DESCO 66408 User manual

Page 1

TECHNICAL BULLETIN TB-2000

Installation and Maintenance of ESD Mats

Introduction

The purpose of an ESD worksurface is to aid in the prevention of damage to ESD sensitive components and assemblies from electrostatic discharge. An ESD worksurface provides protection in the following two ways:

1. Providing an antistatic worksurface area that will limit static electricity generation.

2. Removing the charge from a conductive object placed on the worksurface.

A dissipative worksurface having a surface resistance of at least 1

x 10

, but less than 1 x 109 ohms is recommended by worksurface standard ANSI/ESD S4.1. Dissipative materials minimize the generation of static charges, and will dissipate a charge slow enough so that a spark will not occur. Dissipative materials are usually the preferred choice for bench top worksurfaces.

Conductive materials are the quickest to remove a charge, but they can also cause damage by discharging too rapidly. Conductive materials are usually used as floor mats, which is defined by ANSI/ESD S7.1 as less than 1 x 10

General Grounding Guidelines

1. ANSI/ESD S20.20 requires that all conductors in an ESD

protected area, including personnel, must be grounded.

2. The ESD ground must be tied directly to and at the same

potential as the building or “green wire” equipment ground.

3. Per ANSI/ESD S20.20, the ESD control program can in no

way replace or supercede any requirements for personnel safety. Ground fault circuit interrupters (GFCI) and other safety protection should be considered wherever personnel might come into contact with electrical sources.

4. All electrical outlets should be verified for proper wiring

configuration, resistance or impedance and GFCI function when the mat is installed and periodically thereafter.

Common Point Grounds

A common point ground is defined by the grounding standard ANSI/ESD S6.1, as:

1. A grounded device where two or more conductors are bonded.

2. A system or method for connecting two or more grounding

conductors to the same electrical potential.

Examples of common point grounds with ground cords are illustrated below.

ohms.

Made in the

United States of America

09814

Figure 2. Other ground cords.

Figure 3. 09814 with screw allows ground cord to be bolted to mat to keep cord from disconnecting.

Common point grounds are designed to provide ground for worksurface mats, wrist straps, and other items. NOTE: DO NOT DAISY CHAIN. Because of the high resistances inherent to many types of protective surfaces, daisy chaining of these materials can severely limit their ability to properly dissipate and protect against static charges.

09817

COMMON POINT GROUND

Per ANSI/ESD S6.1, Grounding section 4.1.1 “Every element to be grounded at an ESD protected station shall be connected to the same common point ground.”

ESD Handbook ESD TR20.20 section 5.1.3 Basic Grounding Requirements “The first step in ensuring that everything in an EPA is at the same electrical potential is to ground all conductive components of the work area (worksurfaces, people, equipment, etc.) to the same electrical ground point. This point is called the common point ground. The next step in completing the ground circuit is to connect the common point ground to the equipment ground (third wire, green).”

WRONG!

09835

RIGHT

Figure 4. ESD mats should never be grounded in series, that is

09825

Figure 1. Typical common point grounds.

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09740

09837

daisy chained.

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Grounding Methods

Method 1 (Grounding via ground cords)

1. Desco recommends using a common point ground cord when

grounding via ground cords. Most common point ground cords will ground your ESD worksurface and provide banana jack ground points for two wrist straps.

2. A common point ground should be installed at each workstation

and should be connected directly to a verified “green wire” equipment ground. Only one groundable point should exist on a worksurface.

Figure 5. Common point ground for each workstation.

2. Desco has three types of 10mm (0.395") field installable mat grounding snaps. The first type is a screw-on snap kit Desco item number 09864 Universal Snap Kit.

A. Determine the position of the grounding snap (one only per

mat) and type of fastener you will be installing (socket or stud). Take precautions not to cut your hand, and punch a hole through the material with a small Phillips screwdriver or awl.

B. Remove the release paper from the circular common point

ground label and affix it so that it aligns with the hole on the material.

C. Select one of the screws as follows:

Material less than 0.100" thick - short screw Material greater than 0.100" thick - long screw

D. Insert the screw through the top on the snap stud or socket,

the washer, the label and the material. Affix the assembly with the conical nut supplied with the kit and tighten down the screw using a Phillips screwdriver.

E. Remaining will be either a 10mm stud or socket, and either

a long or short screw to be discarded or saved for another application.

3. Wrist straps should never be grounded through a worksurface, as the added resistance of the worksurface material will prevent the wrist strap from operating properly.

WRONG! RIGHT!

Figure 6. Proper grounding of wrist straps.

4. Per ANSI/ESD S1.1, a current limiting resistor in the wrist strap ground cord is recommended. If other than a one megohm resistor, special marking in red is required.

For additional information on grounding we recommend Desco Technical Bulletin TB-2007.

Groundable Point Installation

1. Before installing a groundable point on your mat you must first determine whether you will need a snap socket or stud, the type of snap hardware and the location.

ASSEMBLE

SCREW, STUD,

WASHER, LABEL

AND CONICAL NUT

USE A PHILLIPS

SCREWDRIVER OR

AWL TO PUNCH

A HOLE IN THE

MATERIAL

AS SHOWN

Figure 8. Installing Universal Snap Kit on mat.

3. The second type of mat grounding snap is the push and clinch snap. This snap is designed for use with any type of soft mat material: dissipative, conductive or multi-layered. It is recommended for use with three-layered material, because it provides excellent contact with the internal con ductive scrim layer. It is recommended that before inserting this snap, the mat be punctured with a sharp tool where the snap will be placed. Take precautions not to cut your hand. Push and Clinch snaps are available as a snap stud as item 09861 and as a snap socket as item 09863.

A. Remove the release paper from the circular label and

affix it onto the mat material in the desired location.

