Prev: Getting a 433MHz antenna going
Next: Multiplex your inductor
From: Tim Williams on 30 Mar 2010 22:43
Z5U at 10kV? Wow, it might actually make a good bypass down under 100V ;-)

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"mook johnson" <mook(a)mook.net> wrote in message
news:Dnysn.172956$wr5.171896(a)newsfe22.iad...
>
> "Bob Eld" <nsmontassoc(a)yahoo.com> wrote in message
> news:hou9h8$mpc$1(a)news.eternal-september.org...
>
>>> ---------------------------------------
>>> Posted through http://www.Electronics-Related.com
>>
>> I've seen similar failures in wire leaded high voltage ceramic caps. Z5R
>> material, 470pf, caps rated at 10,000 volts failed at about 4,500 volts.
>> It
>> seemed to be batch related with a number of failures.
>>
>> Guess where the caps were made?.......Of course kids, China, where else?
>
>
> I'll bet that batch they were wondering of anyone would notice they
> labeled someones 1Kv caps at 10Kv. :)
>
>
>
>


From: mook johnson on 31 Mar 2010 07:11

"eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote in message
news:YomdnfouvP1dKy_WnZ2dnUVZ_gSdnZ2d(a)giganews.com...
> >
>>Cap manufacturers specify a maximum rate of change of temperature vs time
>
>>during the soldering process. This is, most likely, where your problem
> is.
>>
>>We had a lot of problems with high density ceramics. We modified the
> reflow
>>profile and the problems went away.
>>
>>Bob
>>--
>>
>
> One thing that I just realized is the very same capacitor is used in two
> other places on the board. This particular board is a 4 layer board with
> the inner planes devoted to power and ground. Examining the three
> locations
> I noticed the two other locations where this cap is used are tied to the
> inner planes with short traces and a via. The particular cap that is
> failing has one pad tied to ground through a short trace but the other pad
> travels about 2cm (7mil trace) before tying to anything significant.
> Perhaps if this trace was short like the other two locations then the
> problem would disappear?
>
> ---------------------------------------
> Posted through http://www.Electronics-Related.com


How are these boards soldered. Hand, reflow, etc?



From: Bob Eld on 31 Mar 2010 10:51

"Tim Williams" <tmoranwms(a)charter.net> wrote in message
news:houcs9$ksg$1(a)news.eternal-september.org...
> Z5U at 10kV? Wow, it might actually make a good bypass down under 100V
;-)
>
> Tim

That's Z5R


From: qrk on 31 Mar 2010 13:52
On Tue, 30 Mar 2010 15:50:59 -0500, "eeboy"
<jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote:

>I've got a situation where boards are being returned all of the sudden.
>This particular board has been in service well before my time so it seems
>as if it is perhaps related to a particular batch. The problem is with an
>0805 ceramic capacitor. The same capacitor seems to have failed on each.
>The result is a 56 ohm DC resistance. The capacitor is a simple decoupling
>cap for a logic IC. Once removed, the board behaves nicely again. Is this a
>common failure mode for ceramic caps? What's the probability that we simply
>got a bad reel of the component? What potential causes are there for this
>failure?
>
>I can rule out over voltage. The cap is rated at 25V but the maximum
>voltage it would see during operation is 5V. I think I can rule out ESD as
>there are many more sensitive components that would have fried before this
>cap. The circuit is a low power logic circuit... no large switching
>currents.
>
>Any thoughts?
>
>---------------------------------------
>Posted through http://www.Electronics-Related.com

This is an uncommon failure unless you are using crappy or counterfit
parts. Shorts can be caused by stress if it cracks the capacitor. Is
this part stressed during assembly or mounting? Depaneling a board can
stess parts near the edge of the board, especially if the parts aren't
aligned properly. Stress from the mounting points can crack nearby
parts if there is vibration, shipping, or the system is dropped,
especially if the board has insufficient support.

--
Mark
From: Archimedes' Lever on 31 Mar 2010 20:18
On Wed, 31 Mar 2010 06:51:16 -0800, "Bob Eld" <nsmontassoc(a)yahoo.com>
wrote:

>
>"Tim Williams" <tmoranwms(a)charter.net> wrote in message
>news:houcs9$ksg$1(a)news.eternal-september.org...
>> Z5U at 10kV? Wow, it might actually make a good bypass down under 100V
>;-)
>>
>> Tim
>
>That's Z5R
>
Google Z5R and find NOTHING. Google Z5U and find that it is an IEDC
Class 2 dielectric medium.

Maybe you should "try again".

Z5U is a common HV cap dielectric. Never heard of Z5R.
First  |  Prev  |  Next  |  Last
Pages: 1 2 3 4
Prev: Getting a 433MHz antenna going
Next: Multiplex your inductor