An ESD Part That Passes on Receipt Can Drift Before It Ships
What changes in storage
Antistatic and conductive foam formulations rely on additives and on a degree of moisture uptake to reach their target surface resistance band. Very dry conditions push resistance up; high humidity and condensation push it down and, in the wrong combination, degrade the polymer itself. Either direction can take a part out of the band the customer specified.
Heat accelerates the effect. A stock carton stored against a south-facing wall or under a roof deck sees temperatures well above the ambient figure quoted on the datasheet, and the drift over a few months is larger than a single reading would suggest.
Controls that actually work
Keep stock in the original sealed bag until issue; the bag is doing the humidity control. Store off the floor and away from external walls, and keep direct sunlight off the cartons. Apply first-in-first-out by receipt date rather than by shelf position, and record the date on the carton, not just in the system.
Re-verify before shipping rather than only on receipt, particularly for stock held over a season. A surface resistance check on a sample from the batch is far cheaper than a returned lot, and it gives you a trend for the storage location. If the same location keeps drifting, the location is the problem.
FAQ
Does ESD foam expire?
Performance drifts rather than expiring on a date. Storage conditions and elapsed time both matter, so verify resistance before shipping stock held over a season.
How does humidity affect ESD foam?
Very dry conditions raise surface resistance, high humidity can lower it and degrade the polymer. Both directions can take a part outside its specified band.
Should ESD foam stay in its packaging?
Yes. Keep it in the original sealed bag until issue; the bag provides the humidity control during storage.
Where should ESD foam stock be kept?
Off the floor, away from external walls and direct sunlight, on first-in-first-out by receipt date with the date marked on the carton.
All figures above refer to standard product data sheets; final confirmation is subject to written quotation.