Microcontrollers exposed to X-Ray Beam

[Steve Moulding]

Anyone on the list have experience / knowledge of using PIC microcontrollers
which may be exposed to X-ray beams?  A customer has an application for use
in radiation therapy rooms, and the electronics package will occasionally be
in the path of the therapy beam during patient exposure; due to the nature
of the package, this is unavoidable.  The question is: will this eventually
cause the electronics - specifically the microcontrollers - to fail?  Some
empirical testing done Saturday in a Cancer Center showed that the
microcontrollers will eventually fail, but only after extended exposure -
approx. 1 1/2 hours in a continuous beam, something that will not happen
with a patient.  If the package is exposed intermittently, will the
radiation effects be cumulative?  Tried Microchip & Google with very little
useful info uncovered.  Thanks,
Steve



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[David VanHorn-2]

Google on radfet.

It seems that the nature of FETs is to take cumulative damage to the
gate that shows up as a shift in Vth.  This effect can be enhanced,
but it looks like it's present in all fets to some degree.
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[Steve Moulding]

Thanks David.  I found some good information that will be helpful.
Steve


David VanHorn wrote:
> Google on radfet.
>
> It seems that the nature of FETs is to take cumulative damage to the
> gate that shows up as a shift in Vth.  This effect can be enhanced,
> but it looks like it's present in all fets to some degree.



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[Spehro Pefhany]

Quoting Steve Moulding <fti1983@...>:

> Anyone on the list have experience / knowledge of using PIC microcontrollers
> which may be exposed to X-ray beams?  A customer has an application for use
> in radiation therapy rooms, and the electronics package will occasionally be
> in the path of the therapy beam during patient exposure; due to the nature
> of the package, this is unavoidable.  The question is: will this eventually
> cause the electronics - specifically the microcontrollers - to fail?  Some
> empirical testing done Saturday in a Cancer Center showed that the
> microcontrollers will eventually fail, but only after extended exposure -
> approx. 1 1/2 hours in a continuous beam, something that will not happen
> with a patient.  If the package is exposed intermittently, will the
> radiation effects be cumulative?  Tried Microchip & Google with very little
> useful info uncovered.  Thanks,
> Steve

I would expect any problems to be in program memory retention. Maybe you
should socket the chips and then if replacement or reprogramming turns out
to be required it won't be fatal.

Ionizing radiation will eventually cause threshold shifts and changes in
analog parameters, as well as increases in leakage current. You may find
contemporary information on this sort of thing hard to come by- rad-hard
technology is considered military (or dual-use) by some nations, and
suppling information that can be misused is subject to rather severe  
penalties.

Best regards,
Spehro Pefhany
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s...@...             Info for manufacturers: http://www.trexon.com
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[Mike Harrison]

On Mon, 05 May 2008 12:10:38 -0400, you wrote:

>Quoting Steve Moulding <fti1983@...>:
>
>> Anyone on the list have experience / knowledge of using PIC microcontrollers
>> which may be exposed to X-ray beams?  A customer has an application for use
>> in radiation therapy rooms, and the electronics package will occasionally be
>> in the path of the therapy beam during patient exposure; due to the nature
>> of the package, this is unavoidable.  The question is: will this eventually
>> cause the electronics - specifically the microcontrollers - to fail?  Some
>> empirical testing done Saturday in a Cancer Center showed that the
>> microcontrollers will eventually fail, but only after extended exposure -
>> approx. 1 1/2 hours in a continuous beam, something that will not happen
>> with a patient.  If the package is exposed intermittently, will the
>> radiation effects be cumulative?  Tried Microchip & Google with very little
>> useful info uncovered.  Thanks,
>> Steve

If things only ahppen after extended exposure, it is reasonable to assume there is a cumulative
effect.
You should certainly implement checks on program memory & eeprom integrity, but the primary defence
should be lead shielding to avoid the exposure in the first place. I'd think that even a relatively
small thickness would provide a substantial improvement over nothing.
You may also want to look at reducing expiosure by suitable orientation - if you can arrange the
electronics to be side-on instead of face-on to the beam, this will reduce the effective dose
substantially.


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[piclist-7]

So I read up on ESD and a few people stress that you do not actually want
conductive storage like those foil bags or black plastic boxes.

It makes sense.  If I have an open box with a part inside, and I reach in
and touch a lead, any static charge on me can go through the chip, into
the box and ground out.  A non-conductive box would not do that.  Of
course grounding yourself before touching anything is better, but mistakes
happen.

