Forum: Reliability & Maintainability Questions and Answers
Posted by: Glen Hanington Date posted: Mon Mar 5 15:21:34 US/Eastern 2007 Subject: Reliability Testing Message: We have a problem. We've built up very large number of printed wiring assemblies before we discovered that the board itself has a problem. There are 2 pad areas on the board that form connection points to copper busbars. Each pad is 1/2" x 1/2" in area, solder coated, with a 0.150" hole near the middle. A 6-32 square-cone SEMS screw passes through this hole from the back side of the board and screws into each one of the 2 busbars. The hole is plated through and the back side of the board has an identical pad as on the front of the board. The problem is this: solder mask covers both pads except for a 0.250" diameter circle around the hole on both sides of the board, preventing full surface contact with the busbars. Some of our product models have 83 Amps of current pass from the board through each busbar. We've experimented with removing the solder mask, but that isn't possible due to the other components already on the board. I've been tasked with developi! ng a reliability test to prove that if we were to use these boards we would not have a reliability issue in the field. How would you recommend that I go about performing this test? As I see it, this will involve the combined stresses of current, humidity, and vibration. Is there some way to set up this test, or series of tests, to prove that this will not be an issue within our 5-year warranty period? It is also believed that about 1500 of these boards are in the field, but there have been no reported failures as a result of this issue.
Posted by: Rushabh Date posted: Mon Mar 5 15:13:43 US/Eastern 2007 Subject: Why failure rate of a capacitor is higher for non-operating vs operating condition Message: Can you please try to find the failure rate with 10% duty cycle ? I might be that for 0% duty cycle calculation there is some bug in software. Ideally what you pointed out is correct. Operating mode failure rate should be higher than Non Operating.
Posted by: Bob Valerius (robert.valerius@ngc.com ) