Very high value resistors

[Chris]

It seems there are resistors around in the range of 50Gohm! Having never
encountered anything beyond 10M., I never imagined there could be such a
stratospheric value but apparently there is:


http://www.ebay.co.uk/itm/HR1206F-50G5I-WELWYN-RESISTOR-HIGH-
VALUE-50G-25-/390983897740?hash=item5b0874d28c:g:LH0AAOSwaNBUcjx6


What on God's good earth would these possibly be used for?

 

[Jim Thompson]

On Sun, 3 Apr 2016 16:28:35 -0000 (UTC), Chris <cbx@noreply.com>
wrote:

It seems there are resistors around in the range of 50Gohm! Having never
encountered anything beyond 10M., I never imagined there could be such a
stratospheric value but apparently there is:


http://www.ebay.co.uk/itm/HR1206F-50G5I-WELWYN-RESISTOR-HIGH-
VALUE-50G-25-/390983897740?hash=item5b0874d28c:g:LH0AAOSwaNBUcjx6


What on God's good earth would these possibly be used for?

Imaginary currents >:-}

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

The touchstone of liberalism is intolerance

 

[John Larkin]

On Sun, 3 Apr 2016 16:28:35 -0000 (UTC), Chris <cbx@noreply.com>
wrote:

It seems there are resistors around in the range of 50Gohm! Having never
encountered anything beyond 10M., I never imagined there could be such a
stratospheric value but apparently there is:


http://www.ebay.co.uk/itm/HR1206F-50G5I-WELWYN-RESISTOR-HIGH-
VALUE-50G-25-/390983897740?hash=item5b0874d28c:g:LH0AAOSwaNBUcjx6


What on God's good earth would these possibly be used for?

I have some sample surface-mount 1T resistors.

My old Keithley will measure up to 1e14 ohms.

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Welwyn_1G_Keithley.jpg


High-value resistors are useful in photodiode circuits, high-voltage
dividers, leakage measurements, femtoammeters, all sorts of stuff.

A 1G or 10G radial resistor makes a cheap high-voltage probe for a
DVM.

http://www.digikey.com/product-detail/en/ohmite/SM104031007JE/SM104JE-1000M-ND/824191



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Ralph Mowery]

"Chris" <cbx@noreply.com> wrote in message
news:ndrgbj$tt0$6@dont-email.me...

It seems there are resistors around in the range of 50Gohm! Having never
encountered anything beyond 10M., I never imagined there could be such a
stratospheric value but apparently there is:


http://www.ebay.co.uk/itm/HR1206F-50G5I-WELWYN-RESISTOR-HIGH-
VALUE-50G-25-/390983897740?hash=item5b0874d28c:g:LH0AAOSwaNBUcjx6


What on God's good earth would these possibly be used for?

I don't recall the values but at work there was some equipment that used
them They were in part of an amplifier for a radiation detector similar to
a very large geiger counter. It used a detector with a 4 foot long tube.

 

[Ian Field]

"Chris" <cbx@noreply.com> wrote in message
news:ndrgbj$tt0$6@dont-email.me...

It seems there are resistors around in the range of 50Gohm! Having never
encountered anything beyond 10M., I never imagined there could be such a
stratospheric value but apparently there is:

There's a small stash of 100M resistors in my collection.

For anything in the G Ohm range - you should probably check the leakage
resistance of whatever PCB/substrate you're mounting it on.

At the very least, you'll need guard slots cut in any PCB around the
termination points.

 

[Cursitor Doom]

On Sun, 03 Apr 2016 16:10:38 -0700, John Larkin wrote:

[...]

It's pinning the needle on the 1e14 ohm range.

1G is easy. Just don't use water soluble flux, or if you do, clean it
really good.

Nice to see these wonderful old vintage instruments still in use outside
of ham circles. What's it like accuracy wise?

 

[Phil Hobbs]

On 04/03/2016 01:49 PM, John Larkin wrote:

On Sun, 3 Apr 2016 16:28:35 -0000 (UTC), Chris <cbx@noreply.com
wrote:

It seems there are resistors around in the range of 50Gohm! Having never
encountered anything beyond 10M., I never imagined there could be such a
stratospheric value but apparently there is:


http://www.ebay.co.uk/itm/HR1206F-50G5I-WELWYN-RESISTOR-HIGH-
VALUE-50G-25-/390983897740?hash=item5b0874d28c:g:LH0AAOSwaNBUcjx6


What on God's good earth would these possibly be used for?

