ESD ratings of diodes and bipolar transistors

Question

While it's easy to find ESD ratings for ICs (bipolar, CMOS, and any mix) and to some extent for MOS transistors (for the inherent reasons), I don't find ESD rating for many common diodes (left apart TVS and Zener devices, given their use).

Let's say I'm looking for ESD rating of an S1J or S1M diode: no manufacturer seems to detail it. Is it because being massive, high-voltage parts (operating up to 1kV DC) they already are over an "interesting" value?

Again, if I look for the same rating of a BAS21 part, just a 250V diode, I can't find it from common suppliers.

Even going down to an humble BC847 bipolar NPN, no details on ESD rating, looking in a few data sheets.

If any of these parts is handled wrong, or connected to the outside port of a device, could easily come in contact with dangerous voltages. I'd like to know more on these ratings and why they aren't listed.

Answer 1

ICs are ESD protected by connecting diodes from I/O to rails.

How would you protect a diode? By using another diode? The diode has two possibilities when hit with an overload. (a) It conducts in the forward direction. Many diodes have a peak current specification, which tends to be orders of magnitude higher than the sort of diodes you can fit into an IC for protection. (b) It blocks in the reverse direction. You already have a specification for the peak reverse voltage it can take without breaking down.

Transistors are similar. If you hit a junction in reverse with an ESD spike, you already have in the data sheet the voltage limit for that junction, above which it may break down. A forward junction will tend to protect itself as for a diode.

Generally, the common 'cooking grade' transistors (like BC847) are fairly robust, built with big processes. It's ICs with small junctions that need explicit protection, and FETs with a very high impedance gate. You can buy microwave diodes and transistors that are very susceptible to ESD, as they have to be built with tiny junctions to work at high frequency.

Answer 2

Ordinary junctions (think diodes and BJTs) are damaged by heat caused by the current rather than the current alone, so they can dissipate a fair amount of energy before dying. Common diodes an BJTs can dissipate a few millijoules, which is about what a ESD shock delivers.

ESD can easily damage a junction which is reverse-biased in the first place. This is because the initial avalanche current produced by ESD will be sustained by the reverse voltage applied to it, delivery far more energy than the initial ESD discharge.

Answer 3

ESD circuits survive the ESD event by guiding the ESD charge flows to be deep in the silicon, so the BULK is heated up.

Diodes naturally have large volumes to be heated up, at least when forward biased.