Be aware of these factors to help you reduce electrostatic discharge damage to printed circuit boards and electronics parts.
By Justin Bergholz, Regional Product Specialist, and Vicki Heideman, Principal Engineer, Brady Corp.
Editor's Note: This article is adapted from the white paper, “Understanding & Avoiding the Costly Effects of ESD.” Visit http://goo.gl/vSyIlu to download the free, full white paper that has additional information on how to reduce electrostatic discharge (ESD) damage and why label size for electronics parts is important.
Electrostatic discharge (ESD) is the sudden release of static electricity when two objects come in contact. While it can be harmless in some cases, such as walking across carpet and then feeling a small shock when touching a metal surface, this high-voltage electric charge can be disastrous in the electronics industry. It can cause severe and permanent damage to printed circuit boards (PCBs) and electronic components.
ESD has increased because more intricate, smaller technology has greater sensitivity to the discharge. ESD is one of the industry's most costly causes of damage, impacting virtually every area of the electronics environment, including production yields, manufacturing costs, product quality and reliability, and company profitability.
Three electrical properties should be considered when selecting labels used on sensitive components:
#1. Triboelectric Charges.
Triboelectric charging is the creation of an electrostatic charge by the contact or separation of materials. Multiple instances can cause voltage build-up within a label because of triboelectic charging, but the most common occurrence is when the label is removed from the release liner on which the labels are supplied. These types of voltages vary by material type and label size.
While standard labels can be a source of charge, static dissipative labels significantly reduce the potential for an ESD event. The difference between standard and static dissipative labels is the amount of charge they retain on their surfaces.
Standard labels, comprised of layers of insulative materials, can generate and retain hundreds or even thousands of volts when removed from the release liner. Static dissipative labels are modified to allow the charge to dissipate from the label to ground. As a result, static dissipative labels retain significantly less voltage than standard labels and reduce the amount of remaining voltage to a level considered safe for most electric components.
#2. Surface Resistivity.
Surface resistivity must fall within the ≥1x10 to <1 x10 ohms range, as defined by ANSI/ESD S541-2008, to be classified as static dissipative. Measuring adhesive surface resistivity also can help predict a label's voltage behavior, as can measuring static decay time, which is quantified as the rate at which charge dissipates from the label to the ground. Test method EOS/ESD S11.11 is the standard test method for measuring and classifying labels as static dissipative.
Voltage can be measured with a handheld static meter. However, no industry standards exist describing the measurement of label voltage, so test results can vary depending on the meter used, rate of label removal from the liner, angle and direction of label removal from the liner, use of grounding and test environment.
#3. Static-Decay Time.
Static decay refers to the amount of time it takes for the label to dissipate the built-up static, which is generally created by removing the label from the liner. Static decay testing should be performed in accordance with EIA-541, “Packaging Material Standards for ESD Sensitive Items,” Appendix F, “Measurements of Electrostatic Decay Properties of Dissipative Planar Materials.”
The intent of this test is to determine the label material's ability to dissipate 99% of a 5kV charge to ground within a specific time period. The material is considered acceptable if the average static decay time for each test sample is less than 2.0 seconds.
Brady Corp. is a participating Encompass™ Product Partner in the Rockwell Automation PartnerNetwork™. Based in Milwaukee, Wisconsin, the company is a manufacturer and integrator of identification, safety, graphics and coated material products for electrical, electronic, telecom, construction, pulp and paper, and other manufacturing industries.