As is known, static electricity is exactly the same way that a monster does. It will not only shorten electronic products’ shelf life and reduce their reliability, but may cause an absolute failure in end users’ hands as well, which will dramatically decrease company’s reputation that is closely related with market acceptance of their products. ESD (Electrostatic Discharge) damage may be available in each single component, no matter big or small, due to transportation, friction or direct contact and the damage brought by ESD should be minimized in every procedure of electronic product manufacturing. Thus, this article will introduce some commonly-used measures to control ESD damage in SMT (Surface Mount Technology) assembly workshop.
ESD Damage Inspection
To effectively stop static electricity from being generated and ensure the security of ESD, inspection tools and equipment should be termly 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;
• Megger;
• 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 Damage Prevention
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.
ESD manager has to report ESD preventing measures to manufacturing manager and antistatic authority and antistatic implementations should be checked when necessary. The aim of inspection is to make sure that each manufacturing area is compatible with the requirement to control static electricity.
EPA (ESD Protected Area) manager has to summarize ESD inspections and make some conclusions in terms of unqualified ESD measures. As the report is accepted by chief manager, it will be provided directly to EPA manager.
During the last ten-day period of each quarter, comprehensive reviews have to be made by ESD chief manager concerning ESD system and its implementation. The comprehensive review should cover ESD file system, daily ESD record, resource quotation, international standard, ESD implementation recheck etc.
Protection Measures for EPA
The protection measures for EPA should start from the following aspects: EPA operation specification, warning signs, equipment, grounding system of antistatic instrument, ESD data accumulation system, electric leakage and static field control, ESD prevention measures carried out on human, antistatic material control etc.
Prior to SMT assembly manufacturing, work places should be inspected to determine whether issues take place such as broken grounding lines, loose contact and falling off or not. In addition, operation procedures should be inspected to ensure that there are no errors and ion fans should be checked that it is capable of smoothly working. As soon as any issue is found out, operating staff have to report it to manufacturing manager to get it fixed at once. It’s necessary to guarantee the ESD grounding to be neat and standard.
The maintenance of ESD control system in SMT assembly workshop primarily depends on constant inspection that is capable of making issues or errors exposed. After those issues and errors are properly solved, ESD control system will be able to work again. ESD protection measures must be published in the form of formal cause and it should be clarified by manufacturer, supplier and cooperating organizations. Furthermore, a complete integrated ESD protection control regulations have to be established in internal and external company. Therefore, proper focus and control should be laid to corresponding links concerning ESD protection measures so that all the unqualified issues can be in time adjusted and effectively prevented in later SMT assembly manufacturing process.
