Electrostatic Discharge-Sensitive Medical Device Packaging

Protect products from ESD risks in hospital environments.

 

 

By Robert J. Vermillion, CPP/Fellow;
Certified ESD and Product Safety Engineer; iNARTE

 

Figure 1. A walking person could feel ESD after touching doorknobs and devices in conditions of low RH.
(click image to enlarge)

In 1984, electrostatic discharge (ESD)–related issues arguably cost more than $500,000,000 a year, reports the ESD Association. Worldwide ESD damage accounts for more than $40,000,000,000 a year.1 While ESD issues commonly occur in the semiconductor, defense, space agency, and aerospace industries, the scope has widened to include the medical device industry, among others. ESD event failures are now attributed to a variety of microprocessor-based products.

To put things into perspective, the 4004, Intel’s first microprocessor in 1971, was equivalent to 2300 transistors on a single piece of silicon. The Dual-Core Intel Itanium 2 Processor is nearly equivalent to 1,000,000,000 transistors. Challenges from such damage vary in significance. A circuit card–driven washing machine can be repaired. However, an ESD-damaged circuit card of a pacemaker could be life threatening. Medical device packaging designed to minimize ESD effects must survive not only a production environment, but also the hazards of transport and handling by medical personnel, including surgeons.

ESD-sensitive microprocessor-driven technology, such as a pacemaker, falls within the ESD Roadmap from the International Technology Roadmap for Semiconductors. With technologically advanced hospital-monitoring equipment, lock-ups and ESD-related failures are possible. Unexplained equipment fluctuations observed by surgeons have occurred in hospital environments. A hospital worker walking across a tile floor could compromise an ESD-sensitive medical device through charges from a number of sources (see Table I). Although a medical device may be properly stored for ESD protection, it could be tribocharged during handling after removal from its package. For instance, a person walking across a carpet or tile floor to touch a doorknob will feel a discharge from 3000 to 3500 Volts (see Figure 1).

Table I. Common activities could generate high voltage, leading to ESD events.
(click image to enlarge)

Government medical facility specifications allow flooring to generate <3000 V, according to the 2006 ITRS Technical Requirements—Electrostatics, when 35 V represents the upper voltage threshold for an ESD-sensitive device. To maintain ESD-sensitive medical device integrity, operating rooms or critical care areas need to be validated to benchmark the magnitude for both electrostatic fields and events.

The American Heart Association lists precautions for individuals wearing pacemakers; some of the referenced items could represent potential exposures to medical devices when packages remain unshielded from ESD.2 Considerations should include protection against CB radios, ham radios, metal detectors, microwave ovens, TV transmitters, power-generating equipment, arc-welding equipment, and powerful magnets (as in medical devices). They should be factored into an ESD-protected design scheme.

Cases of circuit failures caused by mobile, or cell, phones are starting to be reported. Electromagnetic interference (EMI) from mobile phones has been shown to produce hard and soft failures in circuits.3 Mobile phones are not high-powered devices, but they can be used or stored very closely to some electronic products. When they are as close as the phone is to the device in Figure 2, significant EMI can be generated in the nearby electronic device. There are many cases where mobile phones can be in physical contact with other small electronic devices, such as in a pocket or purse.4

Even hospital apparel is being looked at as a potential source of ESD. Last year the Newark Star-Ledger reported that Scandinavian hospitals may ban Crocs clogs because of concerns that the footwear may generate static electricity that interferes with medical equipment.

Precautions for handling ESD-sensitive devices inside and outside an uncontrolled ESD Protected Area (EPA) environment must include static control packaging. An ideal medical device packaging scheme will ensure protection from damaging ESD events inside and outside an EPA manufacturing area. Unsafe handling practices and exposure to outside influences should be motivation enough.

ESD packaging engineering protocols clearly define requirements for protection inside and outside the EPA protected areas. To determine the robustness of a medical device, organizations will need to conduct air gap and contact discharge testing per IEC-61000-4-2 (see Table II). However, ESD protection measures in an unprotected point-of-use environment may not be adequately addressed by the test method if unforeseen ESD event models are not considered. The Human Body Model, Machine Model, and Charge Device Model, along with the Field Induced Model, must be considered for packaging integrity.

ESD PROTECTIVE PACKAGING REQUIREMENTS

The author has spent many hours auditing medical device manufacturing and pharmaceutical delivery operations with ESD instrumentation. During ESD/Electrostatic Attraction (ESA) audits or troubleshooting, it is not uncommon to find in-process packaging that falls short of proper ESD safeguards.

