Soldering surface mount components

[Terry Given]

Larry Brasfield wrote:

"Ken Smith" <kensmith@green.rahul.net> wrote in message news:cp0a8c$qke$1@blue.rahul.net...

In article <toMsd.18$li7.1870@news.uswest.net>,
Larry Brasfield <donotspam_larry_brasfield@hotmail.com> wrote:
[...]

Methinks that common ceramic capacitors are not
actually piezoelectric.

I think, you think wrongly here. Ceramic capacitors with high K materials
are often enough piezoelectric to make them a bad idea for small signal
work. They make a voltage if you thump on them. This makes your circuit
into a bad microphone.


If you define "piezoelectric" loosely enough, then your "bad
microphone" is relying on piezoelectric effect. By such a
loose definition, even vacuum is piezoelectric. But by the
more discriminating definition Terry quoted, and according
to the usage among people who exploit the piezoelectric
effect, ordinary interactions among separated charges, such
as occur in a charged capacitor when thumped, should not
be deemed "piezoelectric".

What do you think happens when you thump a capacitor
that is not biased? If it was piezoelectric, (and read Terry's
quoted definition carefully), it would produce an electrical
signal. But it does not.

I'm gonna get a steak and cheese pie, then whack up a little test
circuit - inverting amp, cap from -ve i/p to 0V, 100k feedback and bias
comp resistors, +/-5V supplies, and do a few tests. I have some nice
10uF X7R caps, and some 1nF NPOs. I think I have a few Y5Vs too...

anything wrong with this setup? other than the fact I amp applying a
VERY small bias to the cap, around the offset voltage of the opamp - in
this case about 4mV. How can I reduce this further?


And the corollary here is of course thumping a biased cap WILL produce a
signal, as the pressure wave propagates through the cap there will be
deflection of the plates, therefore VdC/dt current must flow. Stiffer
caps have smaller dC/dt, so generate smaller signals - eg film or npo
caps versus air caps (eg trimmers) or electrolytics (there are probably
other things going on inside electrolytics, but I imagine the pressure
wave will actually move the electrolyte much, much more than the atoms
of say NPO will move when thumped).

I do not deny that there are electric/mechanical interactions
in capacitors, or that high K capacitors can be misused.
But nothing you have said goes to show that I am wrong.


kensmith@rahul.net forging knowledge

Cheers
Terry

 

[Ken Smith]

In article <96Osd.22640$9A.388592@news.xtra.co.nz>,
Terry Given <my_name@ieee.org> wrote:

Ken Smith wrote:
In article <toMsd.18$li7.1870@news.uswest.net>,
Larry Brasfield <donotspam_larry_brasfield@hotmail.com> wrote:
[...]

Methinks that common ceramic capacitors are not
actually piezoelectric.


I think, you think wrongly here. Ceramic capacitors with high K materials
are often enough piezoelectric to make them a bad idea for small signal
work. They make a voltage if you thump on them. This makes your circuit
into a bad microphone.

This is where it gets interesting.

... or boring depending on your point of view. Or this may even a way to
start another flame war on the subject.

Testing the microphonics is
relatively straightforward, but would need to be done for a variety of
DC bias conditions and temperatures, and of course differing dielectrics.

It is easier to put in NPO capacitors or design the need for capacitors
out than it is to ensure that the high K ones are not microphonic. The
high K capacitors I had trouble with had no bias voltage on them and were
microphonic at room temperature. I could get a few tens of microvolts
signal from them by dragging my fingernail over the PCB near them.

Even if we tested 100 capacitors of a certain type, we could not really be
sure. What would happen if the next batch were made during a thunderstorm
or just after the crew ate lunch?

How to test the forces generated though...and the mechanical resonant
frequency (that might be easier by calculation given the fairly simple
geometry) of the device under consideration. What about some form of
model using relatively easily measured data to predict the mechanical
effects?

I think the problem will be the loading of the capacitor. Ceramics have a
high "Q" mechanically. It is likely that the PCB loads the mechanical
vibration enough to be the controlling factor in the amplitude of the
stress.

An interesting thought: Tin-lead solder is very lossy mechanically. This
no no-lead stuff may not be as lossy. The no-lead folks may have created
another problem.


--
--
kensmith@rahul.net forging knowledge

 

[Terry Given]

Ken Smith wrote:

In article <RzOsd.22654$9A.388121@news.xtra.co.nz>,
Terry Given <my_name@ieee.org> wrote:

Ken Smith wrote:


[...]


