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Question I would like to learn the ideal humudity level for ESD protective area. –Alp Korkmaz, Karkel Elektronic, Sincan, Turkey
Answer There are several recommendations, depending on which standard or book you read. There is a real cost for the equipment associated to keeping a facility humidified within a specified range as well as to having an overly humidified or very dry work area with respect to corrosion and ESD respectively. It is best to put in place an ESD control program that does not rely on humidification as its primary constituent (as this is sometimes very hard to control) and understand the effects that trying the boundary of the ranges have on your products, equipment and people. From previous Q&As: Q73: What is the specified humidity level for a class 100 clean room to make Hard Disk Assembly? A73: A good range would be between 40% and 55%. You want to minimize corrosion and maximize ESD protection. There is a paper on Humidity for your convenience. Standard Humid air helps to dissipate electrostatic charges by keeping surfaces moist, therefore increasing surface conductivity. Substantial electrostatic voltage levels can accumulate with a decrease in relative humidity, see Table 1 above. However, it is also evident from Table 1 that significant electrostatic voltages can still be generated with relative humidity as high as 90 percent. Relative humidity between 40 percent and 60 percent in ESD protective areas is desirable as long as it does not result in corrosion or in other detrimental effects such as PWB delamination during soldering. Where high relative humidity levels cannot be maintained, ionized air can be used to dissipate electrostatic charges. MIL-STD-1695 specifically addresses relative humidity levels in the range of 30 - 70 percent in areas where electronic parts and hybrid microcircuits (MIL-STD-1695, work areas 5 and 6) are handled or processed. MIL-STD-1695 requires the same level of relative humidity controls for handling and storage areas (MIL-STD-1695, work area 13), except when items are covered or protected.
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