Construction of a new building for a growing business prompted Raltron Electronics to review its methods of protecting crystal oscillators from the damaging effects of ESD. That study resulted in an improved ESD-control program that includes continuous monitoring of all workstations to ensure proper grounding.
Raltron manufactures time and frequency management components, including crystal units, oscillators, filters, and ceramic resonators and supplies them to OEMs around the globe. Founded in 1983, the company began manufacturing low-end crystals and oscillators in the Far East. In 1991, Raltron started production of three types of high-precision oscillators in Miami: oven-controlled crystal oscillators (OCXOs), temperature-compensated crystal oscillators (TCXOs), and voltage-controlled crystal oscillators (VCXOs).
Typical ESD-Control Program
Oscillators can be damaged by as little as 20 V of static electricity, and workers can generate 50 to 100 times that in routine movements such as sliding a part across a table. Initially, the Miami plant had a traditional ESD-control program—wrist and heel straps that were tested daily, static-protective mats that were checked quarterly, and a static-protective wax on the tile floor.
Unfortunately, wrist straps can become overstretched or dirty, and the worker’s skin can become too dry, conditions that can miss detection in periodic testing. The same is true of static-protective mats that are moved or jostled occasionally.
In late 1996, the company became more concerned about ESD with the addition of a Class 10,000 clean room for manufacturing open blank oscillators. These exposed surface-mount devices demanded a comprehensive and consistent program of preventing static damage.
In the new clean room, Raltron installed 3M continuous monitors. Each unit, about the size of a computer mouse, continuously monitors worksurface resistance, wiring connections, and the worker’s skin resistance.
If the resistance between the worker’s skin and the wrist band is greater than 10 MW or the wiring connections exceed 3.7 MW, the monitor emits audible and visible alarms. At first, the alarms went off several times a day. Within a short time, workers learned to secure their ground cords and properly adjust their wrist straps, and quality inspectors were freed to focus on other concerns.
The monitors contributed to the company’s ISO 9001 certification for the design and manufacture of crystal oscillators in May 1997. Raltron started with 10 monitors, one each for two workstations. During the next two years, 11 more monitors were installed in the clean room and the OCXO area.
Plans for a New Building
Meanwhile, Raltron had outgrown its 30,000 sq ft of rented storefronts in Miami. In 1997, the company bought land and drew up plans for a two-story, 51,000 sq ft building. The move provided the opportunity to rethink ESD control, which had come under increasing scrutiny during customer and ISO audits.
The quality team considered installing continuous monitors wherever sensitive components would be handled: two Class 10,000 clean rooms; three manufacturing areas for OCXOs, TCXOs, and VCXOs; engineering; the stock room; and the inspection area. The issue was affordability. Would the return justify the investment?
Another issue was maintenance cost. In the old facility, the ESD floor wax had to be stripped and reapplied every six weeks. The company had experimented with ESD tile as it leased more space, but the difference in flooring complicated the custodial schedule and inventory of cleaning materials. The new building provided an opportunity to achieve improved ESD protection and uniformity and lower maintenance.
Study of Continuous Monitoring
To calculate the return on investment (ROI) for the continuous monitors, the quality team looked at labor costs of periodic testing. The time required for a worker to queue up, individually test the wrist strap and cord, log the results, and return to the workstation was, on average, 3 minutes. As a result, every worker lost 15 minutes a week or 12.5 hours a year. Assuming an average wage of nearly $10 an hour, the cost per worker was $120 a year. This amount was more than the cost of one continuous monitor.
The company already had 21 continuous monitors and needed another 40. With a few exceptions, each monitor would serve two workers. The cost of a monitor, including two jacks and two wrist straps, would be $171.30 or $85.65 for each worker. That amount was 71% of the cost of periodic testing, which meant a complete ROI in 8.5 months.
A further calculation showed that manually testing wrist straps would cost $13,920 a year ($120 a person × 116 workbenches). By contrast, the purchase of 40 monitors, including 85 wrist straps and 116 jacks, would cost $7,220.40. Investing in the monitors would save nearly $6,700 in productivity the first year.
Additional savings would accrue in rework time and returned products, not to mention sparing employees the annoyance of daily testing. As a result, Raltron decided to install continuous monitors throughout the new facility.
Flooring and Other Improvements
For static-protective flooring, the only options that met the criteria were tile and epoxy. Either could be applied over the 20,000 sq ft manufacturing area, providing uniformity and reliable ESD protection.
Both tile and epoxy were available in suitable colors, and other companies that had used the flooring testified about its attractiveness. Finally, both eliminated the need for stripping and rewaxing, a factor that could save an estimated 80% in upkeep. Raltron eventually chose a 3M seamless ESD epoxy. It was less expensive to install and only required damp-mop clean-up.
The company specified a conductive, rather than dissipative, formulation for maximum ESD protection and selected a thickness of 50 mils, ideal for foot and cart traffic. As before, heel straps were required of supervisory personnel and workers who spend most of their time on their feet.
Other improvements included a computer-controlled ventilation system that monitors and adjusts temperature and humidity. All 116 workbenches, made by Production Basics, were surfaced with 3M static-dissipative laminate. The surface resists solder droppings and solvent spills and, when properly connected to ground, provides a safe place on which to lay sensitive components. As a final step, employees unfamiliar with continuous monitors received small-group training.
The move into the new facility occurred in November 1998. The employees are glad to be rid of daily testing and warnings from supervisors about wearing wrist straps and following procedures. Maintenance has been simplified and costs much less than it did before. Cleaning crews damp-mop the floor, and employees wipe off their own tabletops.
Response from customers and ISO auditors has been favorable. They know Raltron considers ESD control a high priority in its commitment to quality manufacturing of crystal oscillators.
About the Author
Frank V. Parra, the quality assurance manager at Raltron, is a certified quality auditor and past examiner for the Florida Sterling Quality Award. He holds a bachelor’s degree in electrical engineering from the University of Miami. Mr. Parra has more than 25 years of experience in quality assurance programs and has been with Raltron for three years. Raltron Electronics, 10651 N.W. 19th St., Miami, FL 33172, (305) 593-6033.
Copyright 1999 Nelson Publishing Inc.
November 1999