B. Center the prongs on the snap assembly with the label. Apply

pressure to the snap until the prongs come through the back of the mat, then clinch over prongs to secure snap as shown in Figure 9.

Figure 7. Three kinds of snaps.

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Figure 9. Installing push and clinch mat grounding snap.

4. The third type is the rivet style mat grounding snap. This type of snap assembly is installed using a rivetting hand tool, item

09867. Male snap studs and rivets are available as item 09856

and female snap sockets and rivets are available as item

09857. Groundable point labels are not included with either the

item 09856 or 09857 snap kits.

3. The 09837 Multi Ground Hub is designed for use as either a multiple grounding block or as a common point ground. The Multi Ground Hub incorporates six standard banana jacks, and six terminations for ring terminals (10-32 screw in threaded holes). Note: Also available as Desco item

19219 Ground Hub

Figure 11. Mounting the

09837 to a table leg.

Monitor

4. The 09740 dual bench mount allows the grounding of two operators at one common point. The 09740 mounts easily under the front edge of a workstation. For detailed information on

this common point grounding

device ask for Technical Bulletin TB-2003.

Socket

Stud

Figure 10. Installation using a rivetting hand tool.

Selection of Common Point and Floor Mat Grounding Systems

1. Determine the type of common point grounding system you will use: barrier strip, bus bar, grounding block, or common point ground cord. Desco recommends the use of common point ground cords or our 09740 dual bench mount.

2. If you determine that you will use ground cords, you must now determine the type of ground cord you will use for your workstation grounds. ANSI/ESD S6.1 recommends that a nonresistor ground cord be used to ground worksurfaces and floor mats. However, cord may have a 1 megohm resistor for non ESD puropses. Selection of the ground cord is determined by user needs and specifications.

Desco Ground Cord Item Numbers

Designed

for Floor

Mat Use

X X X X

Model #

09814

09813 09817 09818 09820 09821 09825 09826 09835 09836 09837 09740 09741

1 Megohm

Resistor

Common Ground Point

Floor Mat Equipment Ground

Ground

Snap

Figure 12. 09740 dual bench mount.

Designed for Worksurface

Use

X X X X X X X X X

Wire

Length

15' 15' 10' 10' 10' 10' 15' 15' 10' 10'

6' 10' 10'

Worksurface Mat Snap Ground

Wrist Strap Ground

Banana

Jacks

0 0 0 0 2 2 2 2 4 4 6 2 2

Do Not Hook A Second Surface or Device Here

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6. The 09813 / 09814 mat ground cord may be either attached to a mat by snapping onto a 10mm socket, or by bolting it to the mat with the hardware supplied with the cord. When bolting the 09814 to the mat use a 3/8" diameter hole punch to create the hole for mounting. This will allow cord to sit flush on the mat. Note: For both applications, remove screw from floor mat ground before attaching to mat.

Figure 13. Installing 09814 to mat using supplied hardware.

Mat Installation - General Information

1. For best results, allow the mats to lay flat for about four hours at room temperature before installing. This will give the material time to flatten out from being rolled for shipment.

2. Test grounds for proper resistance to ground. See Desco Technical Bulletin TB-2007 for a complete discussion of grounds.

3. Lay the mat in position and snap the ground cord to it. Bring the other end of the ground cord to the common ground point and attach it using the ring terminal. A suggested ground point is the center screw of a standard AC electrical outlet. Testing is recommended to ensure that the screw is properly grounded. Tie the ground wire to the bench to keep it out of the way and neat. You may cut and strip the ground wire to a shorter length and attach it with the extra ring terminal included with each Desco ground cord.

RING

“GREEN WIRE”

UTILITY

GROUND

POINTS

TERMINAL

CAN BE

ATTACHED

HERE

7. If you are using a mat kit that includes the wrist strap, install the wrist strap directly to the common point mat ground cord banana jack. Again, test the resistance from the backplate of the wrist strap to the common ground point. It should read 1 Megohm ± 20 percent.

09825 / 09826

Figure 15. Adding the wriststrap.

BE SURE YOU TEST ALL GROUNDS AND THE WRIST STRAP FREQUENTLY.

The following bulletins are available from Desco:

TB-2004 Operation of 19350 Wrist Strap Tester TB-2005 Wrist Straps, Grounding, Testing, Maintenance TB-2007 Safe Grounding of Static Controlled Workstations

Maintenance and Cleaning

For optimum performance, periodic cleaning is required following manufacturer’s recommendations. Desco recommends Reztore™

Surface and Mat Cleaner for workstation mats and other surfaces

and Statguard® Floor Mat Cleaner for floor mats. Note: Desco’s Reztore™ Surface and Statguard® Floor Mat

Cleaners contain no silicone or harsh solvents. Cleaners with silicone leave an insulative residue on surfaces and solvents such as 2-Butoxyethanol or Ethanolamine used in cleaners can dry out the material; both can prevent conductive or dissipative mats from functioning properly.

Limited Warranty, Warranty Exclusions, Limit of Liability and RMA Request Instructions

Figure 14. Hooking up ground cords.

4. If your installation includes a floor mat, you should duplicate step 2 and attach the floor mat ground to the same point as the worksurface ground wire.

5. Measure the resistance from the ground snap on the mat to the common ground point. It should read 1 megohm ± 20 percent if you are using a ground cord with a resistor, and less than 1 ohm if you are using a non-resistor ground cord.

6. Using a surface resistance tester per ESD TR53, test the resistance to ground from the center of the mat surface. Required equipment: a megohmmeter with 100 volt open test circuit voltage and two five pound electrodes per ASTM-150. Desco sells this as the Digital Surface Resistance Meter Kit, item 19787.

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