All ESD damage is not created equal. In fact, there are three different types of ESD damage and they can be classified as a catastrophic failure, a latent defect or an upset failure.
As you would imagine, catastrophic failure is the easiest of the three to detect. This type of ESD damage causes some sort of permanent damage such as an oxide failure or a metal melt. The damage done is irreversible. Any device with catastrophic damage is usually found during the testing process and can be dealt with before shipping out.
Latent defects are a little more difficult to spot. This type of damage would allow a device to work properly for the most part, but over time the small amount of damage might affect the life of the device or its ability to function. The issue with latent defects is that the item usually passes testing and is sent to the customer where it may fail.
Lastly, an upset failure is when ESD damages a device or component but not enough to cause complete failure. But while in use, the component may intermittently result in gate failure and cause problems with software and data storage. Just like latent defects, upset failures will pass testing but may have issues in the future.
Damage from electrostatic discharge can happen to components and devices at any stage during its life, including the manufacturing process when the component is being handled or moved, after final inspection and even when it’s in the customer’s possession. It’s important to remember that even though it can’t be seen or felt, ESD damage to electronics can be costly when it comes to both money and reputation.