I have some sample surface-mount 1T resistors.

My old Keithley will measure up to 1e14 ohms.

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Welwyn_1G_Keithley.jpg


High-value resistors are useful in photodiode circuits, high-voltage
dividers, leakage measurements, femtoammeters, all sorts of stuff.

Yup. A couple of years back, I did a front end for a surface potential
tool for semiconductor measurements that had switchable 1G and 50G
feedback resistors.

There are lots of subtleties in a circuit like that--I had to bootstrap
the coil of the latching relay, and switch it with another (nonlatching)
relay. Also the 1G resistor had to be shorted out when the circuit was
in the 50G mode, because otherwise its current noise would have gone
straight through the capacitance of the open relay contacts (~0.2 pF)
and trashed the measurement.

And, of course, you have to fix up the ridiculous RC rolloff in the
second stage.

The good news about that is that the intrinsic SNR of the measurement
isn't that good, so the RC can roll off a pretty long way before the
second stage's noise becomes important. That's true of high-Z
measurements in general.

The customer (Qcept Technologies) ran out of dough last summer and had
to shut its doors with a bang. A pity--they made good stuff.

Cheers

Phil Hobbs

 

[John Larkin]

On Sun, 3 Apr 2016 16:16:10 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 04/03/2016 01:49 PM, John Larkin wrote:
On Sun, 3 Apr 2016 16:28:35 -0000 (UTC), Chris <cbx@noreply.com
wrote:

It seems there are resistors around in the range of 50Gohm! Having never
encountered anything beyond 10M., I never imagined there could be such a
stratospheric value but apparently there is:


http://www.ebay.co.uk/itm/HR1206F-50G5I-WELWYN-RESISTOR-HIGH-
VALUE-50G-25-/390983897740?hash=item5b0874d28c:g:LH0AAOSwaNBUcjx6


What on God's good earth would these possibly be used for?

I have some sample surface-mount 1T resistors.

My old Keithley will measure up to 1e14 ohms.

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Welwyn_1G_Keithley.jpg


High-value resistors are useful in photodiode circuits, high-voltage
dividers, leakage measurements, femtoammeters, all sorts of stuff.

Yup. A couple of years back, I did a front end for a surface potential
tool for semiconductor measurements that had switchable 1G and 50G
feedback resistors.

There are lots of subtleties in a circuit like that--I had to bootstrap
the coil of the latching relay, and switch it with another (nonlatching)
relay. Also the 1G resistor had to be shorted out when the circuit was
in the 50G mode, because otherwise its current noise would have gone
straight through the capacitance of the open relay contacts (~0.2 pF)
and trashed the measurement.

And, of course, you have to fix up the ridiculous RC rolloff in the
second stage.

The good news about that is that the intrinsic SNR of the measurement
isn't that good, so the RC can roll off a pretty long way before the
second stage's noise becomes important. That's true of high-Z
measurements in general.

The customer (Qcept Technologies) ran out of dough last summer and had
to shut its doors with a bang. A pity--they made good stuff.

Cheers

Phil Hobbs

Yikes, 50 big ones:

http://www.bizjournals.com/atlanta/blog/atlantech/2015/06/50-million-later-atlanta-startup-qcept.html

That happened in the big .com bust here. The landlord or the cleaners
or somebody came by and everyone was gone.

It's gonna happen again.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Sun, 3 Apr 2016 20:07:14 +0100, "Ian Field"
<gangprobing.alien@ntlworld.com> wrote:

"Chris" <cbx@noreply.com> wrote in message
news:ndrgbj$tt0$6@dont-email.me...
It seems there are resistors around in the range of 50Gohm! Having never
encountered anything beyond 10M., I never imagined there could be such a
stratospheric value but apparently there is:

There's a small stash of 100M resistors in my collection.

For anything in the G Ohm range - you should probably check the leakage
resistance of whatever PCB/substrate you're mounting it on.

At the very least, you'll need guard slots cut in any PCB around the
termination points.

Here's a small PCB deliberately glopped with rosin flux and
fingerprints.

