Thanks Gary. I wish I could get them to pay for a real project that would include all stress sources it's exposed to, increased sample size, etc. They want cheap and dirty and he actually brought up the 10C increase. We'll be doing a light output comparison of as received vs after conditioning.
My reading indicates it's a chemical reaction but have found many apply it to electronics. We are not exceeding any component limits so that's a good thing. I haven't found anything yet that says increasing the time at the temperature accelerates the life even more. From: Gary McInturff [mailto:[email protected]] Sent: Monday, October 20, 2014 12:00 PM To: [email protected]; [email protected] Subject: RE: Reliability John you're going to be wrong no matter what you do - depending on who you are talking to. The 10 degree rise = twice the failure estimation is based on the Arrhenius model - which is actually a chemical model, but widely applied to electronics So as a rule of thumb you can state you acceleration factor is based on that - assuming that you product is displaying a normal (Gaussian) random mode failure mechanism and not infant or wear-out modes. The more proper way of finding the actual acceleration rate - for temperature or anything else is to run life tests at low, normal and high temperatures and correlating the failure times - but I'm guessing you (and most people) don't have the time or resources to do that so prediction is the only real tool you have - unless you have an ongoing reliability growth mechanism, which might be in-house testing or working with the field data failures and making adjustments. Getting good field failure data is a real problem on its own. Sample size is going to be a real problem to John. If you have one sample does that represent the whole population, or did you get the one unit that was in the 10th percentile or maybe the 90th percentile. Another rule of thumb is that you need 25 - 30 samples to get a better feeling for the full population size not just the test size. I would work with your customer (engineering staff or external customer) and seek agreement that he accepts the acceleration factor and the sample size. This is a much bigger problem than you may realize but if you can't test many samples for many hours then you have to start somewhere and state your assumptions. A good primer of the subject (although it doesn't do into acceleration factors is Reliability Statistics by Robert A. Dovich ISBN 0-87389-086 (at least that's the number on my version - could be newer editions) This is a big and ugly specialty John. But as a starting point, after agreement with your customer, running the unit(s) at a higher temperature and assuming the 10c doubles the failure rate is at least a starting point. Gmac From: [email protected]<mailto:[email protected]> [mailto:[email protected]] Sent: Monday, October 20, 2014 6:38 AM To: [email protected]<mailto:[email protected]> Subject: [PSES] Reliability Hi, Any reliability engineers out there? Based on every 10° rise reduces life by half, and if I call 1 year at 22C my baseline, conditioning at 62C for 3.25 weeks will equal 1 year. Does conditioning at 62C for 6.5 weeks equal 2 years? Thanks, John - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]<mailto:[email protected]>> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.ieee-2Dpses.org_emc-2Dpstc.html&d=AAMFAw&c=0hKVUfnuoBozYN8UvxPA-w&r=RJLDFgHJo89sjFN46b74hFXEuxvz4Z1iAx-glaOgP0k&m=mutoSjhbOVGNPlqXwnSZ5e4AYSf_N3T--cRZ8Ni24sM&s=Fp19GPr800KCYDmSMF8TnCGWvPm7XENUM6vZleN0yY8&e=> Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/<https://urldefense.proofpoint.com/v2/url?u=http-3A__product-2Dcompliance.oc.ieee.org_&d=AAMFAw&c=0hKVUfnuoBozYN8UvxPA-w&r=RJLDFgHJo89sjFN46b74hFXEuxvz4Z1iAx-glaOgP0k&m=mutoSjhbOVGNPlqXwnSZ5e4AYSf_N3T--cRZ8Ni24sM&s=3VLirc4rYVE3CnT9uBQ9fCJIv7dw8Jc7YJsggqofxV8&e=> can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.ieee-2Dpses.org_&d=AAMFAw&c=0hKVUfnuoBozYN8UvxPA-w&r=RJLDFgHJo89sjFN46b74hFXEuxvz4Z1iAx-glaOgP0k&m=mutoSjhbOVGNPlqXwnSZ5e4AYSf_N3T--cRZ8Ni24sM&s=MObVJcCeSAR_1KgfPG7lfO3lu1paPYYW7rsonPE64a4&e=> Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe)<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.ieee-2Dpses.org_list.html&d=AAMFAw&c=0hKVUfnuoBozYN8UvxPA-w&r=RJLDFgHJo89sjFN46b74hFXEuxvz4Z1iAx-glaOgP0k&m=mutoSjhbOVGNPlqXwnSZ5e4AYSf_N3T--cRZ8Ni24sM&s=4JsWjoHODVx-ccqrncnbWdiXGiC-7RUNyy2JFb4IUKI&e=> List rules: http://www.ieee-pses.org/listrules.html<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.ieee-2Dpses.org_listrules.html&d=AAMFAw&c=0hKVUfnuoBozYN8UvxPA-w&r=RJLDFgHJo89sjFN46b74hFXEuxvz4Z1iAx-glaOgP0k&m=mutoSjhbOVGNPlqXwnSZ5e4AYSf_N3T--cRZ8Ni24sM&s=9CcjclBPH723_4JHHM58cCzD6Ktt7t9Zd4rbVpPqOKk&e=> For help, send mail to the list administrators: Scott Douglas <[email protected]<mailto:[email protected]>> Mike Cantwell <[email protected]<mailto:[email protected]>> For policy questions, send mail to: Jim Bacher <[email protected]<mailto:[email protected]>> David Heald <[email protected]<mailto:[email protected]>> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
