Soldering surface mount components

[Ken Smith]

In article <z82sd.37821$6q2.11018@newssvr14.news.prodigy.com>,
Clarence <no@No.com> wrote:

"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:coq4c5$s69$3@blue.rahul.net...
In article <JDUrd.53480$QJ3.45347@newssvr21.news.prodigy.com>,
Clarence <no@No.com> wrote:
[...]
If your aware of any other piezoelectric materials please list them. I can
think of many applications for a low cost piezoelectric operated mechanical
device.

Both X7R and X5R are slightly piezoelectric. Neither is good enough to be
put to practical use as an actuator. If you put about 500mA at 2KHz
through a 2.2uF X7R cap mounted on a PCB you get just enough motion that
you can hear it.

500mA is a rather substantial level of power for that value. It takes 39.3
Volts sinusoidal directly across the cap.

I didn't suggest it was a good idea to put that much AC through the poor
thing. I just said that it screems if you do.

BTW: 1/( 2 * PI * F * C ) = 36.17 on my slide rule

0.5 * 36.17 = 18.08 Then we have to add a little for the ESR.

Also the ATC capacitors are rated for several Amps at 30MHz.

[...]

As little as a reliable motion of 0.002 for a 100V bias would be useful.
Assume a bar shape for maximum deflection.

A lot depends on what you call reliable. If you want cheap use a plastic
piezoelectric element. There are many makers of piezielectric ceramic
elements. If you are doing something like pushing a grating to tune a
laser, don't use the plastic stuff. It is a good thermometer.

So how much motion do you get at 100KHz? The entire unit is 0.180 long, 0.120
wide, and 0.080 high (max) with tolerances of +/- 0.010 Inches. The cap
element is coated with a resilient encapsulate.

I've never been interested enough to measure it.

The AC component is 30VRMS max and the DC is 80V.
I find nothing that confirms the property, nor the magnitude of the motion.

Try google. I'll bet you will find something from AVX's web site that
confirms the effect and says words like "but our do it less".

BTW, NASA, and FAA do not provide any warnings on these devices.

Im not surprised about the FAA.

NASA does surprise me a bit. They wouldn't allow PVC parts to be used in
the U2/ER2 because of the fume risk to the pilot. This even applies to
the parts that are at outdoors pressure.

How about the X5V material?

I think all high K materials do it to some degree.


--
--
kensmith@rahul.net forging knowledge

 

[John Fields]

On Fri, 03 Dec 2004 19:45:53 -0500, John Popelish <jpopelish@rica.net>
wrote:

Agreed. I have a little pump and dump LED pulser that charges a 1 uf
100 VDC X7R 1210 smt capacitor. I gcharge it up to 50 volts over 900
us and dump it through the LEDs with a peak current of almost 1 amp in
100 us with the current peak controlled by a series inductance. I can
always tell when the circuit is working by the thin whine emitted.
Mylar caps in the same circuit made no noise.

---
"Thin whine"?

If only more of us could write like you do maybe we'd have fewer
disagreements...

--
John Fields

 

[John Popelish]

John Fields wrote:

On Fri, 03 Dec 2004 19:45:53 -0500, John Popelish <jpopelish@rica.net
wrote:
I can
always tell when the circuit is working by the thin whine emitted.
Mylar caps in the same circuit made no noise.

---
"Thin whine"?

If only more of us could write like you do maybe we'd have fewer
disagreements...

Thanks?

--
John Popelish

 

[Clarence]

"John Popelish" <jpopelish@rica.net> wrote

John Fields wrote:
John Popelish wrote:
I can
always tell when the circuit is working by the thin whine emitted.
Mylar caps in the same circuit made no noise.
---
"Thin whine"?
If only more of us could write like you do maybe we'd have fewer
disagreements...
Thanks?
John Popelish

Before it was stated that they would be cracked by the piezoelectric effect!

I buy caps by the roll, and they are installed by many different people, some
by flow soldering, some manually soldered by a convention Iron. Never heard a
peep, nor had a failure due to a crack from soldering. Thermal cycling has
causes a few failures, but only a few. Less than 0.1%!

 

[Clarence]

"Ken Smith" wrote

Clarence wrote
"Ken Smith" <kensmith@green.rahul.net> wrote in message
Clarence <no@No.com> wrote:
[...]
If your aware of any other piezoelectric materials please list them. I
can
think of many applications for a low cost piezoelectric operated
mechanical
device.

Both X7R and X5R are slightly piezoelectric. Neither is good enough to be
put to practical use as an actuator. If you put about 500mA at 2KHz
through a 2.2uF X7R cap mounted on a PCB you get just enough motion that
you can hear it.

500mA is a rather substantial level of power for that value. It takes 39.3
Volts sinusoidal directly across the cap.

I didn't suggest it was a good idea to put that much AC through the poor
thing. I just said that it screams if you do.

BTW: 1/( 2 * PI * F * C ) = 36.17 on my slide rule

Did you allow for ESR? I did!

0.5 * 36.17 = 18.08 Then we have to add a little for the ESR.

Also the ATC capacitors are rated for several Amps at 30MHz.

Which is NOT 2Khz!

As little as a reliable motion of 0.002 for a 100V bias would be useful.
Assume a bar shape for maximum deflection.

A lot depends on what you call reliable. If you want cheap use a plastic
piezoelectric element. There are many makers of piezoelectric ceramic
elements. If you are doing something like pushing a grating to tune a
laser, don't use the plastic stuff. It is a good thermometer.

I'm looking for a pump impeller an implanted medical application.

So how much motion do you get at 100KHz? The entire unit is 0.180 long,
0.120
wide, and 0.080 high (max) with tolerances of +/- 0.010 Inches. The cap
element is coated with a resilient encapsulate.

I've never been interested enough to measure it.

I Goggled, and found no published studies which gave numbers. Only that the
motion was detected.

