The adverse effects of electrostatic discharge (ESD) on electronic components and products need to be controlled in all manufacturing processes. There are many products and solutions that can do so, to meet the needs of the electronics manufacturing industry.
By Baishakhi Dutta
Apart from having cleanrooms as part of an electronics manufacturing process, ESD control products must also be used because electrostatic discharge is harmful to electronic components and products. Static control products are widely used in the electronics, defence, fibre, telecommunications, medical, disk drive and automotive industries to protect sensitive electronic components and products inside and outside the electrostatic-discharge protection area (EPA).
With the growth of the Indian electronics manufacturing industry and greater global demand for locally made electronics, the domestic ESD product market is experiencing a boom. So India’s ESD products are getting upgraded to keep up with international market trends.
Electrostatic discharge protection is critical to all phases and processes of electronics production. ESD is caused by the current flow between two electron-bearing objects, the two most common reasons being the proximity of differently charged objects and the electrical shorts that result from dielectric breakdown.
ESD must be controlled in the cleanroom, especially when it comes to glass, polymer and PTFE insulation materials, because these become highly charged, causing conductive work surfaces to harm humans and ESD-sensitive equipment.
ESD and static discharge is controlled in cleanrooms with the use of ESD workstations that ground work surfaces, people and equipment to the same electrical ground point. All available measures need to be taken to control static electricity. However, some workstations may only require basic ESD controls, while others may require more extensive controls.
ESD and its impact
Electrostatic discharge occurs when electricity accumulates and cannot flow, which is caused by the movement of people and matter within an environment. When the charge is transferred from the material carrying it to a static sensitive device (usually a metal object), it is discharged in the form of a spark. Such ESD sparks can occur in varying degrees of intensity and are detrimental to electronic components and equipment, which is why manufacturers in the electronics industry must have a cleanroom environment.
A cleanroom is where the concentration of particulate matter in the air that has been produced by personnel, processes, facilities and equipment is kept within specified limits. The extent to which these particles need to be removed depends on the desired ESD standards—the most commonly used is Federal Standard 209E, which establishes a globally-accepted level of air purity in cleanrooms and clean areas.
Steps that need to be taken to protect against ESD
The correct combination of the following items will protect people and products in the cleanroom from ESD damage.
- ESD table mat: This is a work surface for removing static electricity from the conductive items placed on it.
- Wrist straps and coil cord sets ground a person working at a station.
Common point ground: This grounds ESD mats providing a path-to-ground for wrist strap wearers, by attaching the strap to the ESD work surface via another 10mm grounding strap.
- ESD floor mats remove static charges from conductive items.
ESD floor mat ground cords: These ground the floor mat with a path-to-ground by using a grounding snap to connect the mat.
- ESD heel grounders: These connect walking or standing personnel to the ground.
Monitors continuously check grounded components on a workstation to eliminate wristband tests and protect against ground failures.
- ESD jackets shield against static charges on clothing by using a hip-to-cuff grounding system to ensure proper grounding without wristbands, as these sometimes inhibit movement.
- ESD equipment testers: These test the working condition of the wrist straps and heel grounds worn by personnel.
- ESD air ionisers remove static charges from insulating materials and isolated conductors, which cannot be grounded by typical means and cannot be removed from the workstation.
A cleanroom environment can store thousands of volts of electrostatic charge, but it requires only 25 volts of electrostatic voltage to cause irreparable damage to the integrated circuit. As the ESD threshold increases, it is important to understand the ESD standards. Proper control in cleanrooms is a concern in all major industries, especially when manufacturing microelectronics and medical devices.
Concerns when choosing cleanroom supplies
A cleanroom is defined as an environment in which the presence of airborne particle matter is controlled to the standards required. Modular cleanrooms can have ESD, non-venting and sterility requirements. Every requirement must be considered when selecting cleanroom supplies.
- Just because a packaging box has ‘cleanroom’ or ‘no cotton’ written on it doesn’t mean this is entirely true. Testing should be performed, and a certificate of conformity or an independent test data sheet should be provided with the cleanroom supplies.
- The lowest priced product does not necessarily imply the lowest level of cleanliness.
Is the cleanroom product manufactured and packaged in a cleanroom? Or is the product made in a standard factory environment and brought into a cleanroom for packaging? It is important to know that, and the first option is definitely preferable.
- The correct cleaning supplies such as mops, buckets and detergents should be selected to prevent contaminants from entering the cleanroom. As a result of such stringent standards, building a new cleanroom typically costs thousands or even millions of dollars. Will the person cleaning the cleanroom leave a residue? Will tiny granules fall off the mop head? Is the bucket, wringer and handle of the mop made of non-corrosive material? Remember, the vacuum cleaner’s motor alone can produce 100,000 particles to pollute the air, during operation.
- Not all products can be autoclaved. Autoclaved cleanroom garments require metal zippers and standard plastics. Carts and shelves should be ordered with autoclavable castors and metal split sleeves. So check the autoclave compatibility before ordering cleanroom products.
- Does the product have a partial antistatic coating or does the product itself have static control characteristics? If the cleanroom-compliant place mat is wiped with detergent, will it eliminate or reduce the mat’s ESD control capabilities? Conductive slots lose static control characteristics over time and should be tested periodically to ensure they maintain proper ESD levels. The carbon fibre in the antistatic garment will decompose during cleaning and needs to be replaced regularly. Choose a fabric with a higher carbon content, preferably containing 2 per cent or 4 per cent, to achieve a higher static dissipation rate.
Cleanroom supplies require proper testing and evaluation to ensure that no additional particles are introduced into the controlled environment.