I am about to begin my adventure breadboarding circuits with CMOS
logic. I have an anti-static mat and a wrist strap. If I ground these to
the case of my power supply or the receptacle plate screw is that
OK?

M

 

If I ground these to
the case of my power supply or the receptacle plate screw is that
OK?

Yes. Just check to see if either/both are actually connected to earth ground.

If you connect your wrist strap to the mat (my mat has a connection point), that will be sufficient in most cases. Relative voltage is more important than absolute voltage. I do that when I'm handling/sorting components away from my bench. I never use the mat on my bench because the mat is too large...

Check your strap from time-to-time to make sure it's still working. Should have a resistance of 1-2MΩ.

Antistatic tools are also handy.

You're wise to be concerned about ESD. If you're lucky, devices will die outright. If you're not, they'll be damaged in some way that affects operation in a subtle way or they'll fail prematurely at some future time.


Members who will claim that they never take ESD precautions and have never damaged a device will be along shortly...

 

Yes. Just check to see if either/both are actually connected to earth ground.

If you connect your wrist strap to the mat (my mat has a connection point), that will be sufficient in most cases. Relative voltage is more important than absolute voltage. I do that when I'm handling/sorting components away from my bench. I never use the mat on my bench because the mat is too large...

Check your strap from time-to-time to make sure it's still working. Should have a resistance of 1-2MΩ.

Antistatic tools are also handy.

You're wise to be concerned about ESD. If you're lucky, devices will die outright. If you're not, they'll be damaged in some way that affects operation in a subtle way or they'll fail prematurely at some future time.


Members who will claim that they never take ESD precautions and have never damaged a device will be along shortly...

Thanks Dennis. Just trying to prevent a calamity!

 

Just trying to prevent a calamity!

Troubleshooting circuits with damaged components can be time consuming. In the past 5 years or so, I've damaged several 2N7000. Unfortunately for me, none of them died outright. They just exhibited leakage which prevented the circuits from working correctly.

 

Commercial bench power supplies usually have a GND terminal. If this is your case, check for continuity between this terminal and the Earth pin on the 3-pin power plug. If your house is not too old, then E-socket on the 3-pin outlet would be grounded. You should check this in any case.

If you have a PSU with a GND terminal then use that for your anti-static grounding.

 

Commercial bench power supplies usually have a GND terminal. If this is your case, check for continuity between this terminal and the Earth pin on the 3-pin power plug. If your house is not too old, then E-socket on the 3-pin outlet would be grounded. You should check this in any case.

If you have a PSU with a GND terminal then use that for your anti-static grounding.


View attachment 313726

Excellent. Thanks.

 

For use while building stuff, aluminum foil on top of the working surface, connected to the anti-static ground you are using,is also useful. BUT not once you are applying power, because of shorted circuit possibilities.

 

A properly grounded mat should have a resistor between the mat and actual ground. If you've bought a good commercial mat then it's likely the resistor is included at the end of the ground cord. It's probably in a shrink sleeving. Mine has the resistor built in as described. My home is 1962 and wasn't wired with many grounds. At best some outlets had a steel wire going from metal box to metal box then was grounded to the water pipe. I've done major upgrades in my house and now have a fully properly grounded service panel. All the new wiring is grounded properly. The FORMER owner thought he'd be cute and in the socket he'd tie ground to neutral. True, they all go to the same place, but there was a wiring error in the basement behind the ceiling panels. Hot and neutral were swapped. That made my computer which was plugged into a mis-wired outlet case hot. When I plugged the printer into a different outlet which was case ground I got a good shock and burned the connector when I tried to plug it in.

Relative voltage is more important than absolute voltage.

This is true. If you are standing at 50KVS (Kilo Volts Static) and your microchip is also at 50KVS then when you touch it there will be no current flow from either you or the chip. However, 50KVS, which is humanly possible, will come with quite a heck of a snap when you touch something that is not at the same potential.

Took two volunteers in an ESD class and had them sit on plastic lawn chairs. The guy on the right stood up. Each had a brass rod. When they touched the two rods together they got a good shock. Then the guy on the right sat down and the guy on the left stood up. When they touched the brass rods together there was a very loud snap and a good deal of cursing. When one guy stood up from the chair he stripped away (assuming) negative ions. When he equalized the charge with the guy sitting down the chair the guy on the right stood up from was positively charged. When he sat down he was now in a positive charge environment. The other guy stood up and took away negative ions. The potential difference between the two of them was doubled. Your chips should have time to rest, five minutes is good, before handling them. People here are going to say they never heard that before. It's not a common practice, but it gives the chips time to neutralize their charge from surrounding ions. Especially if you have an ion generator (not necessary). Then when you're properly grounded and you reach for the chip you're far less likely to damage it.

The comment about damage that doesn't result in total failure is called EOS (Electrical Over Stress) which is a weakening of the component. It may still work but it's unlikely to be reliable.

 

It cannot be over emphasized. The danger is not outright failure. The danger is a weakened structure where the device works now but fails later in the field. A compromised component that cost $1 now, installed in a $1000 piece of equipment would cost $5000 to repair when the equipment fails.

 

Another point about ESD. Most CMOS IC's contain ESD protection, but that protection is only tested to about 2kV. You can easily generate more than 2kV.

 

Another point about ESD. Most CMOS IC's contain ESD protection, but that protection is only tested to about 2kV. You can easily generate more than 2kV.

To add to this - 3KVS is at the minimum threshold you can feel. That's to say you can barely feel it if you pay real close attention to the sensation. Otherwise it goes completely unnoticed.

 

Static shocks can be funny. A while back I posted about the band member who kept asserting that there was a short circuit in the PA system because they always got shocks touching the microphones. This while standing a foot above the wood floor on a dry wood platform insulated with nylon carpet.
Static electricity is totally invisible. and seldom originates in wires.
There is no convincing fools as to any truth, is there??