ELECTROSTATIC DISCHARGE (ESD) PROCEDURE

Transcription

1 Page 1 of 15 Subject: ESD Procedure Purpose: The purpose of this document is to define Flextronics Automotive Inc. standard for Electrostatic Discharge (ESD) control and is written in support of Flextronics Automotive Inc. objective to provide a safe assembly environment using accepted ESD practices Scope: This procedure sets out the minimum requirements for ESD control in Flextronics Automotive Inc. facility covering employees, contractors, visitors and customers. This document applies to activities that: manufacture, process, assemble, install, package, label, service, test, inspect or otherwise handle electrical or electronic parts, assemblies, and equipment susceptible to damage by electrostatic discharges greater than or equal to 100 volts Human Body Model. Responsibility: All Flextronics Automotive Inc. employees. 1.0 Safety Requirements All site safety regulations ARE APPLICABLE during the handling and testing of ESD sensitive parts and shall be observed. Work stations All conductive material must satisfy the electrical requirements of the specific sites Safety and Health manuals* and local electrical codes. Wrist Straps All ESD wrist strap cords must have a built-in one Meg ohm resistor. *Safety requirements, which may pertain to this standard, shall be specified and documented for each site. 2.0 ESD Control Program This document establishes the minimum Electrostatic discharge (ESD) precautionary requirements for handling, any ESD Sensitive (ESDS) assemblies and parts (individually or in bulk) and the associated tools or equipment used in the fabrication or building of these assemblies.

2 Page 2 of ESD Control Program Requirements Level of Protection: The intent of this program is to protect all ESDS items, which are sensitive to 100 volts or higher Human Body Model. ESD Devices that are more sensitive may require additional protection. Customer requirements relating to New Products shall consider levels of protection for all ESDS items as applicable. Program Management and Product Engineering are responsible for communicating this need to the ESD Coordinator ESD Control Program Guidance The primary objective of this Program is to provide continuous ESD protection. Electrostatic control and protection entails implementation of Program requirements during design, production, inspection, test, storage, shipment, installation, use, maintenance, replacement, and repair functions. 2.1 ESD Control Program Administrative Requirements ESD Control Program/Policy Guidelines 1. Always wear ESD Smocks and Safety Glasses in the manufacturing area. 2. Always wear ESD shoes/shoe strap/wrist strap on the manufacturing floor as designated 3. Daily Verify ESD shoes/shoe strap/wrist strap and Sign off against Operation Start up check list Form # as applicable. 4. Always ensure to be grounded when handlings ESDS devices. 5. Food, Beverages, Lunch boxes, Personal belongings (Purse, Sweaters/jackets, Combs/brushes, Lotion bottles) strictly prohibited on the manufacturing floor. 6. SMT Magazines, Carts, Shelves, Table Mats and Equipments shall be grounded at all times in the ESD controlled areas. 7. SMT Magazines shall not be stored on the floor with or with out WIP PCBs. 8. Dragging of Magazines on the floor is strictly prohibited. 9. Manufacturing floor and equipments must be kept clean at all time 10. Doors in ESD controlled areas shall be kept closed at all time for compliance with HVAC controls. 11. Designated boundaries shall be clearly marked for ESD controlled areas. 12. Personnel and visitors are required as applicable to use wrist strap, heel straps, or conductive shoes on the manufacturing floor. 13. ESD controlled areas will be measured in regularly scheduled audits by ESD Coordinator. 14. All work surfaces shall be grounded and static dissipative in the ESD controlled areas and their grounding will be verified against an approved audit 15. Replace used ESD pink foam from black trays with new foam every six month.

3 Page 3 of ESD Control Program Maintenance Table 1 summarizes the actions (described in previous sections) that should be scheduled and regularly performed to maintain an effective ESD control program. Frequency Action Records (maintain min 90 days) Daily Weekly (or as determined by Engr.) Monthly Check wrist straps, heel straps, and conductive shoes (see sections A & B) Verify workstation and table grounding (see section A) ESD self-audit (see section ) Clean and test ionizers Perform functional check of wrist/heel strap testers Six months Replace used ESD pink foam from black trays with new foam Annually Calibrate wrist/footwear tester (see sections b & C) Calibrate auditing equipment ESD review training (see section 2.1.2) Audit smocks (see section C) Audit by corporate/site coordinator (3 rd Party Audits) Operation Start up check list Form # S audit Checklist and written verification of corrective action(s) Preventive maintenance (PM) log Preventive maintenance log or self-audit checklist/record Action item in shut down meetings Maintain records per site calibration procedure Maintain records per site calibration procedure Attendance records Course test results, if applicable Log of test results and corrective actions Checklist and written verification of corrective action(s) Table 1 Site ESD coordinator will be responsible for all ESD related records as outlined in Table 1 or each site will be responsible for defining the requirements.

