*gasp* Useful EDN article on tantalum caps
in [Design]
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From: langwadt on 4 Jun 2010 12:08 On 4 Jun., 16:04, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Fri, 04 Jun 2010 09:47:43 -0400, Phil Hobbs > > <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > >Stupid title, but actual useful info on tantalum cap behaviour: > > >http://www.edn.com/article/509092-What_a_cap_astrophe_.php > > >Now that there's this existence proof, maybe there'll be a bit > >more...perhaps someone will write them another useful article, e.g. a > >compendium of all two-transistor circuits. > > >Cheers > > >Phil Hobbs > > Tantalums fail from excess current, namely dV/dt. MnO2 is an oxidizer > and tantalum is a fuel, and only a tiny ignition source sets it off. > They are fine for current-limited applications but firebombs if used > to bypass power rails. Derate them 3:1 on voltage if you must use them > as power bypasses. Better yet use aluminums, polymer aluminums for > wide-temperature appls > > John yeh luckly I were glasses, I have a scratch one glass from an exploding tant on the output of a switching regulator -Lasse
From: Mycelium on 4 Jun 2010 12:29 On Fri, 04 Jun 2010 10:59:32 -0500, Jim Yanik <jyanik(a)abuse.gov> wrote: > >TEKTRONIX used tantalums for many years in their scopes,and the failures >were not objectionably high. Usage was mostly on power rails,BTW. Yeah, except that they also used mostly mil spec components and production methodologies back then as well, and one (an engineer) could rely on the fact that they had been thoroughly conditioned before use on the production line. A hermetically sealed mil EL cap has a shelf life of decades. A COTS EL cap does not. There are several mechanisms that are/were in place during their manufacture to ensure that reliability level on those specialized caps, even though they differ little at the physical/electrical level... ie they are both paste laminated foil roll-ups.
From: Capt. Cave Man on 4 Jun 2010 12:32 On Fri, 4 Jun 2010 09:08:29 -0700 (PDT), "langwadt(a)fonz.dk" <langwadt(a)fonz.dk> wrote: > >yeh luckly I were glasses, I have a scratch one glass from an >exploding tant >on the output of a switching regulator > >-Lasse Gaze at circuits that you just 'fixed' as you re-energize them often, do ya? (you likely cause their failure with poor solder technique) I tend to gaze at the input current numbers. I do not have such catastrophic failures often, as with proper bench technique, the failure modes can almost always be spotted prior to any such actual event occurs.
From: John Larkin on 4 Jun 2010 12:40 On Fri, 04 Jun 2010 09:29:31 -0700, Mycelium <mycelium(a)thematrixattheendofthemushroomstem.org> wrote: >On Fri, 04 Jun 2010 10:59:32 -0500, Jim Yanik <jyanik(a)abuse.gov> wrote: > >> >>TEKTRONIX used tantalums for many years in their scopes,and the failures >>were not objectionably high. Usage was mostly on power rails,BTW. > > Yeah, except that they also used mostly mil spec components and >production methodologies back then as well, and one (an engineer) could >rely on the fact that they had been thoroughly conditioned before use on >the production line. > > A hermetically sealed mil EL cap has a shelf life of decades. A COTS >EL cap does not. There are several mechanisms that are/were in place >during their manufacture to ensure that reliability level on those >specialized caps, even though they differ little at the >physical/electrical level... ie they are both paste laminated foil >roll-ups. Wet-slugs don't detonate like MnO2 dry tantalums. The MIL CLR-types are very reliable. They have silver cases, so have gotten expensive. I don't think these are roll-ups. They are a sintered tantalum slug floating in a conductive paste, in a silver can. The semi-liquid paste must put the fires out. John
From: Paul Hovnanian P.E. on 4 Jun 2010 12:53
Phil Hobbs wrote: > On 6/4/2010 10:04 AM, John Larkin wrote: >> On Fri, 04 Jun 2010 09:47:43 -0400, Phil Hobbs >> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >> >>> Stupid title, but actual useful info on tantalum cap behaviour: >>> >>> http://www.edn.com/article/509092-What_a_cap_astrophe_.php >>> >>> Now that there's this existence proof, maybe there'll be a bit >>> more...perhaps someone will write them another useful article, e.g. a >>> compendium of all two-transistor circuits. >>> >>> Cheers >>> >>> Phil Hobbs >> >> Tantalums fail from excess current, namely dV/dt. MnO2 is an oxidizer >> and tantalum is a fuel, and only a tiny ignition source sets it off. >> They are fine for current-limited applications but firebombs if used >> to bypass power rails. Derate them 3:1 on voltage if you must use them >> as power bypasses. Better yet use aluminums, polymer aluminums for >> wide-temperature appls >> >> John >> > > The interesting thing in the article is that soldering makes large tants > vulnerable to overvoltage failure well below their rating, and that they > can be reconditioned (and made much more reliable) by putting a current > limit on the power supply. That's more useful for repairs or fixing > problems with a shipping product than for new designs, admittedly. > Still, I thought it was kind of cool, and remarkable for being in EDN! That might make a good argument for a properly thought out burn in procedure. There's too much pressure from management to just build it and ship it (airplanes included). -- Paul Hovnanian paul(a)hovnanian.com ---------------------------------------------------------------------- Have gnu, will travel. |