Monday, June 13, 2005

Are capacitors ESD suceptible?

>> What is the likely device sensitivity of a thru-hole ceramic capacitor?
>> My general understanding is that passive devices are not ESD sensitive.

Many types of component can be damaged by ESD - including passives. Whether damage is likely to occur depends on the ESD withstand of the component and the strength of the ESD. (Taking an extreme example, lightning is a form of ESD!)

In the case of capacitors, damage can occur if the capacitor is charged up enough to exceed the dielectric breakdown voltage. This can occur if sufficient charge is dumped into the component in an ESD event. Low value low voltage types will require less charge to exceed the breakdown voltage and so it is normally these that might be susceptible to damage. Low value MOS capacitors may be particularly prone to damage.

Many higher value capacitors are reasonably rugged from an ESD view and can largely be considered not susceptible to ESD under ordinary circumstances - especially if the y have high breakdown voltage.

Some types of resistor, such as some film resistors, my also be susceptible to ESD damage.

4 comments:

Inhaler Man said...

Hello;

Being an ESD Newbie, I seek to back step just a bit to obtain a clear list (or inventory if you will) of ESD sensitive parts that should be generically considered as important inclusions in any ESD program for control from the point they hit my receiving dock. Is there such an "industry" component list and if so, where may I find it? No sense reinventing the wheel. I can then glean the applicable to include on my list. Any help is greatly appreciated. Thank you!

Static Doctor said...

There is no list as far as I am aware. All semiconductor devices, and some other parts, are ESD susceptible to some extent. The question is, how sensitive are they? Unfortunately manufacturers often don't include that on the data sheet and it can be difficult to find out. There is some generic data in my on-line "ESD Guide" but real components will vary. The commonly used solution is to design your ESD prevention program to protect down to 100V HBM ESD withstand components which will cover most common ones. If you have some below 100V HBM then you may need special measures.

miles5150 said...

So if I have some surface mount caps delivered in non ESD safe packaging that are 25uf 25v that means they have a charge of 0.00025 coulomb which has got to be very ESD sensitive hasn't it??
Can you please advise? Thank you kindly.

Static Doctor said...

A 25microF 25V capacitor is to big to be ESD sensitive by the mechanism I am talking about. 250 microCoulombs is a very large amount of charge compared to most ESD which is measured in nanoCoulombes to microCoulombs. The maximum charge transferred is given by the product of voltage and capacitance. For example, a person of capacitance 150pF charged to 5kV would transfer up to 750nC of charge and theoretically threaten capacitors up to 1nF 750V, or 10nF 75V. A person of 100pF charged to 1000V would threaten 10nF capacitors up to 10V working voltage, or 1 nF up to 100V, or 10pF capacitors up 10kV working voltage. In practice capacitors may withstand voltages higher than their rated working voltage and their ESD withstand is greater than might be expected from this.