4 Page 4 of Training Plan All employees are required to complete ESD training before allowed access to ESD Control Areas. All new employees are required to complete an ESD orientation before they begin work. It is recommended that all employees who handle static sensitive parts/assemblies or who work in ESD control areas should receive an ESD control review course once a year. If the ESD compliance score fall below 85% as per the Flextronics Automotive Inc. audit checklist the site will be required to retrain employees in the affected areas. ESD non-compliances identified during the audits should be the part of the training process. The training department or the supervisors will maintain the training record for all employees trained on ESD. The site ESD Coordinator or his designate shall train and verify the competency of those who deliver ESD training. Verification of competency shall be undertaken for the following - a) Amendments to the corporate training material b) Where the trainer has not been involved in ESD training for a period of 6 months c) Where there are changes in customer ESD requirements Compliance Verification Plan Audit activity is to be conducted in accordance with this document and under the general guidance of the Site ESD Coordinator Program Coordination Site ESD Program Coordinator or Quality Manager shall perform audits, and act as a focal point for ESD problem resolution. A. Site ESD Coordinator Each site shall appoint an ESD Program Coordinator who is competent in ESD theory and practice. The ESD coordinator shall be responsible for ESD problem resolution, ESD compliance audits and consultancy. It is recommended that the Site ESD coordinator audits the system quarterly or ensures that the ESD system is included as part of the ISO/QS/TS audits. B. Supervisor Responsibilities Supervisors are responsible for ensuring that operators are issued the appropriate ESD protective equipment for their job assignment, and that worn or damaged equipment is promptly replaced. Supervisors are responsible for verifying that all operators are performing the daily ESD wrist and heel strap tests and for establishing and maintaining Startup check list. Supervisors who leave an area of responsibility should ensure these records are transferred to the new area supervisor.

5 Page 5 of 15 C. Area/Building ESD Representative Site ESD coordinator could be one group or person. As a minimum, the following audit schedule will be conducted. One monthly audit of designated area is to be done using the Flextronics Automotive Inc. ESD checklist; refer to Table 1 for details. Weekly Audits shall consist of a visual inspection of each static protected work surface and surrounding area for the requirements as stated in this procedure. Audit results should be logged along with any resulting corrective actions. The audit will be conducted as per Flextronics Automotive Inc. checklist. The ESD audit checklist is the minimum requirement for the ESD control program where applicable. Scoring will be done as per the following guidelines: Score Compliance Level Action 0 No Plan, Procedure or compliance level is <= 80% Initiate Formal Corrective Action 0.5 If compliance is between 80% to 90% Revise Plan, procedure or conduct awareness training 1 If compliance is >90% None N/a Where no site specific requirements apply - D. 3 rd Party Audits Third party audits shall be conducted on an annual basis. The audit will be done to verify ESD compliance to Flextronics Automotive Inc. procedure and checklist. The results of the audit will be shared with the Site Operation Manager. 2.2 ESD Control Program Technical Requirements Grounding / Bonding Systems Guidance Grounding of workstations, carts, storage shelving and personnel is necessary (where applicable) to provide a constant and gradual discharge path for static energy so that it is never allowed to build to levels that can damage electronics. Appropriate methods for grounding include but not limited to: A. 3 rd wire AC (Preferred Method) In most cases, the 3 rd wire AC equipment ground is the preferred ESD ground. When this is impractical or not available to use, personnel should be bonded or electrically connected to a conductive element of the ESD item or container using a wrist strap or other grounding system to ensure that all elements are at the same electrical potential i.e., a wrist strap may be connected to a cart or chassis containing ESD items that are being worked on.