Disk-drive and wafer-fabrication industries perform in ESD/ESA (electrostatic attraction) cleanroom environments to ISO Class 3. These materials and their packaging are subjected to a battery of ESD testing protocols and chemical analysis to promote product integrity. Similarly, the medical device and pharmaceutical-delivery sterile environment requirements can be as low as ISO Class 3. As a result, today’s medical device packaging must not only be able to protect products from contamination, shock, and vibration, but also against the hazards of ESD.

Table II.. Medical device manufacturers need to conduct air gap and contact discharge testing per IEC-61000-4-2.
(click image to enlarge)

Many medical device organizations employ ESD engineers to ensure that in-house process manufacturing can provide protection to less than ±100 V. Cooperation among ESD engineers, packaging engineering, quality assurance, and purchasing ensures that the defined requirements will be followed by to packaging suppliers. ESD-compliant packaging and materials must undergo a qualification (validation) process to ensure conformance. The medical device packaging engineer can learn from the semiconductor, defense, and disk drive ESD expertise. Several ESD validation tests should be considered, which will be outlined in the following section.

Terms and Definitions

ANSI/ESD S541-2003, Packaging & Materials Standard, offers a tool that provides invaluable testing methods with defined upper limits. To avoid misconceptions, the following are standard terms used in the ESD field, taken from this ANSI standard.

  • Resistance of Dissipative Materials: A static dissipative material shall have a surface resistance of greater than or equal to 1.0 × 104 Ω but less than 1.0 × 1011 Ω, or a volume resistance of greater than or equal to 1.0 × 104 Ω but less than 1.0 × 1011 Ω.
  • Resistance of Conductive Materials: A surface conductive material shall have a surface resistance of less than 1.0 × 104 Ω. Volume conductive materials shall have a volume resistance of less than 1.0 × 104 Ω.
  • Resistance of Electric Field Shielding Materials: Within the conductive materials classification per ANSI/ESD S541-2003, electric field shielding materials shall have a surface resistance of less than 1.0 × 103 Ω or a volume resistance of less than 1.0 × 103 Ω. Other methods may also define the electric field shielding classification.
  • Resistance of Insulative Materials: An insulative material per ANSI/ESD S541-2003 shall have a surface resistance of greater than or equal to 1.0 × 1011 Ω, or a volume resistance of greater than or equal to 1.0 × 1011 Ω.
  • ANSI/ESD S541-2003 Classification of ESD Packaging Material Properties: Materials and packages that are useful in preventing damage to sensitive electronic devices exhibit certain properties. These properties include:
  1. Low Charging (antistatic).
  2. Resistance:
    a. Conductive.
    b. Dissipative.
    c. Insulative.
  3. Shielding:
    a. Electrostatic Discharge.
    b. Electric Field.

The corporate ESD program manager, ESD site coordinator, packaging engineer, quality assurance technician, or purchasing manager should require ESD materials and products that have undergone a formalized materials qualification process. Qualified products are purchased with a supplier Certificate of Compliance (COC) requirement. By adhering to a Certificate of Conformance (COC) Program, a supplier can pull a defective product from the manufacturing run before being sent to the customer. Thus, incorporating a COC program into the buying process will ensure that both customer and supplier have done their due diligence.

SOME ESD TEST CONSIDERATIONS

Table III.. Resistance ranges as outlined in ANSI/ESD S541-2003.
(click image to enlarge)

ANSI/ESD STM11.11-2006. In 1993, the ESD Association adopted ANSI/EOS/ESD-S11.11-1993 to replace ASTM D257 (Ω/sq), which measured surface resistivity for DC conductance on insulators. The surface resistance of antistatic treated materials will often rise and fall when relative humidity fluctuates. Per ANSI/ESD STM11.11-2006, 1.0 × 1011 ohms is the standard surface resistance cutoff for retention of static dissipative properties. In cold and dry climactic conditions, relative humidity can reach 4% or below. Table III illustrates the resistance ranges as outlined in ANSI/ESD S541-2003.

ANSI/ESD STM11.13-2004. ANSI/ESD STM11.13-2004 is a standard test method for assessing small-profile ESD materials that fall outside the measurement range of a concentric ring fixture specified in ANSI/ESD STM11.11-2006. During vacuum forming, a draw is produced that elongates the material to reduce its starting thickness, which can lead to a loss of favorable electrical properties.

Figure 3. Steps of ANSI/ESD STM11.13-2004 ANSI/ESD STM11.11-2006.
(click image to enlarge)

Figure 3 represents the ANSI/ESD STM11.13-2004 two-point resistance test method for locating hot spots (shown at bottom left). A planar or flat sheet is measured for surface resistance using ANSI/ESD STM11.11-2006 with a concentric ring fixture (see top right).

