Tuesday, September 28, 2010

Why use an ESD seat?

I have read the IEC 61340-5-1/2 and we are building a new production area. If everyone who works with ESDS, uses wrist straps while seated, do they need to sit on an ESD chair? (The floor, the tables, the garments are ESD protected)
If they connected to ground via wrist strap, why should I connect them to ground via chair?

Firstly, the ESD chair is not for grounding personnel. The seat may have quite high resistance to ground, up to 10^10 ohms. For grounding personnel, we need a much lower resistance <35 Mohms and this cannot be achieved by contact with many seats. Contact between the seat and body is unreliable because there are layers of clothing in between!

The purpose of having an ESD seat is so that the material of the seat does not become charged and cause an electrostatic field and ESD risk.

Tuesday, June 15, 2010

What ESD packaging should I use?

We need to move pcbs with ESD sensitive components on from an EPA to another EPA passing through a non-EPA area. What is the recommend method for tranporting these devices to minimise ESD damage? We don't want to use individual shielding bags.

There is no single recommended method or packaging type. However I reccommend the packaging used has the following characteristics:

1) no part of the packaging should be an exposed insulating materila which could charge up and cause ESD risk in an EPA.
2) the material in contact with the ESD sensitive parts should be dissipative
3) there should be a surrounding conductive material to form an electrostatic field shield
4) an air gap, dissipative material or other barrier should prevent ESD currents being conducted from the outside of the packaging to the ESD sensitive parts.

A shielding bag has all these characteristics, but it is quite possible to design a larger packaging system to contain many items that achieves the same using different packaging materials.