One solution I found and wanted an opinion on was from this page:

  http://wiki.xtronics.com/index.php/ESD

  (Hot tip: use an anti-static floor-wax on your plastics and you
  shouldn't have to ever treat them again! Just dip your plastic bins and
  trays in. Then let them drip drain and dry. Think of the antistatic
  floor wax as an almost permanent spray.
  see http://www.rdmoney.com/floor_finish.htm).

Anyone tried this?  I have a lot of storage boxes I use for resistors,
caps and other non transistor based parts, but chips and various bits
find their way into them.  The storage containers rub against each other
and can form a nice static charge by themselves and reaching in for a part
can zap it.  But ESD containers are hard to find and expensive.

If nobody has tried it, I might just grab some of the stuff mentioned in
that link and try it out on a box or two.

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Ian Smith
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[Jon Chandler]

Google "radiation-hardened electronics" and you should find some good
info.  Wikipedia for example has a good discussion of the effects of
radiation.

Jon



Steve Moulding wrote:

> Anyone on the list have experience / knowledge of using PIC microcontrollers
> which may be exposed to X-ray beams?  A customer has an application for use
> in radiation therapy rooms, and the electronics package will occasionally be
> in the path of the therapy beam during patient exposure; due to the nature
> of the package, this is unavoidable.  The question is: will this eventually
> cause the electronics - specifically the microcontrollers - to fail?  Some
> empirical testing done Saturday in a Cancer Center showed that the
> microcontrollers will eventually fail, but only after extended exposure -
> approx. 1 1/2 hours in a continuous beam, something that will not happen
> with a patient.  If the package is exposed intermittently, will the
> radiation effects be cumulative?  Tried Microchip & Google with very little
> useful info uncovered.  Thanks,
> Steve
>
>
>
>  

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[Howard Winter]

Steve,

Just a single point of data: I recently received a pre-programmed 18F252 by post from the 'States, and I found that all of its memory above a certain point was
erased.  It was apparently tested by the sender before despatch and found to be OK, and it re-programmed successfully when I tried that.

The only think I can think would have affected it is being X-Rayed on the journey - being in a package with a lot of electronic parts, I imagine it would have been
"looked" at very closely, so may have had a higher dose than usual.  X-Rays would have the same effect as exposing an EPROM to UV - it "leaks" away the charges
that are how the information is stored.  As you can't predict which of the program's bytes will be erased first, it could produce some very strange behaviour.

Can you not put some lead over the centre of the package, to protect the chip from X-Rays?

Cheers,


Howard Winter
St.Albans, England


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[MicroControllers - PIC mailing list]

In message <Pine.LNX.4.64.0805051308510.2116@...>,
piclist@... writes
>So I read up on ESD and a few people stress that you do not actually want
>conductive storage like those foil bags or black plastic boxes.
I'd rather have them than not thanks. I like to be as certain as I can
that the components work when I put them into a circuit.
>
>It makes sense.
No it doesn't. There's a reason why there are only a *few* people who
stress that whilst the majority say you should have dissipative or
conductive storage.
> If I have an open box with a part inside, and I reach in
>and touch a lead, any static charge on me can go through the chip, into
>the box and ground out.
The whole point  of ESD protection is that you have no static charge
when you touch a component and neither does the component. Remember,
static will damage components if it discharges from you or to you though
the component.
>  Of
>course grounding yourself before touching anything is better, but mistakes
>happen.
Of course you are correct that mistakes happen but the chances of
killing things with static is much higher if you don't store them
correctly.
>
>  (Hot tip: use an anti-static floor-wax on your plastics and you
>  shouldn't have to ever treat them again! Just dip your plastic bins and
>  trays in. Then let them drip drain and dry. Think of the antistatic
>  floor wax as an almost permanent spray.
>  see http://www.rdmoney.com/floor_finish.htm).
How are you going to prove it works though? More to the point, how are
you going to prove it's still working if it ever did? Will you be
keeping a tally of dead devices and waiting for the number to rise?
If it's business use then just buy the correct stuff providing you have
the cash flow, if not, get creative until you do.

If it's home use, any decent component supplier should use proper ESD
packaging so leave the stuff in that until you use it and re-use the
better quality packaging to build yourself a storage system.
>
>--
>Ian Smith

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[Jinx-4]

> Can you not put some lead over the centre of the package, to
> protect the chip from X-Rays?

