies take a dim view of this approach, preferring to show decreases in the amount of VOCs in their area. That is, reduction in the inventory of VOCs is used as a measure of how well the agencies themselves are doing.
Another possibility is to foster aqueous cleaning agents, with the VOC content “as applied” below a certain limit; this approach has been used in Southern California. In some areas and applications, the vapor pressure of the cleaning agent is considered. Not all agencies find this to be appropriate, preferring to effectively expunge non-exempt organic compounds from the list of options for industry.
Alternatively, there is the concept of relative reactivity, 2 where the inherent smog-producing potential of all organic compounds is considered, whether or not these chemicals are in aqueous-based or solvent-based process materials or cleaning agents. There are some moves toward adopting relative reactivity, particularly in California. At the same time, there is some concern, particularly among formulators, that using relative reactivity might result in a recordkeeping quagmire. With the proliferation of spreadsheets and related programs others see those concerns as perhaps less relevant than, say ten years ago. And, there could be an option for suppliers to use either the VOC/exempt approach (an either/or, “line in the sand” approach), or to use the more detailed relative reactivity approach.
The bottom line is that perhaps inventive approaches to how government looks at VOCs could result in greener, more sustainable, and more productive cleaning processes.
Cleaning chemicals have a specific job to do — to break chemical bonds that cause soils to adhere. Since many or most soils are organic, chemicals that are effective for cleaning can interact negatively with biological entities like people. It is therefore, no surprise that many of the most effective cleaning chemistries have toxicity.
One solution, adopted or favored by many regula - tory agencies, is to ban or severely restrict the use of many toxic chemicals. This can have, however, an analogous effect as the use of acetone to reduce VOCs. That is, manufacturers might be driven to use more of a less toxic material when the smaller amount of the toxic, appropriately contained, would be both cost effective and minimize the environmental footprint. The key phrase is “appropriately contained.” There are many ef fective containment processes, with controls, to allow usage with low risk to nearby workers or the community.
LOWERING THE ENVIRONMENTAL FOOTPRINT OF THE CLEANING PROCESS
So how do you do green cleaning? What follows are a few of my own suggestions that may lower the environmental footprint of your cleaning process and move the operation toward green, sustainable cleaning.
Do less cleaning
By this, I do not mean to promote leaving undesirable residue on the component. Quite the contrary. Time invested in planning the product and planning the assembly process can yield benefits in decreased need for cleaning.
In designing new products, it is typical to consider such factors as perfor mance, cost, miniaturization, and the nature of materials of construction. Historically, the ability to assemble the product and to avoid surface contamination has not been high on the list of requirements. I find it encouraging that designers are now asking to be educated in precision cleaning, contamination control, and surface quality. Designers are collaborating with those who will actually fabricate the product. They are learning about the physical and chemical properties and limitations of aqueous and solvent cleaning agents.
Companies with the goal of using water-based cleaning agents exclusively would do well to consider that the surface tension of aqueous cleaning agents limits the spacing of components, the population density of electronics assemblies. Aqueous cleaning agents have to be rinsed with water, so the surface tension of water has to be factored in. Coordinate the product design with the anticipated cleaning process. A process may be environmentally-preferred. However, an inefficient, inef fective cleaning process is not good for the environment; it is not good for product quality; it is not good for the bottom line.
What if the product has a configuration that makes aqueous cleaning impractical? I think it is prudent to understand this at the design stage and to factor in the cleaning equipment and environmental controls as part of the initial design review.
Greener soils and cleaning agents
A processing agent that is essential at a given point in the fabrication process eventually has to be treated as soil, or matter out of place. It needs to be removed to achieve a low-residue surface. It stands to reason that soils that are more readily-removed tend to be greener, in the sense that cleaning steps may be reduced or eliminated. The replacement of rosin flux with “noclean” or low-residue fluxes is an historical example of substituting a soil that decreased the need for defluxing (i.e. cleaning) of electronics assemblies. Certain solder fluxes leave a tolerable level of residue for many applications. For some applications, water or water with low level of additives is used to decrease the level of even the “no-clean” flux residue. Further, with increased miniaturization and higher performance expectations, critical cleaning of electronics assemblies is again becoming a fact of life. In such cases, green cleaning means designing and controlling processes in an effective manner.