The
high K capacitors I had trouble with had no bias voltage on them and were
microphonic at room temperature. I could get a few tens of microvolts
signal from them by dragging my fingernail over the PCB near them.

It probably depends on the rate of change of force, too. Thanks for the
data though - sounds like (sorry, couldnt resist) mV signals ought to be
quite feasible..


It depends on the operating environment. Does your product have to detect
mV signals while being dragged down a dirt road, from the back of a pick
up truck? If not, your life may be easy.


[...]

I think the problem will be the loading of the capacitor. Ceramics have a
high "Q" mechanically. It is likely that the PCB loads the mechanical
vibration enough to be the controlling factor in the amplitude of the
stress.

yes. I am constantly impressed at how damn hard mechanical engineering
really is (if you do it properly). Electronics is often easy by
comparison, and usually devolves into mechanics anyway (thermal etc).


I have met at least 5 people who's busines card said "mechanical
engineer". As far as I can remember, I have actually only met one
mechanical engineer and that is not what his business card reads. The
others were mechanical dunder-heads. I've very often ended up doing my
own mechanical design. It is not the fastest way to get the job done.

I think the problem with mechanics is that it initially is more
accessible than electronics. By that I mean it is easy to get a handle
on say torque - lean on a bar, whereas getting a handle on an electron
is a bit trickier - you cant see it, feel it etc. most of the
electronics people I meet have a fair understanding of second order
systems, stuff like that. but few so-called mechanical engineers do. I
have been fortunate enough to work with some brilliant mechanical
engineers, people who are every bit as clever and creative as the
smartest electronics guys I know (some guys I very briefly worked with
at Penn State were incredible), but most seem a bit thick. Hell, try
getting a sheet metal shop to fold up a box accurately.

Then when you really get into it, mechanics is a lot more complex than
(most) electronics - nothing is isotropic, or homogeneous, or perhaps
even well characterised. Everything is as non-linear as all hell, and
the measurements are a lot harder. I suspect all the clever mech
engineers go work on the really tricky stuff, and leave the rest of the
work to the metal-shop dropouts.

Cheers
Terry

 

[Ken Smith]

In article <RzOsd.22654$9A.388121@news.xtra.co.nz>,
Terry Given <my_name@ieee.org> wrote:

Ken Smith wrote:

[...]

The
high K capacitors I had trouble with had no bias voltage on them and were
microphonic at room temperature. I could get a few tens of microvolts
signal from them by dragging my fingernail over the PCB near them.

It probably depends on the rate of change of force, too. Thanks for the
data though - sounds like (sorry, couldnt resist) mV signals ought to be
quite feasible..

It depends on the operating environment. Does your product have to detect
mV signals while being dragged down a dirt road, from the back of a pick
up truck? If not, your life may be easy.


[...]

I think the problem will be the loading of the capacitor. Ceramics have a
high "Q" mechanically. It is likely that the PCB loads the mechanical
vibration enough to be the controlling factor in the amplitude of the
stress.

yes. I am constantly impressed at how damn hard mechanical engineering
really is (if you do it properly). Electronics is often easy by
comparison, and usually devolves into mechanics anyway (thermal etc).

I have met at least 5 people who's busines card said "mechanical
engineer". As far as I can remember, I have actually only met one
mechanical engineer and that is not what his business card reads. The
others were mechanical dunder-heads. I've very often ended up doing my
own mechanical design. It is not the fastest way to get the job done.

--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <bsOsd.22$li7.2154@news.uswest.net>,
Larry Brasfield <donotspam_larry_brasfield@hotmail.com> wrote:

"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:cp0a8c$qke$1@blue.rahul.net...
In article <toMsd.18$li7.1870@news.uswest.net>,
Larry Brasfield <donotspam_larry_brasfield@hotmail.com> wrote:
[...]
Methinks that common ceramic capacitors are not
actually piezoelectric.

I think, you think wrongly here. Ceramic capacitors with high K materials
are often enough piezoelectric to make them a bad idea for small signal
work. They make a voltage if you thump on them. This makes your circuit
into a bad microphone.

If you define "piezoelectric" loosely enough, then your "bad
microphone" is relying on piezoelectric effect. By such a
loose definition, even vacuum is piezoelectric.

True but I was not defining it loosely as indicated below.

[...]

What do you think happens when you thump a capacitor
that is not biased?

As stated elsewhere, I got tens of uV of signal from a non-biased
capacitor by dragging my fingernail along the PCB material near it.

But nothing you have said goes to show that I am wrong.

How about now?


--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <CMOsd.22681$9A.389016@news.xtra.co.nz>,
Terry Given <my_name@ieee.org> wrote:
[....]

