Re: Tantalum Capacitor Reliability
To all, This discussion has so far pointed to voltage and ripple current as being the main causes for tantalum capacitor mortality. There is, however, another feature of these caps that so far has not been discussed. That is one of temperature, soldering temperature to be exact. We have learned over the last few months that tantalum caps, when subjected to high temperatures (soldering, especially hand soldering), tend to change internally on a physical basis. A few capacitor manufacturers have verified this. After soldering, when a voltage is applied across the tantalum cap, the tantalum cap tries to self-heal itself. In doing so, the tantalum cap appears to re-rate its voltage rating to the applied voltage. The cause of the self-healing appears to be a function of the soldering temperature and the length of time that the temperature is applied. This is greatly egaserbated (sp?) when a soldering iron actually touches a terminal on the tantalum cap. For example and after very hot soldering, a 15V rated tantalum cap could conceivably be re-rated to about 5V if 5V is applied. We learned this the hard way. We are now actively looking for a suitable alternative to the tantalum cap application (buck filter needing low ESR). I wanted to throw in my 2 cents. Best regards, Ron Pickard rpick...@hypercom.com emcconsult...@yahoo.co m To: 72146@compuserve.com, chris.maxw...@nettest.com, emc-p...@ieee.org Sent by: cc: owner-emc-pstc@majordoSubject: Re: Tantalum Capacitor Reliability mo.ieee.org 07/29/02 01:35 PM Please respond to emcconsultant Nonetheless, inrush current aside, a 20V Tantalum is considered marginal for a 12V circuit if reliability is desired. A 60% derating factor was and is a typical max for reliability circuits, i.e a 30V min rated cap is recommended. Tantalums require additional derating than Al-electrolytics. Furthermore, switchers are notorious for destroying Tantalums due to the large and fast V-swings. I don't recall seeing too many Tantalums on switcher designs. --- Cortland Richmond 72146@compuserve.com wrote: Chris, The issue isn't voltage rating; low-ESR caps such as these are susceptible to excessive charging current at turn-on. At a former employer, we saw REALLY GOOD, expensive caps used on a computer's 5V bus exploding at turn-on, even ones rated at 50 volts. Replacing them with cheaper electrolytics (TEN volts!) took care of that. You might be able to alleviate turn-on stress by using a power-on monitor circuit to slow down the initial charge. But it'd be far cheaper to go to electrolytics. Cortland One of my colleagues is testing a new design. He has designed a buck-boost switching converter which has tantalum output capacitors. We have looked at his design and gone through the calculations. His output current is 4 A maximum. His output voltage is 12 VDC His caclulated ripple current is 800 mA. He needed a 120 mV ripple voltage, so he put 8 each of 68 uF, 20 V tantalum capacitors (with 150 mOhm ESR) in parallel on the output. Each cap is rated for approximately 800mA of ripple current. He has seen two failures of these capacitors during initial testing and demonstrations. Meanwhile, many initial units run fine. From what I can gather, he hasn't violated any design rules. He has 20V rated caps on a 12V circuit. He has a ripple current rating
Re: Tantalum Capacitor Reliability
Chris, You may want to look at some of the polymer aluminum electrolytic capacitors from: * Cornell Dubilier. * Elna. * Jaro Components. * Kemet. * Matsushita. * NIC Components Corporation. * Nichicon. * Panasonic. * Samchung. * SDK. * etc. I've used them on the last two controller cards that I designed for my previous employer, for the DC-DC converters and general bypassing, with very good results: * Equivalent series resistance (ESR) down to 0.015 ohms. * No worry about the capacitors catching fire in low-impedance circuits. * Priced about 1/3 of equivalent tantalums. * Readily available in quantity- no worry about being on allocation. They do tend to be a little taller than equivalent tantalums, if you are height-limited. But you don't have to derate them nearly as much as tantalums to be safe. I used the 105C-rated capacitors to ensure a longer lifetime than the more commonly available 85C capacitors. The pin-through-hole (PTH) radial versions had about 2/3 the ESR of the surface mount technology (SMT) versions when I did my last design. So we laid out my cards to use either style, with the SMT bulk capacitors turned 90 degrees from the PTH bulk capacitors, and their footprints overlaying one another for compactness. If you want to stick with tantalums, we have a bibliography for Power Distribution on Printed Circuit Boards at http://www.dbicorporation.com/pwr-bib.htm I just added Ken Javor's report to the bibliography, [215a], so out of the 380+ references, the following ones apply directly to the proper use of tantalum capacitors: [91] Precautions