Moving to water soluble metalworking fluids decreases the amount of cleaning — or not. While water soluble lubricants are inherently more readily removed by water, issues may arise as a result of machining in that the heat and forces involved in the machining process can change the metalworking fluid into something that is not readily soluble in water.
Biobased cleaning agents are being promoted as a green approach to cleaning chemicals. Biobased agents are derived from plants and are sustainable resources. However, it should be noted that the word “biobased” is not a synonym for “effective.” Some biobased agents are effective in a number of cleaning applications. However, they are primarily large molecules that can leave residues unless thoroughly rinsed. In addition, many biobased processes are VOCs. Further, the fact that a chemical is derived from a natural source, the fact that it may have been used at limited concentration for decades without apparent harm to the worker or the environment does mean we are “out of the woods” in terms of toxicity. Toxicity studies are important even for biobased materials. When plantderived chemicals are concentrated and then used in cleaning processes along with heat and force, we have to consider such issues as worker exposure, community exposure, and waste stream management. We have to consider impact on the local and global environment.
Green and document the supply chain cleaning processes
Assure that your suppliers clean the component or sub-assembly promptly. Prompt and effective cleaning by your suppliers minimizes adherent residue.3 With proper testing and documentation, you may be able to eliminate cleaning steps.
Requiring that your suppliers document the cleaning processes and demonstrate effectiveness of the processes can help green your own facility; and, based on experience, it will help you to produce a better quality product, decrease failures, and ultimately will save your company money.
There is a proviso. It is tempting for manufacturers of critical product for applications like medical devices or aerospace components to specify a level of cleanliness achievable only by using very aggressive and heavily-regulated chemicals. While such chemicals can be used in a non-emissive manner with minimal impact on employees, some smaller operations may not be in a position to invest in the appropriate cleaning systems. In my opinion, you are not being green if you require your suppliers to be irresponsible to their workers, their neighbors, or the environment. Instead, require that your suppliers and sub-vendors document that cleaning processes meet or exceed environmental and safety regulations.
IN-HOUSE CLEANING PROCESSES
Worker safety, local environmental concerns, and global environmental concerns
Green is not the same as safe. Initiatives involving worker safety and “green” chemistry may actually be at odds with each other. A chemical may be relatively benign in terms of the impact on the individual worker, but may have a long atmospheric lifetime, and therefore endanger the planet. As recent history illustrates, chemicals that do not impact stratospheric ozone (upper ozone, good ozone) may increase tropospheric ozone or smog, and vice versa.
You have to obey all applicable safety and environmental regulations, and this can be a challenge because regulations may impel you in conflicting directions. In addition, by corporate policy, you may be restricted to certain cleaning agents.
Consider the cleaning process, not just the cleaning agent
Based on my experience, you cannot be green and you cannot assure the safety of the worker based on selecting a supposedly safe and/or green cleaning agent.
You have to consider the process, the way the cleaning agent is used. Concentration, temperature, time, mechanical force, all contribute to the overall safety and environmental preferability of the process. Consider rinse steps, water usage, product rework rate. A supposedly green cleaning process that puts a high proportion of your product in the landfill may not be green for your purposes.
Put your cleaning process on a diet
To me, being truly green means minimizing the impact of your process on workers and on the environment. This does not mean re-using cleaning agents in a way that could potentially contaminate the product. However, consider such approaches as:
- water conservation, recycling, and closed-loop processes
- solvent conservation, in-process recycling, on-site recycling
- well-contained systems
- energy use reduction
- design processes for containment
- consider efficacy of cleaning
We have published or presented case studies illustrating the environmental, economic, quality, and worker safety benefits associated with containing the cleaning process.4 Reduction in energy usage, as it applies to cleaning and manufacturing processes, has great potential, particularly in the design of cleaning process equipment.5
Lean and Green
Lean cleaning ought to include green cleaning. Particularly in the current competitive and intense economic climate, the reality is that an inefficient, ineffective green cleaning process will not be widely adopted. It probably should not be adopted, not in any economic climate. Ideally, green and lean ought to be interchangeable; and at least some regulatory agencies are highlighting the connection. The EPA, in fact, offers “The Lean and Environment Toolkit.”6 In addition, the EPA Partnership Programs7 provide ways for firms, organizations, and individuals to team with the EPA to foster Green or Sustainable efforts. Most people are familiar with the “Energy Star” program due to home appliances with the label “Energy Star.” There are many more partnership programs, including “Labs21,” “Green Engineering,” and “Design for the Environment.”
