Electronics fail in transit for reasons that leave no visible mark. A device can arrive undamaged to look at and still be degraded by an electrostatic discharge, contaminated by shedding foam, or worn by movement inside its cavity. Specifying the case therefore means specifying three things at once.
The Three Requirements
| Requirement | What it protects against | Where it is decided |
|---|---|---|
| ESD control | Electrostatic discharge damaging sensitive devices | Resin formulation and liner material |
| Low particulate | Contamination of components and optical surfaces | Liner surface and edge finish |
| Mechanical fit | Abrasion, lead damage and impact | Cavity geometry and clearance |
Our dedicated guide to ESD and anti-static protective cases covers surface resistivity in detail. The point to carry into this page is that ESD performance is a property of the material system, so the shell, the liner and any dividers all have to be considered together — an anti-static shell lined with ordinary foam is not a static-safe package.
Cleanliness Is a Material Behaviour
Foam interiors shed. Open-cell materials crumble at cut edges and abrade under vibration, and those particles settle exactly where they do most harm: on optical surfaces, connectors and bare die. Where cleanliness matters, prefer:
- Closed-cell or skinned liners that do not crumble at the cut edge.
- Thermoformed surfaces with a continuous skin rather than exposed cells.
- Low-shedding dividers and trays, specified as part of the package rather than sourced separately.
- Smooth shell interiors that can be wiped down between runs.
Fit: The Most Underestimated Factor
A component that can move will move, and every micrometre of movement becomes wear on leads, contacts and finishes. Cavity design should hold items on their robust features, avoid loading fragile elements such as connector pins, and provide enough clearance to remove the item without prising it out.
For boards and populated assemblies, the rule is to never let the assembly rest on its components. Support the board at its edges or mounting points, and keep clearance above the tallest part.
Verifying Before It Reaches the Line
- Measure surface resistivity on the actual liner and shell, not only on the datasheet.
- Run a shedding check: wipe the interior and inspect what comes off.
- Do a fit trial with real parts, including removal and re-insertion.
- Confirm the handling routine: a static-safe case carried across carpet and opened at an ungrounded bench is only half a solution.