The amount of charge generated in the rework and repair areas of electronic products is affected by many factors, including but not limited to the materials used, the amount of friction interaction between materials, and the relative humidity of the environment. In the cold winter in the north, when the heating system dries the air in the workshop and the relative humidity decreases, more electrostatic charges will be accumulated under the same other conditions. Lower humidity will increase the number of ESD events, so theoretically, keeping the rework area at a higher humidity level can reduce the possibility of component damage caused by static electricity.
In order to achieve "appropriate" relative humidity levels in PCB rework / repair areas, several variables need to be considered. The electronic components being reworked need the relative air temperature to reach its specified operating range. In addition, rework processing steps, such as the time required to repair the curing of epoxy resin or the time required to cure the three proofing paint materials, are some process steps affected by the humidity level. High relative humidity level may cause unnecessary quality problems, such as corrosion, manual welding defects and unnecessary MSD damage to humidity sensitive devices. At higher relative humidity levels, the solder paste will not have the correct printing and collapsing characteristics. This may affect the solder paste printing rework process, such as solder paste printing for leadless devices or BGA component locations.
Increasing humidity can be achieved through the humidification system. The humidifier adds water vapor to the air to form a thin protective film on the surface and acts as a natural conductor to dissipate electrostatic charges. When the humidity drops below 40% of the relative humidity, this protection will disappear, thus increasing the possibility of damage or defect of electronic components and devices.
When the air relative humidity is low, there are many risks in completing operations in PCB rework and repair areas. If any existing static electricity monitoring or control system fails (for example, the grounding connection is disconnected, the operator lacks a wrist strap, foot grounding device or grounding pad, which will cause the coating to overflow and make it an insulated surface), the impact of static electricity charging cannot be controlled. Secondly, any reworked PCB that does not contact the ESD safety surface or is not properly handled by the ESD protection rework technician may be damaged. In many cases, it is easier to control the humidity level than to ensure that non charged materials do not enter the work area. These are some of the risks of completing operations in rework areas in low humidity environments.