6 Page 6 of 15 Electrical power ground should be free of hazardous transient voltages, and regularly tested for continuity to ground. Caution: Connections to the electrical safety ground should only be made by person knowledge about the power system being accessed. B. Supporting Pillars Supporting pillars in the buildings campus could be considered grounded. Any rigid, fixed, metallic structure (e.g. copper air tubes) could also be considered ground, provided they are connected to an unpainted section of a supporting pillar in such a way that the connections are reliable and tamper resistant. The pillars should be connected to the earth and regularly tested for continuity to ground. C. Copper Wire The reference for ground could be a solid copper stake at least six feet long and 1 /2 diameter which has been driven into the earth. Brackets should be attached to the top of the stake so that cables can be securely fixed to the stake (see figure 1). Cables should always be connected to the nearest, best ground source. Copper grounding cable Grounded copper tubing Figure 1, Grounding Bracket Ground reference sources and preferred grounding methods shall be defined and documented for each site if necessary Personal Grounding The required ESD protection for "ALL" employees is for each to wear an ESD smock together with heel straps/toe straps or ESD footwear (in ESD safe areas). Smocks shall be worn with at least three of the front snaps closed. Smocks may be worn with sleeves rolled up providing that the clothes underneath the smock do not protrude beyond the sleeve line and, in the case of smocks which function through surface conductivity; there is a portion of sleeve in contact with the wearer s skin. As a general rule, the wearer s clothes should not be exposed to static sensitive devices or assemblies.

7 Page 7 of 15 The person sponsoring the visitor is responsible for ensuring that they; are provided with all required ESD protective equipment when the scope of the visit requires access to ESD sensitive areas, that the visitor has ESD tested and passed the equipment, and that they comply with this procedure while being in a Flextronics Automotive Inc. facility. A. Wrist Straps A wrist strap is required for anyone handling ESD components or assemblies while seated, regardless of heel grounding. (However, personnel exposed to greater than 500V should be considered a special case.) Wrist straps are to be tested at least daily, before handling ESD sensitive items. Putting approved* lotion on the skin contact site and/or adjusting the strap may help it to pass. If the strap still fails it must be replaced. After passing, each operator must sign off startup check list as applicable, which must be current and visible. (*Note: Lotion approved for use in the manufacturing area must be free of silicone and lanolin, and the bottle should be safe for use within an ESD control area, as appropriate. The local Engineering department and ESD coordinator should verify this.) B. Heel Straps Heel straps, or conductive shoes, may be used to ground personnel in areas where there are grounded conductive or dissipative floor mats, or where the floor's resistance to ground measures between 10 4 and 10 9 ohms. The use of heel straps as additional (secondary) grounding devices to help drain static charge generated while walking is encouraged, and may be required by area management. It is required that the personnel wear one heel strap at all times also if wearing ESD safe shoes the personnel does not necessary have to wear the heel strap. ESD shoes must have a visible tag or marking on the outside of the shoe to indicate that they are ESD shoes Conductive heel straps and shoes shall be tested before handling ESD items each day. Heel straps and shoes that fail the test should be cleaned, adjusted, and retested. If the strap/footwear still fails it must be replaced. After passing, each person must sign off startup check list if applicable, which must be current and visible. C. Smocks Smocks must be worn in all manufacturing areas. They must be audited for effectiveness at least annually, and replaced as needed. Smocks may be checked for effectiveness in one of two ways: (1) A surface resistivity meter may be used to check that the point to point resistance of the fabric is within the dissipative range, (2) A charge is applied to the smock (using a charged plate analyzer) and then a field meter or static voltmeter is used to verify that the charge is dissipated across the seams. ESD smocks shall, as a minimum, cover all personal garments above the waste in accordance with JEDEC (625-A) requirements. D. Floor Mats Grounded, conductive or dissipative floor mats may be necessary in areas approved for conductive footwear (see section B). The mats should be cleaned as needed with an approved antistatic cleaner to prevent the buildup of non-conductive particles on the mats.

