In this guide, I'm going to walk you through everything you need to know about electrostatic discharge, from what causes it to how to prevent it.
Let's jump right into it.
What Is ESD?
So what does ESD stand for? The ESD acronym simply means electrostatic discharge.
The easiest ESD definition is as follows:
ESD = sudden flow of electrons between two objects
That sounds pretty simple, doesn't it? If we look closer though, we start to dive into the world of electromagnetism.
We don't want this article to run off into the theoretical deep end, so we will just discuss the gold nuggets that you need to know about.
It turns out that we experience ESD all of the time. Do you ever get shocked when you touch a door knob or close your car door after you have gotten out of the vehicle? Have you ever seen lightning?
These are great examples of everyday ESD events. I'm sure we have all wondered why it happens at some point in time.
The answer is that it's all about building up electric charge.
The best way to think about it is that there are electrons in everything around you. When things contact each other, like rubbing, they usually cause the electrons to move around a bit from one atom to the next.
If you ever drag your feet across the carpet, the rubbing between your feet and the carpet is going to cause electrons to be transferred between your feet and the carpet.
The fancy word for this is called the triboelectric effect.
You have probably run across an electrostatic generator in your life. It's the thing you put your hand on and it makes your hair stick straight up.
What is common here is the exchange of electrons, creating a charge to build up.
Having an excess number of electrons means that something is negatively charged, and having a lack of electrons means that it is positively charged.
Nature loves keeping electrons balanced, so the surplus or deficit of them between two objects usually results in a big rush of electrons moving between them to restore the balance.
There's a catch though, there are materials called dielectrics that usually resist the flow of electrons.
We normally call these materials insulators to make things easier. Air happens to be a pretty good insulator.
The build up of charge cannot balance itself out unless it is big enough to overcome the resistance of the dielectric, or insulator.
Lightning is another great example where air molecules bumping up against each other cause a big charge build up, and when that build up gets high enough, it balances itself out with adjacent clouds or usually the ground with a lightning strike.
When ESD Is Most Likely To Occur
Now that we know more about ESD, let's look at the many different factors that cause it.
Let's have a little fun and figure out how to make the biggest ESD that we can. We can do the following:
- Get materials that are prone to create charge easily: like wool and carpet; blue jeans are good too.
- Let's do a lot of rubbing, the more the better. Dragging our feet, pulling items across the table or floor, and many other activities work well.
- We should pull all of the humidity out of the air with a dehumidifier. Dry air helps things to build up even more charge because it lets the air isolate those objects even more. Dry air at 20% relative humidity (RH) can give us about a 15x more charge build up than 80% RH air.
Those are the main things we can do to create a lot of ESD. The problem is that these conditions aren't so rare in a typical lab or manufacturing facility. That simply means that its very easy under normal conditions to have a lot of ESD events.
Oh, and for the record, my body is a big charge creator. I'm the one that shocks my hand on the door handle every time. Some people don't experience this often. My point is that every person, depending on their specific chemistry, will have different experiences with ESD.
You usually feel a shock when the charge in your body is around 3,000 Volts. That's a lot! It happens frequently, especially in Winter time when the air is much more dry.
It takes much less voltage than when you feel a shock to damage electronics.
And by the way, if you also suffer from door knob shock often, a trick you can do is to touch a non metal part of the door right before you grab the handle to dissipate enough charge slowly off of your body so that when you do touch the metal handle, it won't be a sharp discharge. It only takes a second or two in most cases.
You might want to practice this at home first, as some people might find it weird if they see you do it. You can do it quickly and naturally where no one will notice. Either that, or enjoy getting shocked.
Also, are you tired of getting shocked by closing your car door when you get out of it? Me too. To prevent this, as you are getting out of your car door, hold the door handle. It will keep your body from building up charge so that when you close the car door, no ESD.
The common theme here is that when we ground ourselves properly, we can dissipate any charge build up and limit ESD events.