Whether or not your company chooses to partner with a regulatory agency, the concept of lean and green cleaning should not be ignored.
The concept of green cleaning will continue to evolve. Regulators explain what you have to do; and perhaps they provide guidelines as well. Because regulations will evolve, sometimes in a conflicting manner, the most reasonable approach to insulating against changing regulations is to adopt flexible processes, processes typically not dependent on a single cleaning agent. Characterizing and validating the cleaning processes and documenting acceptable residue levels will also help in coping with the need for the seemingly inevitable periodic process change, the change in response to the new regulations.
I have focused on only a few aspects of what “green cleaning” is or perhaps ought to be. Some of the many additional aspects of green cleaning include:
- minimizing the compounds with long atmospheric lifetimes
- replacing current ozone depleting compounds
- optimizing the energy efficiency of the cleaning process
- minimizing water usage
- assessing environmental persistence in soil, water
In addition, those in manufacturing, those who develop and more importantly utilize cleaning technologies have every business, every responsibility, to provide input and guidance to help green cleaning evolve.
In my view, green cleaning is not about a green chemical. Any effective chemical, including a biobased chemical, is likely to have some sort of environmental or safety baggage. While many might argue the point, there are no ultimate green chemicals, any more than there are any “ultimate foods,” foods that alone contribute to health and happiness. (OK, perhaps dark chocolate is an exception.) Most cleaning chemicals can be used safely and with respect for the environment, under appropriate conditions.
Perhaps green cleaning will become more about the cleaning process, more about incorporating industrial cleaning, precision cleaning, critical cleaning — whatever we want to call it — into the overall manufacturing process. For the manufacturer, in determining green cleaning, it is critical to factor in worker safety, efficiency, process costs, and product quality. Green cleaning is a goal we will probably reach asymptotically, and I suspect that green cleaning may ultimately merge with lean manufacturing.
The author thanks Ed Kanegsberg for his critique and comments.
- EPA Exclusion of Acetone as VOC: www.epa.gov/EPA-AIR/1995/June/Day-16/ pr-752.html
- Carter, William P. L., “Development of Ozone Reactivity Scales for Volatile Organic Compounds,” J. Air & Waste Manage. Assoc., 44: 881–899, (1994).
- “Lean Cleaning with Your Global Supply Chain,” National Manufacturing Week, Half Day Workshop, September 24, 2007, Rosemont, IL.
- “Case Study: Cleaning Process Prior to PVD of Critical Metal Substrates,” Bob Dowell, Plasma Technology; Steve Norris, Plasma Technology; Jim Unmack, Unmack Corporation; and Barbara Kanegsberg, BFK Solutions, Presentation and Proceedings, CleanTech03, Chicago, Il, March 2003
- “Costs of Cleaning,” prepared for University of Massachusetts Lowell, Toxics Use Reduction Institute, presentation, CleanTech 2001, Rosemont, IL, May 2001.
- “The Lean and Environment Toolkit,” EPA, www.epa.gov/lean/toolkit/index.htm
- The EPA gateway for Partnerships Programs: www.epa.gov/partners
Barbara Kanegsberg, BFK Solutions, LLC, is a recognized independent consultant in critical cleaning, contamination control, and surface quality. “The cleaning lady” helps industry achieve high performance and cost effective processes that meet or exceed environmental and worker safety standards. Reach her at Barbara@bfksolutions.com.