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Gloppy_Flux.JPG

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Test.JPG


It's pinning the needle on the 1e14 ohm range.

1G is easy. Just don't use water soluble flux, or if you do, clean it
really good.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[George Herold]

On Sunday, April 3, 2016 at 7:10:39 PM UTC-4, John Larkin wrote:

On Sun, 3 Apr 2016 20:07:14 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:



"Chris" <cbx@noreply.com> wrote in message
news:ndrgbj$tt0$6@dont-email.me...
It seems there are resistors around in the range of 50Gohm! Having never
encountered anything beyond 10M., I never imagined there could be such a
stratospheric value but apparently there is:

There's a small stash of 100M resistors in my collection.

For anything in the G Ohm range - you should probably check the leakage
resistance of whatever PCB/substrate you're mounting it on.

At the very least, you'll need guard slots cut in any PCB around the
termination points.

Here's a small PCB deliberately glopped with rosin flux and
fingerprints.

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Gloppy_Flux.JPG

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Test.JPG


It's pinning the needle on the 1e14 ohm range.

1G is easy. Just don't use water soluble flux, or if you do, clean it
really good.

I've got this "worry" in the back of my head that the leakage won't be linear with voltage. It would be fun to see pcb with rosin flux leakage at
1V, 3V, 10V, 30V, 100V....

George H.

--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Bob Masta]

On Sun, 03 Apr 2016 16:10:38 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Sun, 3 Apr 2016 20:07:14 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:



"Chris" <cbx@noreply.com> wrote in message
news:ndrgbj$tt0$6@dont-email.me...
It seems there are resistors around in the range of 50Gohm! Having never
encountered anything beyond 10M., I never imagined there could be such a
stratospheric value but apparently there is:

There's a small stash of 100M resistors in my collection.

For anything in the G Ohm range - you should probably check the leakage
resistance of whatever PCB/substrate you're mounting it on.

At the very least, you'll need guard slots cut in any PCB around the
termination points.

Here's a small PCB deliberately glopped with rosin flux and
fingerprints.

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Gloppy_Flux.JPG

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Test.JPG


It's pinning the needle on the 1e14 ohm range.

1G is easy. Just don't use water soluble flux, or if you do, clean it
really good.

Been a long time since I used anything in the 100 Meg range
or above, but I recall that there were a lot of recommended
precautions. One was to clean the glass body very carefully
(with alcohol, I think) to remove fingerprints which would
otherwise trap dust, which would then allow humidity to
cause a low-resistance shunt. You also want the body to be
elevated above the board surface for the same reason. I
also seem to recall something about teflon
mounts/feedthroughs at the lead ends, but I can't recall
exactly what that was supposed to do.

Best regards,


Bob Masta

DAQARTA v9.10
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, Pitch Track, Pitch-to-MIDI
FREE 8-channel Signal Generator, DaqMusiq generator
Science with your sound card!

 

[John Larkin]

On Mon, 04 Apr 2016 13:05:43 GMT, N0Spam@daqarta.com (Bob Masta)
wrote:

On Sun, 03 Apr 2016 16:10:38 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

On Sun, 3 Apr 2016 20:07:14 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:



"Chris" <cbx@noreply.com> wrote in message
news:ndrgbj$tt0$6@dont-email.me...
It seems there are resistors around in the range of 50Gohm! Having never
encountered anything beyond 10M., I never imagined there could be such a
stratospheric value but apparently there is:

There's a small stash of 100M resistors in my collection.

For anything in the G Ohm range - you should probably check the leakage
resistance of whatever PCB/substrate you're mounting it on.

At the very least, you'll need guard slots cut in any PCB around the
termination points.

Here's a small PCB deliberately glopped with rosin flux and
fingerprints.

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Gloppy_Flux.JPG

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Test.JPG


It's pinning the needle on the 1e14 ohm range.

1G is easy. Just don't use water soluble flux, or if you do, clean it
really good.

Been a long time since I used anything in the 100 Meg range
or above, but I recall that there were a lot of recommended
precautions. One was to clean the glass body very carefully
(with alcohol, I think) to remove fingerprints which would
otherwise trap dust, which would then allow humidity to
cause a low-resistance shunt. You also want the body to be
elevated above the board surface for the same reason. I
also seem to recall something about teflon
mounts/feedthroughs at the lead ends, but I can't recall
exactly what that was supposed to do.

