Conducting Bench Top Material
Natural materials like wood, cotton, wool and even concrete have an
equilibrium
water content that changes with ambient relative humidity. This makes
these materials
conductive but not conductive enough to carry dangerous currents.
They are still good insulators
for mains voltage.
The textiles can change moisture content and conductivity quite
quickly
as they have fibre diameters of about 20 microns or so, but even at
20% RH static charges
dissipate in seconds. Plastics, however, tend to be very non-
conductive and charges
can be held for hours. Also, some plastics form electrets which stay
"charged" even under water.
A great insight to the static electricity problem came from articles
I read as a young boy in old (1910)
articles such as "make yourself an electrophorous" in popular science
mags.
A can lid was filled with melted resin. When solid it was rubbed with
wool. A metal
disk with insulated handle was placed on the resin and grounded with
a finger.
The disk was then lifted off the resin and would be found to have a
high charge (and voltage) on it.
(half inch fat spark to ground)
This process of induced charging and potential multiplication is the
danger on work benches.
The main way to overcome it is to have an isopotential environment
which naturally occurs with
natural materials where all charges rapidly drain away. Wood is good,
it does not produce charge
when rubbed and rapidly drains any charge away. And unless soaking
wet it will not electrocute you
if you are leaning on it when you touch and active power lead. (my
theory from experience is that
it is the ground that would kill you when if you were electrocuted.
If you have good soles on your shoes
and the other hand in your pocket an accidental touch to high voltage
is survivable)
just a few thoughts,
Neville Michie
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Bill Hawkins wrote:
My first job was in a blasting cap plant in 1960. There were
military devices so sensitive they could be set off by turning
on a nearby fluorescent desk lamp.
I learned that the human body has a capacitance of 400 pico F.
Getting up from a chair could raise a couple of kilovolts. We
walked on conductive rubber floors wearing conductive rubber
shoes. Bench tops were conductive rubber. Nobody had thought of
the wrist strap yet.
In those days, rubber was made conductive with carbon black. It
was almost as effective as a pencil at marking things. If the
anti-static material is not black, maybe it won't be a marking
hazard.
A megohm and 400 pF has a time constant of 400 microseconds, but
you do get the kilovolt spike. The wrist strap looks really good
as long as your motion is the only source of static electricity.
It keeps your body from ever reaching kilovolt potentials.
Your finger and hand makes a 700ps to 1 ns risetime device. Slew-rate
wise you can be up in several milions of V/us. The arm has sufficient
induction that it takes a considerable time before the body discharges,
but the hand creats the leader and then the big blow comes from the body
discharge. Just as a cloud and a ligthning bolt, but in man-size.
However, being ESD aware does not mean going maniac about it. It's more
like don't finger on things which is very hot. You need to build good
habits to avoid doing something bad.
Cheers,
Magnus
Lux, Jim (337C) wrote:
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of Bill Hawkins
I learned that the human body has a capacitance of 400 pico F.
Getting up from a chair could raise a couple of kilovolts. We
walked on conductive rubber floors wearing conductive rubber
shoes. Bench tops were conductive rubber. Nobody had thought of
the wrist strap yet.
If you're in and out of ESD areas, then shoes with conductive soles are easier to use than always wrist strapping. Ditto if you're working on something big where the cord for the wrist strap gets in the way. In some of our clean rooms, we have booties to go over your street shoes that have conductive coatings on them, and a conductive ribbon that you tuck into your sock to make contact. (And you go stand on a test pad to make sure, of course).
I like the conductive shoes approach, it's pretty screw up proof, because you don't have to remember to plug your wrist strap in when you come to the bench, but the floor needs to be conductive, too.
The first greeting a new collueage gets when comming first day to work
is "What shoesize are you?". We order ESD shoes for more or less
everyone. Our US sales-people is known to ask if it is real Birkenstock
shoes. :)
In those days, rubber was made conductive with carbon black. It
was almost as effective as a pencil at marking things. If the
anti-static material is not black, maybe it won't be a marking
hazard.
