Electro-Static Discharge (ESD) is an invisible menace that lurks inside your electronics production areas, including zones dedicated to Research and Development, Manufacturing, Testing and Storage. Very simply, ESD is damage caused to electronic assemblies by high-potential static electricity that collects on the artefacts, including people in the area. As the name suggests, ESD is static i.e. it lacks current flow and remains in place for a long time, until the build-up discharges into another body or device.
ESD has always been around. However, this naturally occurring phenomenon came into broad focus with advent of increasingly miniature and complex electronic components. For a layperson, the common idea of ESD could range from seeing dramatic lightning in a thunderstorm to feeling a small shock when they touch metal after a drive in the car. By contrast, the ESD that we are discussing is invisible and omnipresent, and yet, it can cause widespread havoc in electronic assemblies without any apparent physical manifestation.
ESD can damage and destroy intricate construction of today’s miniature electronic components. Miniaturization packs integrated circuits in smaller spaces while using less semiconductor material and smaller on-chip protective devices. All these factors make modern electronic devices ever more vulnerable to damage by ESD.
ESD Prevention and ESD Protection are vital to improving reliability and reducing defects in today’s electronics manufacturing facility.
Causes of ESD
Static electricity is a result of several processes:
- Tribocharging: This phenomenon occurs on separation of insulating materials that were previously in contact. Example of this effect is a person walking with insulating shoes on a rug or brushing dry hair with a plastic brush.
- Electrostatic Induction: This induction occurs when an electrically charged object is in proximity with a conductive object that is isolated from the ground. For example, plastic items with charged surfaces can result in ESD on sensitive components.
Result of ESD Damage
ESD causes large currents dissipating through the component, taking the lowest impedance path to ground for equalizing potentials. The current may go through the semiconductor in the integrated circuit, causing local hot spots that damage the junctions and breakdown the structure.
- ESD can cause permanent damage to the electronic components, where they stop working completely. This type of damage is relatively easy to segregate during testing, as the product just does not work as intended.
- Even worse, ESD can also result in latent damage that weakens the electronic device resulting in intermediate faults or complete failure at a later stage. This type of damage is very difficult to detect during testing and subsequently rectify before dispatch.
Apart from causing varying degrees of inconveniences to the customer, failure of an electronic item in the field results in loss of reputation, warranty costs, replacement costs and legal liabilities. Industry estimate mention 8% to 33% losses as a direct result of ESD damage. Thus, ESD imposes an unacceptably high cost to the bottom-line and addressing the issues is imperative for any professional organization.
The good news is that ESD prevention and control is easy and sustainable.
Here are some common strategies and methods to overcoming ESD in your electronic assembly area:
Planning and Procedures:
- Create ESD Protected Area (EPA)
This clearly demarcated area has several ESD protection devices to eliminate any static build-up. For demarcation, the area has clear signage as well as decals.
- Implement Access Control
The area has access control ensuring that only trained and properly protected personnel enter this demarcated space. Since people can walk into the EPA with static charge on their bodies, a suitable anti-ESD mat or grounding plate at the access point could help dissipate build-up prior to entry.
- Follow Protocols
ESD protection in EPA’s follow internationally recognized protocols. These protocols take into cognizance the type of electronic product handled in this area and its ability to withstand ESD. Standards such as ANSI/ESD S20.20 and IEC 61340-5-1 explain the ESD protection in EPA’s.
- Nominate an ESD Champion
Implement human leadership by nominating a responsible person in your organization as an “ESD Champion.”
The ESD Champion will:
- Coordinate the various technical efforts and people participation to create an ESD-free area used for handling electronic assemblies.
- Design and implement plans for ensuring ESD controls at a systemic level.
- Testing of ESD Implements
Anti-ESD processes depend on the connections and apparels working correctly.
- Devise a continuous testing program to ensure that the anti-static shoes, straps, clothes, surfaces, furniture, etc. are doing their job.
- Check the efficacy of grounding/earthing systems. Failure of connections, wires, earthing pits, etc. could defeat the ESD protections implemented in an EPA.
- Use ESD monitoring equipment for a real-time check on all the ESD safe items.
- Conduct periodic testing of workstations, chairs, flooring, trolleys and racks.
- Note any deviation from the standard and take corrective measures immediately.
- Develop a Training Plan
- Develop a training plan to educate personnel on handling of ESD sensitive items. This training improves awareness of the anti-ESD precautions required in an EPA.
- Train all personnel who are directly or indirectly in contact with the ESD sensitive products to increase their awareness of the ESD phenomenon.
Ensure Good Grounding/Earthing Practices
A healthy grounding or earthing connection ensures that all implements and surfaces maintain identical potentials. This eliminates any formation of static electricity by draining the charge to earth through the easiest path – the grounding or earthing system.
Use ESD-Safe Products:
Wide varieties of ESD-Safe products are available for fighting static electricity in EPA areas. These include:
- Wrist Straps
ESD-safe wrist strap ground personnel working on the sensitive electronic assemblies and discharge any static build-up on their bodies. The wrist strap is especially important if the personnel use non-ESD qualified furniture.
