Static electricity is what makes your hair stand on end when you comb it dry or when sit in a plastic chair wearing a wool sweater and then get a shock as you touch a doorknob. It is caused by a buildup of electrons, usually sheared from one surface and deposited on another surface by friction. If the charge can raise your hair, it is easily releases over 1,000 volts, but rubbing a balloon on your head can generate a charge over 20,000 volts! Though you hardly notice it, many surfaces can cause this effect, but it takes about 3000 volts for us to feel any sort of shock. Anything below 1,000 volts is not noticeable, but still has the potential to damage sensitive equipment. Merely picking up a circuit board off of a table can generate a charge.
Many electronics can be damaged by shocks of under 200 volts and so we have listed here some common electronic components, as well as the voltage required to damage them:
• MOSFET – 100 to 500 volts
• Fied Effect Transistors 140 to 10,000 volts
• Metal Oxide Semiconductors – 250 to 2,000 volts
• Schottky diodes, 300 to 2,500 volts
• Bi-polar transistors 380 to 10,000 volts
When a label is peeled from a liner, there are interactions between the two surfaces that cause friction, and therefore a shearing of electrons. This friction can cause up to 1,000 volts per square inch, depending on the label material. If the label is being applied to small components or electronic devices, the charge could damage, and dramatically decrease the reliability of your products.
A label classified as an “ESD Label” and applied to a circuit board or electronic device should generate a charge below 200 volts when peeled from its liner. However there is more danger than just removing it from the liner. Much like a comb when you run it through your hair, a label can become storage device for static. If you were to come back to the comb ten minutes later, it could still hold enough charge to electrically divert the flow of a thin stream of water from your faucet. A label applied to a circuit board, would have the same ability to gain and store a charge.
A discharge will be accompanied by a heating of the insulating gates in the sensitive components. This damage can cause the device to completely stop functioning, in which case it experienced “catastrophic” damage. The damage could also be partial or so slight that it is not immediately evident in tests, but it can show up later, in which case it is called “latent” damage. Latent damage is usually the most costly type because the equipment fails during customer use, necessitating the return of the board and replacing the component. It has been estimated that such repair costs average upwards of 100 times the original cost of the components.
To prevent this, labels need to be specifically designed to dissipate a charge over its surface, minimizing the charge created when the label is printed and then peeled from the liner and preventing a significant charge from building up on its surface after it has been applied. Static charge cannot be prevented, but it can be controlled. Be sure to ask for “ESD Labels” when you have concerns about static damaging electronic equipment.