Electrostatic Discharge – Manufacturing’s Silent Killer
March 20, 2010
Electrostatic Discharge or ESD You could be costing your company thousands of dollars in unnecessary rework and repair. By educating yourself in one of the most common issues in electronics you can avoid these common, yet costly defects. Is your company utilizing safe ESD practices?
Lets start with some basic chemistry, everybody is made up of atoms. At the center of an atom is a cluster of protons and neutrons. They are held very tightly together forming a nucleus. Orbiting this nucleus are electrons, which move around rather loosely. There are 115 different types of atoms. All are different because they have different numbers of protons, neutrons and electrons. Protons have a positive (+) charge, electrons have a negative charge (-) and neutrons are neutral. An atom with the same number of protons and electrons will counteract all charges make an atom neutral (having no charge). More protons will make an atom positive while more electrons will make it negative.
Some materials can inhibit the movement of electrons. These materials are called insulators. Examples of insulators are: cloth, glass, air, pure water, plastic, dry wood and oil. Conversely, there are some materials that allow for the free movement of electrons. These materials are called conductors. Examples of conductors are: silver, copper, concrete, dirty water, aluminum and steel.
Electrons have the ability to move freely from one atom to another. In order to get the electrons to move you must create friction. Here is an example, you walk across the carpet at the office and touch the door knob and get shocked, what happened? Walking across the charged carpet created friction. The carpet’s electrons transfer to your body. The doorknob had a corresponding voltage. The zap was the transfer of electrons to that corresponding voltage or, what we call in our industry, an electro-static discharge or ESD
photo courtesy of zb1ek
Another example, in the winter months when you remove your hat from your head, you find that your hair is sticking up, why? When you removed your hat from your hair, it transferred electrons to your hair. The winter months carry less moisture in the air, thereby creating the perfect dry environment electrons need in order to travel. Each strand is charged and each is trying to repel from the other. The furthest it can go is to stand on its end. Dryer conditions, such as the winter season, will cause higher voltages. Think about your clothes dryer and how the friction and heat creates static…starting to make sense?
Current devices that are now installed on PC Boards are so sensitive that they can pick up transfers of electrons that the human body would never sense. Metal oxide devices (MOS) are so sensitive that a discharge of less than 50V can destroy them. Humans usually are unable to detect voltages below 300. One usually feels a shock at 3,500V. This is why it is very important that your business use electrostatic dissipative surfaces when it comes to electronics.