Don't give me any static: resources and tips to help you avoid ESD problems.Q: Could you please provide information about the practices required to control and eliminate electrostatic discharge (hardware, testing) Electrostatic Discharge - (ESD) One kind of test that hardware usually has to pass to prove it is suitable for sale and use. The hardware must still work after is has been subjected to some level of electrostatic discharge. (ESD (1) (Electronic Software Distribution) Distributing new software and upgrades via the network rather than individual installations on each machine. See ESL. ), particularly at the wave soldering Applying liquid solder to the underside of printed circuit boards in order to bond the chips and discrete components that are placed on top of the board and whose metal leads (pins) extend through the board. operation? A: Apparently, you have already determined that the printed circuit assemblies (PCAs) in use are, or may be, sensitive to potential ESD conditions generated by your materials, equipment and processes--including personnel activities and interaction with other items in the facility. Following are general references and recommendations I have found to be effective in many facilities: * The IPC-SM-770 document, Guidelines for Printed Board Component Mounting, Part 6, Section 26, offers recommendations for ESD control practices and the susceptibility ranges of various component types. * Good housekeeping Good Housekeeping is a women's magazine owned by the Hearst Corporation, featuring articles about women's interests, product testing by The Good Housekeeping Institute, recipes, diet, health as well as literary articles. and environmental control, particularly humidity level, are essential. A dry atmosphere is conducive to ESD and resultant, unseen damage to component and assembly circuitry. Litter, dirt, discarded boxes and plastic foam in the facility do not help to eliminate potential ESD problems. * The IPC/EIA J-STD-001C standard, Requirements for Soldered Pronounced "sod-erd." Permanently attached by a hard metal bond. In order to replace a chip soldered to a circuit board, it requires heating the soldering joints until they melt. Contrast with socketed. Electrical and Electronic Assemblies, Section 3.6.1 and 3.6.2, requires that when facility humidity reaches 30 percent or less, the manufacturer must verify that the implemented ESD control program is adequate at such levels. The humidity in many facilities is generally above 30 percent to reduce the possibility of damage and for employee comfort. Other specific recommended humidity levels may be found in the ANSI/ESD S20.20-1999 standard. * When economically feasible, the total assembly area should be equipped with antistatic Eliminating or reducing static electricity. See static electricity, antistatic bag, antistatic device, antistatic liquid and antistatic wristband. floor tile. All personnel, including visitors, dignitaries and management personnel, entering shop areas should wear heel straps and antistatic coats or smocks. Often, visitors and those not familiar with the assembly area are unaware of potential ESD problems--they may touch or pick up assemblies and components. Be sure to explain the need for ESD protection to any and all visitors. Test the heel straps and other prevention measures often and be sure all ESD protective equipment is certified to applicable ESD standards. * Soldering soldering Process that uses metal alloys with low melting points to join metallic surfaces without melting them. Tin-lead solders, once widely used in the electrical and plumbing industries, are now replaced by lead-free alloys. and cleaning equipment and conveyors (to and from the operations) should be grounded. For highly sensitive Adj. 1. highly sensitive - readily affected by various agents; "a highly sensitive explosive is easily exploded by a shock"; "a sensitive colloid is readily coagulated" assemblies, use ESD-safe pallets made of non-metallic composite materials composite material or composite, any material made from at least two discrete substances, such as concrete. Many materials are produced as composites, such as the fiberglass-reinforced plastics used for automobile bodies and boat hulls, but the . * Although resistors are generally built in to protect personnel, do not use grounding wrist straps, heel straps or antistatic table pads when performing maintenance work on equipment. * Tote boxes and tabletops or tabletop mats should be made of antistatic or conductive conductive having the quality of readily conducting electric current. conductive flooring flooring or floor covering made specially conductive to electrical current, usually by the inclusion of copper wiring that is earthed material. Tables should also be grounded. * When tape is applied as a solder mask An insulating pattern applied to a printed circuit board that exposes only the areas to be soldered. on assembly card edge connectors for protection during wave soldering, place the tape on the connectors before assembling components to the board. If the tape must be applied after components are inserted, air ionizers should be used at the operation. Also, exercise care and use air ionizers when removing tape from soldered assemblies. The use of non-solderable metal finger shields, to protect card edge connectors during wave soldering, is actually a better solution than the use of tape. * When possible, do not allow plastic, vinyl or plastic foam in work areas. * Control humidity in the work area--a dry atmosphere is more conducive to static discharge. Maintain a humidity level of 30 percent or higher. * Except when required during test operations, always stand boards on edge--not flat with protruding pro·trude v. pro·trud·ed, pro·trud·ing, pro·trudes v.tr. To push or thrust outward. v.intr. To jut out; project. See Synonyms at bulge. leads touching an unprotected surface. * Require ESD training, with periodic refresher courses, for all employees. * Ensure that all applicable ESD preventative actions and rules are applied throughout the facility. Identify at least one ESD-trained, knowledgeable employee as a source of information about practices to be followed. Visible management support of compliance with ESD prevention requirements, disciplined behavior and a positive attitude are absolutely essential in reducing component and assembly failures resulting from ESD. Send your process, technology or training question to les.hymes@worldnet.att.net. Please type "ASK LES" in the subject line and indicate your name and company or institute affiliation. All questions may not be answered, Les Hymes is the owner of Les Hymes Associates, Surprise, AZ; (623) 544-4646; e-mail: les.hymes@ worldnet.att.net. |
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