Electrostatic Discharge (ESD)

Before you start

Objectives: learn how to protect sensitive components from electrostatic discharge by using anti static mat, anti static wrist strap and how to behave around computer components in general.

Prerequisites: no prerequisites.

Key terms: static charge, discharge, components, static mat, static wrist strap, esd, damage, humidity, protection


Discharge

If we have one object that has a really high positive charge and another object that has a really high negative charge, the charge from the object with the higher electrical potential flows or jumps to the object with the lower potential. That discharge can damage electronic equipment. Computer components such as memory chip, CPU, motherboard, hard drives, and expansion cards can be damaged by an electrostatic discharge as small as 100 volts or less. 100 volts sounds like a lot, but ESD discharge must be about 3000 volts before we can see it or feel it. That means that we could be damaging computer components with smaller voltage which we don’t see or feel. Damage can occur simply by placing a fingertip too close to a component inside the computer case. ESD can cause immediate failure of components, or could gradually degrade components, causing only intermittent problems. To suppress ESD, we can keep the relative humidity between 40-70% and temperature between 72-77 degrees Fahrenheit (22 to 24 degrees Celsius). We should avoid dry air in the computer repair location.

Protection

Before we touch any PC component we should discharge ourselves. There are different ways to do that, but the simplest way is to touch the case frame of the PC system. When we do that any difference in electrical potential is immediately discharged. We can also use a static mat that allows us to equalize electrical potential between us and the PC system. We can also use static floor mats or even static floor materials. Now static floor mat is designed to keep us in balance with the electrical potential of everything around us.

Another thing to consider is, whenever we are handling an electrical component, such as a memory chip or CPU, we should not touch the gold or silver leads on the bottom of the component, or even on the expansion board cards. If a static discharge occurs it will go through those leads. In addition, we should store components in static shielded bags. They have an additional layer built underneath the plastic that absorbs electrical discharges as they occur and dissipates them around the component, instead of letting them go through the component themselves. Static shielded bags are usually grey in color.

Two materials that can easily cause static charges are plastic and Styrofoam. These two materials can build up a lot of electrical charge in us and subsequently shock our components. We should store sensitive components in static-shielded bags (also called anti-static bags) which are usually tinted gray. Static resistant bags are not that effective (usually tinted pink or blue).

Humidity

Humidity helps us to deal with electrostatic discharge. The higher the humidity is, the harder it is for an electrostatic discharge to occur. The humidity in the air acts as a resistor. That means that it doesn’t allow current through it as easily as regular dehumidified air. To keep static down we should keep the relative humidity, if possibly, between 40-70% and temperature between 72-74 degrees Fahrenheit or 22-24 degrees Celsius.

Static Mat

If we often work with PC hardware we should get a static mat to prevent ESD damage from occurring. A static mat is composed of a conductive surface which is designed to conduct electricity. For example, if we take a piece of memory or a CPU and set it on a static mat, it will establish connectivity between that device and the mat. That way, any charge that does get built up dissipates between the part and the mat and whatever the mat is connected to. We can see an example of static mat on the picture below.

Anti Static Mat

Image 165.1 – Anti Static Mat

When we work on a PC we have to establish connectivity between the case, the mat and us, to make sure that the static charges between us and the case are equalized. Using the mat is the best way to do this. First we take the case and put it on the mat. Then we can use that little alligator clip to connect the mat to the case (to ground the case). That way we have connectivity established, so no difference in static charge can be built up between the mat and the case. However, we are also building up a static charge. So, we have to establish connectivity between us and the case. To do that we can use anti static wrist strap. Some mats will also have a second wire which we can use to connect ourselves to the mat.

Anti Static Wrist Strap

Anti Static Wrist Strap

Image 165.2 – Anti-static Wrist Strap

We can use this second wire ie. anti static wrist strap to connect us with the case. We put the strap on our wrist and connect it to the case with a clip. As you can see on the picture above, the wrist strap has a little metal plate that establishes connectivity between us and the case, and also between the case and the mat. When we set up things this way there can be no static charge built up between us, the case and the mat. Anything that does build up immediately gets dissipated through the system. We should ground both ourselves and the computer to the same ground. This provides a single path for the flow of electrical potential. If we don’t have a wrist wrap, we should keep our body in constant contact with the metal frame when working inside the computer.

Important Precaution

We need to make sure that the case is unplugged before we ground ourselves. This is very important, because if the power supply has a fault, we could end up being connected to 110/220 volts. We should not rely on the power cord for an electrical ground. If the current goes through the components which we are grounded to, we could get a shock. Old power supplies had a physical switch that broke the current between the wall and the power supply when we turn off our system. The new power supplies don’t do that. Even though the system is turned off, newer power supplies still provide current to the motherboard. Well, on the motherboard side of the power supply it’s DC current and it probably won’t hurt us much, but if the power supply has a fault we could get in trouble. So, we must unplug the system before we start working on it with the static mat and wrist wrap.

Remember

Electrostatic discharge can damage electronic equipment. Before we touch any PC component we should discharge ourselves. The simplest way to do that is to touch the case frame of the PC system. We should not touch the gold or silver leads on the bottom of any component. Two materials that can easily cause static charges are plastic and Styrofoam. The higher the humidity is, the harder it is for an electrostatic discharge to occur. If often work with PC hardware we should get a anti-static mat and anti-static wrist strap to prevent ESD damage from occurring. We need to make sure that the case is unplugged from the wall before we start working on it.

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