Electrostatic Discharge Protection Requirements

Transcription

1 [Type text] Electrostatic Discharge Protection Requirements This document provides the basic requirements for Service Locations to protect parts from the effects of Electrostatic Discharge. The document itself is not exhaustive, but provides the necessary information to allow a Service Centre to exercise minimum requirements as laid down in Industry Standards for Electrostatic Protection. Further more detailed instructions can be found in: ANSI/ESD S (American National Standard for Protection of Electrical and Electronic Parts, Assemblies and Equipment) IEC (International Electrotechnical Commission Standard for Protection of Electronic Devices from Electrostatic Phenomena General Requirements) EN (European Standard for Protection of Electrical and Electronic Parts, Assemblies and Equipment), now replaced by IEC WARNING: This document does not cover health and safety requirements, and compliance with local regulations and practices should always be observed in this respect. Contents Page What is ESD 2 Why Worry about ESD 3 Key Elements in an ESD Program 4 The ESD Program 4 The Training Program 5 The Audit Program 6 Responsibilities of Personnel 7 General Management Responsibilities 7 ESD Co-ordinator Responsibilities 7 What is an EPA? 8 EPA Design 8 Signs and Boundaries 9 Wrist Straps/Foot Straps 10 Contents (continued) Page Gloves 10 Humidifiers/Ionisers 11 Certificate of Conformance 11 Note: Any hard copy of this document is for reference only. Due to template and application dependencies the header and footer may fail to display correct data. It is the responsibility of the user to ensure that they have a correct and valid version. Any outdated hard copy is invalid and must be removed from possible use.

2 Packaging 11 Summary 12 Illustrations Figure Title Page 1 Electrostatic Discharge 3 2 ESD Test Stations 6 3 Electrostatic Field Test Kit 6 4 Example Electrostatic Protected Area 9 5 Examples of Signs and Boundary Tape 9 6 Wrist Straps and how to wear 10 7 Foot Straps and how to wear 10 8 ESD Compliant Footwear 10 9 ESD Compliant Gloves Humidifier Bench Ionisers ESD Compliant Packaging Examples of Prohibited Materials 12 What is ESD? ESD stands for Electrostatic Discharge. Static electricity is an everyday phenomenon there can be few of us who have not experienced a static shock after walking across a room and touching a door knob, or on getting out of a car. Other static nuisance effects include the cling of some fabrics to the body, the sticking of a plastic document cover, paper sheets sticking together, or the attraction of dust to a TV or computer screen.

3 While we can feel some of these effects, static electricity is normally present at lower levels that we cannot feel, hear or see, but may nevertheless damage sensitive electronic components. It can be built up rapidly on objects, in unexpected ways, to produce surprisingly high voltages. If two objects that have different voltages approach each other closely enough, charge may pass from one to the other in a fast electrostatic discharge. While this only lasts a microsecond or less, the peak discharge current can be several Amperes, and the peak power measured in kilowatts! Figure 1 Electrostatic Discharge Why worry about ESD? ESD can cause unseen damage to electronic components during manufacture and servicing of electronic assemblies and equipment. If the damaged component fails immediately (catastrophic failure), the result will be a board that fails test and requires rework. This represents lost production and additional costs. Worse than this, a component may be partially damaged and weakened. It may suffer a change or drift in characteristics. It may remain in specification, but fail later when in use by a customer (Latent Failure). It has been estimated that 90% of damaged devices are discovered in this way. This is the most expensive type of failure as it represents: Customer dissatisfaction, and the possibility of loss of product reputation and future sales Customer service personnel and facility cost (Call centre complaints) Engineer time and parts replacement costs. In Service Centres most ESD arises from charged personnel, if they are not properly grounded. Most people do not feel an ESD shock unless they are charged to over 4000 Volts (the sensitivity threshold varies between people, and even over parts of the body!). This voltage is quite common in the uncontrolled environment how many of us have not felt the occasional electrostatic shock in everyday life?

