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Question on ESD

Ashok Dhawan


Question on ESD | 24 March, 2000

Two questions on ESD:

1. What is recommended method ( Air ionizer , grounding strip etc. ) for a board prep ? We Kapton Tape for masking pads or not to be soldered areas. or Is there a wet mask recommended for masking boards campatible with NC Soldering process ?

2. For board drying operation, what is recommended method ( (e.g. Air ionizer, Ionizing gun, grounding strap etc.) for ESD protection- when comressed air gun is used for blowing off water from washed assemblies or PCBs ? Ashok


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Re: Question on ESD | 24 March, 2000

Hello Ashok If you are talking about the thousands of volts that is often generated by either simply unrolling the tape to apply or when it is removed from the board after soldering you don't have a lot of choice since it is an insulator. Ionization is about the only way (besides high humidity). Remember that this sort of dissapation is gradual rather than instantaneous so it might not be effective is your operator is zipping the tape off of a populated board. Of course the operator must be also be protected by an appropriate method, usually heel straps (2 each and not seated) or a wrist strap. Is there a reason that you are using a Polyimide tape for this masking? We use a high temperature masking tape (Shercon 118, ComKyl and others)in tape and disk form. It is one quarter of the cost, generates far less ESD and doesn't transfer its adhesive to the board. For liquid mask recommendations look further down on this Forum page and search the archives. For board drying an ionizing blow off gun would be appropriate since the turbulent air would actually be creating the charge. While we don't blow off boards for drying we have a number of applications that require dust removal and static neutralization of plastic LCD screens. We use a small cartridge that screws into a regular blow gun and contains a tiny amount of the radioactive isotope polonium sealed inside. These are replaced once a year. Unlike a regular ionizing gun you have no extra wires, restricted movement, emitter point maintenance, balance testing, or arcing and they are way less expensive (NRD Static Control, 716/773-7634). Again, same caution for operator ESD protection. It goes without saying that they also need eye protection from flying debris, water, chemicals, loose parts, whatever and ear protection from the noise and area containment to protect others. John Thorup

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