[Part I of this article appeared in the December 2005 issue, and Part II in the January issue of
Controlled Environments.) (See Sidebar “Terms and Definitions” for ANSI/ESD S541-2003 terminology used in this article.)

ESD Control Measures in the Cleanroom
Static control products are used throughout the electronics, defense, fiber optics, telecommunications, medical, disk drive, and automotive industries for the protection of sensitive electronic components inside as well as outside of the electrostatic discharge protective area (EPA). The ESD Association has developed an invaluable reference standard and roadmap in the evaluation of packaging and materials.

This three-part article has discussed ESD standards and industry evaluation practices for measuring the effectiveness of selected products used to protect electrostatic sensitive devices from ESD related hazards. The procedures and results of testing static shielding and moisture barrier bags made up Part I of this article followed in Part II by an evaluation of ESD gloves and ICP vacuum formed trays. In this final article, we discuss static decay.

Static Decay
This test measures the rate of decay from a charged isolated object at 10 percent of its original value. Federal Test Method Standard No. 101C, Test Method Number 4046 specifies that the charged object at 5000 volts should drain the voltage to 500 volts in less than 2.0 seconds. Often, 1000 volts to 100 volts are incorporated to measure static decay in less than 2.0 seconds. Therefore, this test represents a material’s ability to dissipate induced voltage with proper grounding.

According to Section 30.5 of the Military Handbook-263A, Appendix H, this test does not always typify real world events. However, it is relatively effective for correlation purposes in a controlled environment. A modification of the Fed Std. 101C, Method 4046 is used widely in the disk drive and semiconductorindustry with a charge plate monitor (Figures 21, 22, 27 and 28).

The decay results for static shielding bags were in accordance with Fed Std 101C, Method 4046 for static decay as verified by the use of an ETS 406C Static Decay Unit and Chamber with an ETS Calibration Fixture on 10/10/05. The static shielding and moisture barrier bags were subjected to 72 hours preconditioning as seen in Table 10. The set up in the chamber is illustrated per Figures 19and 20.

Figure 19

Figure 20