8 Page 8 of Protected Area A. Signs Signs should be posted at all entrances to ESD control areas, and the boundaries of these areas shall be clearly identified. The signs should identify the area as an ESD control area and display the JEDEC (Joint Electronic Device Engineering Council) susceptibility symbol. Yellow or fluorescent orange-red is the preferred colors for ESD caution signs and labels. JEDEC susceptibility symbol Figure 2 B. Floor The floor shall be kept clean at all time, magazines should not be on the floor with or without PCBs. Dragging the magazines on the floor will damage the floor and it s resistance to the ground. The recommended resistance to ground (RTG) of floors in an ESD control area should be maintained between 10 4 and 10 9 ohms (using a 100V test voltage). This condition is mandatory if the floor is used to ground people or carts in the area. Recommended range for newly installed floors the RTG should be between 10 4 and 10 6 ohms. C. Environment Whenever possible, relative humidity in an ESD control area shall be maintained to a minimum of 30%. If the humidity within the production area falls below 30%, the site ESD Coordinator shall assess if an increased ESD risk. Where this is considered to be likely, the site ESD Coordinator shall implement whatever measures are considered necessary to mitigate the increased risk. The temperature shall be between 18 C and 27 C (64.4 degree Fahrenheit 80.6 degree Fahrenheit) Packaging

9 Page 9 of 15 ESD protective packaging and package marking shall be in accordance with the contract, purchase order, drawing or other documentation. When the contract, purchase order, drawing or other documentation does not define ESD protective packaging, the Site shall define ESD protective packaging requirements for ESD items. Some of these types and techniques include low charge generating bags and wraps, air space, dissipative wrap, static shielding, conductive shunts and the use of EMI/RFI shielding. Packaging shall be defined for all material movement within Protected Areas, between job sites and field service operations Marking ESD assemblies and equipment containing ESD parts and assemblies should be marked with an ESD caution symbol as shown in Figure Equipment A. Work Stations and Tables Workstations and tables in an ESD control area must have static dissipative surfaces and should be connected in parallel. Each workstation must have available wrist strap ground connections (two are recommended), preferably banana jack receptacles. Work surfaces should be cleaned daily with an antistatic cleaner, and the resistance to ground should be maintained in the static dissipative range. Surfaces and wrist strap grounding receptacles must be physically wired, in parallel, to the building ground source. All tables and workstations within an ESD control area shall have the grounding electrically verified and recorded monthly as determined by the site ESD Coordinator or management specified representative. (See section C) This plan would be documented in the sitetailoring document. Ground connections should have less than two ohms resistance. B. Wrist Strap Tester Wrist strap testers or continuous monitors must be used to test the functionality of all wrist straps. All testers must be calibrated annually. They should be set to accept on readings from 500,000 ohms to 35 Meg ohms resistance. A monthly functional check of each tester is a requirement. The tester will be checked monthly for functionality the responsibility and authority lies with the Site ESD coordinator. Please refer to Table 1. C. Conductive Footwear Tester Footwear testers must be used to test the functionality of all heel straps and conductive shoes. All testers must be calibrated annually. They should be set to accept on readings from 500,000 ohms to 35 Meg ohms resistance. A monthly functional check of each tester is a requirement. The tester will be checked monthly for functionality the responsibility and authority lies with the Site ESD coordinator. Please refer to Table 1.

10 Page 10 of 15 D. Carts and Movable Racks Cart frames should be static dissipative or conductive. In the case of conductive carts, ESD sensitive materials cannot come in direct contact with the cart. There should be bare metal or cable connections between the shelves and supports to ensure a path to ground for each shelf. The carts must also be grounded (in areas with dissipative flooring, carts may be grounded by means of an attached drag chain, or flat, braided cable, with at least two inches of its length in contact with the floor). E. Power Tools Power tools, including soldering irons, need to be grounded (grounding to the local utility is usually sufficient, but this determination should be made by the site Engineering dept.). F. Air Ionizers Air ionizers may be used to reduce the static charge on objects within the process area, which are chargeable to, or generate greater than 100 volts (as determined by Engineering). Ionizers should be turned on at least 2-3 minutes before unprotected ESD sensitive items are handled nearby, and should primarily be focused such that the ionized air surrounds the sensitive devices. Ionizers shall be cleaned and tested for functionality at least monthly. Air ionizers shall be tested monthly for positive and negative decay and balance, and adjusted, if necessary, to ensure the final balance is below 30V and the decay times do not exceed 5 seconds each. Ionizers shall be serialized and test data recorded by serial number. Ionizer test logs should include, at a minimum: test date, decay time for a positive charge, decay time for a negative charge, final balance, notes of corrective action, and the initials of the person performing the tests. Selfbalancing ionizers, which do not require adjustment according to the manufacturer, need not be tested monthly. However, should receive maintenance according to the manufacturer's recommendations. G. Topical Antistat Topical antistatic treatment of chargeable objects may be used providing that its effectiveness is checked regularly (the recommended frequency is weekly) and renewed as needed. Caution: Some topical antistatic chemicals will cause cracking of polycarbonate plastics. H. Gloves and Finger Cots (Optional) To aid in contamination control and/or to handle hot (high temperature) ESD parts and/or cards, static safe gloves or finger cots may be required. Their function, when and how they are to be used shall be specified in the process routings. Note: Although it is desirable to have conductive or static dissipative gloves for static protection purposes, other issues often force compromises in material selection. Some available gloves are not conductive, but they do not generate static charges during normal use. Questions regarding various glove compositions should be directed to the Site ESD Coordinator. I. Storage Bins