You're probably asking, why should I care about ESD? Well, the answer is because ESD can cause a lot of damage to electronics.
As we discussed earlier, any human activity is going to create a charge build up. Many activities create charges up to thousands of Volts.
By the time you feel an ESD shock event, you are already at 3,000 Volts. Electronics are sensitive and can be damaged at much lower voltages than that.
So how are components like capacitors or chips damaged? Let's go over a specific example to give you an idea.
If you ever dip into the details of how electronic parts are made, usually there are many conductive paths in the part and they are isolated by some kind of insulator, or dielectric.
The most commonly found dielectric is oxide since its easy to manufacture in most materials by adding oxygen under the right kind of environmental conditions.
What happens when you introduce a lot of charge into a component is that the charge will usually be much higher than the dielectric can resist against, and the ESD event will short out between two conductive paths going through the dielectric.
This has a disastrous effect, because it means that the little "lightning strikes" in the part will literally punch holes in the dielectric layer, causing permanent damage.
Pretend we removed the top layer conductor from our prior example after some ESD events. We would be able to see holes that were created by those ESD events in the oxide layer. It only takes one to cause problems.
Then, over time, usually the oxide layer will start to degrade and malfunction. This is how ESD events create latent failures and defects in electronic components.
The damage may not be enough to show problems right away, but can start a problem that eventually cascades into a failure later on.
Electronic Circuit Boards
As we saw earlier, electronic components are very sensitive to ESD. This is because a human hand picking up a part has the ability to put a lot of charge across the component.
When handling an entire circuit board though, it gets a lot more complicated. Now the charge build up has many different paths it can travel down.
In industry, some people believe that electronic boards are immune to ESD, but they are not. There is a little more safety created for individual components, but this is far from making the electronics 100% safe.
You never know where the charge will go, and if it will go into a part and across something sensitive that it will do damage to. It's like playing Russian roulette, you simply don't know and shouldn't take the risk.
There is nothing more annoying than rare and latent failures in electronics. Prevent these as much as possible by protecting your electronic components and boards from ESD.
It's also important to note that there are many diode parts and chips out there to help protect inputs and outputs on circuit cards against ESD.
We covered how ESD works and how it can cause damage to electronic components. Now let's discuss ways on protecting electronics from ESD.
In order to be ESD safe, we want to do our best to reduce the potential for ESD by reducing charge build up.
Two main things within our control are the materials used in the lab, whether its clothing or work items, and also the humidity in the air.
That means we can focus on the items in the work area, and also on controlling the humidity to prevent it from dropping to lower levels.
In summary, here are several ways we can prevent ESD by preventing and controlling the build up of charge. The main ways are:
- Floor control
- What we wear
- Our work area
- Materials we use
- Keep humidity in air at safe levels
One of the best ways to dissipate charge from your body is to be in contact with ground level potentials to allow any charge you build up to be removed.
In most labs and manufacturing facilities, this is accomplished by having conductive floors.
There are many options here. One of the most popular is the application of ESD wax to the floor.
Assuming that conductive floors are available, another component is to have shoes that will transfer charge from your body and into the floor.
You have a mix of options here. Many shoe makers do have ESD safety shoes that are ESD compliant in that they will dissipate any charge you build up to the ground. You can even get them with steel toe and other features.
Often times though, many workers will not have specific shoes that will have this feature.
The other option is add on heal straps.
Heal straps come in two main varieties, the first is the really cheap one time use strips.
These little strips are ones that you can put on the outside part of your shoe at the heel, and then bring the other part up into your sock.
In my experience, they don't perform very well, but they are better than nothing.
The next option is heal straps that you can wear every day whenever you need to go into ESD sensitive areas.
They are actually straps that fit around your heel and usually have Velcro for tightening them to your shoe.
A flexible strap then is placed in between your sock and your skin. These work extremely well.
A top generator of charge is your normal every day clothes. The materials make it very easy to create charge build ups just by moving around with the small amount of rubbing that happens between materials.