These days, the black bins are dissipative and not marking. The black foam is history (we all have ICs with corroded leads in the garage where the black foam turns to goo). Here at JPl, we don't use the pink bags/peanuts/stuff at all, because apparently, the coating can flake or rub off. We use plastic that has a very thin metalized layer, and I think that's pretty much industry standard now.
This is why you guys don't have a pink-day at the office! :)
You got to have a silly pink-day every once in a while just for the fun
of it. I'll see if not the HW department can adapt it, as they have
tried non-casual-friday (usual dress code is... um... casual).
A megohm and 400 pF has a time constant of 400 microseconds, but
you do get the kilovolt spike. The wrist strap looks really good
as long as your motion is the only source of static electricity.
It keeps your body from ever reaching kilovolt potentials.
And the megohm is important to keep you from inadvertently dying when you happen to accidentally contact the AC line.
There is a reason for EKG equipment being measured for isolation
properties. The medical staff wants to select the time and dosage of
larger currents through the heart, and preference is towards patients
that badly need it.
Cheers,
Magnus
Back about 1981, we had piles of 6502s, etc and decide to some "antistatic testing". We put a 40pin ZIF socket into a VIC-20, and then set about trying to fry the uP using carpet, a cat, car seats, etc. The DUT was then put back into the VIC and series of tests run to verify operation. I don't think we ever had a failure. Of course, there may have been some hiding that we missed, but all the static damage I've seen has been pretty severe.
That said, I always use a wrist strap and mat if I'm working on something I don't want to break further.
-Dave
----- Original Message -----
From: "Charles P. Steinmetz" charles_steinmetz@lavabit.com
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Monday, January 25, 2010 11:27:11 AM GMT -07:00 US/Canada Mountain
Subject: Re: [time-nuts] Conducting Bench Top Material
Bruce wrote:
Although over the years the non-conductive top has been an asset in
avoiding short circuits, etc., I am concerned about static discharges when
handling modern semiconductors. Would it make sense to spray the Masonite
with a weak copper sulphate or similar solution so as to make the masonite
slightly conductive, but not so conductive that 155 VAC connections
could not
safely rest upon it? Is there a better-suited material that could be used
to replace the Masonite?
I notice that many folks who have contributed on this thread use
anti-static benchtops, but I have never found it necessary (and I try
to keep the RH in my house under 45% -- it is generally 20% or less
in the winter). I've been fooling with static-sensitive parts for 35
years and haven't lost one to static yet. With that perspective, my
preferred benchtop is white Formica with a very, very slightly
pebbled surface. Very durable, including to molten solder, and small
parts show up well. I use rubberized "gunsmith" mats for preventing
scratches to delicate workpieces (these happen to be anti-static, but
that is not why I have them).
Other bench thoughts:
Bench depth is very important. I sometimes work on equipment that is
more than 24" deep, so I want at least 30" of clear space in front of
any obstructions (power strips, Variac, test equipment,
whatever). In the past, I used a "flying bridge" over the rear 18"
of a 48"-deep bench to elevate the test equipment, which worked very
well. Now I use 24" deep adjustable wire-rack shelving units behind
a 30" benchtop (As others have pointed out, you can do the same with
equipment racks -- I'm not a fan of rack-mounting test equipment
unless the racks are anchored and everything is on slides, which I
was not prepared to do). I don't have enough shop real estate to
have a permanent access aisle behind the test equipment, so the bench
and racks have large (5") locking polyurethane wheels and can be
pulled out relatively easily for reconfiguration. This provides
plenty of stability for electronic projects, but you wouldn't want to
mount a big vise on the bench and try to bend 1" rebar. For that, I
have a separate metalworking shop.
Bench height is also important. I prefer a tall bench, suited to
working standing or sitting on an ergonomic stool, so my bench top is
44" above the floor -- a bit below my standing elbow height.
Finally, one can never have too many power outlets, or too much
light, in a workshop. Lighting should be arranged so that it doesn't
cause specular reflections from the workpiece or the faces of test equipment.