The AC component is 30VRMS max and the DC is 80V.
I find nothing that confirms the property, nor the magnitude of the motion.

I

Try google. I'll bet you will find something from AVX's web site that
confirms the effect and says words like "but our do it less".

BTW, NASA, and FAA do not provide any warnings on these devices.

I'm not surprised about the FAA.

The FAA is very stringent about any condition which might cause a fair or spark
on a board. For instance "Gold caps" often used to maintain a RTD are not
acceptable since they fail (rarely) by out gassing with a flame.

NASA does surprise me a bit. They wouldn't allow PVC parts to be used in
the U2/ER2 because of the fume risk to the pilot. This even applies to
the parts that are at outdoors pressure.

I used many of these in a satellite program.

How about the X5V material?
I think all high K materials do it to some degree.

Very small Degree!


These got clipped from my last mail:

Per AVX:
Effects of Mechanical Stress – High "K" dielectric ceramic capacitors
exhibit 'some' 'low level' piezoelectric reactions under 'mechanical
stress.' As a general statement, the piezoelectric output is higher,
the higher the dielectric constant of the ceramic. 'It is desirable to
investigate this effect before using high "K" dielectrics as coupling
capacitors in extremely low level applications.'

Also found:
Piezoelectric Effect. One minor drawback for X7R dielectrics has been
their sceptibility to 'piezoelectric-induced stresses.' Although this
effect is 'marginal' and 'may be neglected for case sizes smaller than
the 2220,' for larger capacitors it can lead to catastrophic failures
caused by cracking. Modifying the dielectric composition to avoid any
piezoelectric effects within the range of operating frequencies may
skirt this problem.
Whereas the standard X7R material shows piezoelectric noise, this is
almost absent from the new ceramic. These measurements were made
under a 300-V bias at 90°C. Note this effect is not present in film
or aluminum-electrolytic capacitors. With this new development,
ceramics now offer a viable alternative to film and electrolytic
capacitors in the large case sizes.

 

[Ken Smith]

In article <Kw9sd.53752$QJ3.40450@newssvr21.news.prodigy.com>,
Clarence <no@No.com> wrote:

"Ken Smith" wrote
Clarence wrote
"Ken Smith" <kensmith@green.rahul.net> wrote in message
Clarence <no@No.com> wrote:
[...]
If your aware of any other piezoelectric materials please list them. I
can
think of many applications for a low cost piezoelectric operated
mechanical
device.

Both X7R and X5R are slightly piezoelectric. Neither is good enough to be
put to practical use as an actuator. If you put about 500mA at 2KHz
through a 2.2uF X7R cap mounted on a PCB you get just enough motion that
you can hear it.

500mA is a rather substantial level of power for that value. It takes 39.3
Volts sinusoidal directly across the cap.

I didn't suggest it was a good idea to put that much AC through the poor
thing. I just said that it screams if you do.

BTW: 1/( 2 * PI * F * C ) = 36.17 on my slide rule

Did you allow for ESR? I did!

So:

ESR = sqrt( (39.3/0.5)^2 - 36.17^2) = 69.78 Ohms

Holy smoking capacitors Batman were do you buy these caps so I can avoid
them!

0.5 * 36.17 = 18.08 Then we have to add a little for the ESR.

Also the ATC capacitors are rated for several Amps at 30MHz.

Which is NOT 2Khz!

Yes I noticed. The spec. is based on the heating. It doesn't vary that
much with frequency.

I'm looking for a pump impeller an implanted medical application.

You have bio compatibility issues then too don'y you? The plastic stuff
is based on Kynar and nickel plated IIRC. Does the Kynar cause trouble?
Will you keep it out of contact with the host? The Kynar causes larger
motion than the ceramic. The force it can produce is much less and the
losses are greater.

[...]

NASA does surprise me a bit. They wouldn't allow PVC parts to be used in
the U2/ER2 because of the fume risk to the pilot. This even applies to
the parts that are at outdoors pressure.


I used many of these in a satellite program.

There are not many pilots on these satellites are there?

These got clipped from my last mail:

Per AVX:
Effects of Mechanical Stress – High "K" dielectric ceramic capacitors
exhibit 'some' 'low level' piezoelectric reactions under 'mechanical
stress.' As a general statement, the piezoelectric output is higher,
the higher the dielectric constant of the ceramic. 'It is desirable to
investigate this effect before using high "K" dielectrics as coupling
capacitors in extremely low level applications.'

AVX is trying to sell you these capacitors. The fact that the makers seem
so unwilling to put a number on it makes me suspect that they are trying
to downplay it. I know that the piezoelectric effect can be real trouble
in low signal level analog circuits. they make microphones out of the
coupling capacitors.

--
--
kensmith@rahul.net forging knowledge

 

[Clarence]

"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:corc8h$sjf$1@blue.rahul.net...

In article <Kw9sd.53752$QJ3.40450@newssvr21.news.prodigy.com>,
Clarence <no@No.com> wrote:

"Ken Smith" wrote
Clarence wrote
"Ken Smith" <kensmith@green.rahul.net> wrote in message
Clarence <no@No.com> wrote:

BTW: 1/( 2 * PI * F * C ) = 36.17 on my slide rule

Did you allow for ESR? I did!

So:

ESR = sqrt( (39.3/0.5)^2 - 36.17^2) = 69.78 Ohms

Holy smoking capacitors Batman were do you buy these caps so I can avoid
them!

Decimal error somewhere. I got 3.6 ohms which is worst case for the family.

 

[Terry Given]

Clarence wrote:

"Terry Given" <my_name@ieee.org> wrote in message
news:ZZOrd.21704$9A.354354@news.xtra.co.nz...

Clarence wrote:


"Terry Given" wrote


Clarence wrote:


"Terry Given" <my_name@ieee.org> wrote in message
snip


Thanks for the warning about Macon. I'll avoid them!