That's what I was thinking, and the obvious first line of defence

"Recommended Thickness of Lead Shielding for X-Ray Rooms"

Tables -

http://www.alchemycastings.com/lead-products/sheet.htm

A doctor says -

http://hps.org/publicinformation/ate/q44.html

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[Spehro Pefhany]

Quoting Jinx <joecolquitt@...>:

>> Can you not put some lead over the centre of the package, to
>> protect the chip from X-Rays?
>
> That's what I was thinking, and the obvious first line of defence
>
> "Recommended Thickness of Lead Shielding for X-Ray Rooms"
>
> Tables -
>
> http://www.alchemycastings.com/lead-products/sheet.htm
>
> A doctor says -
>
> http://hps.org/publicinformation/ate/q44.html

I might suggest tungsten (or gold) as somewhat slightly less effective  
(for a given thickness), but RoHS-compliant alternatives. ;-)

Best regards,
Spehro Pefhany
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s...@...             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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[Jinx-4]

> I might suggest tungsten (or gold) as somewhat slightly less effective  
> (for a given thickness), but RoHS-compliant alternatives. ;-)

fffffppp, RoHS. Why not just give the PIC victim counselling and
post-trauma support. It'll bounce back like a good'un, fitter than
ever

Where's good old lead paint when you need it

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[William "Chops" Westfield]

On May 5, 2008, at 1:08 PM, Howard Winter wrote:
> X-Rays would have the same effect as exposing an EPROM to UV - it
> "leaks" away the charges that are how the information is stored.

Except that people who WANTED to use X-rays to erase OTP parts found  
that it didn't work.  As the argument went, silicon is very  
transparent to X-rays...  I don't recall ever seeing any actual  
quantitative experiments or even deep theory, but there were people  
who had actually tried it as an erasure technique and had it not work.

BillW

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[Brendan Gillatt]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

piclist@... wrote:
> So I read up on ESD and a few people stress that you do not actually want
> conductive storage like those foil bags or black plastic boxes.
>
> It makes sense.  If I have an open box with a part inside, and I reach in
> and touch a lead, any static charge on me can go through the chip, into
> the box and ground out.  A non-conductive box would not do that.  Of
> course grounding yourself before touching anything is better, but mistakes
> happen.

There are two reasons for the conductive boxes: firstly so that charge
does not accumulate inside capacitors, and also so that when you reach
inside the box the potential between the fingers is shorted as they touch
the sides.

An insulating box would leave the charge on the fingers and let the
chip's FET's 'absorb' the shock.

'Designers have figured out that it takes a spark to have ESD, so modern
electronic products now have their conductive shielding layers buried in
insulating plastic.' The last chip I topped certainly did not have a
'conductive shielding layer'.'

'The volume conductive plastic, instead of protecting, can actually
produce ESD. The black volume conductive acts as one of the conductors
from our list of requirements to produce ESD!'

So what's the difference between touching the component with a
(conductive) finger or (electrically) touching it with a finger via a a
bit of conductive plastic?

'The parts leads can act as the other conductor.'

Exactly as it would if you were to touch the part with a finger.

I could go on...

I would be wary of that article - it is full of speculation and fairly
confused logic.

- --
Brendan Gillatt | GPG Key: 0xBF6A0D94
brendan {a} brendangillatt (dot) co (dot) uk
http://www.brendangillatt.co.uk
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[Sean Breheny]

Hi Ian,

I've seen four categories for static characteristics:

1) Insulating - able to generate charge
2) Insulating - unable to generate charge
3) Dissipative
4) Conductive

An example of #1 would be a plastic shopping bag. #2 would be the pink
ESD bubblewrap
#3 would be ESD foam or carbon-filled plastic. #4 would be metal or
high-carbon content plastic.

Generally, #1 should be kept away from ESD sensitive components at all
times. #2 is acceptable when necessary. #3 is the generally preferred
environment for handling. #4 is necessary in some conditions for
storage and transport.

The distinction between #1 and #2 is that #1 is likely to generate a
charge difference when rubbed against either itself or other common
materials. #2 must not do so. #3 must have a resistance of something
like between 10^9 and 10^6 ohms per unit (ohms per square for a
surface coating, straight ohms for a single wire connection). #4 is
anything more conductive than this.

#3 (dissipative) allows charge to bleed off slowly so that it cannot
accumulate or be deposited AND so that it will not suddenly discharge
(like you said). This is why it is best for handling.

#4 can act as shielding. Generally, it is necessary to protect against
not only an actual discharge but also a high E field. Keeping
components inside a shielded container while in storage and transport
allows them to survive being brought near very strong E fields (like
you might find around plastic bags or dry cardboard)

Most of the conductive ESD bags I've seen are actually THREE layers.
The inside and outside are coated in a dissipative material.
in-between is a layer of metal (so thin that you can still see through
it). The dissipative material prevents the bag from making things
worse (by a sudden discharge) and the inner metal forms a pseudo
Faraday cage.

I was under the impression that the black-coated cardboard (like
corstat) is dissipative, not conductive. It is easy to check with an
ohmmeter. Dissipative should show basically no conductivity on most
meters (do not touch the metal probes with your skin - that is
conductive).

