Electrostatic discharge (ESD) is a common issue in the industry field. Almost any thinkable industrial process can cause an ESD shock! ESD can cause irreversible damage, and this is why ESD protection is essential, especially in the field of electronics and electric devices.
Components and integrated circuits that are sensitive to ESD and affected by it can break down completely or can be degraded and start malfunctioning later, even after passing tests without any issues. Therefore, one essential item of any ESD protected area is an ESD packing table. They are also known as ESD workbenches.
Packing ESD tables are equipped to deal with ESD issues when working with sensitive materials. The tables are basically an assembly of a ground kit, an ESD laminate tabletop with ESD coating, and most times – a few other parts that help discharge the electrostatic on packing materials to ground effectively. An important factor in the usage of an ESD workbench is the face of the bench.
Initial concepts for the ESD protected workbench used conductive tops. However, these are far from a good idea from these perspectives:
High impedance stops short circuits: The conductive surface will shut out any connections making operation and trial of the circuit unfeasible.
High impedance leaks charge more slowly. The conductive surface will offer a low impedance discharge path that will give a very speedy discharge, causing high currents to flow and cause damage
Safety – a conductive surface coupled to wrist straps and the like could present a safety hazard should the ground become “live.” In the improbable event of a ground connection of the bench becoming “live” and hence the connections to the wrist straps, the high impedance becomes a much safer option.
In providing the right environment for an ESD workstation, an ESD workbench should ideally have a static dissipative surface. More reasons for having a high resistance dissipative surface instead of a fully conductive surface are basically safety reasons. If high voltages are present in a system, any accidental touch on a conductive work surface and a high voltage source could be unsafe.
Accordingly, safety precautions make it a compulsion that a high resistance dissipative surface is made use of. An ESD protective work surface should possess a resistance value of <1.0 x 109 Ω, such that when tested, it has a lower limit of 1.0 x 106 ohms as recommended minimum. An ESD packing table consists of functional and interchangeable modules to provide maximum flexibility in creating customized workstations, which satisfy any specific working process requirements, workbenches that can perfectly provide unspecified technical premises and educational facilities.
Suitable workbenches are distinguished by practical modular construction and compact size. They allow effective use of hall space. ESD packing tables come in various forms and specifications, depending on your need single workbench, double workbench, simplified universal workbench, T-shape simplified workbench.
Generally speaking, an ESD workbench may have some or all of these elements:
- Static dissipative work surface: The main element of any ESD workbench is the static dissipative work surface.
- Shelves: As static can be built-up anywhere on a packing table, it is crucial that everything on the bench is static dissipative. As items, either electronics fittings or devices may be placed here, the shelves have to be part of the ESD protected area. Also, if devices are placed on a non-ESD dissipative surface, attract static, and then they are used to work on an electronics assembly, the damage is most likely going to occur.
- Metalwork: The metalwork itself being conductive, the paint used is not ordinarily conductive. For an ESD workbench, it is common to use anti-static paint to prevent any sudden discharges.
- Cupboards: Many workbenches have cupboards/closets attached to them as a necessity for tidy packing. Based on the fact that electronics assemblies or other items such as tools for working on the assemblies may be stored in these cupboards, it is essential that the cabinet itself is safe, i.e. ESD safe
- ESD wrist straps: While at work on an ESD workbench, it is important to be sure that the machinist is also held at the same potential so that no discharges happen. ESD wrist straps are mostly used for this.
- Wiring: It is required to make sure that all static dissipative surfaces, wrist straps, etc. are all linked to a collective grounding point and wired effectively. It is vital that this is achieved effectively and in the correct manner on the basis of general electrical safety.
- Monitoring systems: With wires such as the links to ESD wrist straps, etc. being in regular use, there will be periodic failures. In overcoming these challenges, continuous monitoring systems are available, which are noticeably more satisfactory. These are typically incorporated into the ESD workbench assembly.
Here are a few simple precautions that need to be taken to ensure the ESD workbench/ packing table provides a long and useful life:
- Avoid damaging the ESD dissipative surface of the workbench with sharp objects as these can significantly lessen the efficacy of the surface, particularly if small areas get isolated by cuts, etc.
- Clean the surfaces periodically to prevent the build-up of grease or other layers that will impede the static dissipation. A plain and clean cotton cloth, with diluted ammoniated detergent, is good. Using this, ensure that all dirt films are eliminated from the surface. It is advisable to refer to its manufacturer’s operational manual for the best methods for their particular surface.
- Never use wax-based cleaners or solvents that can affect the surface or alter its properties.
- Never use abrasive cleaners. Don’t use any abrasive cleaning agents as well as abrasive cleaning pads, e.g., kitchen scourers, and the likes. These can take away the ESD dissipative surface and considerably make it ineffective.
It is worth implementing a regular care and maintenance schedule as dirt and grease can build up on an ESD dissipative surface over time, and its performance gradually reduces. As it is difficult to sense any performance degradation visibly, and any effects may come on slowly and not be seen, the only way to get rid of this is to regularly clean and maintain the surface. Testing should also be incorporated into this routine.
The picture above shows a workplace where ESD packing table/workbenches are made use of, and shown below is what an ideal packing table should look like.