Actually its not Marcon per se, its just that the larger ceramic caps
have mechanical resonance's that can be excited electrically. square-loop
ferrite has the same problem - witness the warnings in the Ferroxcube
databook.
Cheers > >>Terry

Like the 2.2mF to 100mF units I normally use?

Never seen any warnings. They are not piezoelectric.


C4532X7R2A225M By TDK 2.2uF 100V (since your into SI (stupid interference))
Up to and including C4532Y5V1A107Z 100uF 10V
And NOJC107M004RWJ 100uF 4V Y5V

These are all 1812 SMT parts.

I'm curious about using Y5V - you have a 100uF 10V cap. TDK spec Y5V as
+22%/-85% over -30C - +85C range. Using the AVX data (TDK dont seem to
mention this) the voltage coefficient is -90% at 60% rated Vcc, -80% at
40% Vcc. Assuming Vcc = 4V = 40% of rated voltage, you therefore only
have 20uF of overall capacitance. You probably use a 10V cap at more
like 6-7V, so its more like 10uF. Add in the temperature effects, and
its looking more like 1.5uF.

X7R = +/- 15% over -55C - +125C. AVX give -10% at 100% rated voltage. A
22uF 10V X7R cap comes in a 1210 package from TDK, and will have MORE
CAPACITANCE than the 100uF part you are currently using. Unless of
course you are using it at very low voltage (< 20% rated), with
temperature between 0-45C. Given that this is a space application, I
doubt the temperature is that well controlled.

Mind you you might be using the cap as a DC bias/temperature/vibration
detector, in which case Y5V would be a very good choice.

you use 0.1 farad ceramic caps? those I'd like to see. What's the
dielectric? (or perhaps you use "mF" to mean micro-Farads - quaint but
confusing, given the preponderance of SI units nowadays). I did once see
a 100uF 200V (IIRC) NPO cap (mil smps). very very expensive - US$300 IIRC.

AFAICR the piezoelectric behavior was not the issue - just electrically
exciting them at their mechanical resonant frequencies.


Electrical excitation to mechanical resonance is the DEFINITION of
"piezoelectric."

No its not. The IEEE standard dictionary of electrical and electronics
terms, 6th ed. defines piezoelectric effect as:

"Some materials become electrically polarized when they are mechanically
strained. The direction and magnitude of polarization depend upon the
nature and amount of the strain, and upon the direction of the strain.
In such materials the converse effect is observed, namely, that a strain
results from the application of an electric field."

Note the complete and utter lack of the word "resonance" or any of its
variants.

It also appears you are suggesting there are no forces whatsoever inside
a capacitor, other than those caused by the piezoelectric effect. That
would be a fairly neat trick if it were true, and would doubtless be a
major concern to the manufacturers of electrostatic loudspeakers, which
by now ought to have all stopped working in light of this revelation.


Cheers
Terry

 

[Clarence]

"Terry Given" <my_name@ieee.org> wrote in message

John Fields wrote:
On Thu, 02 Dec 2004 23:06:21 GMT, "Clarence" <no@No.com> wrote:

Like the 2.2mF to 100mF units I normally use?
---
Pretty large value for ceramics, eh?
---
Actually,NO! But the higher values are generally too expensive.

Never seen any warnings. They are not piezoelectric.
---
It's not necessary for a capacitor to be piezoelectric to exhibit a
mechanical resonance or to be microphonic. All that's required is for
the dielectric to be mechanically deformable by the forces exerted by
the electric field across it or for the dielectric to be deformed by
external mechanical forces.

This has nothing to do with part damage due to a piezoelectric property. Many
types of Capacitors including AIR dielectric are subject to "PURELY MECHANICAL"
variation.
I used to use WOBULATORS to modulate a VFO for a particular type of FM. Driving
a split stator ball bearing variable capacitor with a motor to generate a wide
frequency variation at a controlled rate. So what has this kind of mechanical
change of capacity have to do with piezoelectric damage to a part?

And if the mechanical resonant frequency is the same as the electrical
excitation, significant (wrt the cap) forces can build up over time.
2220 and bigger were noted in the Marcon paper.

Cheers
Terry

Since I do not use the larger package size, I see no relevance.

 

[Clarence]

"Terry Given" <my_name@ieee.org> wrote

Clarence wrote:
"Terry Given" <my_name@ieee.org> wrote in message
Clarence wrote:
"Terry Given" wrote
Clarence wrote:
"Terry Given" <my_name@ieee.org> wrote in message
snip
Thanks for the warning about Macon. I'll avoid them!

Actually its not Marcon per se, its just that the larger ceramic caps
have mechanical resonance's that can be excited electrically. square-loop
ferrite has the same problem - witness the warnings in the Ferroxcube
databook.
Cheers > >>Terry

Like the 2.2mF to 100mF units I normally use?

Never seen any warnings. They are not piezoelectric.

C4532X7R2A225M By TDK 2.2uF 100V (since your into SI (stupid
interference))
Up to and including C4532Y5V1A107Z 100uF 10V
And NOJC107M004RWJ 100uF 4V Y5V

These are all 1812 SMT parts.

I'm curious about using Y5V - you have a 100uF 10V cap. TDK spec Y5V as
+22%/-85% over -30C - +85C range. Using the AVX data (TDK dont seem to
mention this) the voltage coefficient is -90% at 60% rated Vcc, -80% at
40% Vcc. Assuming Vcc = 4V = 40% of rated voltage, you therefore only
have 20uF of overall capacitance. You probably use a 10V cap at more
like 6-7V, so its more like 10uF. Add in the temperature effects, and
its looking more like 1.5uF.

X7R = +/- 15% over -55C - +125C. AVX give -10% at 100% rated voltage. A
22uF 10V X7R cap comes in a 1210 package from TDK, and will have MORE
CAPACITANCE than the 100uF part you are currently using. Unless of
course you are using it at very low voltage (< 20% rated), with
temperature between 0-45C. Given that this is a space application, I
doubt the temperature is that well controlled.