I'm gonna get a steak and cheese pie, then whack up a little test
circuit - inverting amp, cap from -ve i/p to 0V, 100k feedback and bias
comp resistors, +/-5V supplies, and do a few tests. I have some nice
10uF X7R caps, and some 1nF NPOs. I think I have a few Y5Vs too...

anything wrong with this setup? other than the fact I amp applying a
VERY small bias to the cap, around the offset voltage of the opamp - in
this case about 4mV. How can I reduce this further?

2SK170
30mH 0.1u !--- ect
--------+----------- -------->!
( ! )( !--- ect
( --- )(
( --- )(
( ! )(
--------+----!!----- ----------- ect
C2 SP-4
Triad
1K:200K


The 30mH has a SRF above 10KHz, is air cored, and has a resistance of
about 13 ohms. It is made from 2 15mH coils pointing in opposite and
matched so that their distance source pickup is under 1 turn on a 3
sqr-inch area worth. The coil is then placed in a 3 layer shield can.



--
--
kensmith@rahul.net forging knowledge

 

[Larry Brasfield]

"Ken Smith" <kensmith@green.rahul.net> wrote in message news:cp0kvj$1a3$5@blue.rahul.net...

In article <bsOsd.22$li7.2154@news.uswest.net>,
Larry Brasfield <donotspam_larry_brasfield@hotmail.com> wrote:
"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:cp0a8c$qke$1@blue.rahul.net...
In article <toMsd.18$li7.1870@news.uswest.net>,
Larry Brasfield <donotspam_larry_brasfield@hotmail.com> wrote:
[...]
Methinks that common ceramic capacitors are not
actually piezoelectric.

I think, you think wrongly here. Ceramic capacitors with high K materials
are often enough piezoelectric to make them a bad idea for small signal
work. They make a voltage if you thump on them. This makes your circuit
into a bad microphone.

If you define "piezoelectric" loosely enough, then your "bad
microphone" is relying on piezoelectric effect. By such a
loose definition, even vacuum is piezoelectric.

True but I was not defining it loosely as indicated below.

Ok, I am going to have to take a more nuanced position here.

You and I were addressing two different phenomena.

Your issue is with capacitors which have, in fact, developed a
piezoelectric characteristic. (Not terribly surprising since high
K capacitors are made of materials similar to those use for
piezoelectric tranducers.)

My issue is with incorrectly calling any instance of mechanical
transduction in a capacitor "piezoelectric". As my point about
vacuum should make clear, that usage is sloppy and at odds
with the accepted definition. (Of course, with enough usage,
sloppier definitions become accepted. Such is language.)

What do you think happens when you thump a capacitor
that is not biased?

As stated elsewhere, I got tens of uV of signal from a non-biased
capacitor by dragging my fingernail along the PCB material near it.

I might squirm out here by insisting that your capacitor was in fact
biased, even if you could not measure DCV at its terminals. That
would be a fair description of the condition of a poled PZT, (from
which your capacitor was likely made). But that would not be an
out, because my original position, "[C]ommon ceramic capacitors
are not actually piezoelectric.", is not quite right, as your experience
shows. So I will grant your point without negating the essential
truth of what I was stating.

Your poor microphone, at some time during its life, transitioned
from being a mere capacitor into a piezoelectric device. This
most likely occured when it was held under bias for a long
period of time. (It could occur in a short time at a temperature
higher than most electronics see.) It became poled, probably
not very well since it was inadvertant. You may have seen or
heard of dielectric absorption. High K capacitors are also
subject to it, and until their internal and only slowly available
charge is gone, they will be slightly piezoelectric, as your poor
microphone undoubtedly was.

You may also have heard biased capacitors, when subject to
AC currents having components in the audio range, make a
sound. In all likelyhood, that sound is not due to piezoelectric
effect. (A very small fraction of it could be, but not enough
to reach audibility.) It is due to simple compression of the
dielectric, by opposing charges, which varies in degree as
the AC occurs.

At any rate, under your relentless, pinpoint attack, I must
alter my position: Common ceramic capacitors are not
piezoelectric simply because they are made from materials
used for their ablity to be made piezoelectric. They may
become slightly piezoelectric for that reason, but without
being poled either above their Curie temperature or for a
long time, they cannot exhibit strong piezoelectric effects.
Nevertheless, weak piezoelectric effect is a hazard to be
aware of with all capacitors and especially high K ones.

But nothing you have said goes to show that I am wrong.

How about now?