Sounds like urban myths. 100M is regular PC board turf, axial or
surface-mount parts. Fingerprints seem to have no effect in 1G ohm
circuits.

Glass resistors are overkill in the low Gohm range.

High voltage breakdown is another matter. Fingerprints and dust can
reduce breakover voltages, in the many-kilovolt domain.

Water-wash flux is evil. It can leave hygroscopic crud on and under
parts.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Sun, 3 Apr 2016 23:32:38 -0000 (UTC), Cursitor Doom
<curd@notformail.com> wrote:

On Sun, 03 Apr 2016 16:10:38 -0700, John Larkin wrote:

[...]
It's pinning the needle on the 1e14 ohm range.

1G is easy. Just don't use water soluble flux, or if you do, clean it
really good.

Nice to see these wonderful old vintage instruments still in use outside
of ham circles. What's it like accuracy wise?

It's hard to tell, but it agrees pretty well with purchased or sample
high-ohm resistors, usually to around 5% or better. It's better on the
lower (<= 1G ohm) ranges, which could be the meter or could be the
resistors themselves.

These meters show up on ebay now and then. Keithley used to make great
stuff... not so much any more.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Phil Hobbs]

On 04/04/2016 12:08 PM, John Larkin wrote:

On Mon, 04 Apr 2016 13:05:43 GMT, N0Spam@daqarta.com (Bob Masta)
wrote:

On Sun, 03 Apr 2016 16:10:38 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

On Sun, 3 Apr 2016 20:07:14 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:



"Chris" <cbx@noreply.com> wrote in message
news:ndrgbj$tt0$6@dont-email.me...
It seems there are resistors around in the range of 50Gohm! Having never
encountered anything beyond 10M., I never imagined there could be such a
stratospheric value but apparently there is:

There's a small stash of 100M resistors in my collection.

For anything in the G Ohm range - you should probably check the leakage
resistance of whatever PCB/substrate you're mounting it on.

At the very least, you'll need guard slots cut in any PCB around the
termination points.

Here's a small PCB deliberately glopped with rosin flux and
fingerprints.

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Gloppy_Flux.JPG

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Test.JPG


It's pinning the needle on the 1e14 ohm range.

1G is easy. Just don't use water soluble flux, or if you do, clean it
really good.

Been a long time since I used anything in the 100 Meg range
or above, but I recall that there were a lot of recommended
precautions. One was to clean the glass body very carefully
(with alcohol, I think) to remove fingerprints which would
otherwise trap dust, which would then allow humidity to
cause a low-resistance shunt. You also want the body to be
elevated above the board surface for the same reason. I
also seem to recall something about teflon
mounts/feedthroughs at the lead ends, but I can't recall
exactly what that was supposed to do.


Sounds like urban myths. 100M is regular PC board turf, axial or
surface-mount parts. Fingerprints seem to have no effect in 1G ohm
circuits.

Glass resistors are overkill in the low Gohm range.

High voltage breakdown is another matter. Fingerprints and dust can
reduce breakover voltages, in the many-kilovolt domain.

Water-wash flux is evil. It can leave hygroscopic crud on and under
parts.

Sure is. So is garden-variety IPA solvent. In high-Z circuits, I
usually used guard traces top and bottom (with the solder mask removed)
and a slot under the photodiode and the feedback resistor (and cap, if
any). Being able to get solvent under the components helps a lot with
the 1/f noise and stability.

The popcorn noise you get from a board washed with drugstore IPA has to
be seen to be believed.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Cydrome Leader]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

On 04/04/2016 12:08 PM, John Larkin wrote:
On Mon, 04 Apr 2016 13:05:43 GMT, N0Spam@daqarta.com (Bob Masta)
wrote:

On Sun, 03 Apr 2016 16:10:38 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

On Sun, 3 Apr 2016 20:07:14 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:



"Chris" <cbx@noreply.com> wrote in message
news:ndrgbj$tt0$6@dont-email.me...
It seems there are resistors around in the range of 50Gohm! Having never
encountered anything beyond 10M., I never imagined there could be such a
stratospheric value but apparently there is:

There's a small stash of 100M resistors in my collection.

