Worksurfaces Resistance Measurements

Transcription

1 Reaffirmation of NSI/ESD S For the Protection of Electrostatic Discharge Susceptible Items Worksurfaces Resistance Measurements Electrostatic Discharge ssociation 7900 Turin Road, ldg. 3 Rome, NY n merican National Standard pproved July 17, 2006

2 ESD ssociation Standard for the Protection of Electrostatic Discharge Susceptible Items - Worksurfaces Resistance Measurements pproved February 26, 2006 ESD ssociation

3 CUTION NOTICE ESD ssociation standards and publications are designed to serve the public interest by eliminating misunderstandings between manufacturers and purchasers, facilitating the interchangeability and improvement of products and assisting the purchaser in selecting and obtaining the proper product for his particular needs. The existence of such standards and publications shall not in any respect preclude any member or non-member of the ssociation from manufacturing or selling products not conforming to such standards and publications. Nor shall the fact that a standard or publication is published by the ssociation preclude its voluntary use by non-members of the ssociation whether the document is to be used either domestically or internationally. Recommended standards and publications are adopted by the ESD ssociation in accordance with the NSI Patent policy. Interpretation of ESD ssociation Standards: The interpretation of standards in-so-far as it may relate to a specific product or manufacturer is a proper matter for the individual company concerned and cannot be undertaken by any person acting for the ESD ssociation. The ESD ssociation Standards Chairman may make comments limited to an explanation or clarification of the technical language or provisions in a standard, but not related to its application to specific products and manufacturers. No other person is authorized to comment on behalf of the ESD ssociation on any ESD ssociation Standard. DISCLIMER OF WRRNTIES The contents of ESD s standards and publications are provided as-is, and ESD makes no representations or warranties, express or implied, of any kind with respect to such contents. ESD disclaims all representations and warranties, including without limitation, warranties of merchantability, fitness for particular purpose or use, title and non-infrigement. Disclaimer of Guaranty: ESD standards and publications are considered technically sound at the time they are approved for publication. They are not a substitute for a product seller s or user s own judgment with respect to any particular product discussed, and ESD does not undertake to guaranty the performance of any individual manufacturers products by virtue of such standards or publications. Thus, ESD expressly disclaims any responsibility for damages arising from the use, application or reliance by others on the information contained in these standards or publications. Limitation on ESD s Liability: Neither ESD, nor its members, officers, employees or other representatives will be liable for damages arising out of or in connection with the use or misuse of ESD standards or publications, even if advised of the possibility thereof. This is a comprehensive limitation of liability that applies to all damages of any kind, including without limitation, loss of data, income or profit, loss of or damage to property and claims of third parties. Published by: Electrostatic Discharge ssociation 7900 Turin Road, ldg. 3 Rome, NY Copyright 2006 by ESD ssociation ll rights reserved No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher. Printed in the United States of merica ISN:

4 (This foreword is not part of ESD ssociation Standard S ) Foreword The purpose of an ESD protective worksurface is to aid in the prevention of damage to ESDsusceptible parts. There are several ways these surfaces may act to provide this protection and they are often confused in practice. One involves the removal of charge residing on the surface of a material. second charge-removal task involves the charge on an object such as a tote box that is placed on the surface. In this case, the charge must flow across the zone between the object and the worksurface, which can interpose a considerable contact resistance. third charge removal task involves current flow from a charged, susceptible device placed on the surface. In this case, a low discharge current may be desirable. The degree of protection afforded by a worksurface is strongly related to the time needed to discharge an object. In practice, some form of resistance value is commonly given as an indication of the effectiveness of the worksurface. Strictly speaking, this description is incomplete since discharge time depends on several other factors such as the effective capacitance of the worksurface, contact resistance and the actual discharge path. However, the capacitance does not usually vary as much as resistance. The other effects are very dependent on the individual situation. s a result, resistance seems the best single predictor of performance of ESD-protective worksurfaces. This standard relies on resistive measurements, utilizing standard instruments, to provide a means of evaluation materials or installed worksurfaces. Conversely, resistivity is measured by specific equipment and is used to establish an intrinsic material property. Resistivity measurements are not within the scope or purpose of the standard. This standard sets forth resistance test methods that can be used to characterize worksurfaces and to obtain relative estimates of their ability to remove electrical charge from non-insulative objects placed on the surface. worksurface, which is conductive enough to discharge an object, may also pose a safety hazard. The work performed on the worksurface often entails the use of tools and test instruments, which operate at voltages high enough to cause electrical shock. The presence of a worksurface tested using the methods described in this document will not guarantee personnel safety. This standard was originally designated NSI/ESD S and approved on September 20, This standard is a reaffirmation of NSI/ESD S and was approved on February 26, This standard was prepared by the 4.0 Worksurfaces Subcommittee. The 1997 version was prepared by the 4.0 Worksurfaces Subcommittee. t that time the 4.0 Worksurfaces Subcommittee had the following members: Dale Parkin, Chair IM rent eamer Static Control Components William Klein K&S Labs Larry urich Lockheed Ronald Schwartz Stanley Vidmar Larry Green USF Shane Wooldridge Kewaunee Scientific i

