Key takeaways
- A topical anti-static coating is applied much like a varnish, has a limited shelf life, and works well for single-use or short-cycle trays.
- An in-resin anti-static additive is compounded into the material and keeps protecting for years. This is the so-called permanent effect.
- Neither is better than the other. The choice depends on the tray's service life.
- Washing, friction, and dry air reduce the protection, so returnable trays need periodic checks.
Choosing between topical and in-resin anti-static treatment comes down to how long the tray needs to protect the part. A topical anti-static coating is applied much like a varnish, has a limited shelf life, and works well for single-use or short-cycle trays. An in-resin anti-static additive is compounded into the material and keeps protecting for years (the so-called permanent effect). This treatment suits trays with a service life of three to five years. The deciding question is how long the tray will stay in circulation.
What's the difference between topical and in-resin anti-static?
Both treatments have the same goal: keep the tray from building up a charge and causing an electrostatic discharge (ESD) to the component. The difference is where the protection sits. A topical anti-static coating is applied over the tray, like a varnish. An in-resin anti-static additive is compounded into the material itself.
With an in-resin treatment, the additive gradually migrates to the surface and renews the protective layer. That's why the protection lasts longer (the so-called permanent effect), even though the additive reserve shrinks over the years. In general, both treatments work by attracting a thin film of moisture from the air, which lets the charge spread out and bleed off the tray.
A conductive tray, with carbon compounded into the resin, is a different case. The material itself conducts the charge, with no need for an additive to migrate. That's a decision about ESD class, covered in our article on conductive vs. dissipative trays. Both decisions are part of our guide to specifying trays by life cycle.
Why can the protection run out before the tray does?
A properly sized returnable tray can stay intact, with no cracks and the part still fitting correctly, after its anti-static protection has already drifted out of the specified range. Nothing looks different. Operators keep using the tray, and the component loses its protection without anyone on the line noticing.
This happens when the life of the protection isn't matched to the life of the tray. A typical case is specifying a topical anti-static coating, which has a limited shelf life, for an in-plant logistics tray that will circulate between departments for years. Some everyday factors also speed up the loss of protection.
- Frequent washing, especially with detergents or solvents, which strips the surface layer.
- Friction from handling, from stacking, and from parts sliding in the cavities.
- Dry air, which reduces the moisture the anti-static treatment needs to work.
- High temperatures in storage or in the process, which can speed up additive depletion.
- Storage time before use, for topical anti-static coatings, since the shelf life generally keeps running even while the tray sits unused.
How do you match the life of the protection to the tray's life cycle?
Start with the tray's life cycle. If the tray makes a single trip and ends up at the customer's assembly line, a topical anti-static coating works well and keeps the cost in line with how the tray is used. The same goes for trays that make only a few trips, as long as their use ends within the protection's shelf life.
If the tray is returnable and will circulate for years, inside the plant or between supplier and customer, an in-resin anti-static additive keeps pace with that cycle. It's recommended for trays with a service life of three to five years. For these applications, see our returnable trays and our article on expendable vs. returnable trays.
Some applications require stable protection that doesn't vary with humidity or washing. In those cases, our engineering team may recommend a material with the ESD class built into the resin itself, such as a conductive grade. In short, the match usually looks like this.
- Single use or a few trips: topical anti-static.
- Returnable with a three-to-five-year service life: in-resin anti-static.
- Protection that must not vary with humidity or washing: review the material's ESD class with our engineering team.
How do you check that the tray still protects?
With returnable trays, the protection should be checked throughout their use, not just at receiving. Periodic sampling, with surface resistance measured at defined points on the tray, shows whether the lot is still within the specified range. ESD control programs based on IEC 61340-5-1 or ANSI/ESD S20.20 typically call for this kind of check.
Record the ambient humidity and temperature with each measurement, because both affect the reading. Trays that fall outside the range are pulled from service in areas that handle ESD-sensitive components. If your procedure allows it, they can stay in use in applications that don't require ESD protection.
What should you ask your supplier about how long the protection lasts?
Before you approve the specification, it's worth getting in writing how the protection was designed for your use cycle. These questions help guide the conversation with your supplier.
- Is the protection topical or in-resin, and why?
- What's the shelf life of the topical coating, and when does the clock start?
- How does the washing process on our line affect the protection?
- What resistance range does the technical data sheet (TDS) list, and what test method was used to measure it?
- Does the material's ESD class meet our customer's requirements?
Tell us how many years the tray needs to circulate, how it's washed, and what environment it works in, so our engineering team can recommend the appropriate treatment. Send this information along with your part details through our quote form, and find the other specification decisions in our tray specification guide.
Anti-static treatments usually depend on relative humidity. In dry environments, surface resistance tends to rise. That's why every verification measurement should record the ambient humidity and temperature.
Frequently asked questions
A topical anti-static coating generally lasts six months to two years, depending on handling. The shelf life of each material, which also depends on storage, is stated in the specification. Given its limited life, it's a good fit for single-use or short-cycle trays. For trays that will circulate for years, an in-resin anti-static additive is usually the better match.
Yes. Washing tends to strip a topical anti-static coating, reducing the protection with each cycle. With an in-resin treatment, the additive migrates back to the surface after washing, but the reserve shrinks over the years. If the tray will be washed frequently, include the cleaning process in the specification.
An in-resin anti-static additive protects for years, hence the so-called permanent effect. The additive compounded into the material gradually migrates to the surface and keeps the tray protected. Because the reserve shrinks over time and with washing and friction, this treatment is recommended for trays with a service life of three to five years, with periodic resistance checks.