How about not sufficiently nuanced?

kensmith@rahul.net forging knowledge
--

--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Ken Smith]

In article <GUQsd.22738$9A.390381@news.xtra.co.nz>,
Terry Given <my_name@ieee.org> wrote:
[...]

I think the problem with mechanics is that it initially is more
accessible than electronics.

Yes I agree. People should be able to get a feel for the basic lever
problem just from living in the universe. You don't see electrons in the
play yard much.

[...]

at Penn State were incredible), but most seem a bit thick. Hell, try
getting a sheet metal shop to fold up a box accurately.

Or put the PEMs in the right way.

Then when you really get into it, mechanics is a lot more complex than
(most) electronics - nothing is isotropic, or homogeneous, or perhaps
even well characterised. Everything is as non-linear as all hell, and
the measurements are a lot harder.

And the units of measure are all weird. "Shore D" indeed.

I think I'll use a 3/8th cable over a 10 CM pully.

--
--
kensmith@rahul.net forging knowledge

 

[Larry Brasfield]

"Terry Given" <my_name@ieee.org> wrote in message
news:CMOsd.22681$9A.389016@news.xtra.co.nz...

Larry Brasfield wrote:
....
What do you think happens when you thump a capacitor
that is not biased? If it was piezoelectric, (and read Terry's
quoted definition carefully), it would produce an electrical
signal. But it does not.

I'm gonna get a steak and cheese pie, then whack up a little test circuit - inverting amp, cap from -ve i/p to 0V, 100k feedback
and bias comp resistors, +/-5V supplies, and do a few tests. I have some nice 10uF X7R caps, and some 1nF NPOs. I think I have a
few Y5Vs too...

anything wrong with this setup? other than the fact I amp applying a VERY small bias to the cap, around the offset voltage of the
opamp - in this case about 4mV. How can I reduce this further?

Why not use a bigger capacitor to AC couple the
capacitor under test? Then you could use a large
resistor to enforce (nearly) 0 VDC bias.

I question what your setup can show. New ceramic caps
are very unlikely to exhibit a piezoelectric effect. But high
K caps that have been biased may be slightly poled and
respond to a "thump". Please see my response to Mr.
Smith where I had to back off my initial position a tad.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Terry Given]

Larry Brasfield wrote:

"Ken Smith" <kensmith@green.rahul.net> wrote in message news:cp0kvj$1a3$5@blue.rahul.net...

In article <bsOsd.22$li7.2154@news.uswest.net>,
Larry Brasfield <donotspam_larry_brasfield@hotmail.com> wrote:

"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:cp0a8c$qke$1@blue.rahul.net...

In article <toMsd.18$li7.1870@news.uswest.net>,
Larry Brasfield <donotspam_larry_brasfield@hotmail.com> wrote:
[...]

Methinks that common ceramic capacitors are not
actually piezoelectric.

I think, you think wrongly here. Ceramic capacitors with high K materials
are often enough piezoelectric to make them a bad idea for small signal
work. They make a voltage if you thump on them. This makes your circuit
into a bad microphone.

If you define "piezoelectric" loosely enough, then your "bad
microphone" is relying on piezoelectric effect. By such a
loose definition, even vacuum is piezoelectric.

True but I was not defining it loosely as indicated below.


Ok, I am going to have to take a more nuanced position here.

You and I were addressing two different phenomena.

Your issue is with capacitors which have, in fact, developed a
piezoelectric characteristic. (Not terribly surprising since high
K capacitors are made of materials similar to those use for
piezoelectric tranducers.)

My issue is with incorrectly calling any instance of mechanical
transduction in a capacitor "piezoelectric". As my point about
vacuum should make clear, that usage is sloppy and at odds
with the accepted definition. (Of course, with enough usage,
sloppier definitions become accepted. Such is language.)


[...]

What do you think happens when you thump a capacitor
that is not biased?

As stated elsewhere, I got tens of uV of signal from a non-biased
capacitor by dragging my fingernail along the PCB material near it.


I might squirm out here by insisting that your capacitor was in fact
biased, even if you could not measure DCV at its terminals. That
would be a fair description of the condition of a poled PZT, (from
which your capacitor was likely made). But that would not be an
out, because my original position, "[C]ommon ceramic capacitors
are not actually piezoelectric.", is not quite right, as your experience
shows. So I will grant your point without negating the essential
truth of what I was stating.

Your poor microphone, at some time during its life, transitioned
from being a mere capacitor into a piezoelectric device. This
most likely occured when it was held under bias for a long
period of time. (It could occur in a short time at a temperature
higher than most electronics see.) It became poled, probably
not very well since it was inadvertant. You may have seen or
heard of dielectric absorption. High K capacitors are also
subject to it, and until their internal and only slowly available
charge is gone, they will be slightly piezoelectric, as your poor
microphone undoubtedly was.

