Issue



Contamination control starts far upstream of the cleanroom


04/01/2007







Minimize contamination by gaining an understanding of early-stage contamination issues

By Barbara Kanegsberg, BFK Solutions LLC

It is important to remember that a cleanroom is not a cure-all; even a cleanroom with the most stringent controls cannot correct a contaminated product. To fabricate critical product, you must understand, document and standardize all the cleaning and manufacturing processes. To facilitate the assembly and contamination control protocols for critical product, it is essential to control production processes from as early a stage as feasible. Although the cleanroom becomes a “safe haven” for critical product, many controls must precede the cleanroom activities.

Do you produce the entire product in your facility?

Probably not. But if not, contamination can be difficult to control and the contaminants may be more adherent than expected. Some keys to improving the quality of surfaces include:

  • identifying early manufacturing steps
  • identifying responsible groups (subvendors, sub-subvendors)
  • clarifying early cleaning and contamination control processes
  • documenting and restricting the processes
  • ongoing monitoring and auditing
  • subvendor/supplier education

This article is written primarily from the vantage point of the group doing the final assembly. However, if your group is engaged in earlier stages of production, or if you do contract manufacturing, understanding potential contamination problems and communicating your concerns and process control with your client can put you far above the competition. Roles at various stages of production are summarized in Table 1.

Why worry about earlier phases of production?

We often consider the immediate sources of contamination in a cleanroom-sources that include people, air, process chemicals, and process equipment. These are immediate, usually readily corrected problems.

The most effective contamination control begins with prevention, and prevention implies prompt removal-sometimes within seconds-of contamination. When you receive the component or subassembly days, weeks or months later, it is often too late.

The reason is that soils, both particles and thin films, that are allowed to remain on the part become more adherent through a number of factors and mechanisms. These are the same factors that must be considered in developing a validated cleaning process:

  • process chemical
  • reaction products (including oxidation)
  • temperature
  • force
  • time
  • drying

Reactivity happens during the assembly process. For example, many companies that do final assembly specify water-soluble lubricants. They work under the sometimes erroneous assumption that water-soluble products will be more readily removed, particularly with aqueous-based cleaning processes, than will organic solvent-based chemicals. However, the term water-soluble refers to the original lubricant, not to the lubricant after it has been used in the process. Temperature, time, physical forces, and drying of the lubricant can result in chemical changes and an adherent residue. Other process chemicals, cleaning agents, and additives can oxidize. The oxidation product may not be as readily removed as the original chemical.

Design specifications vs. assembly process

Many manufacturers look to control the supply chain. However, that control is all too often based on design specification, tolerance and surface finish. One reason is that surface cleanliness, residual contaminants, qualities and attributes are variable and are not well understood. Therefore, the details of industrial cleaning processes, specific surface attributes, overall residue levels, species of residue and residue toxicity are not as likely to be specified as are tolerances, materials of construction and surface coating. Although we occasionally quip that design engineers can be our best source of future clients, we increasingly observe that thoughtful, proactive engineers are concerned about critical cleanliness and surface quality during product design.

The most effective and convenient time to specify cleaning processes is when relationships among groups in the supply chain are being established. A supplier of parts or components will often proudly provide details of the cleaning process.

What about the established supply chain?

As a productive educational exercise in proactive worrying, please take a moment to imagine that your product has developed a particulate or thin-film contamination problem, a surface defect or a coating issue. Or suppose that your customer or an environmental regulatory agency has targeted a particular process, molecule or atom for elimination.


Table 1. Roles in critical and industrial cleaning for optimal production
Click here to enlarge image

It is prudent to set up cleaning and contamination requirements with an established supply chain, even if there are no observed contamination problems. However, identifying and controlling an established process can become a bit more challenging. Relationships are established; contracts and requirements are in place. If a contamination problem is discovered, it may be difficult to retrofit an agreement that does not specify the contamination level or even the build process.

It takes a global village

Who actually produces the subassembly? The first thing to determine is the role of the immediate supplier of the part or component. Specifically, you have to determine who is doing the assembly, who is doing the critical cleaning, and perhaps who is doing the coating or surface treatment. In fact, the coating or surface treatment may have associated cleaning steps.

When working with clients, this is the stage in which we are continually amazed at the complexity and specialization involved in assembly of sophisticated products. In an age of specialization and global accessibility, a single subassembly may travel from continent to continent on its way to your facility.

The great unknown: Components purchased from distributors

When we troubleshoot with a client to track down contamination problems, sometimes we find that components are supplied by a distributor, who may purchase the component from any of dozens or even hundreds of suppliers. This situation is acceptable for non-critical components or in situations where it is readily feasible to do critical cleaning of the component at your facility. However, for complex components with tight spacing, in order to achieve the wetting associated with cleaning, solvent-based processes may be required. Worker safety and environmental regulatory considerations may preclude the use of such processes without special capital equipment, engineering controls and recordkeeping. This can make the process costly and more time-consuming. It is better to obtain a product that has been cleaned to your requirements so that you can avoid cleaning or use relatively benign (albeit sometimes relatively non-aggressive) cleaning processes.

Therefore, even though distributors of components can often provide a favorable price, such savings can be a false economy for critical components. It is a good idea to specify not only the physical properties and materials used but also the surface attributes, which are more difficult to define.

