We’re all familiar with the simple electro magnetic shock we can get from walking across a carpeted room. Unfortunately, that same energy has the ability to damage internal parts of office imaging equipment which can lead to intermittent device failures. Electro Static Discharge or ESD is the release of stored energy (static electricity) between two points with different potential voltages. Ideally, special precautions should be taken to avoid ESD, especially with Printed Circuit Boards (PCB) & subassemblies that contain components that are ESD sensitive.

Let’s start with a little science, getting a better understanding of how these voltages are generated. Static electricity is most commonly created by friction or separation.  The amount of static electricity generated depends on the materials subjected to that friction or separation. Another factor is the amount of humidity in the air.  As we are in the winter months, low humidity (dry air) will increase the amount of static charge created. Most boards can be damaged or harmed with a voltage of 30 volts or more, while hard disk drive components can be harmed with less than 10 volts.
 

For example, something as simple as walking across carpet, vinyl floors, or even working at a certain bench can generate as much as 12,000 volts!  What this means is that the circuit board or Hard Drive that your service technician just picked up could now be permanently damaged. That is costly so precautions are in order to help avoid that outcome.

Precautions field service technicians should take:

• Awareness of what can happen

• Use ESD mats and wrist straps when installing/removing circuit board or sensitive component’s

• Transport circuit boards in ESD bags or cases

• Minimize movement while handling unprotected boards

• Place only the board in ESD protective packaging – other objects such as paper, plastic bags, generate ESD that can damage the board

The use of a wrist strap is one of the most effective means to reduce the chances of ESD damage to a PCB. Neutralizing the potential voltage differences to a common point ground will prevent damage to the board.  Wrist straps should be used at all times by the Field Engineer (FE) while handling PCB’s. Also, once the PCB is removed from the protective packaging, the FE should reduce the amount movement while handling the unprotected board.

Get the 1-2-3 on ESD
1 Integrated circuits are made from semiconductor materials such as silicon and insulating materials such as silicon dioxide. Either of these materials can suffer permanent damage when subjected to high voltages; as a result there are now a number of antistatic devices that help prevent static build up.

2.More specifically, one of the causes of ESD events is static electricity. This is often generated through tribocharging, the separation of electric charges that occurs when two materials are brought into contact and then separated. Another cause of ESD damage is through electrostatic induction. This occurs when an electrically charged object is placed near a conductive object isolated from the ground. The presence of the charged object creates an electrostatic field that causes electrical charges on the surface of the other object to redistribute.
 

3. Regarding precautions, due to the dielectric nature of electronics component and assemblies, electrostatic charging can not be completely prevented during handling of devices. ESD prevention activities are therefore important with those processes where the component is touching on equipment surfaces. Interestingly, humid conditions prevent electrostatic charge generation because the thin layer of moisture that accumulates on most surfaces serves to dissipate electric charges.
 

Don Meis is the Service Director of Hytec Dealer Services Inc, located in Florida.  Hytec is the industry leader In Circuit board repair and logistic services for the office imaging equipment industry. Visit www.hytecrepair.com. To learn more about ESD and ESD protection, go to www.esda.org