We use a lot of Through-hole X7R, and Z5U 20% tol. in the range of 1nF to 330nF. After Wave the capacitance may increase to 40% over nominal value. This increase lasts several weeks, and all manufacturers I talk to confirm this is normal. This has no real affect on our applications, as they are used for power supply bypass. Kemet has a published application note: "AGING - Capacitance Change Due to Time or Exposure to High Temperature". This was written by Dick Thompson, Apr, 1995. Pete Hanamann EAC/Plexus ---------- ---------- From: TechNet-request To: TechNet Subject: RE: ASSY: Problems with 50V ceramic capacitor at Wave Soldering Date: Tuesday, February 04, 1997 8:45AM Alain, All capacitors will experience a capacitance shift when ran through any heating cycle. Your problem could be at what time you actually measure the capacitance. My first question is if you leave the board sitting for 24 hours are the capacitors in tolerance? If that is the case, then you will know that your problem is a temporary heating situation. I do not know what type of ceramic capacitor you use. There are some real gotcha's when measuring hot capacitors though. For example, if you use a NPO type capacitor, the capacitance change is usually in the 30 PPM region and is linear over temperature. However, X7R capacitors can vary +\- 15% over temperature and are highly non linear in the temperature region. Then you get into Y5U +20% to -55%, Y5V +22% to -82%, and Z5U which is +22% to -56% over operating temperature. Since a solder pot is way hotter than any operating specification on a capacitor, I am not surprised that you would find a lot of capacitors 25% or more out of tolerance. We have found in the past when using Z5U material that we had to let the board cool for almost 24 hours before the capacitors would come back into tolerance. I hope this helps your problem. Max Bernhardt Woodward Governor Co. 970-962-7376 ---------- *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************