4 Key elements in an ESD Program There are many ways in which the effects of ESD can be overcome. To provide the best protection the problem of ESD must be addressed from several angles: An area which is static free must be created. This area is known as the Electrostatic Protected Area (EPA) and must be used whenever Static Sensitive Devices (SSD s), or boards containing SSD s are to be handled. Non ESD compliant materials should be excluded from this area, unless they can be protected (i.e. paper should be contained in ESD compliant folders or wallets, and not left loose on benches). Any SSD s or boards containing SSD s must be stored in conditions where they are not subjected to the effects of static. People who come into contact with electronic components or assemblies should be made aware of the effects of static discharges. There are three simple principles we can use to protect ESD sensitive components from ESD damage: Only handle sensitive components in an ESD Protected Area (EPA) under protected and controlled conditions Protect sensitive devices outside the EPA using ESD protective packaging. Keep all prohibited materials out of the EPA. The EPA must be maintained in a clean and tidy condition. Smoking, eating and drinking is prohibited inside an EPA. Unapproved tools, static generating materials, and materials not essential in the work area are also prohibited. It is essential therefore that a Service Location must have an effective ESD Program. The program contains three key elements: The ESD Program. This is a document that specifies the equipment used, and procedures to be followed in order to ensure electrostatic safe handling. The Training Program. This is required in order to ensure that everyone (not just those working inside the EPA) is aware of, and understands the ESD program, use of equipment, and correct procedures. The Audit Program. This is required in order to make sure that equipment remains functional, and that the ESD Program procedures are correctly followed. If any of these three elements are not present, it is likely that the ESD prevention measures will eventually fail. A fourth element is also extremely important Management Commitment. If management does not provide the resources and authoritative support required, it is unlikely that the ESD Program will succeed. The ESD Program document should be a controlled document, understood by all who have need to be aware of the requirements for ESD protection, including non-technical staff and visitors. The Training Program, as defined in the Standards, should provide training for all personnel who handle ESD s, and those who manage or supervise them. The objective of the training is to effectively use the materials, equipment and procedures defined in the ESD Program document, and to understand why they are needed. Training should be provided as part of the employee induction program, and should be appropriate to the ability and job function of the trainee. A register of trained personnel should be maintained.

5 The training course should include: Theory of electrostatic charging Basic knowledge of electrostatic discharge Special handling procedures Knowledge of ESD protective equipment and items Identification of Static Sensitive Devices (SSD s) The limits of ESD protection measures SSD sensitivity Use of new techniques & processes before implementation Any conflicts with safety requirements Follow-on training should be provided at an appropriate (documented) interval specified by the ESD Coordinator, and no longer than annually. A typical training scheme will include three levels: Level 1: Do s and Don ts list for visitors, customers, temporary employees and contractors, etc. This could be handed to personnel at reception or just before entry into the EPA. Level 2: A course for permanent employees, as part of their induction course or periodic training course. This will consist of theory and practical aspects, as well as use of equipment and packaging. Typically a course may be 1 2 hours long, and may use a variety of formats. A formal test, or some feedback, of individual performance should be given and recorded. Level 3: This would typically be specialist training given to particular personnel according to their job requirements. This level would be taken after a level 2 training course. The Audit Program, as set out in the ESD Standards, is designed for use with Quality Systems such as ISO9000, and should therefore be considered mandatory. The Audit Program should ideally consist of the following elements: Daily Checks It is essential that wrist straps and cords, heel and toe straps or ESD shoes are tested for conformance BEFORE entering the EPA. It is recommended that this is done each time personnel enter the EPA, although the standard only requires daily checks. These tests must be documented.

6 Figure 2 ESD Test Stations A visual inspection must be made of the EPA, trolleys and packaging for excluded items, and ionisers checked for location and orientation if appropriate. It is not necessary to document these checks. Monthly Checks The continuity of equipment earth bonding and the functionality of ionization systems should be completed on a sample basis. These should be documented. Six Month Checks Check electrostatic fields <10kV/m, or alternatively potentials <100V. Check conformance of signs, labels and ESD garments. These should be documented. Periodic Audit Figure 3 Electrostatic Field Test Kit Periodic audits should be completed at no more than 12 month intervals. A follow-up audit should be scheduled if appropriate and an Audit Report circulated. This report should be available in the event of an Audit by Sony Ericsson. The audit should check: Wrist strap discipline, and the conformance of wrist strap and footwear testers. EPA Signs and labels Conformance of the resistance of floors, work surfaces and seating Conformance of tools Conformance of packaging and disposal of discarded packaging and materials Electrostatic fields <10kV/m, or alternatively potentials <100V Conformance of Ionisers

7 Humidity control Records and selection procedures. Responsibilities of Personnel All personnel handling sensitive devices have a responsibility to be aware of the ESD threat to reliability of electronic components. They have prime responsibility to implement and maintain ESD prevention measures. Any failures to do so should be reported to the ESD Co-ordinator. All personnel are expected to inform the ESD Co-ordinator of any unsatisfactory measures, and suggest improvements or corrective actions if appropriate. General Management Responsibilities ESD Standards place responsibility for implementation of the guidelines clearly in the hands of General Management. They are also ultimately responsible for making sure that all aspects of ESD handling are carried out, including: Maintaining a register of trained personnel Providing appropriate training for all personnel Ensuring inspection, supervision and maintenance of EPA facilities are carried out General Management bear the responsibility for appointment of a site ESD Co-ordinator. A named ESD Co-ordinator is required for each site. They must be given total management back-up, and adequate resources and authority. ESD Co-ordinator Responsibilities The ESD Co-ordinator is responsible to the Management for all site ESD matters. This includes: Ensuring that a copy of the ESD Program, or IEC is available for all relevant personnel Specifying and maintaining a list of ESD equipment Making sure ESD training is adequate and conforms to the requirements Maintaining a list of trained personnel Ensuring that all equipment and procedures conform to the standard Inspection, maintenance and verifying conformance of the EPA Carrying out audits on the ESD program Making ESD program tailoring requirements when required Giving assistance when required.