11 Page 11 of 15 All parts bins and containers used in any manufacturing process must be static dissipative or antistatic. Sensitive parts should remain in the original protective container if practical until assembled. J. Shelving and Cabinets All shelving and cabinets used for storage of ESD components must provide a grounded surface unless the parts remain fully enclosed within shielding-type packaging such as approved ESD bags or original manufacturer s packaging such as SMT reels and IC trays Handling Direct handling of unprotected ESD sensitive (ESD) parts, assemblies, or products, shall only be by grounded personnel within an ESD control area. Unprotected ESD items should not be allowed to come in direct contact with grounded, conductive equipment housings or metal surfaces (for example, metal shelves and carts). To move ESD parts or assemblies inside an ESD control area, use one of the following: a. Static dissipative containers b. Static shielding containers c. Conductive containers or board carriers d. Grounded movable racks (see section D) Open containers and board carriers should be transported on grounded carts A. Transportation Off-Site: To move components and assemblies off-site, use only closed static shielding containers (original, closed, vendor packaging is also acceptable). Antistatic packaging (for example, DIP tubes) alone is not sufficient for this purpose. The containers should also be labeled as containing static sensitive items. Between Buildings On Site: To move components and assemblies between buildings (intra-site), use only closed static shielding containers, and ESD safe carts and/or in Faraday cage. (See sec D). All ESD protection measures must be utilized and items must not be left unattended while in transit Between ESD Control areas within Building: All ESD protection measures must be utilized and items may not be left unattended while in transit B. Static Generating Material All process essential insulators that have electrostatic fields that exceed 2,000 volts should be kept at a minimum distance of 12 inches from ESD items. If these "static generators" are essential to the effective operation of processes in the area, steps must be taken to minimize the risk the materials represent (see Table 2). Any signs posted at workstations shall be posted in anti-static sheet protectors or plain paper. Ordinary plastic sheet protectors or document holders should be avoided in an ESD safe area and in any case must not come within 12 of unprotected parts or assemblies.

12 Page 12 of 15 Methods for Minimizing ESD Risk of Process-Essential Static Generators* Containment Methods/Options Remove from control area Replace with ESD-safe alternatives Apply Ionization (see section F) Separate from ESD items by at least 12 inches Shield charge from ESD items May treat with topical antistatic Static Generating Material Example Excess boxes and packaging material, Styrofoam Tape, binders, page protectors, plastic bags and boxes, foam Plastic connector packaging, plastic casewith-board assembly (e.g. mouse assembly) Exterior packing foam (for outgoing product) Computer displays (VDT's) Computer keyboards and monitor cases, plastic "windows" or "guards" on machinery *Note: A combination of methods may be required. The material types shown are examples; individual static generators should be evaluated by engineering for the best ESD minimization method(s) to use. Table 2

