The constant improvement of antistatic measures implementation depends on normalized regulations in SMT assembly workshop. As soon as any issue is exposed concerning ESD, suitable measures should be made in time to prevent ESD damage.
In accordance with the application or frequency of different infrastructure, equipment and system, inspection should be made once a week, a month or a quarter. ESD manager should be available in each manufacturing area and inspection items should cover environment, equipment, instrument, tools, fixture, staff, antistatic equipment, materials etc. The inspection results should be provided as a file surrounding previous problems concerning ESD.
It’s unlikely you can eliminate ESD completely from any site. However, experience has shown that the following guidelines are helpful:
- Keep all synthetic materials at least 4 in. away from electronic equipment.
- When cleaning printed circuit boards, use a spray labeled as non-static forming.
- When troubleshooting electronic equipment, always wear a static wrist strap that’s grounded to the frame of the device. Also, wear the wrist strap when handling printed circuit boards.
- Treat carpets and floors with compounds that reduce the buildup of static charges.
- Use static floor mats where necessary.
- Make sure the grounding system for equipment has a low impedance for ESD currents to dissipate to an earthing reference.
How to process ESD damage inspection?
To effectively stop static electricity from being generated and ensure the security of ESD, inspection tools and equipment should be inspected to meet its reliability standard including antistatic wrist band, antistatic shoes, ion fan etc.
The tools and equipment for ESD inspection that are usually used in SMT assembly workshop mainly include:
• Surface resistance checker
• Static field meter
• Ion fan
• Ion balance tester
• Non contact voltage tester
• Wristband tester
• Human body comprehensive static tester
Equipment and system for ESD protection should be inspected under the practical guidance of QA (Quality Assurance) and QE (Quality Engineering). Generally speaking, appropriate tools and methods should be applied t be compatible with different material and tool requirement. For example, when a simple surface resistance checker is being used on some soft material such as overall with rough surface, cystosepiment or bubble bag, pressure should be put valuing 4 to 6 kilograms so that the contact will be excellent between test electrode and material surface and test should be valid as well. Additionally, as a megger is used to measure the surface resistance of tested material, a megger should be picked up with 100V DC.
ESD can occur in a variety of forms. One of the most common is through human contact with sensitive devices. Human touch is only sensitive on ESD levels that exceed 4,000V.
A recent investigation found the human body and its clothing capable of storing between 500V and 2,500V electrostatic during the normal workday. This is far above the level that damages circuits yet below the human perception threshold.