5 The following people made significant contributions to this document: Steve Gerken USF Ron Johnson Intel Fred Tenzer Duracoat Leo G. Henry MD Dave Diegan FM Inc. John Kinnear IM Ron Gibson Celestica ii

6 TLE OF CONTENTS 1.0 PURPOSE SCOPE REFERENCE DOCUMENTS DEFINITION OF TERMS PERSONNEL SFETY TEST METHODS PPRTUS REQUIREMENTS Resistance Measuring pparatus Electrodes Environmental Chamber Specimen Support Surface MTERIL EVLUTION Specimen Preparation Specimen Pre-Conditioning Cleaning Humidity Exposure Test Configuration Resistance-to-Groundable Point (Low Humidity) Resistance between Two Locations on Top of Surface (Low Humidity) Resistance-to-Groundable Point (Moderate Humidity) Resistance between Two Locations on Top of Surface (Moderate Humidity) Reporting Test Results VERIFICTION OF INSTLLED WORKSURFCES Worksurface Preparation Resistance-to-Groundable Point Identification of Groundable Points Identification of Measurement Positions Meter Connections Measurement Procedure Resistance between Two Points on the Surface Identification of Measurement Positions Meter Connections Measurement Procedure Reporting Test Results PERIODIC WORKSURFCE TESTING Worksurface Preparation Resistance-to-Groundable Point Resistance between Two Points on the Surface Reporting and Using Results... 5 iii

7 7.0 OTHER CONSIDERTIONS RESISTNCE GUIDELINES... 6 FIGURES Figure 1: Resistance to Groundable Point... 7 Figure 2: Resistance Point to Point... 8 Figure 3: Resistance to Groundable Point - New Installations... 9 Figure 4: Resistance Point to Point - Installed Worksurface iv

8 ESD ssociation Standard NSI/ESD S ESD ssociation Standard for the Protection of Electrostatic Discharge Susceptible Items Worksurfaces Resistance Measurements 1.0 PURPOSE This standard provides test methods for evaluating and selecting worksurface materials, testing of new worksurface installations, and the testing of previously installed worksurfaces. 2.0 SCOPE This standard establishes methods for resistance measurements of worksurface materials used at workstations where protection of ESD susceptible items is required. These methods are designed to establish accurate and repeatable resistance measurement techniques for resistance ranges above 1 megohm. The resistance measurement techniques described in this document may be applied to worksurface materials with resistance below 1 megohm. However, changes in equipment and test voltages may be required and are beyond the current scope of this document. 3.0 REFERENCE DOCUMENTS STM F , Standard Test Method for Electrical Resistance of Conductive Resilient Flooring 1 ESD DV1.0, Glossary of Terms 2 NFP 99 Health Care Facilities DEFINITION OF TERMS Many terms relating to this standard are defined in the ESD ssociation Glossary of Terms. The following is an additional term relating to this standard. Groundable Point. designated connection, location or assembly used on an electrostatic discharge protective material or device that is intended to accommodate electrical connection from the device to an appropriate electrical ground. 5.0 PERSONNEL SFETY 5.1 The procedures and equipment described in this document may expose personnel to hazardous electrical conditions. Users of this document are responsible for selecting equipment that complies with applicable laws, regulatory codes and external and internal policy. Users are cautioned that this document cannot replace or supersede any requirements for personnel safety. The ultimate responsibility for personnel safety resides with the end user of this document. 5.2 Ground Fault Circuit Interrupters (GFCI) and other safety protection should be considered wherever personnel might come into contact with electrical sources. 5.3 Electrical hazard reduction practices should be exercised and proper grounding instructions for the equipment shall be followed when performing these tests. 1 merican Society for Testing and Materials (STM), 100 arr Harbor Drive, West Conshohocken, P , ESD ssociation, 7900 Turin Road, ldg. 3, Ste 2, Rome, NY , National Fire Protection ssociation, 1 atterymarch Park, P.O. ox 9101, Quincy, M