and guidelines for users (Tantalum), Nippon Chemi-con. (download from http://www.chemi-con.co.jp/english/support/tantal_note_e.html) [92] Precautions in Using Tantalum Capacitors. (download from http://www.bostonaic.com/tantalum/precautions4.html) [107] Tantalum Capacitors With Solid Electrolyte (Chip Type), Mectron. (download from http://www.mectron.co.kr/components/tan-2.html) [145] Cain, Jeffrey, Comparison of Multilayer Ceramic and Tantalum Capacitors. (download from http://www.avxcorp.com/docs/techinfo/mlc-tant.pdf) [180] Franklin, R. W., Equivalent Series Resistance of Tantalum Capacitors. (download from http://www.avxcorp.com/docs/techinfo/eqtantcp.pdf) [181] Franklin, R. W., Ripple Rating of Tantalum Chip Capacitors. (download from http://www.avxcorp.com/docs/techinfo/rpleinfo.pdf) [190] Gill, John, Surge in Solid Tantalum Capacitors. (download from http://www.avxcorp.com/docs/techinfo/solid_ti.pdf) [215a] Javor, K., Investigation Into the Effects of Microsecond Power Line Transients on Line-Connected Capacitors, NASA/CR-2000-209906, NASA Marshall Space Flight Center, AL 35812, February 2000. (download from http://mtrs.msfc.nasa.gov/mtrs/2000/cr209906.pdf) [271] Loh, Eugene, Physical Interpretation of the Tantalum Chip Capacitor Life-Test Results, IEEE Transactions on Components, Hybrids, and Manufacturing Technology, vol. CHMT-3 no. 4, pp. 647-654, Dec. 1980. [280] Mattingly, David, Increasing Reliability of SMD Tantalum Capacitors in Low Impedance Applications. (download from http://www.avxcorp.com/docs/techinfo/rel_ti.pdf) [283] Mogilevsky, Boris and Shirn, George A., Surge Current Failure in Solid Electrolyte Tantalum Capacitors, IEEE Transactions on Components, Hybrids, and Manufacturing Technology, vol. CHMT-9 no. 4, pp. 475-479, Dec. 1986. I wrote design guidelines for, and gave a couple of informal seminars on this subject, at my former employer in 2000. My boss there has given me permission to publish the design guidelines on dBi's web site after I remove the proprietary information (about 10% of the document) and get his approval. So far I haven't had time to work on that task, but it is in my queue. John Barnes dBi Corporation http://www.dbicorporation.com/ --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Tantalum Capacitor Reliability
On Mon, 29 Jul 2002 15:41:32 -0400, Chris Maxwell chris.maxw...@nettest.com wrote: One of my colleagues is testing a new design. He has designed a buck-boost switching converter which has tantalum output capacitors. We have looked at his design and gone through the calculations. His output current is 4 A maximum. His output voltage is 12 VDC His caclulated ripple current is 800 mA. He needed a 120 mV ripple voltage, so he put 8 each of 68 uF, 20 V tantalum capacitors (with 150 mOhm ESR) in parallel on the output. Each cap is rated for approximately 800mA of ripple current. He has seen two failures of these capacitors during initial testing and demonstrations. Meanwhile, many initial units run fine. From what I can gather, he hasn't violated any design rules. He has 20V rated caps on a 12V circuit. He has a ripple current rating of 8 X 800mA (8 caps in parallel). It is tempting to just increase the voltage rating to 25V or 35Vbut why? Even if he does, how do you prove that the problem is fixed. It would take months of testing the new capacitors to get the history that we have on the existing design. I guess what I'm looking for is some tantalum capacitor wisdom... Should we just go ahead and use 25 V or 35V caps in this 12 V application? Are tantalum caps that flaky? What is the possibility that we don't have a design problem; but just a couple of bad capacitors? Is there some piece of knowledge out there that would help us tell the difference? Tantalum capacitors tend to short-circuited and can cause fire when used in low impedance circuit. I think many capacitor manufacturers suggest not to use their tantalum capacitors in low impedance circuit. Well, changing 25V to 35V will decrease the failure rate, but it may not enough. Low ESR aluminum electrolytic capacitors are available these days, and I think they are easier to use in such case. Yet another possible choice may organic-semiconductor capacitors, such as OS-CON from Sanyo. (http://www.sanyo.com/industrial/components/oscon_home.html) Regards, Tom -- Tomonori Sato vef00...@nifty.ne.jp URL: http://member.nifty.ne.jp/tsato/ --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Tantalum Capacitor Reliability
Been a while, but the voices from a former life in my head are reminding me of something to the effect that rated ripple current of cap is based on a perfect sine wave of ripple. Any other type of waveform can drastically effect that rating. SuperLo ESR caps were used one time to solve such a problem. Not sure if that applies here. The voices are pulling back, now. Regards, Doug McKean --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Tantalum Capacitor Reliability