For anything in the G Ohm range - you should probably check the leakage
resistance of whatever PCB/substrate you're mounting it on.

At the very least, you'll need guard slots cut in any PCB around the
termination points.

Here's a small PCB deliberately glopped with rosin flux and
fingerprints.

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Gloppy_Flux.JPG

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Test.JPG


It's pinning the needle on the 1e14 ohm range.

1G is easy. Just don't use water soluble flux, or if you do, clean it
really good.

Been a long time since I used anything in the 100 Meg range
or above, but I recall that there were a lot of recommended
precautions. One was to clean the glass body very carefully
(with alcohol, I think) to remove fingerprints which would
otherwise trap dust, which would then allow humidity to
cause a low-resistance shunt. You also want the body to be
elevated above the board surface for the same reason. I
also seem to recall something about teflon
mounts/feedthroughs at the lead ends, but I can't recall
exactly what that was supposed to do.


Sounds like urban myths. 100M is regular PC board turf, axial or
surface-mount parts. Fingerprints seem to have no effect in 1G ohm
circuits.

Glass resistors are overkill in the low Gohm range.

High voltage breakdown is another matter. Fingerprints and dust can
reduce breakover voltages, in the many-kilovolt domain.

Water-wash flux is evil. It can leave hygroscopic crud on and under
parts.

Sure is. So is garden-variety IPA solvent. In high-Z circuits, I
usually used guard traces top and bottom (with the solder mask removed)
and a slot under the photodiode and the feedback resistor (and cap, if
any). Being able to get solvent under the components helps a lot with
the 1/f noise and stability.

The popcorn noise you get from a board washed with drugstore IPA has to
be seen to be believed.

I'd believe it. The drugstore stuff I've used (lots of it over the years)
seems to have denaturing agents added or some other alcohols even though
it's not needed.

Optical cleaning grade IPA doesn't seem to have the other "stuff" in it.

 

[whit3rd]

On Friday, April 8, 2016 at 3:21:57 PM UTC-7, Cydrome Leader wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

Water-wash flux is evil. It can leave hygroscopic crud on and under
parts.

Sure is. So is garden-variety IPA solvent....

The popcorn noise you get from a board washed with drugstore IPA has to
be seen to be believed.

I'd believe it. The drugstore stuff I've used (lots of it over the years)
seems to have denaturing agents added...

Isopropanol (IPA) has low surface tension, so it forms a film. It's also hygroscopic, so
it becomes (after some evaporation) a water film full of any crud you can imagine.
And when it dries, all the empty board space looks clean, because the dissolved
stuff is deposited at the capillary-attractive sites you DON'T see. Water, by comparison,
has higher surface tension, forms droplets you can remove with airflow.

Wash with IPA, rinse with distilled water, blow dry (with clean air) then bake dry
at low temperature for an hour, if you really want to clean.

 

[John Larkin]

On Fri, 8 Apr 2016 22:21:54 +0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
On 04/04/2016 12:08 PM, John Larkin wrote:
On Mon, 04 Apr 2016 13:05:43 GMT, N0Spam@daqarta.com (Bob Masta)
wrote:

On Sun, 03 Apr 2016 16:10:38 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

On Sun, 3 Apr 2016 20:07:14 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:



"Chris" <cbx@noreply.com> wrote in message
news:ndrgbj$tt0$6@dont-email.me...
It seems there are resistors around in the range of 50Gohm! Having never
encountered anything beyond 10M., I never imagined there could be such a
stratospheric value but apparently there is:

There's a small stash of 100M resistors in my collection.

For anything in the G Ohm range - you should probably check the leakage
resistance of whatever PCB/substrate you're mounting it on.

At the very least, you'll need guard slots cut in any PCB around the
termination points.

Here's a small PCB deliberately glopped with rosin flux and
fingerprints.

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Gloppy_Flux.JPG

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Test.JPG


It's pinning the needle on the 1e14 ohm range.

1G is easy. Just don't use water soluble flux, or if you do, clean it
really good.

Been a long time since I used anything in the 100 Meg range
or above, but I recall that there were a lot of recommended
precautions. One was to clean the glass body very carefully
(with alcohol, I think) to remove fingerprints which would
otherwise trap dust, which would then allow humidity to
cause a low-resistance shunt. You also want the body to be
elevated above the board surface for the same reason. I
also seem to recall something about teflon
mounts/feedthroughs at the lead ends, but I can't recall
exactly what that was supposed to do.