Mind you you might be using the cap as a DC bias/temperature/vibration
detector, in which case Y5V would be a very good choice.

Rest assured that the components we used were applied properly and with the
approval of the design staff, and NASA, who along with myself, recommended this
approach to solve another problem.

<snip>

AFAICR the piezoelectric behavior was not the issue - just electrically
exciting them at their mechanical resonant frequencies.

This appears to be a change of subject from the effect being due to forces from
piezoelectric characteristics. I see nothing relevant to discussing this!

Electrical excitation to mechanical resonance is the DEFINITION of
"piezoelectric."

No its not. The IEEE standard dictionary of electrical and electronics
terms, 6th ed. defines piezoelectric effect as:

"Some materials become electrically polarized when they are mechanically
strained. The direction and magnitude of polarization depend upon the
nature and amount of the strain, and upon the direction of the strain.
In such materials the converse effect is observed, namely, that a strain
results from the application of an electric field."

Note the complete and utter lack of the word "resonance" or any of its
variants.

I'll concede the IEEE is correct, I should have quoted precisely.

It also appears you are suggesting there are no forces whatsoever inside
a capacitor, other than those caused by the piezoelectric effect. That
would be a fairly neat trick if it were true, and would doubtless be a
major concern to the manufacturers of electrostatic loudspeakers, which
by now ought to have all stopped working in light of this revelation.

Again, your attempting to change the subject, unless you are asserting that
electrostatic loudspeakers operate on and are damaged by piezoelectric forces.

I have not addressed such speakers, and INDEED have no interest in them.

I think this is no longer a matter of sharing different experiences, rather is
appears to be you trying unsuccessfully to prove you knowledge is greater and
more correct than someone else's. I don't care to play. I designed weapons
system components for use in Vietnam which are still working and in use. I
have nothing I care to prove to you. Your entitled to your opine. So am I!

 

[Terry Given]

Clarence wrote:

"Terry Given" <my_name@ieee.org> wrote

Clarence wrote:

"Terry Given" <my_name@ieee.org> wrote in message

Clarence wrote:

"Terry Given" wrote

Clarence wrote:

"Terry Given" <my_name@ieee.org> wrote in message
snip
Thanks for the warning about Macon. I'll avoid them!

Actually its not Marcon per se, its just that the larger ceramic caps
have mechanical resonance's that can be excited electrically. square-loop
ferrite has the same problem - witness the warnings in the Ferroxcube
databook.
Cheers > >>Terry

Like the 2.2mF to 100mF units I normally use?

Never seen any warnings. They are not piezoelectric.

C4532X7R2A225M By TDK 2.2uF 100V (since your into SI (stupid

interference))

Up to and including C4532Y5V1A107Z 100uF 10V
And NOJC107M004RWJ 100uF 4V Y5V

These are all 1812 SMT parts.

I'm curious about using Y5V - you have a 100uF 10V cap. TDK spec Y5V as
+22%/-85% over -30C - +85C range. Using the AVX data (TDK dont seem to
mention this) the voltage coefficient is -90% at 60% rated Vcc, -80% at
40% Vcc. Assuming Vcc = 4V = 40% of rated voltage, you therefore only
have 20uF of overall capacitance. You probably use a 10V cap at more
like 6-7V, so its more like 10uF. Add in the temperature effects, and
its looking more like 1.5uF.

X7R = +/- 15% over -55C - +125C. AVX give -10% at 100% rated voltage. A
22uF 10V X7R cap comes in a 1210 package from TDK, and will have MORE
CAPACITANCE than the 100uF part you are currently using. Unless of
course you are using it at very low voltage (< 20% rated), with
temperature between 0-45C. Given that this is a space application, I
doubt the temperature is that well controlled.

Mind you you might be using the cap as a DC bias/temperature/vibration
detector, in which case Y5V would be a very good choice.


Rest assured that the components we used were applied properly and with the
approval of the design staff, and NASA, who along with myself, recommended this
approach to solve another problem.

I have yet to see an area where Y5V caps are actually worth using.
Absence of proof is not however proof of absence; I assume there are in
fact very good reasons why you chose Y5V, and was kind of hoping you
would share those reasons, so that I and others could learn from your
experience.

I am however constantly surprised by how few engineers seem to know
about the voltage characteristics of Y5V, or for that matter the
temperature characteristics - odd when you consider most manufacturers
supply that information (although TDK seems to want to hide the voltage
coefficient, Philips (or whatever they are now called), AVX and others
do not).

snip

AFAICR the piezoelectric behavior was not the issue - just electrically
exciting them at their mechanical resonant frequencies.


This appears to be a change of subject from the effect being due to forces from
piezoelectric characteristics. I see nothing relevant to discussing this!

**YOU** brought up the piezoelectric effect, then incorrectly defined
it, and erroneously said X7R and Y5V are not piezoelectric.

Electrical excitation to mechanical resonance is the DEFINITION of
"piezoelectric."

No its not. The IEEE standard dictionary of electrical and electronics
terms, 6th ed. defines piezoelectric effect as:

"Some materials become electrically polarized when they are mechanically
strained. The direction and magnitude of polarization depend upon the
nature and amount of the strain, and upon the direction of the strain.
In such materials the converse effect is observed, namely, that a strain
results from the application of an electric field."

Note the complete and utter lack of the word "resonance" or any of its
variants.


I'll concede the IEEE is correct, I should have quoted precisely.

I'll concede I'm a pedant

(but the resonance was enough of a red herring to warrant correction)

It also appears you are suggesting there are no forces whatsoever inside
a capacitor, other than those caused by the piezoelectric effect. That
would be a fairly neat trick if it were true, and would doubtless be a
major concern to the manufacturers of electrostatic loudspeakers, which
by now ought to have all stopped working in light of this revelation.


