Don't know from knowledge but intuitively my hypothesis: There are a number of dissimilar metals involved here in lead frame, silver loaded polymer as well as the graphite/manganese/carbon/silver being at other possible potentials. IN these devices the capacitance is generated across a very thin film and they do not have infinite resistance, so small currents may flow. So now add damp and a few volts or possibly even just damp, and leave for a year or three or four or.... You now have a little battery or corrosion cell The dissimilar metals will be in galvanic corrosion resulting in erosion and/or change in internal volumes from reaction products, eventually disrupting the insulating film. As soon as that happens but not before, device turns into a heating element. Be interesting to see what leakage volts are on similar age units? Mike ----- Original Message ----- From: "Alan Peters" <[log in to unmask]> To: <[log in to unmask]> Sent: Friday, August 04, 2000 9:24 AM Subject: [TN] Solid tantalum capacitor failures > I have been asked to investigate two failures of 10u 25v solid tantalum capacitors. > > They are rectangular plastic/resin encapsulated, sintered tantalum/ manganese > dioxide/ graphite-silver types. > These items are "cremated" beyond investigation! > > I am lead to believe (hmm!) all correct operating conditions have been met/not > exceeded i.e. excessive voltage, ripple and reverse voltage. > The capacitors have seen service for at least 5 years in a very humid environment. > I am not aware if they are from the same batch. One was fitted across a +15v rail > in one unit and the other was fitted across a -15 rail in another unit. > > Question? Does anyone know of an ageing condition, or what the effects of humidity > are that can lead to failure of these capacitors? > > Alan Peters > Failure Analysis Engineer > Materials & Components Labs > > ############################################################## > TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c > ############################################################## > To subscribe/unsubscribe, send a message to [log in to unmask] with following text in > the body: > To subscribe: SUBSCRIBE TECHNET <your full name> > To unsubscribe: SIGNOFF TECHNET > ############################################################## > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional > information. > If you need assistance - contact Keach Sasamori at [log in to unmask] or > 847-509-9700 ext.5315 > ############################################################## > ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ##############################################################