T
Terry Given
- Jan 1, 1970
- 0
Clarence said: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).
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.
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)
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