13 Page 13 of 15 Records Retained for a period of one year. Definitions Antistatic Material material, which resists triboelectric charge generation (i.e. generating static charges by rubbing or other type of contact). Antistatic materials are not static shielding (see Table 3). Conductive Material material with surface resistivity less than 10 5 ohms per square. Conductive material will shield an object completely enclosed within it from a charge, will dissipate charges immediately, and must be grounded. Ungrounded conductive materials will accept/generate charge (see Table 3). Decay Time the time required to reduce the initial voltage, U 1, of a charged material to a defined lower voltage level, U 2. ESD electrostatic discharge. A sudden transfer of electrostatic charge between objects at different potentials caused by direct contact or induced by an electrostatic field. ESD Control Area any area where unprotected static sensitive parts may be handled (see section 2.1). ESD Model Human Body Model (HBM) - Three-circuit models are used to analyze the effects of ESD. They are The Human Body Model (HBM), The Charged Device Model (CDM) and The Machine Model (MM). These models help determine the resistive ranges for safe static discharge. People are a primary source of static charge accumulation. Hair, hair products, types of clothing and type of shoes worn all affect the way the human body can collect and store a charge. Actions such as walking, sitting, or handling a product can cause an ungrounded body to develop a significant static charge. The Human Body Model (HBM) characterizes a static event resulting from a charged person discharging to a static sensitive device. Typically, the human body senses (hear, see, feel) static discharges at levels above 3500 volts. We hear the POP! We see the SPARK! We feel the JOLT! At levels below 3500 volts, we cannot (through the use of the body) detect when a static event occurs. The charge that the human body is able to carry is sufficient to damage an ESD-sensitive component. The damaging effects of electrostatic discharge are not always immediate and often difficult to detect. A card could be damaged due to a static event and still pass in-circuit and functional tests! The safest practice to guard against static discharge from people is personnel grounding. ESD Sensitive (ESD) Describes any device or assembly whose electrical characteristics or performance can be altered by exposure to static electric charge or a discharge through its conductors.

14 Page 14 of 15 Faraday Cage a closed conductive container, which provides ESD protection because all external charges are distributed over its outside surface. No externally caused field is detectable inside a Faraday cage. Ground a conductor connected to the earth, and hence, used as a reference point for zero potential ( hard ground ). Insulative Material material with a surface resistivity greater than or equal to ohms per square. Insulative material accepts/generates charges readily but will not dissipate a charge. The material cannot be grounded and is not static shielding (see Table 3). RTG resistance to ground Static Dissipative Material material with a surface resistivity greater than or equal to 10 5 but less than ohms per square; however, the preferred operating definition for non-packaging materials is >10 5 and <10 9 ohms per square. Static dissipative material is not static shielding, will dissipate charges in a controlled manner and must be grounded. Ungrounded static dissipative materials will accept/generate charge (see Table 3). Static Shielding Material material with a conductive layer or surface. Containers made of static shielding material should completely enclose their contents and be able to be sealed. When a static shielding container is closed, the conductive layer in the material forms a Faraday cage that does not allow an ESD or electrostatic field to pass, penetrate or puncture through the material. Surface Resistivity a measure of the resistance of a material to electric current on its surface. It is the ratio of direct current (dc) voltage to the current that passes across the surface of a material (expressed in ohms per square).

15 Page 15 of 15 Summary Table of Key Definitions Static Conductive Dissipative Surface resistivity Static Dissipative (packaging materials only) <10 5 Ohms/ sq >10 5 and <10 9 >10 5 and <10 12 Resistance to ground (RTG) <10 5 Ohms/sq >10 5 and <10 9 >10 5 and <10 12 Antistatic N/A N/A Insulative >10 12 >10 12 Must be grounded yes yes yes N/A N/A Can't be grounded N/A N/A N/A N/A yes Attachments Accepts/generates charge Dissipates charge Static shielding N/A only if ungrounde d yes, immediately, if grounded yes if container is closed only if ungrounded yes, controlled, if grounded Table 3 only if ungrounded yes, controlled, if grounded no N/A yes no no no no no Ref. Documents ANSI/ESD S ESD Association Std for the Development of an EDC program- IPC/JEDEC J-STD-033 Standard for Handling, Packing, Shipping and Use of Moisture/ Reflow Sensitive Surface Mount Devices. JEDEC625-A Requirements for Handling Electrostatic-Discharge- Sensitive (ESDS) Devices GOP Accessories Parts Management for SMT Lines GOP Product Purging Procedure Revision History: Description of Change Date ECN# Originator Sign-off Replaced log sheet with startup check list E06001 A. Hamid Initial Release Oct09, A. Hamid