Static electricity damaging modern touch screens?

CVMichael

Joined Aug 3, 2007
419
Amm... doesn't the device need to be grounded (at some point) in order for the static electricity to pass through, and therefore damage it ?

For example, with a monitor it makes sense, because it takes the power from the grid, so when you touch the screen, the static charge goes through the screen and then through the grid.

With the iphone, you hold it in your pocket, and the charge builds together with you, there is nothing to make the charge flow through the iphone... right ? probably it will damage at the moment you put it on the table, then the charge flows through it...
 

Wendy

Joined Mar 24, 2008
23,476
Hard grounds are not needed for ESD, but it can make them worse. Anytime you have metal that is part of the circuit exposed you can have a killer ESD event, but I suspect most of them will be latent, which is another way of saying your electronics will die for no apparent reason later.

ElectroStatic Discharge
 

Ghar

Joined Mar 8, 2010
655
Static just needs a voltage difference between two objects.
Your body's voltage and the voltage of the iPhone are probably different. Most tables aren't grounded and neither are cars and doorknobs but you still get shocks with them.

The ESD current will flow through the capacitance to the environment. In the iPhone the biggest capacitance should be the big metal back plate.
Just having the plate is apparently quite a bit of protection because it's inbetween the electronics and the environment, reducing the electronics' capacitance while having a larger capacitance itself.
 

R!f@@

Joined Apr 2, 2009
9,921
The ESD current will flow through the capacitance to the environment. In the iPhone the biggest capacitance should be the big metal back plate.
Just having the plate is apparently quite a bit of protection because it's inbetween the electronics and the environment, reducing the electronics' capacitance while having a larger capacitance itself.
I did not follow you :confused:
 

Ghar

Joined Mar 8, 2010
655
I did not follow you :confused:
It's like a capacitor with one plate being the iPhone and the other plate being the environment around you.

esd.png

To go through the electronics the current would go through the two series capacitors, which is a smaller capacitance (higher impedance) than either individual capacitance.
The chassis-ground capacitance is the lowest impedance there so most ESD current should go through it.

If the electronics are clamped to the chassis with TVS diodes or whatever the board will rise in voltage with the chassis and there shouldn't be any damaging voltage differences across the board itself.

At least, that's my understanding after reading some stuff on ESD... I haven't really practiced any of this yet.
 
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