Out with the laminar flow hoods, in with the cleanrooms


by Mark A. DeSorbo

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These are the times that try the souls of optical component manufacturers. No matter where they turn, they are faced with heated demands for bandwidth; ever-changing network traffic patterns; a slew of fiber deployments; emerging technologies; and, of course, increased costs and competitive pressures. And it could be said that optical network designers and builders, in some way, inadvertently hold component manufacturers accountable in upping production and increasing yields.

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OMM Inc., a San Diego-based manufacturer of photonic switches that utilize micro-electro-mechanical systems (MEMS), is feeling that pressure.

The company had been using laminar flow hoods to manufacture it MEMS-based photonic switching subsystems, but the throughput with those types of minienvironments was not enough to meet the demand, says James Hartman, OMM's vice president of manufacturing.

The company needed cleanrooms, as this type of optical component must be assembled in a controlled environment, which is highly susceptible to contamination and is hermetically sealed.

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Photo 1: MEMS assembly in OMM's ISO Class 5 cleanroom; Photo 2: Wire bonding of a MEMS chip; Photo 3: OMM uses positive airflow gloveboxes as its MEMS seam sealing station; Photo 4: Switch subsystems being prepared for die attach.

The company needed cleanrooms, as this type of optical component, which is highly susceptible to contamination and is hermetically sealed, must be assembled in a controlled environment.

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“Although it was once a medical device manufacture facility that already had ISO Class 6 and 7 (Class 10,000 and 100,000) cleanrooms, it was a new construction because we gutted it and made the manufacturing area into an ISO Class 5 (Class 100) cleanroom with a raised-floor and pressurized plenum,” Hartman says.

The Class 5 ballroom, he explains, was completed this past September. It took an in-house project team, which worked with Role Construction Corp. (San Diego), about 12 weeks to finish.

“The in-house team did a lot of the upfront planning,” Hartman says. “They know the right and wrong things to do when building a cleanroom. We had a full plan of exactly what we wanted to do, and we did have long-lead times on some items, such as flooring, HEPA filters and structural steel. There were also some issues while we poured the concrete,” Hartman says.

But despite a few snags, the project was completed ahead of schedule. OMM, he adds, was able to work with vendors or found new suppliers to procure long-lead items. The design and build team also reconfigured the structure to remedy concrete problems.

When it was all said and done, Hartman says OMM had a 13,000-square-foot Class 5 manufacturing area, along with an attached gowning room. “There's also a 4,000-square-foot ISO Class 7 (Class 10,000) space for engineering labs, supervisor labs, storage for cleanroom supplies,” he says.

Along with ultra-cleanliness, the manufacturing area required some other unique conditions. Because MEMS-based photonic devices comprise several tiny mirrors, which multiplex and divert light through several optical fibers, they are delicate and need to be cradled in a nearly vibration-free environment.

“We have to have less than 50 nanometers of vibration,” Hartman says. “Even people walking on the floor creates too much vibration, so we have to acoustically isolate it.”

The in-house team designed a vibration-isolation system that has also been incorporated into tooling. The system, Hartman says, consist of three layers on which the raised cleanroom floor rests.

First, there's a layer of granite fitted with rubber mounts. The mounts form a platform for either air or oil cushions, which cradle another layer of granite. But that vibration system design presented some other challenges when it came to the “Christmas tree” utility access layout underneath the raised flooring.

“No part of the utilities could touch the isolation pads or the raised floor, and it all had to fit within the floor grid, so we had to work around [the vibration system] to span all of that,” he says.

The “Christmas tree” utility access layout beneath the raised floor, Hartman says, has 120- and 220-volt outlets as well as connections to compressed air, ultra-pure nitrogen, helium and vacuums.

“There's piping every 12 feet, which means whereever you are on the floor, you're within eight feet of having full access to utilities,” he explains. “The whole key to the facility is the floor had to be flexible. We needed the ability to pull up the floor in order to install equipment anywhere and when we choose to do so.”

A super structure over the cleanrooms houses a pressurized plenum. Cleanrooms are outfitted with controls from Siemens Corp. (New York), air handlers from McQuay International (Jakarta), air dehumidifiers from Munters Corp. (Amesbury, MA) and humidifiers from Dri-Steem Humidifier Co. (Eden Prairie, MN).

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OMM used cleanroom walls from Plascore Inc. (Zeeland, MI). Ceilings were equipped with HEPA filters from Envirco Corp. (Alberquerque, NM), while Acco Systems Inc. (Warren, MI) designed and installed the HVAC systems.

Cleanroom personnel are required to wear full bunny suits, facemasks, goggles and vinyl, double-layered gloves.

“There are separate entrances and exits to cleanrooms, and anyone going in and out of the cleanrooms goes through three layers; through sliding doors to the changing room, then to an air shower and then into the cleanroom. It's the same process only in reverse on the way out,” Hartman says.

Positive airflow within the ESD-sensitive cleanrooms is re-circulated and maintained at a temperature of 68 degrees Fahrenehit, plus or minus 2 degrees, with an RH of 35 percent, plus or minus 2 percent.

All in all, Hartman says the cleanrooms give us the capability to manufacture the devices at a high yield and greater.

“For the industry, it means the demand is met because we have a higher yield,” he says. “Before we just used laminar flow hoods, and with the cleanrooms we have seen the impact on yield and because we can easily modify the floor to increase productivity.”


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