9 6.0 TEST METHODS This section describes the test methods to be used to measure the worksurface materials: ) prior to installation ) during initial worksurface installations C) for periodic worksurface testing 6.1 pparatus Requirements Resistance Measuring pparatus Self-contained resistance meter or meters or power supplies and current meters shall be used in the appropriate configuration for resistance measurement with ± 10% accuracy For the material evaluation tests of 6.2, this apparatus shall have open circuit voltages of 10 ± 1 V and 100 ± 10 V, and be able to measure resistance values from 1.0 x 10 5 to 1.0 x For the installed worksurface tests of 6.3 and 6.4, this apparatus shall be capable of an open circuit voltage of 100 ± 10 V and be capable of reading resistance values at least a factor of ten higher and a factor of ten lower than the expected resistance values of the worksurface. In addition, both test leads should be isolated from ground Electrodes Two cylindrical 2.27 ±.06 kg (5 pound ± 2 oz) electrodes with a diameter of 63.5 ±.25 mm (2.5 ±.1 inches) each having contacts of electrically conductive material with a Shore- (IRHD) durometer hardness between 50 and 70. The resistance between the two electrodes placed on a metallic surface should be less than 1,000 when measured at 10 V Environmental Chamber n enclosed chamber capable of controlling relative humidity to 12 ± 3% RH and 50 ± 5% RH and temperature to 23 ± 1 C. The humidity indicating instrumentation shall be accurate to ± 3% RH in the operational range and traceable to NIST Specimen Support Surface surface that has a point-to-point resistance of greater than 1.0 x such as PMM, PTFE or polycarbonate. 6.2 Material Evaluation Specimen Preparation total of six specimens with minimum dimensions of 25.4 x 61 cm (10 x 24 inches) are required. These specimens should be labeled numerically from 1 to 6. Each sample should have two ground connections that simulate end-use grounding procedures. 2

10 6.2.2 Specimen Pre-Conditioning Cleaning The test specimens and electrodes shall be cleaned twice with a minimum 70% isopropanolwater solution using a clean, low-linting cloth each time Humidity Exposure Low Humidity Immediately after cleaning, specimens 1, 2 and 3 shall be placed in an environmental chamber preset to 23 ± 1 C, 12 ± 3% relative humidity for 48 hours, minimum. If the specimens are mounted, the exposure period shall be 72 hours, minimum Moderate Humidity Immediately after cleaning, specimens 4, 5 and 6 shall be placed in an environment or chamber at 23 ± 1 C, 50 ± 5% relative humidity and preconditioned for 48 hours, minimum. If the specimens are mounted, the exposure period shall be 72 hours, minimum Test Configuration Specimens shall be placed on a test surface as defined in ll testing shall be conducted in the conditioned environment. The electrode and grounding configurations are given in Figures 1 and Resistance-to-Groundable Point (Low Humidity) Temporarily ground specimen 1 to remove any residual charge. Remove the ground connection before proceeding with this test. The sensing lead of the resistance meter shall be connected to groundable point (Figure 1) and the voltage lead to the electrode. Set meter output to 10 V. Place electrode at position 1. pply test voltage; if the indicated resistance is > 1.0 x 10 6, remove test voltage and set meter output to 100 V. pply test voltage and record the resistance after 15 seconds of electrification. Remove test voltage and remove electrode from surface. Repeat entire procedure for electrode positions 2 and 3 using groundable point Repeat procedure for electrode positions 1, 2 and 3 using groundable point Repeat procedures and for specimens 2 and Resistance between Two Locations on Top of Surface (Low Humidity) Meter Connections Clean the electrodes with a minimum 70% isopropanol-water solution. Connect the voltage lead to one electrode and the sensing lead to the second electrode Temporarily ground specimen 1 to remove any residual charge. Remove this ground connection before proceeding with the test. Place the electrodes in the positions indicated in Figure 2(). Set the meter output to 10 V. pply the test voltage; if the indicated resistance is > 1.0 x 10 6, remove test voltage and set meter output to 100 V. pply the test voltage and record the resistance after 15 seconds. Remove test voltage and remove electrodes from the surface. Repeat this procedure for the electrode positions indicated in Figure 2().. 3