So, my understanding of general ESD precautions is this: Components
should be directly packaged in dissipative materials (like ESD plastic
or foam). This, along with an ESD workstation, is best for at-bench
handling. However, whenever components or boards need to leave the
bench (for storage or transport), they should be put in a three-layer
bag (dissipative-conductive-dissipative), and may also still be in
their dissipative plastic or foam. Finally, any packing material used
along with the devices should be either dissipative or non charge
generating (category #2).

Sean


On Mon, May 5, 2008 at 1:18 PM,  <piclist@...> wrote:

> So I read up on ESD and a few people stress that you do not actually want
>  conductive storage like those foil bags or black plastic boxes.
>
>  It makes sense.  If I have an open box with a part inside, and I reach in
>  and touch a lead, any static charge on me can go through the chip, into
>  the box and ground out.  A non-conductive box would not do that.  Of
>  course grounding yourself before touching anything is better, but mistakes
>  happen.
>
>  One solution I found and wanted an opinion on was from this page:
>
>   http://wiki.xtronics.com/index.php/ESD
>
>   (Hot tip: use an anti-static floor-wax on your plastics and you
>   shouldn't have to ever treat them again! Just dip your plastic bins and
>   trays in. Then let them drip drain and dry. Think of the antistatic
>   floor wax as an almost permanent spray.
>   see http://www.rdmoney.com/floor_finish.htm).
>
>  Anyone tried this?  I have a lot of storage boxes I use for resistors,
>  caps and other non transistor based parts, but chips and various bits
>  find their way into them.  The storage containers rub against each other
>  and can form a nice static charge by themselves and reaching in for a part
>  can zap it.  But ESD containers are hard to find and expensive.
>
>  If nobody has tried it, I might just grab some of the stuff mentioned in
>  that link and try it out on a box or two.
>
>  --
>  Ian Smith
>  --
>  http://www.piclist.com PIC/SX FAQ & list archive
>  View/change your membership options at
>  http://mailman.mit.edu/mailman/listinfo/piclist
>

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[Jinx-4]

> use X-rays to erase OTP parts found that it didn't work

Googled for erase otp x-rays

The experience here

http://www.classiccmp.org/pipermail/cctech/2003-January/008750.html

is that

"X-rays will erase the part at high energy levels, but this will
also  degrade the part to the point where it will fail soon, or
die during erasure"

and

"This subject has been discussed on sci.electronics multiple
times in the past, and the consensus was that the frequency of
Xrays is such that they have no direct effect on the stored data.
But at very high exposures it is definitely possible to damage
the part"


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[Sergey Dryga-2]

Spehro Pefhany <speff <at> interlog.com> writes:

>
> Quoting Jinx <joecolquitt <at> clear.net.nz>:
>
> >> Can you not put some lead over the centre of the package, to
> >> protect the chip from X-Rays?
> >
> > That's what I was thinking, and the obvious first line of defence
> >
> > "Recommended Thickness of Lead Shielding for X-Ray Rooms"
> >
> > Tables -
> >
> > http://www.alchemycastings.com/lead-products/sheet.htm
> >
> > A doctor says -
> >
> > http://hps.org/publicinformation/ate/q44.html
>
> I might suggest tungsten (or gold) as somewhat slightly less effective  
> (for a given thickness), but RoHS-compliant alternatives.
>
> Best regards,
> Spehro Pefhany

Clear acrylic shielding is often used for radiation protection in research labs.
 Depending on energy that might be an option.  Some plastics are "fortified"
with lead to increase protection.  Example is here:
http://www.vwrsp.com/catalog/product/index.cgi?catalog_number=66001-124&inE=1&highlight=66001-124

Hope this helps,

Sergy Dryga

http://beaglerobotics.com



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[Apptech]

> So I read up on ESD and a few people stress that you do
> not actually want
> conductive storage like those foil bags or black plastic
> boxes.


I do the following in some instances.
YMMV.

- Whiff plastic boxes with Zinc electrostatic screening
spray - intended to provide capacitive shielding for plastic
enclosures. A very light layer will provide an ugly speckled
incomplete paint finish that will allow charge to equalise
over container. Available in spray cans. Degree of
conductivity will be controlled within reason by coating
thickness. A little goes a long way.

- Place a sheet of butyl rubber (as used for eg waterproof
roofing and similar) under plastic trays. This is variably
conductive due (I think) to the carbon black loading used in
its manufacture. Two meter probes stuck into surface produce
readings of low k-ohms to megohms, variable by product
source. (This resistance is (ABOUT) the same regardless of
probe separation due to "resistance per square"
effect).Probes laid lightly on surface tend to show high