The people that do testing and manufacturing at our company use antistatic wrist straps and ESD mats when handling potentially sensitive electronic components. There are also ESD floor mats available.
As Johnfound already pointed out, most devices are pretty resistant. But if you make ESD protected handling part of your production flow, you can be pretty sure that defects that occur during product lifetime are not the result of pre-damaged components due to ESD.
While it is less likely to create hard-faults with Electrostatic Charge in a component that is not connected to any bulk surface to dissipate or equalise the initial impulse, it is still possible.
Say you are negatively charged compared to the chip, that means you have "excess electrons", so when you tough a pin of the device, that pin will be connected to your excess and will "want" to become the same charge. This induces a current. It may be shorter in duration and could be smaller than when the chip is "grounded", but it can be enough to kill it, depending on the chip's innards.
Even the over-charge on one pin compared to another can destabilise some constructs in Chips, especially MOS devices, sometimes even permanently.
Note about "Anti-Static" bags, There's a couple types:
- Pink Anti-Static: Not safe at all for ESD sensitive chips
- Black Dissipative: Very safe for ESD sensitive devices, but less so than the metal-foil ones.
- Metal Foil Conductive: Extremely safe.
The Pink bags are only anti-static: It does not create charge when rubbed by another surface. So they are nice in a shipment with several bags, to prevent static to build up, but a human-body zap can very easily go straight through the plastic to any chip.
The black dissipative actually conducts a bit of electricity, usually a few hundred kOhm to a MOhm per square of resistance, and they will dissipate any charge built up across it and human-body discharges are extremely unlikely to penetrate the bag to the chip, but high level discharges may still affect the chip.
Metal foil conductive: The name says it all, has a very low resistance per square. Some bags have the foil (or a micro-laser-perforated foil to allow some see-through) on the inside, some have an extra layer of dissipative material over it, to protect the metal film. It will be extremely hard to have any kind of zap go through the bag, as the foil will conduct it from one side to the other. Even high intensity discharges will have trouble getting through, with the exception of discharges that will vaporize the foil, since that will make the bag (and chip) explode. And of course a few below that level, but I wanted to conjure the image of an exploding ESD bag.
Best Answer
It's very tempting to casually say that the discharge is the return path, but it would be more correct to say that it is a path of resolution which dilutes an imbalance of charge created by some other means.
We tend to think of current flow circuits but actually, circuits are just one particular behavior of charge.
Another is the accumulation of charge (say, triboelectric, ie, feet on carpet charge). This is a "static" charge - absent a pathway to neutralization, the excess or shortage of electrons "just sits there" on a charged object.
When the charged object comes close enough to an object connected to a large reservoir of more neutral charge (either via wiring back to the earth itself, or simply a conductive object having its own charge capacity such as a doorknob) then the electric field resulting from the difference in charge may in exceed the breakdown voltage of air for a specific geometry, and a spark may result.
In the case of diodes intended to present a shunt path for ESD, that reservoir of more neutral charge could anything from an actual grounding system, to the bulk of the devices's own supply rails/network. Ultimately an ESD event is a brief current spike to equalize charge, and since the possibility of damage from over-voltage is ultimately about over-voltage relative to other semiconductor segments equalizing charge with the powered or unpowered supply rails is sufficient.