Ceramic Capacitor Failure
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From: mook johnson on 30 Mar 2010 18:55 "eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote in message news:LICdnRkDnPyu-S_WnZ2dnUVZ_gidnZ2d(a)giganews.com... > 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 Probably as everyone said its a fracture that wicked in some contaminant that caused the short. The cracks usually ocur on soldering but also cna occir due to board flex and are aggrivated by vibration and thermal cycles. As carefully as you can remove a few and send them in the the manufacturer to let them have a look.
From: BobW on 30 Mar 2010 21:13 "eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote in message news:LICdnRkDnPyu-S_WnZ2dnUVZ_gidnZ2d(a)giganews.com... > 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? > 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 -- == All google group posts are automatically deleted due to spam ==
From: Bob Eld on 30 Mar 2010 21:46 "eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote in message news:LICdnRkDnPyu-S_WnZ2dnUVZ_gidnZ2d(a)giganews.com... > 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 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?
From: mook johnson on 30 Mar 2010 22:24 "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: eeboy on 30 Mar 2010 22:43 > >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
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