Aging of ceramic capacitors is real. This phenomena is more pronounced in higher K dielectric capacitors such as Y5V or Z5U. Reflow temperature profiles will (at least partially) de-age the capacitor since it will take the ceramic above the Curie temperature. For a more detailed discussion see http://www.novacap.com/DielectricProperties.pdf Bob Veale Rockwell Automation Cleveland Ohio Martin Christie <[log in to unmask]>@IPC.ORG> on 02/01/2000 03:42:00 AM Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond to Martin Christie <[log in to unmask]> Sent by: TechNet <[log in to unmask]> To: [log in to unmask] cc: Subject: [TN] Ceramic chip capacitors > >Technet guru's, > >We have a problem with a 1uF 10v -20/+80% (0805) chip capacitor. We have >seen some failures at in-circuit test for low capacitance (much less than >the -20% tolerance). Some of our test operators have found that by reflowing >(hand flowing) the component they can bring it back into tolerance. I've had >some of these components micro-sectioned and on one particular example, have >found a crack under the metallisation. After checking components off the >reel I've found them to be very low, in a lot of cases they were well below >the -20% tolerance (I've yet to get some micro-sectioned). I've not ruled >out the possibility that it could be our placement equipment or thermal >shock but we haven't found the same failure mode on any other similar value >components that we're placing. The reel has now been quarantined and another >reel (which is well within tolerance) fitted. I'm still awaiting the results >of the next production. > >To satisfy my curiosity that it wasn't variation in our meter, I measured >some (12 in number) similar value components straight off of another reel >from a different manufacturer. I found that they were within tolerance but >when measured over a period of 3 hours their capacitance increased by about >10% (I confirmed it wasn't our meter by measuring a known value component >over the same period and found less than 3% variation). After contacting the >manufacturer, I was told it was not unusual for reeled capacitors over 2 >years old to exhibit this phenomena (well known in his industry) and that a >bake should be undertaken to bring the components up to their nominal values >(although he would not comment on the bake parameters). The components were >manufactured in 1998. > >I and my colleagues (including our Test Engineers) have never heard of this >before. Does anyone have any further information on this subject or know >what the recommended bake is? > >Regards, >Martin Christie ############################################################## 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 Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ############################################################## ############################################################## 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 Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################