Again, your attempting to change the subject, unless you are asserting that
electrostatic loudspeakers operate on and are damaged by piezoelectric forces.

I originally stated:
"AFAICR the piezoelectric behaviour was not the issue - just
electrically exciting them at their mechanical resonant frequencies."

I am merely asserting that forces act on capacitors, regardless of any
piezoelectric effect. I had a look, but cant dig up the Marcon paper; I
suspect that you are probably right about the piezoelectric effect being
the predominant issue though.

I have not addressed such speakers, and INDEED have no interest in them.

Nor do I, except they provide a fairly graphic demonstration that forces
act on capacitors.

I think this is no longer a matter of sharing different experiences, rather is
appears to be you trying unsuccessfully to prove you knowledge is greater and
more correct than someone else's. I don't care to play. I designed weapons
system components for use in Vietnam which are still working and in use. I
have nothing I care to prove to you. Your entitled to your opine. So am I!

Not at all. I greatly enjoy technical discussions, I often learn a lot
from them - for example I didnt really know much at all about
microphonics until following discussions here - in smps use the
piezoelectric effect of caps is pretty much negligible (unless, of
course, your large caps break due to exciting the mechanical resonance).

The OP is of course about soldering smt parts. The TDK app notes here:

http://www.component.tdk.com/ceramic.asp

are quite useful. "Common cracking modes" is particularly pertinent. TDK
state that the main causes of cracking are mechanical damage - impact
damage or pcb flexure. But they also talk about how uneven soldering
causes stress concentrations that exacerbate flexure related cracking
(probably a lot less of an issue on Aluminium cored boards than FR4).
They very briefly (one sentence) mention thermal stress, in-circuit
testers (impact I presume) and H2 absorption as possible failure modes.

Something I did not know about high-K caps was the ageing effect - the
"what is the capacitance of this capacitor" document talks about it.
Another thing due to the use of Barium Titanate. And the ageing is a
reversible process! See, lots of interesting things to learn.

I can share a funny story about pcb flexure - our production dept.
wanted to reduce the build time on a gatedriver pcb (6 per product) so
smt'd it, and panelised about 20 onto an A4 sized FR4 pcb. Rather than
routing the pcb and using breakouts as advised, they V-grooved it and
got the mechanical workshop to produce a guillotine-like device to cut
the individual PCBs out. As the guillotine sliced the PCB it bent
significantly, and all the caps and resistors disappeared off the PCBs,
leaving only their endcaps behind. The really sad part is that
production abandoned the product, rather than simply routing the
panelised PCB. ISTR the original PCB hand assembly cost about the same
as the parts themselves, and the smt pcb was almost half the price.
Adding in the extra money for routing would have added around 10% to the
cost of the smt pcb, so it was still a lot cheaper.

The same guys also built a Jig to insert a pcb into a press-fit plastic
enclosure, by pressing on the top of a 1206 resistor. We had a 100%
failure rate on the first couple of hundred PCBs, but the tech never
mentioned that every single resistor broke in half when he desoldered
them. The real funny bit was there was huge amounts of space, the mech
guys never looked but miraculously picked the one spot there was a
resistor - that Murphy fellow again....


Cheers
Terry

 

[Boris Mohar]

On Wed, 1 Dec 2004 09:55:52 -0800, "Larry Brasfield"
<donotspam_larry_brasfield@hotmail.com> wrote:

"Clarence" <no@No.com> wrote in message
news:mTfrd.36936$6q2.19094@newssvr14.news.prodigy.com...
"Larry Brasfield" <donotspam_larry_brasfield@hotmail.com> wrote in message
news:nQcrd.395$O54.36918@news.uswest.net...
"John Larkin" <jjlarkin@highSNIPlandTHIStechPLEASEnology.com
wrote in message news:a7lpq05v0jvt6vqbg354pm22iubjgkma8j@4ax.com...
Surface-mount parts are designed to be soldered in a reflow oven,
where the entire loaded board gets heated above solder-melt
temperature for a minute or so. Most parts don't mind. I just solder
them by hand, and it pretty much always works.

Hand soldering can be very hard on SMD ceramic capacitors.
The high temperature gradiant created by applying heat suddenly
at one end can fracture the ceramic. This can lead to excess noise
or a tendency to break down at a lower than rated voltage as
moisure gets into the crack(s). The insidious aspect of this kind
of damage is that it can show up in the field, quite some time
after the parts perform alright in initial testing.

At Siemens Ultrasound, we learned this the hard way, then had it
confirmed by at least one vendor's examination of abused parts.

--Larry Brasfield

Of course this may have actually happened,

Yes, of course.

and Boy, you had some pretty lousy assembly people.

They were quite skilled and competent, generally. If you knew
the circumstances under which the hand soldering occured, you
might not be so willing to denigrate them. (But who knows?)

I've seen the pre-prod units used for test assembled and
soldered by hand and subjected to extensive testing. Never saw a solder
related failure of a component.

To see the excess noise phenomenon, you would have to be
looking at a circuit handling low level signals which would be
affected by random parametric shifts. To see the drop in
voltage withstand, you would have to be using parts at an
appreciable fraction of their rated voltage, or subject them
to conditions under which moisture would enter the cracks.
So the fact that you never saw that is not much reassurance.

We tested for very long periods on many boards.

But what were you testing for? Did the environment
promote moisture ingression into the cracks? Was there
thermal cycling? I must say, your failure to see that
phenomenon is weak evidence against its reality.

Of course we also inspected the boards before applying power and
checking for damage. Rarely had to retouch a board after the first three.

The damage I mentioned is nearly impossible to see without
a microscope. Typically, the micro-cracks do not extend
clear thru the part, and they tend to be closed, being held
together by the unbroken material. I doubt your inspection
would have caught that damage.