Best regards,
Charles
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Hi
If you are manually loading up a wire bonder with conventional CMOS chips, ESD damage is a very real thing. You can haul the chip over to a SEM and actually take pictures of he craters you blast in it. Very cool pictures. No cat's, carpets, or Windhurst machines needed. Just normal operators with missing wrist straps will do the trick quite nicely.
Bob
On Jan 26, 2010, at 2:21 AM, d.seiter@comcast.net wrote:
Back about 1981, we had piles of 6502s, etc and decide to some "antistatic testing". We put a 40pin ZIF socket into a VIC-20, and then set about trying to fry the uP using carpet, a cat, car seats, etc. The DUT was then put back into the VIC and series of tests run to verify operation. I don't think we ever had a failure. Of course, there may have been some hiding that we missed, but all the static damage I've seen has been pretty severe.
That said, I always use a wrist strap and mat if I'm working on something I don't want to break further.
-Dave
----- Original Message -----
From: "Charles P. Steinmetz" charles_steinmetz@lavabit.com
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Monday, January 25, 2010 11:27:11 AM GMT -07:00 US/Canada Mountain
Subject: Re: [time-nuts] Conducting Bench Top Material
Bruce wrote:
Although over the years the non-conductive top has been an asset in
avoiding short circuits, etc., I am concerned about static discharges when
handling modern semiconductors. Would it make sense to spray the Masonite
with a weak copper sulphate or similar solution so as to make the masonite
slightly conductive, but not so conductive that 155 VAC connections
could not
safely rest upon it? Is there a better-suited material that could be used
to replace the Masonite?
I notice that many folks who have contributed on this thread use
anti-static benchtops, but I have never found it necessary (and I try
to keep the RH in my house under 45% -- it is generally 20% or less
in the winter). I've been fooling with static-sensitive parts for 35
years and haven't lost one to static yet. With that perspective, my
preferred benchtop is white Formica with a very, very slightly
pebbled surface. Very durable, including to molten solder, and small
parts show up well. I use rubberized "gunsmith" mats for preventing
scratches to delicate workpieces (these happen to be anti-static, but
that is not why I have them).
Other bench thoughts:
Bench depth is very important. I sometimes work on equipment that is
more than 24" deep, so I want at least 30" of clear space in front of
any obstructions (power strips, Variac, test equipment,
whatever). In the past, I used a "flying bridge" over the rear 18"
of a 48"-deep bench to elevate the test equipment, which worked very
well. Now I use 24" deep adjustable wire-rack shelving units behind
a 30" benchtop (As others have pointed out, you can do the same with
equipment racks -- I'm not a fan of rack-mounting test equipment
unless the racks are anchored and everything is on slides, which I
was not prepared to do). I don't have enough shop real estate to
have a permanent access aisle behind the test equipment, so the bench
and racks have large (5") locking polyurethane wheels and can be
pulled out relatively easily for reconfiguration. This provides
plenty of stability for electronic projects, but you wouldn't want to
mount a big vise on the bench and try to bend 1" rebar. For that, I
have a separate metalworking shop.
Bench height is also important. I prefer a tall bench, suited to
working standing or sitting on an ergonomic stool, so my bench top is
44" above the floor -- a bit below my standing elbow height.
Finally, one can never have too many power outlets, or too much
light, in a workshop. Lighting should be arranged so that it doesn't
cause specular reflections from the workpiece or the faces of test equipment.
Best regards,
Charles
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I am concerned about static discharges when
handling modern semiconductors.
These days it's not just semiconductors at risk given the tiny geometry of
passives. At work we had a work station where we assembled a board with
all passive components, so no thought was given to ESD control. We traced
a series of mysterious failures to ESD affecting the value of some
resistors. Now ESD control is just about everywhere!
-Joe Fitzgerald KM1P
Everything old is new again.
The 25+ year old HP Bench Brief that I referred to a few messages back
warns about that.
Ed
Joe Fitzgerald wrote:
I am concerned about static discharges when
handling modern semiconductors.
These days it's not just semiconductors at risk given the tiny geometry of
passives. At work we had a work station where we assembled a board with
all passive components, so no thought was given to ESD control. We traced
a series of mysterious failures to ESD affecting the value of some
resistors. Now ESD control is just about everywhere!