When we started seeing 50 volt caps blowing up on a 5 volt output it became evident that the problem _we_ had, instant mortality (grin), was over-current, not over-voltage. We didn't actually see a voltage transient - a 'scope had in fact ruled that out - but someone in management had apparently thought it would be quicker to assume there WAS one. Cortland Hans Mellberg wrote: Nonetheless, inrush current aside, a 20V Tantalum is considered marginal for a 12V circuit if reliability is desired. A 60% derating factor was and is a typical max for reliability circuits, i.e a 30V min rated cap is recommended. Tantalums require additional derating than Al-electrolytics. Furthermore, switchers are notorious for destroying Tantalums due to the large and fast V-swings. I don't recall seeing too many Tantalums on switcher designs. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Tantalum Capacitor Reliability
Chris, I've had this same problem over the years with many man hours spent looking for why. We changed to 35 and 50 V parts to good effect in some cases. Other cases were not so easy. I like Cortland's idea the problem is charge current at turn-on. We had a 5 output 350 watt supply and there were definitely some heavy currents flowing at turn-on. In fact, that is when we saw most of the failures, turn it on and blow the caps clean across the test floor. Started a small fire once. We incorporated soft start into our power supplies at some point in time and this problem seemed to go away too. Coincidence? Never did know for sure. Anyway, good luck! Scott At 04:10 PM 7/29/02 -0400, Cortland Richmond wrote: Chris, The issue isn't voltage rating; low-ESR caps such as these are susceptible to excessive charging current at turn-on. At a former employer, we saw REALLY GOOD, expensive caps used on a computer's 5V bus exploding at turn-on, even ones rated at 50 volts. Replacing them with cheaper electrolytics (TEN volts!) took care of that. You might be able to alleviate turn-on stress by using a power-on monitor circuit to slow down the initial charge. But it'd be far cheaper to go to electrolytics. Cortland One of my colleagues is testing a new design. He has designed a buck-boost switching converter which has tantalum output capacitors. We have looked at his design and gone through the calculations. His output current is 4 A maximum. His output voltage is 12 VDC His caclulated ripple current is 800 mA. He needed a 120 mV ripple voltage, so he put 8 each of 68 uF, 20 V tantalum capacitors (with 150 mOhm ESR) in parallel on the output. Each cap is rated for approximately 800mA of ripple current. He has seen two failures of these capacitors during initial testing and demonstrations. Meanwhile, many initial units run fine. From what I can gather, he hasn't violated any design rules. He has 20V rated caps on a 12V circuit. He has a ripple current rating of 8 X 800mA (8 caps in parallel). It is tempting to just increase the voltage rating to 25V or 35Vbut why? Even if he does, how do you prove that the problem is fixed. It would take months of testing the new capacitors to get the history that we have on the existing design. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Tantalum Capacitor Reliability
I don't think you can use this directly, but I ran hours of tests on a tantalum cap at full rated potential while applying large amplitude microsecond spikes with no hiccups, no heating until I got quite extreme. The cap was rated at 30 WVDC and I biased it at 28 Vdc, while applying all kinds of nasty spikes. The report accounts for at least seven hours of applied bias potential and spikes, with no failure until after several hours of a multi-kilovolt, 20 us long spike finally destroyed it. The reference is: K. Javor, Investigation Into the Effects of Microsecond Power Line Transients on Line-Connected Capacitors, NASA/CR-2000-209906, NASA Marshall Space Flight Center, AL 35812, February 2000, pp. 33. and it can be found at: http://see.msfc.nasa.gov/see/ee/eepub.html -- From: Chris Maxwell chris.maxw...@nettest.com To: EMC-PSTC Internet Forum emc-p...@majordomo.ieee.org Subject: Tantalum Capacitor Reliability Date: Mon, Jul 29, 2002, 2:41 PM Hi all, By the way, thank you to the various group members for the responses regarding the hazardous atmosphere classifications. One of my colleagues is testing a new design. He has designed a buck-boost switching converter which has tantalum output capacitors. We have looked at his design and gone through the calculations. His output current is 4 A maximum. His output voltage is 12 VDC His caclulated ripple current is 800 mA. He needed a 120 mV ripple voltage, so he put 8 each of 68 uF, 20 V tantalum capacitors (with 150 mOhm ESR) in parallel on the output. Each cap is rated for approximately 800mA of ripple current. He has seen two failures of these capacitors during initial testing and demonstrations. Meanwhile, many initial units run