Electrostatic discharge damages components in two ways: a sudden discharge that destroys a part, and a lower-energy event that degrades it so it fails later. Packaging exists to prevent both, and it does it by controlling how charge moves – not by blocking it.
The three categories
Conductive materials let charge flow freely. They drain quickly and, because they drain quickly, they can discharge fast enough to damage a component if a charged part contacts them directly.
Dissipative materials let charge flow slowly, in a controlled way. This is what most ESD packaging is, and it is usually what you want: charge bleeds away without a damaging surge.
Insulative materials do not let charge flow at all. Standard polypropylene is insulative, and that is the problem it creates – charge generated by movement sits on the surface and stays there.
Why plain plastic is the issue
Any plastic crate or tray moving on a conveyor generates static by friction, and an insulative surface holds it. A tray that has been sliding along a belt can carry a substantial charge, and the component placed into it is then in a charged environment.
So the issue is not that plastic is somehow dangerous. It is that untreated plastic does nothing about a problem that untreated plastic creates.
What treatment actually does
An anti-static or dissipative additive makes the surface slightly conductive, enough for charge to bleed away rather than accumulate. It is usually measured as surface resistivity, and the useful range for packaging is a band rather than a single value – too conductive and you get fast discharge, too resistive and nothing drains.
Ask for the surface resistivity figure and the range it falls in. A supplier quoting “anti-static” without a number is not giving you anything to specify against.
Two things that undermine it
Wearing off. Some anti-static treatments are surface coatings that wash or abrade away. Others are built into the resin and last the life of the part. Ask which. For anything that gets washed, a coating is the wrong answer.
Humidity. Some treatments depend on ambient humidity to work and stop working in a dry environment. A dry electronics assembly area is exactly where ESD packaging is needed, so this is worth asking about specifically.
Two things that undermine a good specification
The liner. A dissipative box with a standard plastic bag inside it is a dissipative box wrapped in an insulator. Whatever is in the bag is in an insulative environment regardless of what the box does. If you line, line with something that is also dissipative.
The bench. ESD control is a system: bench surface, flooring, operator wrist strap, packaging. A perfect dissipative box on an insulative bench with no earthing is not a controlled environment. Packaging is one part and it cannot carry the others.
We say this because ESD packaging is often bought to solve a problem that is really elsewhere, and the packaging then gets blamed when the failures continue.
What we can do
We supply PP corrugated ESD boxes with dissipative properties built into the material rather than applied as a coating. Tell us the components, the environment and whether the packaging gets washed, and we will tell you what resistivity band suits – including when a standard box with a separate liner is enough.