8 The ESD Co-ordinator has responsibility for making certain technical decisions in tailoring the implementation of the ESD program: Defining the boundaries of Electrostatic Protected Areas (EPA s) Defining and selecting equipment for use within the EPA Construction and Certification of EPA s Deciding which (if any) of the recommended measures are not required Deciding the frequency of certain audit actions The ESD Co-ordinator can appoint deputies if required, who will have the same responsibilities as the coordinator. What is an EPA? EPA Design An EPA is an area that is maintained safe for handling static sensitive components by keeping electrostatic fields and voltages to an insignificantly low level. An EPA should have well defined boundaries so that it is clear where the safe area is entered and left. Insulating materials are strong ESD sources and so they are excluded from the EPA where possible. Where this is not possible special measures such as ionisers are used to neutralise electrostatic charges. All non-insulating and conductive objects are grounded, so that electrostatic charge cannot build up on these. Most importantly, all personnel (people are conductive objects!) entering the EPA must be grounded so that they do not charge to high voltages. There are two ways in which people can be grounded: Using a grounded wrist strap (This is a minimum requirement, and should be used in conjunction with Using conductive footwear (conductive or dissipative shoes, or heel & toe straps on BOTH feet) in conjunction with a grounded conductive floor, or grounded conductive floor mats, and properly groundable seating. ESD safe conductive clothing (jackets or coats) can also be used in conjunction with the above.

9 Figure 4 - Example Electrostatic Protected Area Signs and Boundaries Personnel must be able to see signs complying with the Standards before they enter the EPA. Where appropriate (i.e. in a multistation EPA), compliant signs must also be visible within the EPA, and exit signs should mark the boundary of the EPA. Figure 5 Examples of Signs and Boundary Tape

10 Wrist Straps and Foot Straps A wrist strap has a snugly fitting band worn around the wrist, and cord fitted with a quick release connection. A foot strap (Heel or toe) fastens around the footwear with a conductive cord. Conductive shoes, although more expensive, are much the best solution. Figure 6 Wrist Straps and how to wear Figure 7 Foot Straps and how to wear Gloves Figure 8 ESD Compliant Footwear ESD Compliant gloves or Finger Cots fulfil a twofold requirement. Not only do they protect assemblies and components from the effects of ESD when handled, but modern components are Hydroscopic, and can absorb moisture from the fingers. Wearing gloves reduces the risk of moisture and natural oils from the skin affecting components. Figure 9 ESD Compliant Gloves

11 Humidifier/Ionisers Where it is not practical to have full ESD protection in a work area, or where there are climatic considerations, Humidifiers can be used to keep relative humidity within limits. Ionisers can also be used to reduce the potential due to charge in a specific area. Figure 10 Humidifier Figure 11 Bench Ionisers Certificate of Conformance The ESD Co-ordinator must audit a new or modified EPA to ensure compliance is achieved, and must issue a Certificate of Conformance before the EPA is used. Departures from the Standard should be recorded on the Certificate of Conformance, along with any extra equipment or procedures required to ensure ESD protection. Packaging Packaging generally comes in two main types, Shielding or Conductive/Dissipative Shielded Packaging is the best way to protect components and assemblies when they are outside the EPA, i.e. when moving from one EPA to another. Conductive/Dissipative packaging forms a Faraday Cage around the component, and should be used where components are stored. If necessary this can form an inner packing for Shielded Packaging should an SSD be moved from one EPA to another. In the ideal world, Sensitive components and assemblies will only be removed from their packaging inside the EPA, on a protected bench just before required for use Figure 12 ESD Compliant Packaging

12 Summary Proper ESD protection is essential to protect components and assemblies from the effects of static discharge. It is essential that the whole workforce, from engineer to management is adequately and appropriately trained, and take all necessary possible precautions to minimise the risk of ESD damage. Good housekeeping is essential to maintain the integrity of Electrostatic Protected Areas. As far as practical all prohibited materials must be excluded from the EPA. This includes external packaging, cardboard, paper, food, drink, non compliant tools, etc. Figure 13 Examples of Prohibited Materials Management should appoint a specific person to take control of all aspects of ESD prevention (ESD Coordinator). Adequate resources should be available for this, including (where appropriate) ESD Testing Stations Wrist Straps Foot Straps or ESD Footwear ESD Jackets Signs and Boundary Markers ESD Compliant Benches or work mats ESD Compliant flooring or floor mats ESD compliant seating ESD compliant packaging It is essential that all Sony Ericsson Service Partners comply fully with the requirements of IEC , as outlined in this document and although this is provided for guidance only, the minimum standard should be regarded as mandatory for all approved Service Partners. The Standards are included in the routine audit program by various appointed agencies, and compliance will be monitored regularly.