Sounds like urban myths. 100M is regular PC board turf, axial or
surface-mount parts. Fingerprints seem to have no effect in 1G ohm
circuits.

Glass resistors are overkill in the low Gohm range.

High voltage breakdown is another matter. Fingerprints and dust can
reduce breakover voltages, in the many-kilovolt domain.

Water-wash flux is evil. It can leave hygroscopic crud on and under
parts.

Sure is. So is garden-variety IPA solvent. In high-Z circuits, I
usually used guard traces top and bottom (with the solder mask removed)
and a slot under the photodiode and the feedback resistor (and cap, if
any). Being able to get solvent under the components helps a lot with
the 1/f noise and stability.

The popcorn noise you get from a board washed with drugstore IPA has to
be seen to be believed.

I'd believe it. The drugstore stuff I've used (lots of it over the years)
seems to have denaturing agents added or some other alcohols even though
it's not needed.

Optical cleaning grade IPA doesn't seem to have the other "stuff" in it.

On my bench, if I'm too lazy to take a board downstairs to the solvent
cleaner machine, I use acetone. Cleans rosin flux nicely.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Ian Field]

"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message
news:ug4ogbtiemmd4h6707o11n6ke2ekaa3j0l@4ax.com...

On Fri, 8 Apr 2016 22:21:54 +0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
On 04/04/2016 12:08 PM, John Larkin wrote:
On Mon, 04 Apr 2016 13:05:43 GMT, N0Spam@daqarta.com (Bob Masta)
wrote:

On Sun, 03 Apr 2016 16:10:38 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

On Sun, 3 Apr 2016 20:07:14 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:



"Chris" <cbx@noreply.com> wrote in message
news:ndrgbj$tt0$6@dont-email.me...
It seems there are resistors around in the range of 50Gohm! Having
never
encountered anything beyond 10M., I never imagined there could be
such a
stratospheric value but apparently there is:

There's a small stash of 100M resistors in my collection.

For anything in the G Ohm range - you should probably check the
leakage
resistance of whatever PCB/substrate you're mounting it on.

At the very least, you'll need guard slots cut in any PCB around the
termination points.

Here's a small PCB deliberately glopped with rosin flux and
fingerprints.

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Gloppy_Flux.JPG

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Test.JPG


It's pinning the needle on the 1e14 ohm range.

1G is easy. Just don't use water soluble flux, or if you do, clean it
really good.

Been a long time since I used anything in the 100 Meg range
or above, but I recall that there were a lot of recommended
precautions. One was to clean the glass body very carefully
(with alcohol, I think) to remove fingerprints which would
otherwise trap dust, which would then allow humidity to
cause a low-resistance shunt. You also want the body to be
elevated above the board surface for the same reason. I
also seem to recall something about teflon
mounts/feedthroughs at the lead ends, but I can't recall
exactly what that was supposed to do.


Sounds like urban myths. 100M is regular PC board turf, axial or
surface-mount parts. Fingerprints seem to have no effect in 1G ohm
circuits.

Glass resistors are overkill in the low Gohm range.

High voltage breakdown is another matter. Fingerprints and dust can
reduce breakover voltages, in the many-kilovolt domain.

Water-wash flux is evil. It can leave hygroscopic crud on and under
parts.

Sure is. So is garden-variety IPA solvent. In high-Z circuits, I
usually used guard traces top and bottom (with the solder mask removed)
and a slot under the photodiode and the feedback resistor (and cap, if
any). Being able to get solvent under the components helps a lot with
the 1/f noise and stability.

The popcorn noise you get from a board washed with drugstore IPA has to
be seen to be believed.

I'd believe it. The drugstore stuff I've used (lots of it over the years)
seems to have denaturing agents added or some other alcohols even though
it's not needed.

Optical cleaning grade IPA doesn't seem to have the other "stuff" in it.

On my bench, if I'm too lazy to take a board downstairs to the solvent
cleaner machine, I use acetone. Cleans rosin flux nicely.

Exotic chemicals and solvents are hard to come by in the UK - car spay paint
thinners is less difficult to obtain.

It shifts rosin flux very well, but is destructive to some components.