fine. From what I can gather, he hasn't violated any design rules. He has 20V rated caps on a 12V circuit. He has a ripple current rating of 8 X 800mA (8 caps in parallel). It is tempting to just increase the voltage rating to 25V or 35Vbut why? Even if he does, how do you prove that the problem is fixed. It would take months of testing the new capacitors to get the history that we have on the existing design. I guess what I'm looking for is some tantalum capacitor wisdom... Should we just go ahead and use 25 V or 35V caps in this 12 V application? Are tantalum caps that flaky?What is the possibility that we don't have a design problem; but just a couple of bad capacitors? Is there some piece of knowledge out there that would help us tell the difference? Chris Maxwell | Design Engineer - Optical Division email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Tantalum Capacitor Reliability
Nonetheless, inrush current aside, a 20V Tantalum is considered marginal for a 12V circuit if reliability is desired. A 60% derating factor was and is a typical max for reliability circuits, i.e a 30V min rated cap is recommended. Tantalums require additional derating than Al-electrolytics. Furthermore, switchers are notorious for destroying Tantalums due to the large and fast V-swings. I don't recall seeing too many Tantalums on switcher designs. --- Cortland Richmond 72146@compuserve.com wrote: Chris, The issue isn't voltage rating; low-ESR caps such as these are susceptible to excessive charging current at turn-on. At a former employer, we saw REALLY GOOD, expensive caps used on a computer's 5V bus exploding at turn-on, even ones rated at 50 volts. Replacing them with cheaper electrolytics (TEN volts!) took care of that. You might be able to alleviate turn-on stress by using a power-on monitor circuit to slow down the initial charge. But it'd be far cheaper to go to electrolytics. Cortland One of my colleagues is testing a new design. He has designed a buck-boost switching converter which has tantalum output capacitors. We have looked at his design and gone through the calculations. His output current is 4 A maximum. His output voltage is 12 VDC His caclulated ripple current is 800 mA. He needed a 120 mV ripple voltage, so he put 8 each of 68 uF, 20 V tantalum capacitors (with 150 mOhm ESR) in parallel on the output. Each cap is rated for approximately 800mA of ripple current. He has seen two failures of these capacitors during initial testing and demonstrations. Meanwhile, many initial units run fine. From what I can gather, he hasn't violated any design rules. He has 20V rated caps on a 12V circuit. He has a ripple current rating of 8 X 800mA (8 caps in parallel). It is tempting to just increase the voltage rating to 25V or 35Vbut why? Even if he does, how do you prove that the problem is fixed. It would take months of testing the new capacitors to get the history that we have on the existing design. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list = Best Regards Hans Mellberg Regulatory Compliance EMC Design Services Consultant By the Pacific Coast next to Silicon Valley, Santa Cruz, CA, USA office:831-454-9450, cell:408-507-9694, fax:831-454-0755 __ Do You Yahoo!? Yahoo! Health - Feel better, live better http://health.yahoo.com --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Tantalum Capacitor Reliability
Chris, The issue isn't voltage rating; low-ESR caps such as these are susceptible to excessive charging current at turn-on. At a former employer, we saw REALLY GOOD, expensive caps used on a computer's 5V bus exploding at turn-on, even ones rated at 50 volts. Replacing them with cheaper electrolytics (TEN volts!) took care of that. You might be able to alleviate turn-on stress by using a power-on monitor circuit to slow down the initial charge. But it'd be far cheaper to go to electrolytics. Cortland One of my colleagues is testing a new design. He has designed a buck-boost switching converter which has tantalum output capacitors. We have looked at his design and gone through the calculations. His output current is 4 A maximum. His output voltage is 12 VDC His caclulated ripple current is 800 mA. He needed a 120 mV ripple voltage, so he put 8 each of 68 uF, 20 V tantalum capacitors (with 150 mOhm ESR) in parallel on the output. Each cap is rated for approximately 800mA of ripple current. He has seen two failures of these capacitors during initial testing and demonstrations. Meanwhile, many initial units run fine. From what I can gather, he hasn't violated any design rules. He has 20V rated caps on a 12V circuit. He has a ripple current rating of 8 X 800mA (8 caps in parallel). It is tempting to just increase the voltage rating to 25V or 35Vbut why? Even if he does, how do you prove that the problem is fixed. It would take months of testing the new capacitors to get the history that we have on the existing design. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
