CMOS handling

Thread Starter

quadhed

Joined Jan 13, 2016
23
Hello I realize that you should ground yourself when handling a cmos component, but what about after it's in the board/socket? I want to put a cmos 4017 decade counter in a plastic model. Will this be protected after it is installed?.Can it go bad?
 

dl324

Joined Mar 30, 2015
13,535
Will this be protected after it is installed?.Can it go bad?
As usual, it depends. A plastic enclosure can collect charge. If you collect sufficient charge, it could arc and potentially damage static sensitive parts inside. That said, it should be reasonably safe if there are things to limit discharge voltage on the inputs and outputs of CMOS ICs (like caps on the supply).
 

Thread Starter

quadhed

Joined Jan 13, 2016
23
As usual, it depends. A plastic enclosure can collect charge. If you collect sufficient charge, it could arc and potentially damage static sensitive parts inside. That said, it should be reasonably safe if there are things to limit discharge voltage on the inputs and outputs of CMOS ICs (like caps on the supply).
I'm somewhat of a novice, but what do you mean by capacitors on the supply? Between the positive and negative terminals? It would be powered from a 12 volt wall wart.
 

dl324

Joined Mar 30, 2015
13,535
I'm somewhat of a novice, but what do you mean by capacitors on the supply? Between the positive and negative terminals? It would be powered from a 12 volt wall wart.
When using CMOS logic, you need to have decoupling capacitors on the power supply so that switching outputs won't put spikes on the power rail. The inputs and outputs of CMOS devices have diodes that clamp them to the supply rails, so my thinking is that they would mitigate (not eliminate) ESD risk.

The diodes on the input are explicit ESD protection and the outputs have parasitic diodes that clamp the outputs to one diode drop above or below the power rails.
 

MrChips

Joined Oct 2, 2009
24,625
CMOS or no CMOS, you need to protect all ESD sensitive semiconductor devices.
Here are some general guidelines.

1) Store all devices and boards in anti-static bags, rails, containers.
2) Wear a properly grounded wrist straps at all times when handling ESD sensitive components and boards.
3) All workbenches must be grounded.
4) Use an anti-static mat on the surface of the work area.
5) Use grounded solder and rework stations.

A semiconductor device may be compromised and you would not know it, resulting in premature failure sometime later.
A failure of a $1 component may result in $100 repair expense later when the device is in the field.
 

ErnieM

Joined Apr 24, 2011
8,196
Irregardless of the box it is in, what happens to the pins of the 4017? Do any of them get exposed to the outside world, is there any risk of pesky little fingers poking at them?

If not, rest easy. If so, you may need some further protection, which can be as simple as a series resistors. I cannot offer any recommendations without seeing the schematic and perhaps the layout & assembly too.

The input protection diodes inside a CMOS IC are actually fairly effective.

Now a war story: A while back we had a very high failure rate (30%?) of a simple hybrid circuit (ie, built using bare silicon chips) where the CMOS gate was failing. Without any obvious stress seen I wrote a change notice that when wire bonding the chip (placing thin gold wires from each "pin" to the board) to first do the +power pin, then the - power pin, then all others in any order. The fail rate plumeted and was mostly miswires and such, no more changing chips.
 
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