The ESD discussion usually starts with a damaged component. The more common problem starts earlier: a charged surface attracts particles from the air, holds them against a wipe or an air stream, and releases them later onto something that matters. The particle count looks stable because the particles are no longer airborne.
How a surface gets charged
Two materials touch and separate, and charge moves from one to the other. In a cleanroom this happens constantly: a glove peeling off a liner, a wipe pulled from a pack, a cover film lifted from a tray, a garment sleeve brushing a bench. The amount depends on the materials, the contact area, the speed of separation and the humidity.
Dry rooms make it worse. Below about 30% relative humidity, charge dissipates slowly through the air, so a surface that would neutralise in seconds at 50% can stay charged for minutes. That is why a dry room and a cleanroom have different static behaviour even at the same particle class.
Why particles care
A charged surface produces an electric field that attracts charged and polarisable particles. The force is strongest at edges and corners, which is why the contamination concentrates where a wipe cannot easily reach: the lip of a tray, the edge of a frame, the rim of a port.
Once attached, the particle is held by the field as well as by van der Waals forces. A dry wipe can break the adhesion and leave the particle charged again, which is how cleaning sometimes moves contamination rather than removing it.
The three controls that work
Humidity is the first and cheapest. Raising relative humidity to 40–50% in a room that can tolerate it reduces charging and increases dissipation. It is not always possible, especially in dry rooms and some pharmaceutical areas, but where it is possible it is more effective than any wipe.
Grounding and ionisation are the second. Ground the fixture, the bench and the tool, not just the operator. Ionisers neutralise the air near a critical surface; they need maintenance and a balance check, and a failed ioniser is invisible without one.
Materials are the third. A dissipative wipe or swab does not generate the charge that a standard polyethylene or dry polyester can, and it does not hold a charge against the surface it cleans. This is the reason ESD references exist, and it is a contamination control measure as much as an electronic one.
Measuring what you cannot see
A field meter gives a number for a surface. Measure the same spot before and after a wipe, and after a glove has touched it. If the number goes up after cleaning, the cleaning is generating charge, and the next particle count will show the result somewhere else.
For a line, a simple survey works: measure at the loading point, the inspection point and the packing point, at the start and end of a shift. The trend tells you whether the problem is the material, the humidity or the people.
A survey you can run in an hour
Take a field meter to the line at the start of a shift and at the end. Measure the bench, the tray edge, the inside of a cover and the glove after it has handled a liner. Write the numbers down with the humidity reading beside them.
Repeat on a dry day and a humid day. The difference tells you whether the problem is the material or the room, and it costs less than replacing every wipe on the site with an ESD reference that may not address the cause.
Does an ESD wipe need to be grounded?
No. A dissipative wipe spreads charge and prevents local build-up; it is not a grounding path. The fixture or the operator should be grounded separately.
Can we just use an ioniser?
An ioniser neutralises air and surfaces in its coverage area, but it does not remove particles that are already attached. Use it with a wipe that lifts the particle, not instead of one.
Is humidity control enough on its own?
Rarely. It reduces generation and speeds dissipation, but a dry wipe on a dry surface can still charge locally. Combine humidity with dissipative materials at the critical points.