 

[George Herold]

On Monday, April 11, 2016 at 5:18:59 PM UTC-4, Ian Field wrote:

"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message
news:ug4ogbtiemmd4h6707o11n6ke2ekaa3j0l@4ax.com...
On Fri, 8 Apr 2016 22:21:54 +0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
On 04/04/2016 12:08 PM, John Larkin wrote:
On Mon, 04 Apr 2016 13:05:43 GMT, N0Spam@daqarta.com (Bob Masta)
wrote:

On Sun, 03 Apr 2016 16:10:38 -0700, John Larkin
jjlarkin@highlandtechnology.com> wrote:

On Sun, 3 Apr 2016 20:07:14 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:



"Chris" <cbx@noreply.com> wrote in message
news:ndrgbj$tt0$6@dont-email.me...
It seems there are resistors around in the range of 50Gohm! Having
never
encountered anything beyond 10M., I never imagined there could be
such a
stratospheric value but apparently there is:

There's a small stash of 100M resistors in my collection.

For anything in the G Ohm range - you should probably check the
leakage
resistance of whatever PCB/substrate you're mounting it on.

At the very least, you'll need guard slots cut in any PCB around the
termination points.

Here's a small PCB deliberately glopped with rosin flux and
fingerprints.

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Gloppy_Flux.JPG

https://dl.dropboxusercontent.com/u/53724080/Gear/Keithley/Leak_Test.JPG


It's pinning the needle on the 1e14 ohm range.

1G is easy. Just don't use water soluble flux, or if you do, clean it
really good.

Been a long time since I used anything in the 100 Meg range
or above, but I recall that there were a lot of recommended
precautions. One was to clean the glass body very carefully
(with alcohol, I think) to remove fingerprints which would
otherwise trap dust, which would then allow humidity to
cause a low-resistance shunt. You also want the body to be
elevated above the board surface for the same reason. I
also seem to recall something about teflon
mounts/feedthroughs at the lead ends, but I can't recall
exactly what that was supposed to do.


Sounds like urban myths. 100M is regular PC board turf, axial or
surface-mount parts. Fingerprints seem to have no effect in 1G ohm
circuits.

Glass resistors are overkill in the low Gohm range.

High voltage breakdown is another matter. Fingerprints and dust can
reduce breakover voltages, in the many-kilovolt domain.

Water-wash flux is evil. It can leave hygroscopic crud on and under
parts.

Sure is. So is garden-variety IPA solvent. In high-Z circuits, I
usually used guard traces top and bottom (with the solder mask removed)
and a slot under the photodiode and the feedback resistor (and cap, if
any). Being able to get solvent under the components helps a lot with
the 1/f noise and stability.

The popcorn noise you get from a board washed with drugstore IPA has to
be seen to be believed.

I'd believe it. The drugstore stuff I've used (lots of it over the years)
seems to have denaturing agents added or some other alcohols even though
it's not needed.

Optical cleaning grade IPA doesn't seem to have the other "stuff" in it.

On my bench, if I'm too lazy to take a board downstairs to the solvent
cleaner machine, I use acetone. Cleans rosin flux nicely.

Exotic chemicals and solvents are hard to come by in the UK - car spay paint
thinners is less difficult to obtain.

It shifts rosin flux very well, but is destructive to some components.

Acetone is considered exotic? Here (in the US) we can walk into any hardware
store and buy Acetone/ alcohols/ other stuff.

George H.

 

[Cursitor Doom]

On Tue, 12 Apr 2016 07:13:39 -0700, George Herold wrote:

Acetone is considered exotic? Here (in the US) we can walk into any
hardware store and buy Acetone/ alcohols/ other stuff.

There is still *something* very nasty that can be bought over the counter
in the UK and that is 99% pure sulphuric acid which is readily available
from plumbers merchants and DIY sheds like Homebase and is used for -
among other things - unblocking drains. I was trying to explain this to a
pal of mine in Germany who's a plumber but he couldn't get his head
around it. Must have sounded outrageous to him with their strict
environmental laws over there.
I expect they'll ban it soon, though. It's recently become a fashionable
way to exact revenge on someone that's disrespected a bro among the black
community: squirt it in their face! Makes an awful mess of human flesh.
Still, that's their culture so we should really celebrate it, I guess.
:-/