ESD Foam vs ESD Shielded Bag

ian field

Joined Oct 27, 2012
6,536
I read in another post that using ESD foam (in the context of protecting ICs from ESD) is "Not as good as a Faraday cage, but it will reduce the possibility of damage."
http://forum.allaboutcircuits.com/t...-for-logic-and-other-esd-sensitive-ics.57154/

If one has an IC inserted in ESD foam and a static event occurs (e.g. the ungrounded person touches a pin on the IC directly and zaps it), how does the ESD foam reduce the possibility of damage when compared to a ESD shielded bag (i.e. a Faraday cage) ?
The black foam is pretty conductive - you should breathe on devices so the humidity in your breath dissipates any static charges on the pins before pressing the pins into the foam - its suddenly discharging these charges that causes current spikes that do the damage.

The pink bags merely "discourage" static. the metalised polyester bags are better - but not as good as the thick black plastic anti static bags.
 

MCU88

Joined Mar 12, 2015
358
I read a book that claimed metal film resistors could be possible victims of ESD (Electro Static Discharge)

You really think? I store my parts neat and organized, but I have to admit that I pay little attention to ESD.
 

ian field

Joined Oct 27, 2012
6,536
I read a book that claimed metal film resistors could be possible victims of ESD (Electro Static Discharge)

You really think? I store my parts neat and organized, but I have to admit that I pay little attention to ESD.
The real "gotcha" is that parts can be merely "compromised" by an ESD event, they test OK before you use them - but can fail properly at some random time once in service. I'm pretty sure you'd need an awfully big ESD to damage a resistor though!

The danger zone is moving parts from one place to another, in transit they can get joggled about in their packaging - if its not anti-static packaging, that can generate charges. If you place a chip on a surface that grounds its pins, that will short any stray charges - that's what causes destructive current spikes.
 

MCU88

Joined Mar 12, 2015
358
The real "gotcha" is that parts can be merely "compromised" by an ESD event, they test OK before you use them - but can fail properly at some random time once in service.
That explains why some of my projects are an fail.

The danger zone is moving parts from one place to another, in transit they can get joggled about in their packaging - if its not anti-static packaging, that can generate charges. If you place a chip on a surface that grounds its pins, that will short any stray charges - that's what causes destructive current spikes.
A BIG retail outlet in Australia, the keep all CMOS devices on foam with an layer of tin foil, but with TTL they just throw them in the drawer...
 

ian field

Joined Oct 27, 2012
6,536
That explains why some of my projects are an fail.


A BIG retail outlet in Australia, the keep all CMOS devices on foam with an layer of tin foil, but with TTL they just throw them in the drawer...
Ironically; DTL can be more fragile than TTL, once I tried testing the input diodes on a DTL gate for leakage - the AVO8 I used has a 30V battery for the high Ohms range, apparently that's more than the breakdown voltage of DTL diodes.
 

cmartinez

Joined Jan 17, 2007
8,220
You're lucky. :rolleyes:
Static discharge damaging sensitive components is not BS.
Down where I live the weather is so humid that ESD is seldom a problem... though it can happen, of course. Anyway, I have hundreds of static-sensitive components stored in plastic containers that are not ESD protected and I've never had a problem... though I always take my precautions when I handle them and "touch ground" before I start to work.
I imagine that in places like Arizona or Nevada ESD must be a much bigger problem.
 

DickCappels

Joined Aug 21, 2008
10,152
The foil-on-foam trick is dangerous to parts. Since the foil is highly conductive (once the aluminum oxide is pierced or broken down) it allows high currents to flow from the pin of a charged device. The only safe ESD solutions are those that dissipate energy, such as that black foam (but look at what happens to component leads that have been in that stuff for 35 years!) and dissipative shield bags.
 

cmartinez

Joined Jan 17, 2007
8,220
The foil-on-foam trick is dangerous to parts. Since the foil is highly conductive (once the aluminum oxide is pierced or broken down) it allows high currents to flow from the pin of a charged device. The only safe ESD solutions are those that dissipate energy, such as that black foam (but look at what happens to component leads that have been in that stuff for 35 years!) and dissipative shield bags.
Interesting. Do you have any pictures of components that have been kept in black foam that long?
 

DickCappels

Joined Aug 21, 2008
10,152
It is a 1974 Solid State Scientific SCL4017. Note the bits of foam adhering to the pins. Not as obvious but visible is that the lower parts of the pins are tarnished.

1974-SSS-IC.jpg
 
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