Q: Can you provide an overview on the use of mini-environments in cleanrooms?
A: “Good things come in (sometimes) small(er) packages.”
-Proverb (edited)
There was a time when micro- and mini-environments were hailed as “the next big thing.” When they appeared on the scene, some of the more rash futurists (generally not engineers) predicted that they would someday be the death knell of the cleanroom. Obviously not so—as evidenced in the electronics industry by the ongoing evolution to 450 mm wafers. Despite remaining and unprecedented technical challenges, the 450 mm movement will drive the largest electronics industry retooling in history. 450 mm fabs are projected to cost approximately $10 billion—with the first slated to come on line in 2017. Hardly the whimpering expected from the deathbed of any facility type.
Definitional confusion
There was (and still continues to be) some confusion, or perhaps flexibility, around terminology: mini-environments versus micro-environments. And common usage can vary from industry to industry, sometimes used a bit loosely, and extend to additional industry specific terms, like isolation units.
For the purposes of this column, we’ll consider the terms mini-environment and micro-environment interchangeable but use the term mini-environment. We’ll exclude classically defined micro-environments, such as containers to enclose wafers for transport or isolate parts of a wafer. For clarity, we’ll define mini-environments as an engineered enclosure, custom built or pre-manufactured, that controls and maintains a specified environment around a production process or product to protect either the product or the operator. Whether to accommodate specialty coatings processes, pharmaceutical production, or critical dryroom humidity controls for a lithium-ion battery manufacturer, the root purpose of a mini-environment remains the same: to enhance the controlled environment to a higher standard, creating a higher class cleanroom within an existing clean facility.
Mini-environments can be controlled for particulate matter concentration, humidity, temperature, pressure, make-up and re-circulated air, gaseous infiltration, or hazardous chemical containment to protect the operator. In short, consider these environments “a cleanroom within a cleanroom” used to enhance the environment within a cleanroom to a higher standard for either process, protection, or production purposes.
Size matters
Don’t let the use of words like “mini” and “micro” fool you. Mini-environments can range from small gloveboxes to an enclosure the size of a room. Sizing specs are generally dictated by the industry sector, as well as the specific process an engineer is designing to. For example, in the solar industry it would be common to insert a 10 ft. by 10 ft. mini-environment into the beginning and end of a 100 ft. long production process, to protect against exposure. Recently, for a pharmaceutical client, we designed a 20,000 lb. glovebox. While it was dimensionally 4 ft. by 10 ft., it required full lead lining due to its requirement to handle radioactive materials. In a vivarium, the facilities engineer may opt to control throughout the entire facility housing the animals, or create individual mini-environments the size of cages to allow for variable air circulation, as well as temperature and humidity control.
Design considerations
First, a basic premise: you can’t create a clean mini-environment within a dirty environment. Mini-environments are often inserted in a cleanroom when flexibility, expansion, process requirements, energy, or cost are the driving considerations. The use of a mini-environment can be more cost effective, for example, when one aspect of a production process requires a class upgrade not required for the rest of the production cycle. It can be less expensive to insert a mini-environment controlled for a higher standard of particulate control, humidity, or air flow, for example, than to upgrade an entire clean manufacturing facility.
The selected use of mini-environments can also dramatically reduce the cost of new construction, as it can be more cost effective and operationally efficient to selectively insert mini-environments to accommodate higher level processing needs than to overdesign an entire controlled environment facility. This cost savings can manifest itself both in initial construction and ongoing operations.
Mini-environments can be custom designed and constructed or purchased as a pre-fabricated unit. The decision to deploy a pre-manufactured unit or custom build will be driven by a variety of factors, including but not limited to product dimensions, availability, critical components the mini environment must regulate and control, schedule, and anticipated future expansion needs.
The design considerations in creating a mini-environment go well beyond the scope of this article. The seminal guide to recommended practices in the engineering of mini-environments is IEST (RP)CC 028.1 (available at www.iest.org).
IEST (RP) CC 028.1 was six years due in part by the continuing evolution of this concept and its adaptation to various industries. The guide covers, among other topics:
• Applications and Concepts: An overview of mini-environments, and their use, applications, and characteristics (with sketches).
• Planning: This section reviews not only the advantages and disadvantages one should consider when analyzing the use of a mini-environment, but it also delves into the always important (but too often overlooked) facility support needs. As a facilities engineer considers the use of mini-environments, it’s important to define, for example, how often one needs to adjust the equipment and what clearances are required to easily access the process equipment.
• Design Considerations: Every facility engineer’s favorite topic! The RP delves into topics including construction materials, temperature and humidity controls, vibration and noise considerations, electromagnetic compatibility, lighting, safety, and ergonomic issues.
• Evaluation and Testing: Providing a methodology for testing and evaluating mini-environments, the RP helps guide the facilities engineer or operator through a sound evaluation process of various mini-environments. Specified test methods are outlined for particle counts, air flow issues, as well as air velocity, volume, and pressurization among other factors.
The RP does not address microbiological issues or applications. The document was prepared by Working Group 028 of the IEST Contamination Control Division.
Mini-environments raise macro questions for the facilities engineer— and the best advice going is to use the ISPE Best Practice document as a guideline to be sure you walk through and answer the myriad questions any sound planning process requires.
Richard Bilodeau’s 30-year career includes plant engineering positions in clean manufacturing. He has designed, operated, and supervised the construction of advanced technology facilities and engineered clean manufacturing facilities for lithium-ion batteries, medical devices, electronics, and pharmaceuticals. Contact: [email protected]
This article appeared in the May 2013 issue of Controlled Environments.
