Electronics > Manufacturing & Assembly

Carry PCB across carpet and get ESD damage?

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Faringdon:
Hi,
At work recently, i could hear them talking about a board with  ADC and DAC chips on it,  etc etc, and micro's. (0.5mm pitch and 0.65mm pitch)..it had previosuly worked, but now was malfunctioning...a strange delay of some 15 seconds was holding up a signal.
I had seen them carrying this board bear handed, whilst walking across the office carpet...several times.
I mentioned that ESD could be the problem but they poo-poo'd  the idea strongly.

Have you any good videos , or proof, that such PCBs should not be carried bear handed across  office carpets?

People say its OK to do it in eg UK , as the climate is humid and ESD charges dont build up, even if walking across an office carpet.

TimFox:
Lots of stuff on the web, such as  https://www.industrial-electronics.com/proeeap_6.html

With your UK spelling, you seem to believe in the right to arm bears...

Back in college, the corridors in my dormitory were carpeted.  During Minnesota winters, with almost no indoor humidity, I needed to walk down the hall with a 10 k resistor borrowed from the physics lab, touching metal door frames as I passed.  Otherwise, the electrostatic discharge was actually painful.

edpalmer42:
Carrying the board is okay.  The problem comes when you set it down.

Back in the 1980s, HP published a document on this question.  It's still extremely relevent.  But note that today, I think there are more synthetic materials in our clothing and carpeting than there were back in the 1980s.  Synthetics typically build up more static charge than natural materials.

http://hparchive.com/Bench_Briefs/HP-Bench-Briefs-1983-03-05.pdf .

It's very hard to set up a demonstration of this problem unless you want to test 100 cards and see how many fail.  There are just too many variables.

I've heard of companies where failure to follow antistatic procedures after you've been trained on them will get you fired.  That's not a policy that a company would put in place on a whim.

Ed

tomgat:

--- Quote from: Faringdon on October 26, 2022, 09:24:55 pm ---Hi,
At work recently, i could hear them talking about a board with  ADC and DAC chips on it,  etc etc, and micro's. (0.5mm pitch and 0.65mm pitch)..it had previosuly worked, but now was malfunctioning...a strange delay of some 15 seconds was holding up a signal.
I had seen them carrying this board bear handed, whilst walking across the office carpet...several times.
I mentioned that ESD could be the problem but they poo-poo'd  the idea strongly.

Have you any good videos , or proof, that such PCBs should not be carried bear handed across  office carpets?

People say its OK to do it in eg UK , as the climate is humid and ESD charges dont build up, even if walking across an office carpet.

--- End quote ---

I cant speak for all chips, but allot of my designs use 24-bit delta sigma ADCs, and once the chips are mounted on a board I dont think I have ever had any issues with static damage whatsoever.  By themselves they can get static damage, however.  Im not saying its not possible, though. Just not very likely.  Obviously I dont know what your design is, but if this issue happened immediately after reflowing, well then you probably know the drill to fix it.  If it happened over time, then I would suggest looking for a cold solder joint (assuming your running SAC) before thinking of static damage taking out the ADC.  If it was me, (I'm lazy) I probably would just dip the board in liquid flux and reflow it again.  Sure it looks ugly when it comes out, but will look brand new again once it comes out of the isopropyl bath.

twospoons:
ESD is a very real possibility. Worst is the damage can be subtle instead of catastrophic - instead of instant silicon death you can have parts slowly degrade in normal use after an ESD hit.

Why take a chance? Just use anti-static bags to carry boards about, and have an ESD mat on every desk.  Its dead simple, and a good habit to get into.

One office I was in I would get zapped just getting off my chair.

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