The facts I have related regarding the failure mechansim,
and the strong disrecommendation against hand soldering
ceramic SMD capacitors, came to me directly from a well
known and reputable supplier of such parts. You, or other
"we got away with something, so it must be fine" kind of
folks can disregard it and often not pay the price. Those
who desire reliability will more likely heed it.

Any particular brand of capacitors? Any particular dielectric? Over years
we hand assembled a number of prototypes and small production runs that used
plenty of ceramic capacitors. These included high voltage, tuned and timing
circuits where a partial value failure would show up. At up to 30 power
magnification there were no visible cracks. The dielectric materials varied
from NPO to Y5V. We use Metcal MX with 700˜ tips and organic flux. The
environment is geophysical instrumentation which can be pretty demanding.

We had two component failures directly attributable to hand soldering. One
was stacked film chip capacitor where there was a drastic drop in value due
to internal stack disconnects from the end termination. The other was a
resetable fuse where the end termination cracked. The fuse was still
operational.

Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs http://www3.sympatico.ca/borism/

void _-void-_ in the obvious place



Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs http://www3.sympatico.ca/borism/

 

[Larry Brasfield]

"Boris Mohar" <borism_-void-_@sympatico.ca> wrote in message news:4746r0plfmppuj19038ah3sjlforvq0q61@4ax.com...

On Wed, 1 Dec 2004 09:55:52 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:

[Brasfield earlier wrote:]
Hand soldering can be very hard on SMD ceramic capacitors.
The high temperature gradiant created by applying heat suddenly
at one end can fracture the ceramic. This can lead to excess noise
or a tendency to break down at a lower than rated voltage as
moisure gets into the crack(s). The insidious aspect of this kind
of damage is that it can show up in the field, quite some time
after the parts perform alright in initial testing.

At Siemens Ultrasound, we learned this the hard way, then had it
confirmed by at least one vendor's examination of abused parts.
....
To see the excess noise phenomenon, you would have to be
looking at a circuit handling low level signals which would be
affected by random parametric shifts. To see the drop in
voltage withstand, you would have to be using parts at an
appreciable fraction of their rated voltage, or subject them
to conditions under which moisture would enter the cracks.
....
The damage I mentioned is nearly impossible to see without
a microscope. Typically, the micro-cracks do not extend
clear thru the part, and they tend to be closed, being held
together by the unbroken material.
....
The facts I have related regarding the failure mechansim,
and the strong disrecommendation against hand soldering
ceramic SMD capacitors, came to me directly from a well
known and reputable supplier of such parts.
....

Any particular brand of capacitors?

I'm sorry that I cannot recall, precisely. It was one of the
Japanese producers. A representative of theirs gave a
presentation to (some of) our engineers (including myself)
where the effects of that abuse where shown in micro-
photographs. From my visual memory of it, I suspect
the magnification was well in excess of 30, and the cracks
were somewhat subtle in appearance because they were
closed and on the corners.

Any particular dielectric?

I am sure it was NPO. I expect all the vendors are using
similar ceramics, at least with respect to the mechanical and
thermal properties that relate to thermally induced microcracking.

Over years
we hand assembled a number of prototypes and small production runs that used
plenty of ceramic capacitors. These included high voltage, tuned and timing
circuits where a partial value failure would show up. At up to 30 power
magnification there were no visible cracks. The dielectric materials varied
from NPO to Y5V. We use Metcal MX with 700~ tips and organic flux. The
environment is geophysical instrumentation which can be pretty demanding.

We were doing Doppler processing where minute phase
or amplitude shifts would be interpreted as meaningful.
The cracked capacitors would create artifacts. These
were not much above the noise floor, so they would
have been 50 to 70 dB below the signal that had been
modulated by the parametric noise to make the artifact.
(This, too, is a demanding application.)

We had two component failures directly attributable to hand soldering. One
was stacked film chip capacitor where there was a drastic drop in value due
to internal stack disconnects from the end termination. The other was a
resetable fuse where the end termination cracked. The fuse was still
operational.

We would see this failure maybe in 1 out of 5000 parts.
Perhaps the parts in your prototypes that had to be very
stable were lucky, or the person doing the soldering was
applying the iron to the pad, which is gentler thermally.

Even after seeing that effect, I hand solder SMD ceramic
capacitors for initial prototypes. But I take care (or have
care taken by the assembler) to not apply the iron to the
endcaps. And the finished article is not fielded. I cannot
consider them reliable because of potential cracking.

Regards,

Boris Mohar
--

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

 

[John Fields]

On Sun, 05 Dec 2004 10:30:41 GMT, "Clarence" <no@No.com> wrote:

"Terry Given" <my_name@ieee.org> wrote in message
John Fields wrote:
On Thu, 02 Dec 2004 23:06:21 GMT, "Clarence" <no@No.com> wrote:

Like the 2.2mF to 100mF units I normally use?
---
Pretty large value for ceramics, eh?
---
Actually,NO! But the higher values are generally too expensive.

---
I would think so, especially that 100milliFarad unit you normally use?
---

Never seen any warnings. They are not piezoelectric.

---
The piezoelectric characteristics of the part are not normally
something which warrants a "warning", since operation within the
specified electrical and mechanical limits for the part will not cause
a failure because of the piezoelectric nature of the dielectric.
Rather it's an inherent characteristic of the device which must be
taken into account when using the part and its contribution "designed
out" if necessary.
---

---
It's not necessary for a capacitor to be piezoelectric to exhibit a
mechanical resonance or to be microphonic. All that's required is for
the dielectric to be mechanically deformable by the forces exerted by
the electric field across it or for the dielectric to be deformed by
external mechanical forces.

This has nothing to do with part damage due to a piezoelectric property.

---
????? I don't believe I said that it did.
---

Many types of Capacitors including AIR dielectric are subject to
"PURELY MECHANICAL" variation.

---
Yeah, I see you have a remarkable grasp of the obvious, but so what?