I'm a bit out of my depth here (but still floating), but this sounds
very similar to the ageing effect discussed by TDK in this paper:

http://www.component.tdk.com/components/whatisthecapofthiscap.pdf

"over time the internal molecular structure changes in such a way as to
create an alignment of electrical dipoles. This alignment results in a
structure that can hold less electrical charge than when the molecules
are in a totally random state, such as at the time of heating or
mounting on a printed circuit board"

and

"heating the capacitor above its curie temperature causes the
crystalline structure to return to its optimal unaligned configuration,
resulting in maximum capacitance. TDK recommends 150C/1 hour for
de-aging" which alas is far too long to assert that soldering actually
REDUCES the piezoelectric effect - just as well really, considering this
thread.

I had a quick squiz thru "surface wave filters", Mathews, John Wiley &
Sons, but no real info on the piezoelectric materials themselves. I
probably have the info kicking around (50 years of UFFC publications on
20 CDROMs) but digging it out looks time consuming.

It sounds like some sort of "forming" process is required for
piezoelectric devices - is that what you are referring to when you say
"poled" Larry? Care to describe the process a bit please?

You may also have heard biased capacitors, when subject to
AC currents having components in the audio range, make a
sound. In all likelyhood, that sound is not due to piezoelectric
effect. (A very small fraction of it could be, but not enough
to reach audibility.) It is due to simple compression of the
dielectric, by opposing charges, which varies in degree as
the AC occurs.

I would reason that electrolytics would be worse in this regard, as the
dielectric is not a solid.

At any rate, under your relentless, pinpoint attack, I must
alter my position: Common ceramic capacitors are not
piezoelectric simply because they are made from materials
used for their ablity to be made piezoelectric. They may
become slightly piezoelectric for that reason, but without
being poled either above their Curie temperature or for a
long time, they cannot exhibit strong piezoelectric effects.
Nevertheless, weak piezoelectric effect is a hazard to be
aware of with all capacitors and especially high K ones.


But nothing you have said goes to show that I am wrong.

How about now?


How about not sufficiently nuanced?


kensmith@rahul.net forging knowledge

Thanks guys, this is fascinating.

Cheers
Terry

 

[Terry Given]

Larry Brasfield wrote:

"Terry Given" <my_name@ieee.org> wrote in message
news:CMOsd.22681$9A.389016@news.xtra.co.nz...

Larry Brasfield wrote:

...

What do you think happens when you thump a capacitor
that is not biased? If it was piezoelectric, (and read Terry's
quoted definition carefully), it would produce an electrical
signal. But it does not.

I'm gonna get a steak and cheese pie, then whack up a little test circuit - inverting amp, cap from -ve i/p to 0V, 100k feedback
and bias comp resistors, +/-5V supplies, and do a few tests. I have some nice 10uF X7R caps, and some 1nF NPOs. I think I have a
few Y5Vs too...

anything wrong with this setup? other than the fact I amp applying a VERY small bias to the cap, around the offset voltage of the
opamp - in this case about 4mV. How can I reduce this further?


Why not use a bigger capacitor to AC couple the
capacitor under test? Then you could use a large
resistor to enforce (nearly) 0 VDC bias.

If I have 2 caps, how do I tell which caused the signal?

I question what your setup can show. New ceramic caps
are very unlikely to exhibit a piezoelectric effect. But high
K caps that have been biased may be slightly poled and
respond to a "thump". Please see my response to Mr.
Smith where I had to back off my initial position a tad.

I question my setup too. The X7Rs I have have all been biased to 50%
rated voltage for weeks. The pie was very nice, but I got sidetracked.
Bac to the soldering iron...

Cheers
Terry

 

[Larry Brasfield]

"Terry Given" <my_name@ieee.org> wrote in message news:NrSsd.22767$9A.390821@news.xtra.co.nz...

Larry Brasfield wrote:

"Terry Given" <my_name@ieee.org> wrote in message
news:CMOsd.22681$9A.389016@news.xtra.co.nz...

Larry Brasfield wrote:

...

What do you think happens when you thump a capacitor
that is not biased? If it was piezoelectric, (and read Terry's
quoted definition carefully), it would produce an electrical
signal. But it does not.

