1.1 This technical specification is intended to cover the protection from ESD damage of all electronic devices with voltage sensitivity of not lower than 100 V through their entire life. This is from the commencement of manufacture, through product assembly, product use and possible repair until the end of the product life. This technical specification is intended to cater for electronic components, assemblies and subassemblies with a sensitivity of 100 V or greater (human body model (HBM)), and as such covers most items available. There are on the market a few items which may suffer damage at lower levels. Where these are used, additional or alternative methods should be used. These are not covered by either IEC 61340-5-1 or this user guide, as it would not be reasonable or economic to equip the general EPA to cater for these. Additional information on these may be found in many of the references in the bibliography. The HBM has been chosen as the major criteria, as damage from human contact is still the most common source even in todays automated society. There are several values given in different sources for HBM, but the chosen one is 100 pF and 1 500 ohms. 1.2 Low humidity At low relative humidities the dissipation of static charges often becomes more difficult, and some materials may not work efficiently. Above about 20 % relative humidity most materials maintain most of their efficiency. Where relative humidity may go lower the user should pay particular attention that the materials selected will perform effectively at the minimum expected relative humidity. This is of particular importance in very cold and non-oceanic climates. 1.3 Clean rooms For clean rooms, the specialist areas are considered to be class 100 or tighter. Many of the techniques in current use for ESD protection will not satisfy the clean room constraints, for example, carbon breaking down, ionics from spray or particles from ionizer needles. Some alternative materials are available, with improved ones still being developed, that will cope with both conditions and these should be used. This area is particularly important as clean operation is an essential part of semiconductor manufacture. Damage occurring at this stage may result in undetected "walking wounded" devices which can have very expensive results. The clean room application is currently the most difficult to control, particularly in class 10 and class 1 rooms. IEC 61340-5-1 embodies current technology. As new and improved materials and techniques become available this area will be improved, with benefits in reliability. 1.4 High voltages The term high voltage in this context is used to mean any voltage in excess of 250 V a.c. or 500 V d.c. This terminology differs from the definition used in some areas, such as some European standards where the reference is to higher voltages. Accessible high voltages are not normally available in most assembly areas. There are areas which require accessible voltages in excess of the mains supply. Examples are areas for high-voltage safety tests and areas such as CRT test and repair. Means of preventing ESD damage while maintaining personnel safety are specified. For these purposes, high voltage is considered to be all voltages in excess of the standard electrical mains, including three-phase supplies. This is currently 230 V or 117 V nominal in most world areas, and to cater for tolerance 250 V a.c. is permitted, which equates in most safety areas to 500 V d.c. 1.5 Relative humidity (r.h.) In areas where relative humidity is controlled for both ESD control and other reasons, 50 % r.h. suits most processes. Changes both in r.h. and rate of change of r.h. should be minimized. The characteristics of material during changes in r.h. vary widely according to the materials. In very general terms, material with a high conductivity (<107 ohms surface resistance) will change very little, whereas materials with a higher resistance will undergo a substantial resistance increase as r.h. decreases. This is not a linear effect, and resistance changes above 40 % r.h. are normally minimal, but from 20 % to 30 % changes can be as much as two orders of magnitude, a factor of 100, with further increases below 20 %. Some natural materials such as cotton can undergo a very large change in resistivity over a narrow band of r.h. The use of a charge decay characteristic is technically the correct measurement and where problems are likely, charge decay measurement should be also used in addition to resistance measurements. When measurements are being carried out for high-resistance materials at high r.h. levels, care may be needed to ensure that the resistance measured is that of the material and not that of its affected surface or surrounds. Use of high r.h. environments is not considered to be a prime method of controlling ESD, and high humidity environments may cause additional unwanted effects such as corrosion.
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