The best way to handle this is with an ESD smock.
Typical smocks like this will have better materials, including conductive materials that will help prevent the charge generation from occurring.
The design of the smocks usually create a Faraday cage around your torso area, which helps keep everything pretty balanced on your body charge wise.
Keep in mind that you must wear the smock properly. If you fail to button or zip it all the way and don't wear it as designed, the capability is greatly diminished.
For extremely sensitive electronics, ESD gloves are also available.
Nitrile gloves are commonly used for this type of solution. They are also great chemical barriers as well, so they have multiple functions.
In special cases, there are also cloth based gloves available as well that are effective at preventing charge build up.
In order to be completely ESD safe, all electronic work should be done at a proper ESD workbench.
This typically includes a metal table that is properly grounded to building ground, and that has plenty of space for a mat and wrist strap.
Workbenches of this type can range from cheap to very expensive depending on the different capabilities and features.
ESD mats are the heart of a great protection strategy. Working on a flat surface often times creates a lot of opportunity for charge build up.
That is why a mat that doesn't build up a charge is important, as well as one that will dissipate any charge that occurs.
A mat of this type is conductive and has a connection point that must be connected to building ground for the mat to be effective.
Otherwise any charge that pops up has no where to dissipate to.
ESD Wrist Strap
An ESD wrist strap is our 2nd most important safety protector.
When properly used, a strap will dissipate most of the charge that you build up by normal human activities like moving your arm or doing normal work.
An ESD strap, also known as an ESD bracelet, goes around your wrist and plugs into either your workbench or into your mat, depending on your setup.
There is usually a big resistor between the wrist and the end plug built into the strap to ensure that there is a path for charge dissipation, but that you are not connected directly to the grounding setup.
One way these straps fail is if the user stretches the wrist band area where the metal portion is not making skin contact. This effectively renders the strap useless.
To counter this problem, the more expensive straps have metal wrist bands where it is impossible to lose skin contact with the strap.
When it comes to transferring electronics from one place to another, there are multiple chances of ESD problems to occur.
To combat this, there are two main options for an ESD bag:
- Conductive bags
- Dissipative bags
Conductive bags are your best form of protection. They are usually a silvery or metallized film material.
When zipped up completely, the outer film layer forms a Faraday cage that will redirect any ESD around the surface of the bag, preventing anything inside from getting damaged.
If these bags are not zipped fully, or are punctured in any way, the protection capability is greatly diminished.
Dissipative bags on the other hand are for less sensitive components. They are usually made from polyethylene and pink in color.
These type of bags help prevent any sort of charge from building up on the surface of the bag.
However, the bag cannot protect from an ESD event, which will travel through the bag and into the contents, possibly causing damage to what's inside.
Often in electronic assemblies, there is a need for tape to bond two items together.
But did you know that normal every day scotch tape is a huge generator of static charge?
That is where ESD tape enters the picture.
There are two common types, which are conductive tape or Kapton tape.
Conductive tape is great for electronic packaging to help reduce ESD risk. It works like regular tape and is pretty strong.
Kapton tape is miracle material. It has great mechanical and electrical properties, so it's definitely an electronic circuit's best friend.
The tape is often used on circuit boards, in electronic assemblies, and generally anywhere in the lab that tape is often needed.
It can also withstand extreme temperatures.
What makes it so great is that its not too expensive either.
When it comes to testing for ESD, two of the biggest factors is testing heel straps and wrist strips for conductivity.
There are several companies that make wall units where the user can walk up and put their foot on a pad while wearing their heel straps and then push a button for a quick test.
This is important since heal straps should be tested every time the worker enters the work area.
The wall units sometimes have a way to hook a wrist strap as well to test its conductivity.
Often times, the workstation will have a dedicated wrist strap unit that will continuously check conductivity while a strap is plugged in, and will have an audible alarm if something goes wrong.
Product Images Sourced From: Link