ESD Auditing and Verification in Assembly
An ESD programme is a set of measurements rather than a set of signs. Everything in it can be tested, and the testing is what shows whether the protection is actually in place.
What Is Measured
Wrist straps, heel grounders, bench mats, flooring, ionisers, containers and soldering iron tips are the common items. Each has a specification and each can be tested with a portable instrument.
The specification depends on the sensitivity of the devices handled. Our component notes describe the classification.
Daily and Periodic Checks
A wrist strap is tested when it is put on, which makes it a daily check performed by the wearer. A bench mat is tested at a longer interval, and the floor and the ground connections at a longer one still.
The intervals should be written. Our floor control notes describe the arrangement.
Grounding and Common Point
Every conductive item is connected to a common ground point, and the connection is what makes it work. A mat that has been moved without reconnecting its lead looks correct and provides nothing.
The connection should be part of the visual check. Our fabrication notes list the points to confirm.
<img src="https://www.gopcba.com/wp-content/uploads/2026/06/AI-Hardware-Manufacturing.jpg" alt="Surface resistance meter on an ESD bench mat” />
Ionisers and Their Maintenance
An ioniser neutralises charge on insulating surfaces that cannot be grounded. Its output falls as the emitters become contaminated, and the decay time is the measurement that shows it.
The emitters are a wear item. Our maintenance notes describe the schedule.
The Solder Iron Tip
A soldering iron tip is grounded, and its resistance to ground and its leakage voltage are specified. A tip that is not grounded transfers charge directly to the joint.
The measurement is quick and it is often skipped. Our joint notes describe the exposure.
Records and Follow-Up
The records show which item failed, when, and what was done. A failed item is removed from service rather than exchanged between benches.
The follow-up is what makes the programme effective. Our quality notes describe how the records are held.
Verification
The verification is a written interval for each item type, a daily wrist strap check recorded by the wearer, a periodic test of mats, floors and ionisers, and a record of every item removed from service.
Our first pass yield notes describe how the results are used.
Process Control and Verification
The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed. A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance.
Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used.
Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design. The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel.
Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage. Keeping a sample from the panel turns a dispute into a measurement, because the same coupon can be re-examined by both parties without rebuilding the batch.
Checks Before Release
The checks that matter are the ones performed on the product rather than on a sample kept for the purpose, because a coupon that travels with the panel is the only evidence about that panel. Where a requirement can be measured, it should be measured at the point of manufacture and recorded against the board or the lot it applies to.
A parameter that is set once and never re verified drifts, and the drift is usually discovered by a defect rather than by the record. The tooling, the material and the profile form one system, and a change to any of them should be assessed against the other two before it is released.
Where the process window is narrow, the measurement resolution has to be better than the window, or the data cannot distinguish a good part from a marginal one. A record that identifies the operator, the date and the settings is worth more than a record that identifies only the result.
The acceptance criteria should be written before the work starts, so that the decision is made by the specification rather than by the person inspecting.
FAQ
Is a wrist strap enough on its own? No. The strap protects the person; the mat, the flooring and the containers protect the board from the charge the person and the surroundings carry.
How often should an ioniser be tested? At an interval set by the environment and by the emitters, with the decay time measured rather than the indicator lamp observed.
What does gopcb provide for ESD control? We provide a written test interval for each item type, a daily wrist strap check recorded by the wearer, periodic testing of mats, flooring and ionisers by decay time, soldering iron tips measured for grounding and leakage, and a record of every item removed from service.
