How to Use an Anti Static Mat and Wrist Strap

When working on anything electronic you want to make sure you take precautions against static electricity and ESD (electrostatic discharge) from damaging your work. This is accomplished by electrically bonding yourself to ground.

Mats bond work surfaces. Wrist straps bond people.

Since insulators can hold multiple positive and negative charges in pockets across their surface there is no safe way to eliminate them other than to cover them with an anti static mat, wear static shielding clothing with a wrist strap that is connected to the electrical ground, eliminate insulative materials completely from the work area, or use ionization to blow static electricity off ourselves and the work surfaces. To be entirely safe some engineers choose to implement all of the above in their ESD program.

For example, if we are using a wood table we would want to cover that with an anti static mat that is grounded into the electrical outlet. If we have plastic shelving, we would want to replace it with metal shelving. If we are working in low humidity, we may want to use ionization at workstations.

To ensure ESD safe work surfaces for assembling electronics manufacturers use anti static mats that are static dissipative. Static Dissipative is defined in ohms resistance to charging:

• Anything less than 1 x 10e6 ohms is considered Conductive.

•Anything above 1x10e12 ohms is considered Insulative.

• Anything between these two points is considered Static Dissipative.

However, the ESD Association recommends that an anti static mat has surface resistance on its top side between 1 megohm (1 x 10e6 ohms) and 1 gigohm (1 x 10e9 ohms).

This can be measured regularly using a surface resistivity meter.

ARTICLE LINK: How to Use a Meter to Test ESD Mats

Whether you are using a metal table or wood table underneath the anti static mat you still will want to give static electricity a dedicated path from the mat into a grounded electrical outlet. This is accomplished by connecting a grounding cable to the mat via using snaps for mats.

While the top side is static dissipative, the bottom side is usually conductive. In fact, since most electronics manufacturers use grounded workstations and grounded floors they prefer that the bottom side is conductive so that there is no electrical barrier between the matting and what’s below.

Grounding Cables come in several different types. The grounding cable is what connects the anti static mat being used as a work surface to the grounded electrical outlet.

There are grounding cables for mats, wrist straps, and common point grounds for both. Alternatively, you can use a continuous monitor to make sure you know your mats and wrist straps are grounded constantly.

What you do not want to do is to use the alligator clip to clip the wrist strap to the anti static mat. This will not work. In fact, this will increase the total system resistance to ground over the 35 megohm limit recommended per ANSI /ESD 20.20 [ESD Handbook Tr20.20-2008 section 5.3.2.2.2]

Unless you have to, it’s recommended not to use the alligator clip. While it seems convenient, it is best used only when you are sure of the pathway to ground you are attaching it to.