Tuesday, August 02, 2005

>> My company would like to implement an ESD program because we handle
>> electronic repair parts for our semiconductor capital equipment.
>> 1. Would you recommend having different levels of protection for
>> components in different HBM classes?
>> 2. We do not manufacture the parts and do not receive any technical spec.
>> sheets to determine which parts are ESD sensitive. How would you
>> recommend we go about determining which type of parts, in our list of
>> thousands of repair parts, are susceptible to ESD damage?
>> Creating a comprehensive list of parts or even types of parts seems
>> daunting, especially without convenient access to the technical
>> specification sheets.

Normally I would not recommend having diferent levels of ESD program unless there were highly different requirements in some areas, for example < 100V HBM parts handled in a specific area.

It can be very difficult to get ESD data. There is some generic information in our on-line ESD Guide .

You can assume that almost any semiconductor device, or pcb containing such a device, is ESD susceptible. The usual approach is to implement an 100V HBM ESD control program which would cover almost everything. However if you handle more sensitive parts, you need to identify these and may need very stringent handling measures.

Monday, August 01, 2005

Can static electricity cause skin rash resembling insect bites?

There are occasional reports of skin rashes resembling insect bites attributed to static electricity (often associated with dry air conditions). I am are not fully convinced that static electricity is the cause. However I understand that some professionals in the pest control industry believe that this can be the case.

Chester County Council stated in an on-line article that :
""The environmental problems, however, have gone on from there as our buildings and their furnishings become increasingly modernised and synthetic. Sharp paper dust particles cause skin irritations, and in Chester the culprit has usually been pig-hair carpeting. In addition, certain combinations of temperature and relative humidity seem to set the stage for itches. The skin becomes hypersensitive and then contaminants irritate it.
Whenever someone walks across a carpet – or other floor covering – the friction between their soles and the flooring generates an electrostatic charge. This passes onto their skin and accumulates with each step. The charge drains slowly from the body back to the floor, but, when walking quickly or for a long distance, people accumulate static electricity on their bodies faster than it can drain away. Problems arise, if someone takes 20 or 30 paces across the floor and then touches or passes very near another object.
Although the discharge occurs unnoticed, it is often sufficient to cause localised skin irritations and leave a tiny red rash similar to an insect bite. Temperature and relative humidity influence the magnitude of the discharge, while sweat, oils and other materials on the skin improve the electrical conductivity of the body surface and aggravate the situation. ""
(See: Trafford Council Cable bug article )

I do not necessarily agree with the Trafford Council analysis but if static is involved it is likely that dry air conditions, and the floor covering material, are both major factors. We would expect the inhabitants would also receive shocks from static discharge, they would feel, hear, and possibly see the spark that accompanies the discharge. The voltage required for humans to feel these effects ( above about 3000 volts ) would easily be generated by walking on a nylon, or other man made fibre, carpet and other insulating materials.

For further interest, see also http://citybugs.tamu.edu/FastSheets/Ent-1012.html