The wrist strap provides a conductive path from the person to the EPA’s earth potential through a flexible grounding cord. While the straps may appear in good shape, they are susceptible to frequent failures. To avoid an inadvertent collection of ESD, test the straps on a regular basis.
Walking on a regular surface wearing shoes with insulating soles could build-up considerable amount of static charge. In areas that require personnel’s mobility, use ESD-safe footwear and ESD-safe flooring to prevent static from building-up. This flooring and footwear, made from special material, conduct static to ground and effectively prevent ESD to personnel working in an EPA.
In addition, ESD-safe flooring provides a common ground path to special ESD-safe equipment such as chairs, workstations, material-handling equipment like the trolleys, whose special wheels conduct static build-up to the floor.
Fabric and other clothing generate electro-static charges. As clothing is usually insulative, the accumulated surface charge does not discharge through body to the ground. Personnel working in EPA’s and Clean Rooms must wear ESD-safe clothing.
ESD standard ANSI/ESD S20.20 and garment standard ANSI/ESD STM2.1 define 3 categories of ESD-safe clothing, of which you could choose the one suitable for your requirements.
- ESD-Safe Furniture
Several varieties of ESD-safe furniture like workstations and chairs are available in the market. However, most of them do not consistently deliver the specified ESD range, especially after wear and tear of regular use.
Desirable Characteristics of ESD-Safe Furniture:
- Follows ESD Standards ANSI/ESD S20.20-2014 and IEC 61340.
- Allows uniform elimination of ESD charge using dissipative surfaces with discharge path to ground within a specific duration.
- Uses new generation material with Volume ESD protection.
- Volume ESD material ensures that surfaces such as the tabletop of the workstation and seat/backrest of the chair, uses material that is certified ESD-safe, even when tested at a particulate level.
- Volume ESD material ensures that the ESD protection remains constant over the lifetime of the workstation/chair, despite wear and tear of usage.
- Even damage, cuts and nicks to the surface will not reduce the anti-static protection of the Volume ESD material.
- Ensures proper grounding of the workstation. For chairs, grounding should be through the ESD-safe castors and not using an unreliable chain dangling from the chair’s base that is connected to ground potential.
- Ensures that ESD-safe workstation and chairs do not generate any charge by themselves.
- Ensures that the ESD safe workstation and chairs do not generate any electromagnetic fields or electromagnetic interference.
- Ensures good design practices in design and manufacture.
- ESD-safe workstation should be ergonomic, modular, lightweight and easily customizable.
- The furniture should meet all future expansions needs without requiring drastic changes.
- Ensures ergonomic placement of all electrical components, instruments and computer peripherals. This placement enables maximum work surface, while ensuring easy accessibility to frequently required implements.
- Provides ergonomic design that allows the user to sit comfortably for long hours without fatigue. This scientifically designed comfort helps in improving concentration and enhancing productivity.
- Provides inbuilt cable chambers ensuring a neat and clean workspace.
- Provides peace of mind.
- The workstation and the chairs are covered by a comprehensive warranty against manufacturing defects as well for ESD-safe properties.
The EPA must be equipped with ESD safe tools. ESD sensitive component should be handled only with ESD safe tools. The tools must not collect static charges that may discharge into the electronic components.
Some elements in EPA cannot be rendered ESD-safe as they are isolated or they cannot be grounded. These include insulative materials like common plastics. Air ionizers help mitigate static collection on such elements.
Air ionizers neutralize the static charge on insulative or isolated objects by releasing an equal amount of positive and negative charges in the air. Any charge present on the body attracts the opposite charge and gets neutralized.
However, ionization is not a substitute for grounding. The technique should be used to eliminate the static charges when no other grounding options are available.
ESD-Safe Material Handling and Storage Products
- ESD Safe Racks
Storage of ESD sensitive components is a critical aspect of an efficient EPA. Storage methods are often overlooked and that lapse could result in ESD related failure. An EPA should have ESD-safe storage racks and cabinets.
- ESD Safe Trolley
ESD sensitive material can get damaged by electro-static charge generated by the friction of wheels on a regular trolley. The EPA should have ESD-safe trolleys for transporting components within the EPA. Critical parts of these trolleys, including the wheels, are constructed with ESD-safe materials.
- ESD Safe Storage Bins
ESD sensitive items such as circuit boards, semiconductor and electronics components should be stored in ESD-safe storage bins. During work, these bins can attach on the workstation for holding components. During transportation within the EPA, these bins can be kept on trolleys and racks.
ESD safe packaging
ESD sensitive components should be stored in ESD-safe packaging. This storage should be implemented not just in the EPA but throughout the company premises.
These shielding bags should have a special ESD warning sticker.
Multiple types of ESD packaging exist. Of these, the pink colored poly products have anti-static properties that degrade with age. Hence, use these pink poly products only for temporary packaging.
Messung Group is pioneers of the Indian Industrial Automation industry. With long and diverse experience in handling of electronic products, Messung Group now offers complete solutions to all your ESD problems.
At Messung, our objective is to deliver solutions to the electronic manufacturing industry. Our commitment is to bring innovative technologies into the Indian market.