I'm gonna get a steak and cheese pie, then whack up a little test circuit - inverting amp,
cap from -ve i/p to 0V, 100k feedback and bias comp resistors, +/-5V supplies, and
do a few tests. I have some nice 10uF X7R caps, and some 1nF NPOs. I think I have
a few Y5Vs too...

anything wrong with this setup? other than the fact I amp applying a VERY small bias to the cap, around the offset voltage of the
opamp - in this case about 4mV. How can I reduce this further?

Why not use a bigger capacitor to AC couple the
capacitor under test? Then you could use a large
resistor to enforce (nearly) 0 VDC bias.

If I have 2 caps, how do I tell which caused the signal?

Thump just one? Acousticly isolate the one with 4 mV
on it, and use a modern low Eios opamp. Maybe thump
both caps to bound the confounding factor.

I question what your setup can show. New ceramic caps
are very unlikely to exhibit a piezoelectric effect. But high
K caps that have been biased may be slightly poled and
respond to a "thump". Please see my response to Mr.
Smith where I had to back off my initial position a tad.

I question my setup too. The X7Rs I have have all been biased to 50% rated voltage for weeks. The pie was very nice, but I got
sidetracked. Bac to the soldering iron...

Are you attempting to see how good a microphone an
unbiased capacitor can be? That would require some
selection of capacitors with various histories. Are you
attempting to show that not all ceramic capacitors are
piezoelectric? That would require new parts, maybe
even a few that were baked above the Currie point.

Cheers
Terry

Regards,
--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Larry Brasfield]

"Terry Given" <my_name@ieee.org> wrote in message news:_oSsd.22766$9A.390821@news.xtra.co.nz...

Larry Brasfield wrote:
....
Your poor microphone, at some time during its life, transitioned
from being a mere capacitor into a piezoelectric device. This
most likely occured when it was held under bias for a long
period of time. (It could occur in a short time at a temperature
higher than most electronics see.) It became poled, probably
not very well since it was inadvertant. You may have seen or
heard of dielectric absorption. High K capacitors are also
subject to it, and until their internal and only slowly available
charge is gone, they will be slightly piezoelectric, as your poor
microphone undoubtedly was.

I'm a bit out of my depth here (but still floating), but this sounds very similar to the ageing effect discussed by TDK in this
paper:

http://www.component.tdk.com/components/whatisthecapofthiscap.pdf

"over time the internal molecular structure changes in such a way as to create an alignment of electrical dipoles. This alignment
results in a structure that can hold less electrical charge than when the molecules are in a totally random state, such as at the
time of heating or mounting on a printed circuit board"

and

"heating the capacitor above its curie temperature causes the crystalline structure to return to its optimal unaligned
configuration, resulting in maximum capacitance. TDK recommends 150C/1 hour for de-aging" which alas is far too long to assert
that soldering actually REDUCES the piezoelectric effect - just as well really, considering this thread.

Those considerations arise for the same underlying reasons
that some materials become piezoelectric when poled.

I had a quick squiz thru "surface wave filters", Mathews, John Wiley & Sons, but no real info on the piezoelectric materials
themselves. I probably have the info kicking around (50 years of UFFC publications on 20 CDROMs) but digging it out looks time
consuming.

Google for "PZT" and "poling". That should keep you busy
for quite awhile. This subject is not treated much in usual
electronics related publications. The usual assumption is
that a cap is a cap and if not, it's the engineer's problem,
not the theortician's.

It sounds like some sort of "forming" process is required for piezoelectric devices - is that what you are referring to when you
say "poled" Larry? Care to describe the process a bit please?

Poling is a process where a tranducer (to be) has a voltage
applied for awhile when above the Curie temparature. The
voltage is typically also applied as the device cools. This
leaves a (more or less) permanent shift of certain polarized
molecules within the crystalline structure.

You may also have heard biased capacitors, when subject to
AC currents having components in the audio range, make a
sound. In all likelyhood, that sound is not due to piezoelectric
effect. (A very small fraction of it could be, but not enough
to reach audibility.) It is due to simple compression of the
dielectric, by opposing charges, which varies in degree as
the AC occurs.

I would reason that electrolytics would be worse in this regard, as the dielectric is not a solid.

For the gaseous electrolytics, I would expect the same
due to higher compressiblity. For tantylum electrolytics,
I could not venture a guess without some research.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Terry Given]

Larry Brasfield wrote:

"Terry Given" <my_name@ieee.org> wrote in message news:NrSsd.22767$9A.390821@news.xtra.co.nz...

Larry Brasfield wrote:


"Terry Given" <my_name@ieee.org> wrote in message
news:CMOsd.22681$9A.389016@news.xtra.co.nz...


