Electrostatic Discharge: Sources, Dangers, and Solutions
May 1, 2017
We’ve all been zapped by static electricity — the common term for electrostatic discharge — after walking across a carpet and reaching for the door handle or a light switch. But if that were to happen in our manufacturing facility here at Electro Soft, the results could be disastrous. Even one single, tiny spark or shock can severely damage sensitive electrical equipment.
That’s why we take electrostatic discharge seriously. Our production staff wears ESD jackets and heel straps while working in Electrostatic Discharge Protected Areas (EPA), and we follow the American National Standards Institute (ANSI) direction on ESD safety.
But what, exactly, is electrostatic discharge (ESD), and why can it cause such damage to electronics?
Science tells us that ESD is caused when the electrons that have built up on an object do not equal the object’s number of protons. The electrons have to go somewhere to balance things out, which is what causes those tiny sparks. Think of ESD as a miniature lightning storm. Like its big brother, ESD energy will find its way to, and through, the nearest object.
An ESD can be thousands of volts, so when it comes into contact with electronics circuitry designed for much lower voltage, it can easily destroy critical components. What’s more, the damage caused by an ESD might not be immediately apparent — electronics that have been exposed to a static discharge might pass testing and work as intended for some time, but have a much shorter useful lifespan.
ESD isn’t a new problem. There’s evidence that, as far back in history as the 1400s, military forts in Europe and the Caribbean had methods in place to prevent static electricity from igniting gunpowder supplies. Static electricity has even been blamed for the 1937 Hindenburg disaster — researchers say it probably ignited the hydrogen that kept the aircraft aloft.
Today, electronics are present in almost every aspect of our daily lives. For manufacturers of electronics components, that means proper control and mitigation of ESD is a must. Cost alone is one factor — the EOS/ESD Association has released figures that estimate 25 percent of damaged electronics in which a source can’t be identified were most likely damaged by ESD. The organization has also estimated that the yearly cost to industry due to ESD is as high as $5 billion.
When a large amount of static is discharged into a device, the evidence is usually visible: Careful study of a damaged circuit board, for instance, might show a minuscule hole that’s been blown into the surface of the board — just like a lightning strike will leave a hole in the ground.
A smaller discharge, as mentioned earlier, will shorten a component’s life. This is called “latent failure mode.” The component passes testing, but later on it fails during use by the customer for no apparent reason. This, of course, leads to dissatisfied customers and can harm the reputation of the manufacturer.
Static discharge can come from sources you probably wouldn’t even consider — for instance, the tape used to seal up a box of components. We’ve conducted tests in our facility that show the simple act of pulling out a piece of tape can generate 3,000 static volts. Handling a component bag can generate anywhere from 100 to more than 800 static volts. Thirsty? Your water bottle can produce over 5,000 volts.
We use several tools and methods to mitigate these problems. On a workbench, for example, a special table mat, which consists of a dissipative material (often called an anti-static mat or an ESD mat), collects static and then discharges it through a grounding wire. An ESD wrist strap serves a similar purpose by channeling any built-up charge to a ground source. We use special parts bins and containers as well, which conduct any static charge through to the anti-static mat. On our floor, we use ESD mats, which work like the table mats to dissipate electricity safely.
When the component we’ve assembled leaves the ESD protected area, we place it into an ESD dissipative tote or a special metallized bag, which is then closed and sealed. Finally, all ESD-protected areas are carefully and clearly marked by signs and placards that warn you before you enter or leave the area. Anything that’s not necessary for the project must be left outside the area.
By following these steps and maintaining this controlled environment, we’re able to meet all ANSI/ESD S-20.20 Standards, protecting our components — and our customers — in the process.