I mean, what point are you trying to make?

You've already demonstrated that you know nothing about the
manufacture of ceramic dielectric capacitors as evidenced by your
ignorance of the fact that barium titanate is a commonly used
dielectric, yet here you are throwing around platitudes as if they
were rare gems. In all fairness though, perhaps they are... to you.
---

I used to use WOBULATORS to modulate a VFO for a particular type of FM. Driving
a split stator ball bearing variable capacitor with a motor to generate a wide
frequency variation at a controlled rate. So what has this kind of mechanical
change of capacity have to do with piezoelectric damage to a part?

---
Absolutely nothing, so why are you even bringing it up?
---

And if the mechanical resonant frequency is the same as the electrical
excitation, significant (wrt the cap) forces can build up over time.
2220 and bigger were noted in the Marcon paper.

Cheers
Terry

Since I do not use the larger package size, I see no relevance.

---
Duck, or bob and weave?

--
John Fields

 

[Terry Given]

Larry Brasfield wrote:

"Boris Mohar" <borism_-void-_@sympatico.ca> wrote in message news:4746r0plfmppuj19038ah3sjlforvq0q61@4ax.com...

On Wed, 1 Dec 2004 09:55:52 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:


[Brasfield earlier wrote:]

Hand soldering can be very hard on SMD ceramic capacitors.
The high temperature gradiant created by applying heat suddenly
at one end can fracture the ceramic. This can lead to excess noise
or a tendency to break down at a lower than rated voltage as
moisure gets into the crack(s). The insidious aspect of this kind
of damage is that it can show up in the field, quite some time
after the parts perform alright in initial testing.

At Siemens Ultrasound, we learned this the hard way, then had it
confirmed by at least one vendor's examination of abused parts.

...

To see the excess noise phenomenon, you would have to be
looking at a circuit handling low level signals which would be
affected by random parametric shifts. To see the drop in
voltage withstand, you would have to be using parts at an
appreciable fraction of their rated voltage, or subject them
to conditions under which moisture would enter the cracks.

...

The damage I mentioned is nearly impossible to see without
a microscope. Typically, the micro-cracks do not extend
clear thru the part, and they tend to be closed, being held
together by the unbroken material.

...

The facts I have related regarding the failure mechansim,
and the strong disrecommendation against hand soldering
ceramic SMD capacitors, came to me directly from a well
known and reputable supplier of such parts.

...

Any particular brand of capacitors?


I'm sorry that I cannot recall, precisely. It was one of the
Japanese producers. A representative of theirs gave a
presentation to (some of) our engineers (including myself)
where the effects of that abuse where shown in micro-
photographs. From my visual memory of it, I suspect
the magnification was well in excess of 30, and the cracks
were somewhat subtle in appearance because they were
closed and on the corners.


Any particular dielectric?


I am sure it was NPO. I expect all the vendors are using
similar ceramics, at least with respect to the mechanical and
thermal properties that relate to thermally induced microcracking.


Over years
we hand assembled a number of prototypes and small production runs that used
plenty of ceramic capacitors. These included high voltage, tuned and timing
circuits where a partial value failure would show up. At up to 30 power
magnification there were no visible cracks. The dielectric materials varied
from NPO to Y5V. We use Metcal MX with 700~ tips and organic flux. The
environment is geophysical instrumentation which can be pretty demanding.


We were doing Doppler processing where minute phase
or amplitude shifts would be interpreted as meaningful.
The cracked capacitors would create artifacts. These
were not much above the noise floor, so they would
have been 50 to 70 dB below the signal that had been
modulated by the parametric noise to make the artifact.
(This, too, is a demanding application.)


We had two component failures directly attributable to hand soldering. One
was stacked film chip capacitor where there was a drastic drop in value due
to internal stack disconnects from the end termination. The other was a
resetable fuse where the end termination cracked. The fuse was still
operational.


We would see this failure maybe in 1 out of 5000 parts.
Perhaps the parts in your prototypes that had to be very
stable were lucky, or the person doing the soldering was
applying the iron to the pad, which is gentler thermally.

Even after seeing that effect, I hand solder SMD ceramic
capacitors for initial prototypes. But I take care (or have
care taken by the assembler) to not apply the iron to the
endcaps. And the finished article is not fielded. I cannot
consider them reliable because of potential cracking.

Ditto. And I *NEVER* re-use ceramic smt parts. I just buy values 1,000
at a time. But me and my METCAL MX2 (and my binocular microscope) have
soldered many, many thousands of 0603 parts (when a prototype uses 1400
parts, and you re-build it 5 times, thats a lot of dead parts) over the
last month or so, and no parts have failed (yet). But of course it aint
going to a customer.

I mostly break 0603 parts by moving the tweezers after soldering one end
only; both Cs and Rs are susceptible to this, but its fairly obvious
when you do it. perhaps 1% break like this.

1206 quad pack resistors are a pain to solder, especially when I lay out
my pcb so closely the tweezers are obstructed Self inflicted, so no
sympathy I guess

Regards,

Boris Mohar

Cheers
Terry

 

[Clarence]

"Terry Given" <my_name@ieee.org> wrote in message
news:dfDsd.22266$9A.382071@news.xtra.co.nz...

Clarence wrote:
"Terry Given" <my_name@ieee.org> wrote
Clarence wrote:
"Terry Given" <Terry Given@ieee.org> wrote in message
Clarence wrote:
"Terry Given" wrote
Clarence wrote:
"Terry Given" <my_name@ieee.org> wrote in message

<snip>

AFAICR the piezoelectric behavior was not the issue - just electrically
exciting them at their mechanical resonant frequencies.

This appears to be a change of subject from the effect being due to forces
from
piezoelectric characteristics. I see nothing relevant to discussing this!

**YOU** brought up the piezoelectric effect, then incorrectly defined
it, and erroneously said X7R and Y5V are not piezoelectric.