Larry Brasfield wrote:

...


What do you think happens when you thump a capacitor
that is not biased? If it was piezoelectric, (and read Terry's
quoted definition carefully), it would produce an electrical
signal. But it does not.

I'm gonna get a steak and cheese pie, then whack up a little test circuit - inverting amp,
cap from -ve i/p to 0V, 100k feedback and bias comp resistors, +/-5V supplies, and
do a few tests. I have some nice 10uF X7R caps, and some 1nF NPOs. I think I have
a few Y5Vs too...

anything wrong with this setup? other than the fact I amp applying a VERY small bias to the cap, around the offset voltage of the
opamp - in this case about 4mV. How can I reduce this further?

Why not use a bigger capacitor to AC couple the
capacitor under test? Then you could use a large
resistor to enforce (nearly) 0 VDC bias.

If I have 2 caps, how do I tell which caused the signal?


Thump just one? Acousticly isolate the one with 4 mV
on it, and use a modern low Eios opamp. Maybe thump
both caps to bound the confounding factor.

Bounded confounding. I like it

I question what your setup can show. New ceramic caps
are very unlikely to exhibit a piezoelectric effect. But high
K caps that have been biased may be slightly poled and
respond to a "thump". Please see my response to Mr.
Smith where I had to back off my initial position a tad.

I question my setup too. The X7Rs I have have all been biased to 50% rated voltage for weeks. The pie was very nice, but I got
sidetracked. Bac to the soldering iron...


Are you attempting to see how good a microphone an
unbiased capacitor can be? That would require some
selection of capacitors with various histories. Are you
attempting to show that not all ceramic capacitors are
piezoelectric? That would require new parts, maybe
even a few that were baked above the Currie point.

Just interested to look at an npo vs an x7r cap, of roughly the same
size, to see what effect is due to the dielectric alone, for a range of
uncalibrated thumps.

Cheers
Terry

Regards,

 

[John Woodgate]

I read in sci.electronics.design that Larry Brasfield <donotspam_larry_b
rasfield@hotmail.com> wrote (in <BESsd.32$li7.2960@news.uswest.net&gt
about 'Piezoelectric caps [was: Soldering surface mount components]', on
Sun, 5 Dec 2004:

That would require new parts, maybe even a few that
were baked above the Currie point.

Korma or vindaloo?
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Clarence]

"Terry Given" <my_name@ieee.org> wrote in message
news:hCMsd.22359$9A.387186@news.xtra.co.nz...

Had nothing of value to add!


Plonk

 

[Bob Masta]

On Mon, 06 Dec 2004 17:05:55 +1300, Terry Given <my_name@ieee.org>
wrote:

I think the problem with mechanics is that it initially is more
accessible than electronics. By that I mean it is easy to get a handle
on say torque - lean on a bar, whereas getting a handle on an electron
is a bit trickier - you cant see it, feel it etc. most of the
electronics people I meet have a fair understanding of second order
systems, stuff like that. but few so-called mechanical engineers do. I
have been fortunate enough to work with some brilliant mechanical
engineers, people who are every bit as clever and creative as the
smartest electronics guys I know (some guys I very briefly worked with
at Penn State were incredible), but most seem a bit thick. Hell, try
getting a sheet metal shop to fold up a box accurately.

Then when you really get into it, mechanics is a lot more complex than
(most) electronics - nothing is isotropic, or homogeneous, or perhaps
even well characterised. Everything is as non-linear as all hell, and
the measurements are a lot harder. I suspect all the clever mech
engineers go work on the really tricky stuff, and leave the rest of the
work to the metal-shop dropouts.

When I was in engineering school, everyone took pretty much
the same core curriculum for the first 2 years. Then you got
to select whether you were going to be an EE, ME, or IE
(Industrial Engineer). The administration tried to steer you
into one of these based on your grade average: EE if you got
good grades, ME if mediocre, else IE. (With my average, I
had to *fight* for an EE slot!)

Best regards,




Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

 

[Ken Smith]

In article <QNRsd.28$li7.2677@news.uswest.net>,
Larry Brasfield <donotspam_larry_brasfield@hotmail.com> wrote:

"Ken Smith" <kensmith@green.rahul.net> wrote in message
[...]
Ok, I am going to have to take a more nuanced position here.

You and I were addressing two different phenomena.

Yes, it appears so.

My issue is with incorrectly calling any instance of mechanical
transduction in a capacitor "piezoelectric". As my point about
vacuum should make clear, that usage is sloppy and at odds
with the accepted definition. (Of course, with enough usage,
sloppier definitions become accepted. Such is language.)