-Joe Fitzgerald KM1P
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Ed Palmer wrote:
Everything old is new again.
The 25+ year old HP Bench Brief that I referred to a few messages back
warns about that.
"Nothing usefull could be found in old documents, they just didn't have
the same technology as we have, and hence not the problems." Well, not
that much different. Scale is the main thing. People have been studying
all kinds of things, so good clues may still lay around if you dare look
for them.
Thanks for remembering this stuff.
Cheers,
Magnus
Hi
If you are manually loading up a wire bonder with conventional CMOS chips, ESD damage is a very real thing. You can haul the chip over to a SEM and actually take pictures of he craters you blast in it. Very cool pictures. No cat's, carpets, or Windhurst machines needed. Just normal operators with missing wrist straps will do the trick quite nicely.
Bob
On Jan 26, 2010, at 2:21 AM, d.seiter@comcast.net wrote:
Back about 1981, we had piles of 6502s, etc and decide to some "antistatic testing". We put a 40pin ZIF socket into a VIC-20, and then set about trying to fry the uP using carpet, a cat, car seats, etc. The DUT was then put back into the VIC and series of tests run to verify operation. I don't think we ever had a failure. Of course, there may have been some hiding that we missed, but all the static damage I've seen has been pretty severe.
That said, I always use a wrist strap and mat if I'm working on something I don't want to break further.
-Dave
----- Original Message -----
From: "Charles P. Steinmetz" charles_steinmetz@lavabit.com
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Monday, January 25, 2010 11:27:11 AM GMT -07:00 US/Canada Mountain
Subject: Re: [time-nuts] Conducting Bench Top Material
Bruce wrote:
Although over the years the non-conductive top has been an asset in
avoiding short circuits, etc., I am concerned about static discharges when
handling modern semiconductors. Would it make sense to spray the Masonite
with a weak copper sulphate or similar solution so as to make the masonite
slightly conductive, but not so conductive that 155 VAC connections
could not
safely rest upon it? Is there a better-suited material that could be used
to replace the Masonite?
I notice that many folks who have contributed on this thread use
anti-static benchtops, but I have never found it necessary (and I try
to keep the RH in my house under 45% -- it is generally 20% or less
in the winter). I've been fooling with static-sensitive parts for 35
years and haven't lost one to static yet. With that perspective, my
preferred benchtop is white Formica with a very, very slightly
pebbled surface. Very durable, including to molten solder, and small
parts show up well. I use rubberized "gunsmith" mats for preventing
scratches to delicate workpieces (these happen to be anti-static, but
that is not why I have them).
Other bench thoughts:
Bench depth is very important. I sometimes work on equipment that is
more than 24" deep, so I want at least 30" of clear space in front of
any obstructions (power strips, Variac, test equipment,
whatever). In the past, I used a "flying bridge" over the rear 18"
of a 48"-deep bench to elevate the test equipment, which worked very
well. Now I use 24" deep adjustable wire-rack shelving units behind
a 30" benchtop (As others have pointed out, you can do the same with
equipment racks -- I'm not a fan of rack-mounting test equipment
unless the racks are anchored and everything is on slides, which I
was not prepared to do). I don't have enough shop real estate to
have a permanent access aisle behind the test equipment, so the bench
and racks have large (5") locking polyurethane wheels and can be
pulled out relatively easily for reconfiguration. This provides
plenty of stability for electronic projects, but you wouldn't want to
mount a big vise on the bench and try to bend 1" rebar. For that, I
have a separate metalworking shop.
Bench height is also important. I prefer a tall bench, suited to
working standing or sitting on an ergonomic stool, so my bench top is
44" above the floor -- a bit below my standing elbow height.
Finally, one can never have too many power outlets, or too much
light, in a workshop. Lighting should be arranged so that it doesn't
cause specular reflections from the workpiece or the faces of test equipment.
Best regards,
Charles
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--
Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.
Steve wrote.
Wasn't life so much easier with valves (tubes)...