Define the subvendors/fabricators; get to know them

Many of us appreciate the importance of specifying and qualifying specific subvendors. It is really important to get to know the fabricators of the components.

Certification programs are valuable. However, we have to consider what the certifications actually require of the supplier. For complex products, performance specs and materials specs do not cover all the bases. It is important to establish process specifications as well, not only for the cleaning agents but all processing agents and for the process itself. Often, lubricants are not specified except perhaps to a requirement that they be synthetic or semisynthetic or water-soluble metalworking fluids. Such processing fluids are complex blends or microemulsions containing organic solvents, water and other inorganic materials. Allowing the use of such a wide range of products may not provide sufficient process control. When the process agent changes, cleaning requirements may change and surface residue may change. Often, the cleaning process is not tracked or coordinated with the fabrication process.

In addition, fabrication and cleaning chemistries may be obtained from sources with minimal technical product support, so contamination problems are compounded.

In tracking down supply chains, we often run into situations where a subassembly or component, nominally from one source, is actually fabricated at multiple sites by several independent companies.

Fixing the process problem by edict or mandate is not likely to be productive. We often hear the suggestion that subvendors be required to use certain processes. Some companies, in fact, produce voluminous materials and process specifications, and then attempt to impose them on the subvendor. Many of these specifications cannot be readily implemented by the subvendor, given economic or environmental constraints. Further, we occasionally observe contradictions within a given process specification. Smaller, specialized subvendors often make every effort to comply with your requests. However, if they have hundreds of clients, each with a separate set of certifications and requirements, complete compliance is problematic.

Observe, ask questions

For complex subassemblies, vendor certification is not enough. We often suggest an old-fashioned business relationship, but with good documentation. To achieve this, routine, ongoing, interactive communication is crucial.

Partnering with the subvendor is not quite the appropriate strategy. After all, as the customer, you have certain requirements and expectations. At the same time, it can be very productive to take advantage of the experience and expertise of people at specialized fabricators.

If communication has been restricted to the procurement group, we often suggest getting the engineers involved. Sometimes, the engineers involved attempt to impose a fabrication process on the subvendor or contract fabricator. Such arbitrary impositions tend to be glossed over at best; at worst, an inferior product may result.

If you are an engineer tasked with working with suppliers, communicate. E-mail is a start, but picking up the phone is better. Ask questions about the process specs. Then, if at all possible, visit the site. Perhaps you need several site visits if your subvendor has subvendors. If you can meet with the techs, do so. If the site visit is not an audit and not connected with a product defect, very often the techs will carefully explain what they have actually been doing to produce a good product. The information you provide may not necessarily be what is written in the official procedure.

Listen, evaluate, document

The actual process, documented or not, may be a valid one. In this case, you and the subvendor should document the process, which should then become the official process.

What if there are problems? Perhaps you discover chemistries or processes that will result in residue, materials compatibility issues, or an undesirable surface. Obviously, the situation must be corrected. Rather than issuing orders, it is again more productive to find out why the process was adopted. It could be a matter of expediency or ignorance. On more than one occasion, however, we have unearthed valid, technical reasons why the official process could not be used. If this happens, correct the official process.

With the subvendor, define and restrict the process

Defining the process and casting it in concrete happens after the initial discussions, site visit and evaluations. Did we say concrete? A generation or two ago, this may have been possible. However, it is not practical to mandate an eternal, never-changing fabrication process. Evolving environmental regulations and changes in technology will from time to time impel changes. The important thing is to develop a system that facilitates informed, rational changes, where the impact of those changes has been carefully evaluated.

Ongoing monitoring and auditing

A well-designed set of requirements that has been put together collaboratively with the subvendor is more likely to result in compliance, and more important, in a subassembly that actually works.

The adage “trust but verify” still applies. This means that certification is not enough. Monitoring the subassembly, at least for particles and/or non-volatile residue, is useful. In some cases, speciating to detect certain residues or classes of residue may be appropriate. This is especially important for medical devices, where residue toxicity must be minimized or where subtle changes in surface quality can impact osseointegration or other interactions with the recipient.

Periodic audits and site visits are an excellent, cost-effective way to head off trouble. If there is a positive, ongoing business relationship, these site visits can be a good time to review the process, to discuss performance issues and even to begin discussing process updates.

Education

Many companies involve their subvendors in education programs. A productive education program goes far beyond indoctrination and rote training. Of course, the critical members of the supply chain have to understand the requirements for process, performance, contamination control and surface quality.

However, a good educational program can also include discussions of upcoming product changes, impending environmental regulations, new customer requirements and major process changes. Particularly where smaller, specialized subvendors are involved, the educational program may remind them of issues they had not thought about. An effective educational program can be a jumping off point for brainstorming; this is where everyone benefits.

Conclusions

Effective critical cleaning and contamination control programs begin far upstream of final assembly in the cleanroom. Certification programs for subvendors are only the beginning. The time invested in gaining an understanding of the fabrication, cleaning and potential contamination issues faced at early stages of the supply chain yields benefits in terms of reducing the need for cleaning in the final stages of production.

Barbara Kanegsberg, BFK Solutions LLC, is an independent consultant who helps final assemblers and suppliers with cleaning, surface quality, contamination control and with educational training. She can be reached at (310) 459‑3614 or via e-mail at Barbara@bfksolutions.com