11 Repeat procedure for specimens 2 and Resistance-to-Groundable Point (Moderate Humidity) Repeat procedure for specimens 4, 5 and Resistance between Two Locations on Top of Surface (Moderate Humidity) Repeat procedure for specimens 4, 5 and Reporting Test Results Report minimum, median and maximum readings in at low and moderate relative humidities for both resistance-to-groundable point and point-to-point resistance. lso report temperature and relative humidity at the time of testing, actual duration of conditioning and test equipment used. 6.3 Verification of Installed Worksurfaces This method may be used to verify newly installed worksurfaces or existing worksurfaces that have not been qualified by 6.2. If a surface is moved, modified or fails periodic testing, it should be retested according to this section Worksurface Preparation The installed worksurface shall be cleared and cleaned twice with 70% isopropanol-water using a clean, low-linting cloth each time. llow surface to "air dry" for at least 15 minutes prior to testing Resistance-to-Groundable Point Identification of Groundable Points Identify groundable point or points to be used in the test. When one or more installed points are provided, they shall all be used. If no such points are provided, use a point or points that represent the manner in which the surface is grounded in use Identification of Measurement Positions For each installed groundable point, identify the following measurement positions (Figure 3): 7.6 cm (3 inches) from the groundable point to edge of electrode, and at least 5 cm (2 inches) from each edge of the worksurface., C and D Positions in the farthest corners from the groundable point and 5 cm (2 inches) from each edge. E The geometric center of the worksurface Meter Connections Clean the electrodes with a minimum 70% isopropanol-water solution. Connect the voltage lead to the electrode and the sensing lead to the groundable point Measurement Procedure Place the electrode at position. Set the meter output to 100 V. Measure and record the resistance after 15 seconds of electrification. Remove test voltage and remove the electrodes from the surface. Repeat for measurement positions, C, D and E. 4

12 Repeat procedure for each installed (or equivalent) groundable point Resistance between Two Points on the Surface Identification of Measurement Positions Identify the four sets of measurement positions as indicated in Figure Meter Connections Clean the electrodes with a minimum 70% isopropanol-water solution. Connect the voltage lead to one electrode and the sensing lead to the second electrode Measurement Procedure Place the two electrodes in measurement configuration. Set the meter output to 100 V. Measure and record the resistance after 15 seconds of electrification. Remove the electrodes from the surface. Repeat this procedure for measurement configurations, C and D Reporting Test Results Report minimum and maximum values in for both resistance-to-groundable point and point-topoint resistance. lso report temperature and relative humidity at the time of testing. 6.4 Periodic Worksurface Testing Worksurface Preparation Do not clean the worksurface. Remove from the surface only those items that might interfere with the test. ESDS devices shall also be removed, and the workstation operator shall be clear of the test area Resistance-to-Groundable Point Measure the resistance from the groundable point or points in use to the farthest convenient point on the surface using the procedure described in Perform additional measurements from the groundable points to the most commonly used or most worn area Resistance between Two Points on the Surface Measure the resistance between two points cm (10 inches) apart in the most commonly used portion of the worksurface using the procedure in If the most used portion is not obvious, use two points near the center of the surface Reporting and Using Results Report maximum and minimum values measured for both resistance-to-ground and point-to-point resistance in. If any values lie outside an established range of acceptable performance, clean the surface and retest. 7.0 OTHER CONSIDERTIONS Other properties may be important in the selection of a worksurface installation. The chemical resistance and mechanical behavior may indirectly affect the ESD protective capability of the surface. Special attention should be paid to the mechanical and electrical integrity of the connection made between the groundable point and that portion of the worksurface intended by the manufacturer for 5

13 grounding purposes. lso other electrical properties such as charge decay, triboelectric charge generation and surface voltage suppression can provide additional information. The relevance of these and other considerations is strongly dependent on the specific installation and the type of products and devices being handled 8.0 RESISTNCE GUIDELINES Due to a wide variety of applications for worksurfaces, specific requirements that could be broadly applied are difficult to determine. However, the following set of guidelines can be used as a starting point for establishing local requirements for the resistance of worksurfaces: Resistance-to-groundable point 1 x 10 6 to 1 x 10 9 Resistance from point to point 1 megohm These guidelines represent a range of resistance that has generally been proven to provide protection in the manufacturing environment. They also are loosely based on models for the effects of ESD on devices. It should be noted that worksurfaces with point-to-point resistances below 1 megohm may be a hazard where exposed voltage may contact the user or the worksurface. 6

14 5.08 cm (2") 1 Electrodes cm (2") Groundable Point Groundable Point 5.08 cm Electrodes cm (2") Groundable Point Groundable Point 5.08 cm Electrodes cm (2") Groundable Point 25.4 x 61 cm (10 x 24") specimens Groundable Point Figure 1: Resistance-to-Groundable Point 7

15 5 cm (2") Electrodes TLE TOP TLE TOP Electrodes 5 cm (2") 25.4 x 61 cm (10 x 24") specimens Figure 2: Resistance Point to Point 8

16 Groundable Point D 7.6 cm (3") C E To:,, C, D, E 5 cm (2") 5 cm (2") - Corner Groundable Worksurface Point Groundable Point D 7.6 cm (3") C E To:,, C, D, E 5 cm (2") 5 cm (2") - Center Groundable Worksurface Point Figure 3: Resistance-to-Groundable Point New Installations 9

17 25.4 cm (10") 25.4 cm (10") 5 cm (2") 5 cm (2") 5 cm (2") C 5 cm (2") D Figure 4: Resistance Point to Point - Installed Worksurface 10