ESD Mats and safe soldering of sensitive devices

[rwd...@gmail.com]

ESD Mats and safe soldering of sensitive devices.

I have a question regarding ESD Mats to reduce electrostatic damage while soldering. Amazon describe several of their mats as having a surface resistance of 106Ω-109Ω.

However both my mats show high resistance (infinite) if I put the probes of my multimeter to it.

What should I expect and is this normal?

I have not lost any components to static yet, but is that luck or good practice?

Cheers

Richard

[Tom Storey]

Ive never used an ESD mat, and rarely use an ESD strap, and never lost a component (yet?) either. So it could just be pure luck more than anything else.

I believe you should typically find that an ESD strap has a resistance of 1Mohm, and I would expect a mat to also be of a high resistance.

Dave from EEVblog did a video some time back on the resistance of ESD mats in relation to the effect on measurements, maybe that would help answer some questions?

https://www.youtube.com/watch?v=7FFrZl9ymFw

I would also think that such a low resistance would be a safety hazard.

--
You received this message because you are subscribed to the Google Groups "retro-comp" group.
To unsubscribe from this group and stop receiving emails from it, send an email to retro-comp+...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/retro-comp/51ebff61-0f51-4848-a165-cac3a509c001n%40googlegroups.com.

[Phillip Stevens]

Richard wrote:

I have not lost any components to static yet, but is that luck or good practice?

Possibly not scientific, but when I'm handling static sensitive components I tend to take off my shoes and socks and work barefoot.

Then my movement is not restricted by mats or straps, etc.

The human skin resistance is between 1000 ohm to 100 kohm, and this is enough to prevent static buildup.

Of course, not everyone enjoys the benign climate of Australia, where being barefoot is acceptable dress for most of the year.

P.

[rwd...@gmail.com]

Thanks guys, sounds like my mats are ok.

Phillip - Barefoot with all the poisonous snakes, spiders, Kookaburras that enjoy stealing a bit of meat (toe?) and the pain of dropping a chilled stubby on your foot? :) 

Richard

[Douglas Miller]

Richard, I know you are not a fan of excruciating and expensive debugging, so please ignore the ESD-deniers and use your mat and strap diligently, and make sure to use a solid electrical ground (e.g. a faucet is NOT grounded if the house is plumbed with plastic pipe!). You also may need to use hand lotion, to ensure good skin-conductivity. Air humidity makes a BIG difference, for example in my area the indoor humidity bottoms-out around 15% in the winter, and so lotion is imperative.

I invested in proper ESD equipment (although I didn't buy on Amazon... I used DigiKey... but that's just my own trust issues) and have never regretted it. I've seen enough real-life horror (that could only be traced back to ESD damage) "to make you up-chuck in your shorts" (John Ratzenberger, "House II").

[Kurt Pieper]

Hi,

that fits well.
I
I bought silicone mat, ESD tweezers, ESD brush last week.

I've been in the hobby since about 1975 and have never had a problem
with my boards. No static discharge.
In 2020-21 I populated many Z80 boards with backplan, CF card etc. There were about 30 boards. Everything without problems.

I always wear rubber shoes when soldering.

My apartment has floor tiles. It's good.

greeting

Kurt

[Alan Cox]

I have not lost any components to static yet, but is that luck or good practice?

Most of the components used in RC2014 are fairly large features and modern designs with good anti-static protection internally. It's still good practice to use anti-static mats and keep earthed but the risk is pretty low unless you are in an environment where static can build up easily or wear lots of static generating clothes.

Like a lot of people I normally just touch an earthed object regularly as I work on RC2014 stuff but I'm also in Wales so dry air and static build up from it are kind of rare 8)

I do have straps, mats and anti-static shirt for working on actual old machines because some of them can be very fragile.

RC2014 is a bit lax in general on these issues - there are no 74LS or similar buffers on the serial TTL lines for example.

Alan

[Douglas Miller]

One of the most insidious things about ESD is that most of the time the damage is not immediately obvious. You may be wounding the chip(s) and shortening their useful lifespan. Because of the small features used these days, it takes a very small amount of voltage to affect the chip - imperceptible by humans. It's really not worth the risk of causing mysterious, complex, failures later on. Granted, we're all just "hobbyists" here, but there are reasons the "big guys" invest so much in ESD protection and I prefer to emulate them when possible, within reason.

