Qualcon provides continuous-flow electronics manufacturing services including turnkey procurement and assembly, box-build and deployment services, labor-only assembly of customer-consigned components, and functional and in-circuit testing to original equipment manufacturers (OEMs). Because we intended to offer customers a one-year warranty against manufacturing defects, we decided at the outset to eliminate ESD as one source of possible defects.
In October 1997, as the foundation for the overall ESD control program, we installed 17,000 sq. ft of 3M conductive floor tile throughout the manufacturing area, including the engineering offices and the receiving/shipping stock room. To control static levels to less than 100 V, we require all workers to wear ESD grounding straps on each foot, a system that maintains a total resistance to ground of less than 35 MW.
With this system, any charge generated by standing or walking on the floor is drained from the person’s body through the footwear and floor to ground. The building renovation included temperature and air controls that keep relative humidity at 50 to 55% and temperatures at about 76°.
We set up two continuous-flow production lines with the flexibility to manufacture four to six products at a time. The surface of each workstation—16 prewave-solder, 16 postwave-solder, 10 box-build, and six test—is covered with 3M ESD laminate.
Each workstation also is equipped with ESD chairs. The chairs, manufactured by HAG of North Carolina, were selected to ensure that seating would not be a source of large ESD in the work area.
The test stations are low enough that workers always are seated. Consequently, they must wear wrist straps in addition to the foot straps to maintain grounding should they raise their feet off the floor. These stations are equipped with 3M monitors that continuously check wrist straps and other connections to ensure constant grounding.
It soon became apparent that workers often chose to sit rather than stand at the higher workstations in the manufacturing area. Faced with having to wear wrist straps, workers asked for continuous monitors. Their experience in the test area had shown that these monitors would alert them any time a connection was broken, such as when they reached for something and overextended the cord or strap or when the skin around the wrist became too dry for proper conductivity. As a result, monitors are installed at all the solder and box-build stations so that workers can plug their wrist straps into the monitor jacks whenever they move to those stations.
Testing and Audits
Because ESD control is an ongoing program, we established operating procedures and regular audits. Thomco, an authorized distributor of 3M static-control products in Atlanta, conducts an audit of the flooring and worksur-faces every six months.
Permanent conductivity is built into the vinyl tile, so the floor never needs waxing for ESD control or brightness. When the tile becomes soiled, the facilities manager cleans and buffs it to its original whiteness and sheen.
Training in the basics of static control is given to new employees and repeated for all employees on an annual basis. All employees test their foot straps twice a day—in the morning upon entering the plant and after lunch—and sign a log-in sheet.
Continuous monitoring makes wrist-strap testing unnecessary. If a monitor indicates a problem, the worker immediately checks everything: wrist strap, cord, and connections. If the wrist skin becomes dry, the worker applies a lotion that does not contain silicon or oil, potential circuit-board contaminants.
The company prequalifies suppliers of ESD handling and packaging, and a receiving clerk inspects materials as they arrive. Finished products are packaged in ESD bags and secured with ESD tape for shipping.
Conclusion
The emphasis on ESD control has contributed to the company’s performance, which includes a 97 to 99% first-pass yield on nonprototype items and 98% on-time deliveries. Along with ISO 9000 registration, the ESD control program is used as a sales and marketing tool, particularly when customers tour the factory.
Employees understand the program’s importance and appreciate the results. Most importantly, ESD control bolsters our confidence in offering a one-year warranty against manufacturing defects on our products.
About the Authors
Douglas Philbrick is an operating partner and vice president of operations at Qualcon. He has more than 23 years of experience in the electronics manufacturing industry, including 10 years as president and CEO of F.A.S.T., a contract manufacturer, and 10 years as a manager at Amistar. As a member of Georgia Tech’s Economic Development Institute Advisory Board, Mr. Philbrick is working to include an ESD control program in the university’s Center for Board Assembly Research.
Mark Whitaker is the performance measurement manager at Qualcon. He has more than 12 years of experience in quality assurance, including seven as a quality engineering specialist in the medical electronics division of Medex and two years of consulting with clients in automotive, consumer goods, and electronics manufacturing.
Qualcon, Quality Contract Manufacturing, 4362 Thurmond Tanner Rd., Flowery Branch, GA 30542, 770-965-3300.
Published by EE-Evaluation Engineering
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December 2000