Desco - Questions And Answers

When an operator holds populated PCB, he gets shock occasionally, kindly suggest the solution.. - Gnag, Bangalore, India

First, the populated PCB should be stored or transported in an enclosed conductive (<1x10^1 ohms) container such as a metal-in shielding bag. When an operator wants to handle this board at a controlled workstation, the following should occur. Operator is grounded with wrist strap or other direct ground path workstation surface is grounded (dissipative mat connected with ground cord) operator puts container with PCB inside on dissipative grounded mat wait about 2 seconds to ensure container is at same potential as operator and mat open container and remove populated PCB board perform test or manufacturing operations place PCB back in container and seal it. By following the above steps, when the operator handles the PCB, there should not be any discharges. If there are, then isolated conductive parts on the board may be charged from tribogeneration or field induction. In this case, since we can’t ground isolated conductors (because they are isolated) a bench ionizer would solve the charging problems. Also check the relative humidity (RH) of the facility. If below 35%, then extra ESD precaution should be considered, such as ionization, when handling ESD sensitive (ESDS) components or devices.

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