Amen brother.
Regards.
Max. K 4 O D S.
Email: max@maxsmusicplace.com
Transistor site http://www.funwithtransistors.net
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----- Original Message -----
From: "Steve Rooke" sar10538@gmail.com
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Wednesday, January 27, 2010 8:23 PM
Subject: Re: [time-nuts] Conducting Bench Top Material
Wasn't life so much easier with valves (tubes)...
:-)
Steve
2010/1/27 Bob Camp lists@cq.nu:
Hi
If you are manually loading up a wire bonder with conventional CMOS chips,
ESD damage is a very real thing. You can haul the chip over to a SEM and
actually take pictures of he craters you blast in it. Very cool pictures.
No cat's, carpets, or Windhurst machines needed. Just normal operators
with missing wrist straps will do the trick quite nicely.
Bob
On Jan 26, 2010, at 2:21 AM, d.seiter@comcast.net wrote:
Back about 1981, we had piles of 6502s, etc and decide to some
"antistatic testing". We put a 40pin ZIF socket into a VIC-20, and then
set about trying to fry the uP using carpet, a cat, car seats, etc. The
DUT was then put back into the VIC and series of tests run to verify
operation. I don't think we ever had a failure. Of course, there may have
been some hiding that we missed, but all the static damage I've seen has
been pretty severe.
That said, I always use a wrist strap and mat if I'm working on something
I don't want to break further.
-Dave
----- Original Message -----
From: "Charles P. Steinmetz" charles_steinmetz@lavabit.com
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Monday, January 25, 2010 11:27:11 AM GMT -07:00 US/Canada Mountain
Subject: Re: [time-nuts] Conducting Bench Top Material
Bruce wrote:
Although over the years the non-conductive top has been an asset in
avoiding short circuits, etc., I am concerned about static discharges
when
handling modern semiconductors. Would it make sense to spray the
Masonite
with a weak copper sulphate or similar solution so as to make the
masonite
slightly conductive, but not so conductive that 155 VAC connections
could not
safely rest upon it? Is there a better-suited material that could be
used
to replace the Masonite?
I notice that many folks who have contributed on this thread use
anti-static benchtops, but I have never found it necessary (and I try
to keep the RH in my house under 45% -- it is generally 20% or less
in the winter). I've been fooling with static-sensitive parts for 35
years and haven't lost one to static yet. With that perspective, my
preferred benchtop is white Formica with a very, very slightly
pebbled surface. Very durable, including to molten solder, and small
parts show up well. I use rubberized "gunsmith" mats for preventing
scratches to delicate workpieces (these happen to be anti-static, but
that is not why I have them).
Other bench thoughts:
Bench depth is very important. I sometimes work on equipment that is
more than 24" deep, so I want at least 30" of clear space in front of
any obstructions (power strips, Variac, test equipment,
whatever). In the past, I used a "flying bridge" over the rear 18"
of a 48"-deep bench to elevate the test equipment, which worked very
well. Now I use 24" deep adjustable wire-rack shelving units behind
a 30" benchtop (As others have pointed out, you can do the same with
equipment racks -- I'm not a fan of rack-mounting test equipment
unless the racks are anchored and everything is on slides, which I
was not prepared to do). I don't have enough shop real estate to
have a permanent access aisle behind the test equipment, so the bench
and racks have large (5") locking polyurethane wheels and can be
pulled out relatively easily for reconfiguration. This provides
plenty of stability for electronic projects, but you wouldn't want to
mount a big vise on the bench and try to bend 1" rebar. For that, I
have a separate metalworking shop.
Bench height is also important. I prefer a tall bench, suited to
working standing or sitting on an ergonomic stool, so my bench top is
44" above the floor -- a bit below my standing elbow height.
Finally, one can never have too many power outlets, or too much
light, in a workshop. Lighting should be arranged so that it doesn't
cause specular reflections from the workpiece or the faces of test
equipment.
Best regards,
Charles
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Steve Rooke - ZL3TUV & G8KVD
A man with one clock knows what time it is;
A man with two clocks is never quite sure.
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