A tray that carries PCBs or ICs through your line has to handle static charge as well as hold the part. Suppliers label ESD trays "conductive", "dissipative" or "anti-static", and these labels mean different things. This guide explains each type, the resistance ranges the industry uses, and what to ask before you place an order.
Aravinth Polymers vacuum forms ESD trays in Chennai, with moulds made in-house and a minimum order of 500 pieces.
Why Static Matters for PCBs and ICs
An electrostatic discharge can damage a component when its voltage is too low for a person to feel. The damage may stop the part working at once. It may also leave a weakened junction that fails later in the field, which costs far more to trace.
Trays matter because parts sit in them, slide against them and move with them from station to station. A tray made from ordinary plastic can hold a charge and release it into the next part that touches it. ESD trays control how fast charge moves across or through the tray.
The Three Resistance Classes
ANSI/ESD S541, the ESD Association standard for packaging materials, groups materials by surface resistance, measured in ohms.
| Class | Surface resistance | How charge behaves |
|---|---|---|
| Conductive | Below 1 x 104 ohms | Moves very fast across the surface |
| Dissipative | 1 x 104 to below 1 x 1011 ohms | Drains at a controlled rate |
| Insulative | 1 x 1011 ohms and above | Stays where it lands |
Conductive trays carry charge away fast. When the tray sits on a grounded mat or rack, charge drains to ground. Conductive sheet is usually carbon-loaded and black. These trays suit components that are handled on a grounded workstation.
Dissipative trays let charge flow, but slowly enough that a charged device placed on the tray does not discharge in one sharp spike. Many buyers choose dissipative trays for sensitive devices for this reason.
Insulative trays are standard plastic. They have no place in an ESD protected area unless another control covers them.
Where "Anti-Static" Fits
"Anti-static" usually describes a sheet that has an antistatic coating on its surface or an antistatic additive mixed into the polymer. These treatments reduce the charge the tray builds up when it rubs against other materials.
That is a different property from resistance. A low-charging tray can still measure in the insulative range. Some coatings also wear off with handling and washing, and some additives work less well in dry air.
If a supplier offers an anti-static tray, ask for the measured surface resistance. Without that figure, you cannot tell which class the tray falls into.
How Resistance Is Measured
Two ESD Association test methods cover planar materials such as tray sheet:
- ANSI/ESD STM11.11 measures surface resistance, using a probe set on the face of the material.
- ANSI/ESD STM11.12 measures volume resistance, through the thickness of the material.
Both methods condition the sample at set temperature and humidity before testing, because moisture in the air lowers the reading. A tray that passes at high humidity can drift toward insulative when the air is dry. If your plant runs air conditioning or dehumidifiers, the low-humidity result matters more to you.
Forming also matters. Vacuum forming stretches the sheet, and the deepest corners of a pocket end up thinner than the flat sheet. If you buy formed trays, ask whether the supplier measured the formed tray or only the flat sheet.
What to Ask an ESD Tray Supplier
Use these questions when you compare quotes:
- Which class is the tray: conductive, dissipative or low-charging only?
- What is the measured surface resistance, and which test method was used?
- At what relative humidity was the test run?
- Was the formed tray tested, or only the raw sheet?
- Do you supply a test report for each lot, or only for the sheet grade?
- Is the property built into the polymer or applied as a coating?
- Will washing or reuse change the reading?
Aravinth Polymers forms ESD trays to your part drawing. Ask us what sheet grades, test data and documentation we can supply for your order.
What to Send Us
To quote an ESD tray, we need:
- A drawing, CAD file or sample of the component
- Parts per tray and the stacking method
- The resistance class your quality team requires
- Quantity per order and per year
- Any handling, washing or automation requirements
We will reply with sheet and mould options, and with what we can and cannot document for your audit.