[Bill Shen]

I worked in arid New Mexico for 35 years on high-rel electronics so you can imagine ESD control was enforced even with TTL logic of 1970's.  ESD damages are seldom catastrophic immediately but will affect its long-term reliability.  Most devices have some levels of built-in ESD protection but the damages are there and sometimes subtle.  Measuring the quiescent current is a common way of detecting ESD damage.  I've seen enough electron microscope pictures of oxide ruptures to know ESD damages are real yet a gate with a big oxide punch through can still function amazingly well.

As a hobbyist I no longer don ESD suit or even ESD lab coat, but I have the life-long habit of touching earth ground as I getting up and sitting down.  I also wear cotton shirts and pants while working in the lab.  IMO, these basic precautions are adequate for retro technology.  Don't forget many of our parts are used and without chain of custody in ESD handling; furthermore our products are for hobbyists and we don't need a rocket ride to earth orbit to replace a defective box.
  Bill

[Owen Randle]

There's probably an issue with the typeface, and the 6 & 9 should have been superscrpt
So they meant 10^6 (1 Meg Ohm) to 10^9 (1000 Meg Ohm).

ESD mats do usually have quite-high resistances, as they are not designed to discharge things quickly - Just to stop static-charge build-up.
The leads also usually have a 1Meg safety resistance built-in, so that you don't get electrocuted if there's an earth fault, as you are meant to connect a wrist mat to the mat and that to mains-earth to be fully-effective against ESD.
ESD-damaged to IC's may not necessarily cause immediate damage, but multi ESD Zaps can cause premature failure.
So whilst a good idea for production / using expensive IC's, they may be a bit OTT for home use if just using old TTL and NMOS etc. IC's that didn't tend to be that sensitive  (Although SRAM's may be a bit more)  to ESD .

However, they do often make quite good soldering (even cutting) -mats / protection for table-tops.
Although many I've seen on Amazon are quite small A4-size, rather than the full bench-area size true ESD mats, that have the special connectors at the corners).

Note: The black most-conductive side goes underneath. And the rubberised top surface will measure a much higher resistance.
And even with the proper ESD Testing-tools,. may need some ESD-spray to get a 'Pass'

[Alan Cox]

Related question - on old PC cards in particular there are often very small (47pf or so) capacitors to ground on all the I/O lines that are exposed from the case. Am I right in assuming that's also for static protection in part ?

Alan

[Owen Randle]

No, those 47pF capacitors will most-likely be for ElectroMagnetic Compatibility (EMC) -Compliance reasons, to help prevent Radio Frequency Interferrence (RFI) from fast-edges on the various signal lines. The extra -capacitance will reduce the slew-rate / rise-time of these a bit, lessening the harmonics to a degree.

Although capacitance can sometimes also help to prevent high voltage-transients occurring 
- But can sometimes resonate with wiring inductances and cause input-transients. It all depends on the values, and whether there is any damping resistances.
So ESD-clamp / steering rail-to-rail diodes are the more usual ESD-protection methods.

[horus falcon]

You'll hear these referred to as "bypass capacitors".  They are more about signal conditioning during operation, (they are usually in circuit around a resistive load to bypass any AC component to ground),  Static electricity is usually a high-potential DC voltage.  After they charge, capacitors present a high impedance to DC signals.  I wouldn't think they would aid much in static protection.

I could be wrong, but that's what I remember of the basic theory.

Respectfully,
David

On 3/20/22 10:42, Alan Cox wrote:

Related question - on old PC cards in particular there are often very small (47pf or so) capacitors to ground on all the I/O lines that are exposed from the case. Am I right in assuming that's also for static protection in part ?

Alan

--
You received this message because you are subscribed to the Google Groups "retro-comp" group.
To unsubscribe from this group and stop receiving emails from it, send an email to retro-comp+...@googlegroups.com.

To view this discussion on the web visit https://groups.google.com/d/msgid/retro-comp/CAK9X0%2Buy_OH4hL59j7DWS%2BLTqGX8hS8cjzERc8bNDMLCDA9RnQ%40mail.gmail.com.

[fixit9660]

I have to heartily endorse Doug Millers comments: I worked for BT in the 80's repairing computers, switched mode power supplies, and fairly high power radio transmitters. We had it drummed into us that ESD kills components. They spent tens of millions of pounds outfitting all the repair centres, stores, and every engineer with ESD work stations and all the staff had to undergo training courses on it's use. They didn't take it lightly and I still don't. "Walking wounded", devices that are damaged but still appear to work okay, are the worst as they have unpredictable lifespans and operational reliability. It's your choice, but when that module misbehaves intermittently, or your system takes a dive for an unknown reason, just think about how all of your devices and card assemblies entire lives to date have been treated. It only takes one unprotected handling to do the damage.