No, I said they were not damaged by a piezoelectric effect while hand
soldering.

I only miss quoted the definition. So what?

As I said:

I'll concede the IEEE is correct, I should have quoted precisely.
snip
Not at all. I greatly enjoy technical discussions,

You are also something of a pest. I got nothing from this except going over
very old ground which was not the topic.

 

[Larry Brasfield]

"Terry Given" <my_name@ieee.org> wrote in message news:dfDsd.22266$9A.382071@news.xtra.co.nz...
[huge snip]

I have yet to see an area where Y5V caps are actually worth using. Absence of proof is not however proof of absence; I assume
there are in fact very good reasons why you chose Y5V, and was kind of hoping you would share those reasons, so that I and others
could learn from your experience.

I am however constantly surprised by how few engineers seem to know about the voltage characteristics of Y5V, or for that matter
the temperature characteristics - odd when you consider most manufacturers supply that information (although TDK seems to want to
hide the voltage coefficient, Philips (or whatever they are now called), AVX and others do not).

I once had a knarly argument with a guy who thought I
was irresponsible for using a high K capacitor in a circuit
whose accuracy relied on charge balancing rather than
the particular capacitance or even its linearity. He had
adopted a rule resembling "Y5U's are crap". (I think he
may have eschewed them even for bypass applications.)

[snip]

**YOU** brought up the piezoelectric effect, then incorrectly defined it, and erroneously said X7R and Y5V are not piezoelectric.
....
No its not. The IEEE standard dictionary of electrical and electronics
terms, 6th ed. defines piezoelectric effect as:

"Some materials become electrically polarized when they are mechanically
strained. The direction and magnitude of polarization depend upon the
nature and amount of the strain, and upon the direction of the strain.
In such materials the converse effect is observed, namely, that a strain
results from the application of an electric field."

Methinks that common ceramic capacitors are not
actually piezoelectric. The forces that occur with
applied voltage are different in character from what
is defined as piezoelectric effect. Consider that the
dielectric of a charged capacitor is compressed
regardless of the polarity of the charge. This differs
from what happens with (properly poled) piezoelectric
ceramics, where one polarity compresses and the other
decompresses. For similar reasons, a capacitor with
no charge on it will not transduce mechanical strain
into an electrical output, while a piezoelectric device
will transduce without an ostensible external charge.
(The poling produces a situation similar to applied
charge, but it is not available at the terminals unless
the device temperature is elevated.) So, to sum up,
a material that *can be used* to obtain piezoelectric
effects (when poled) is not necessarily piezoelectric.
Commonly sold ceramic caps are not piezoelectric.

Cheers
Terry
Regards,

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

 

[Terry Given]

Hi Larry,

Larry Brasfield wrote:

"Terry Given" <my_name@ieee.org> wrote in message news:dfDsd.22266$9A.382071@news.xtra.co.nz...
[huge snip]

I have yet to see an area where Y5V caps are actually worth using. Absence of proof is not however proof of absence; I assume
there are in fact very good reasons why you chose Y5V, and was kind of hoping you would share those reasons, so that I and others
could learn from your experience.

I am however constantly surprised by how few engineers seem to know about the voltage characteristics of Y5V, or for that matter
the temperature characteristics - odd when you consider most manufacturers supply that information (although TDK seems to want to
hide the voltage coefficient, Philips (or whatever they are now called), AVX and others do not).


I once had a knarly argument with a guy who thought I
was irresponsible for using a high K capacitor in a circuit
whose accuracy relied on charge balancing rather than
the particular capacitance or even its linearity. He had
adopted a rule resembling "Y5U's are crap". (I think he
may have eschewed them even for bypass applications.)

To be honest I just avoid Z5U/Y5V (and in fact seek them out for
criticism/removal during design reviews), but in theory I would be quite
happy with using one in a charge-balancing circuit. In practice I would
be concerned about having them on the shelf, because some bright spark
in production is bound to use them in the wrong place (hey, lets put
them in this active filter...).

And when it comes to bypass applications, I still havent seen a valid
reason for using them - by the time you work out what the actual
capacitance is under DC bias and operating temperature range, its so low
that you can invariably get an X7R cap for the same price that has about
the same (if not much more) overall capacitance, and its usually the DC
bias that is the strongest factor - who runs caps at 10% of rated
voltage? thats just wasteful.

But, if you have a good reason, I'd love to hear it.

[snip]

**YOU** brought up the piezoelectric effect, then incorrectly defined it, and erroneously said X7R and Y5V are not piezoelectric.

...

No its not. The IEEE standard dictionary of electrical and electronics
terms, 6th ed. defines piezoelectric effect as:

"Some materials become electrically polarized when they are mechanically
strained. The direction and magnitude of polarization depend upon the
nature and amount of the strain, and upon the direction of the strain.
In such materials the converse effect is observed, namely, that a strain
results from the application of an electric field."


Methinks that common ceramic capacitors are not
actually piezoelectric. The forces that occur with
applied voltage are different in character from what
is defined as piezoelectric effect. Consider that the
dielectric of a charged capacitor is compressed
regardless of the polarity of the charge. This differs
from what happens with (properly poled) piezoelectric
ceramics, where one polarity compresses and the other
decompresses. For similar reasons, a capacitor with
no charge on it will not transduce mechanical strain
into an electrical output, while a piezoelectric device
will transduce without an ostensible external charge.
(The poling produces a situation similar to applied
charge, but it is not available at the terminals unless
the device temperature is elevated.) So, to sum up,
a material that *can be used* to obtain piezoelectric
effects (when poled) is not necessarily piezoelectric.
Commonly sold ceramic caps are not piezoelectric.


Cheers
Terry

Regards,

Something to think about. Thanks.

Cheers
Terry

 

[Terry Given]

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. 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.

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?

Cheers
Terry

 

[Larry Brasfield]

"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 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

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