Volume Resistance (Figure 4) per ANSI/ESD STM11.12-2007 should be considered for materials that exhibit conductivity throughout the material.

Figure 4. For materials that exhibit conductivity, consider ANSI/ESD STM11.12-2007.
(click image to enlarge)

Electrostatic discharge shielding resistance. During the taping application of a regular slotted corrugated (RSC) container, an electrostatic field can be induced through the box traveling on a grounded conveyor as metal guides assist in the flap closure process to produce voltages up to 25,000 V at a distance of 2 ft. To evaluate ESD shielding effectiveness, many companies utilize a controversial test consisting of a 3M Static Event Detector, current probe, or ESD event detector configured into a modified capacitive sensor and placed inside a fully enclosed ESD-compliant package. An ESD simulator is set between 1000 to 5000 V or greater to produce a high voltage discharge to determine the shielding effectiveness of the package.

ANSI/ESD STM11.31-2006. This standard provides a test method for testing and determining the shielding capabilities of electrostatic shielding bags. A 1-kV discharge to the outer package is conducted. The fixture then measures the current across a resistor connected to the fixture’s upper and lower sensing plates. The current and resistance are used to calculate energy seen inside the package during the discharge event (see Figure 5). This test has the objective of measuring stored energy (<50 nJ) per specified relative humidities (12% or 50%).

Figure 5. ANSI/ESD STM11.31-2006 provides a method for testing the capabilities of electrostatic shielding bags.
(click image to enlarge)

Military Standard 3010A-2005 for Electrostatic Decay. This test method can be modified to measure the rate of decay of a charged isolated object to 10% of its original value. A common voltage range of ±1000 V to ±100 V is used to determine the decay time of less than 2.0 seconds. This test represents a material's ability to dissipate induced voltage with proper grounding.

Noncontact Voltage-Measurement ESD Adv. 11.2-1995. The technique for pinpointing hidden charges (hot spots) is accomplished by using a noncontact voltage-measurement device. A charge plate is charged to ±1k V and then grounded. The residual charge remaining on the package is measured with a noncontact voltage meter. A disk drive company will limit the voltage to <±10 V, whereas a medical device company may set its threshold at <±100 V.

Intel�s first microprocessor in 1971 was equivalent to 2300 transistors on a single piece of silicon. The Dual-Core Intel Itanium 2 Processor is over 1,000,000, 0000 transistor equivalent.
(click image to enlarge)
 

Faraday Cup Measurement ESD Adv. 11.2-1995. Another method for measuring residual charge on materials is the use of a Faraday Cup. Measurements less than 1nC/pF (100 V) are acceptable for polymer materials in the semiconductor industry. In this case, the tray was charged to ±1000 V and then grounded after free-falling into the Faraday Cup.

CONCLUSION

ESD medical device packaging must be subjected to a series of test methods to ensure product integrity. As ESD design safeguards are sacrificed in microprocessor-driven devices for additional “real estate,” an estimated $40,000,000,000 worldwide problem will continue to increase as component platforms become smaller and faster.

Bob Vermillion, CPP/Fellow, is a certified ESD and Product Safety Engineer through the International Association for Radio, Tele­communi­cations, and Electromagnetics (iNARTE), who holds a U.S. patent with several patents pending.

Vermillion is forming an ESD Task Force with the Institute of Packaging Professionals (visit www.iopp.org/pages/index.cfm?pageid=361).

One of his recent developments has been approved for a NASA Mars Mission. A coauthor of the ANSI/ESD S541-2003 document and member of the ESD Association Standards Committee, Vermillion conducts ESD Seminars in the USA and abroad. He is president of RMV Technology Group LLC, a third-party ESD Materials Testing and Consulting Company. He can be reached at bob@esdrmv.com.


References

1. http://qa.jpl.nasa.gov/EAAT_02/ESD_02/ JPL Publication

2. www.americanheart.org/presenter.jhtml?identifier=4676

3. http://www.esdrmv.com/DougSmith.asp

4. http://www.emcesd.com/tt2007/tt080107.htm


Further Reading

1. ESD from A to Z, Dr. John Kolyer and Watson, 2nd Edition

2. Mil Handbook 1686C-1995

3. Mil Handbook 263B-1994

4. EIA 541 1988 Appendix C

5. “Triboelectric Charge Testing of Intimate Packaging Materials,” Electronic Industries Association.

6. ANSI/ESD S541-2003.

7. ESD Advisory 11.2-1995.

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