Yes, sloppy language can lead to all sorts of curious statements and odd
misunderstandings.

[...]

I might squirm out here by insisting that your capacitor was in fact
biased, even if you could not measure DCV at its terminals. That
would be a fair description of the condition of a poled PZT, (from
which your capacitor was likely made). But that would not be an
out, because my original position, "[C]ommon ceramic capacitors
are not actually piezoelectric.", is not quite right, as your experience
shows. So I will grant your point without negating the essential
truth of what I was stating.

Your poor microphone, at some time during its life, transitioned
from being a mere capacitor into a piezoelectric device. This
most likely occured when it was held under bias for a long
period of time.

Actually it got pulses in one direction. The pulse was on the order of
0.1 seconds and about 5V. It had been unbiased for many seconds when I
did the test. Since it was in parallel with an inductor, any voltage on
it at that time would have been very small.


[...]

You may also have heard biased capacitors, when subject to
AC currents having components in the audio range, make a
sound. In all likelyhood, that sound is not due to piezoelectric
effect. (A very small fraction of it could be, but not enough
to reach audibility.) It is due to simple compression of the
dielectric, by opposing charges, which varies in degree as
the AC occurs.

I think I have to disagree with you on this. It takes very little actual
energy to be heard so very little piezoelectric effect is needed.

Imagine a circuit like this:


--------------- +30V
! !
O S1 O S2
/ /
! ! 3 x 2.2uF
! +-------!!----------
! ! \
! ! /
! ! \ 12R
! ! /
+---------- ! -----------------
! !
O O
/ S3 / S4
! !
-------------- GND


If the H bridge is driven at 50-50 duty cycle, the net bias on the
capacitor is small or perhaps zero. If the bridge rests in one state, the
capacitor will have a constant bias on it during the rest state. This
will give the material lots of time to get poled.

BTW: This is a simplified version of the actual circuit.

How about now?

How about not sufficiently nuanced?

Agreed

--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <_oSsd.22766$9A.390821@news.xtra.co.nz>,
Terry Given <my_name@ieee.org> wrote:
[....]

You may also have heard biased capacitors, when subject to
AC currents having components in the audio range, make a
sound. In all likelyhood, that sound is not due to piezoelectric
effect. (A very small fraction of it could be, but not enough
to reach audibility.) It is due to simple compression of the
dielectric, by opposing charges, which varies in degree as
the AC occurs.

I would reason that electrolytics would be worse in this regard, as the
dielectric is not a solid.

I would argue that one electrode is the metal, the other is the liquid and
that the dielectric is the thin layer on the surface of the metal. This
layer is solid. I would expect less microphonics in a electrolytic
capacitor.


--
--
kensmith@rahul.net forging knowledge

 

[Terry Given]

Bob Masta wrote:

On Mon, 06 Dec 2004 17:05:55 +1300, Terry Given <my_name@ieee.org
wrote:



I think the problem with mechanics is that it initially is more
accessible than electronics. By that I mean it is easy to get a handle
on say torque - lean on a bar, whereas getting a handle on an electron
is a bit trickier - you cant see it, feel it etc. most of the
electronics people I meet have a fair understanding of second order
systems, stuff like that. but few so-called mechanical engineers do. I
have been fortunate enough to work with some brilliant mechanical
engineers, people who are every bit as clever and creative as the
smartest electronics guys I know (some guys I very briefly worked with
at Penn State were incredible), but most seem a bit thick. Hell, try
getting a sheet metal shop to fold up a box accurately.

Then when you really get into it, mechanics is a lot more complex than
(most) electronics - nothing is isotropic, or homogeneous, or perhaps
even well characterised. Everything is as non-linear as all hell, and
the measurements are a lot harder. I suspect all the clever mech
engineers go work on the really tricky stuff, and leave the rest of the
work to the metal-shop dropouts.



When I was in engineering school, everyone took pretty much
the same core curriculum for the first 2 years. Then you got
to select whether you were going to be an EE, ME, or IE
(Industrial Engineer). The administration tried to steer you
into one of these based on your grade average: EE if you got
good grades, ME if mediocre, else IE. (With my average, I
had to *fight* for an EE slot!)

Best regards,




Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

And the mech guys drank the most booze, by far. Honestly, I was
seriously impressed by the guys at Penn State, they were easily the
smartest bunch of people I have met. And man did they do some cool
stuff. I especially liked the sterling cycle engine powered by a block
of burning lithium (in a seriously strong room with a Cu powder fire
extinguisher handy).

Cheers
Terry