Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum (src_forum@alionscience.com )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Original Message:

Posted by: Ümit BÜLBÜL (ubulbul@aselsan.com.tr )
Organization:aselsan inc.
Date posted: Mon Mar 14 5:02:00 US/Eastern 2005
Subject: MIL-STD-217F
Message:
Dear Sirs, I am an hardware design engineer in a firm called Aselsan Inc, mostly serving in military areas. I have a general question related to the applicability and validity of MIL-STD-217F as regards the new technological progress taken in electronic/electrical components. Could you share your thoughts about my comments(or questions) given below and suggest alternative methods if possible : Question_1) We design many products consisting mostly MOSFETs, ceramic capacitors, opto-couplers etc. But according to MIL-STD-217F BJT transistors seem to be superior than MOSFETs. But as you know MOSFET technology has improved for the past years and I think MOSFETSs now are more rugged than BJTs (if you take necessary consideration against ESD disadvantage of MOSFETs). Also according to MIL-STD-217F chip ceramic capacitors seem to be worse than chip tantalum capacitors. Apart from the cracking problems observed in ceramic capacitor I think that ceramics are better than tantalum. Question_2) If MIL-STD-217F standard is a good approximation to component failure rates what is the reason of the big difference between MIL-STD-217F Notice1 and Notice2 regarding failure rate equations and different coefficients suggested in these revisions? Question_3) According to MIL-STD-217F to get a good MTBF data for a complex system (e.g. tanks, gun systems etc.) we should use at least JANXXX type components which are becoming more difficult to find and even in case we find, it is nearly impossible to satisfy the other system criteria if we use JANXXX (because JANXXX type components are somehow old and not competetive regarding packet size, efficiency and other advantages of todays' high technology components. What is your suggestion on this ? Question_4) For the MTBF data of mechanical components which standard should we use for military projects? In summary in our military designs we have some difficulty to satisfy the MIL-STD-217F Notice2 specifications coming from customer side. Therefore your comments are valuable for us to reevaluate these requirements and provide alternative but reasonable solutions to MTBF requirements of our customers? best regards, Ümit BÜLBÜL Electronics Eng.

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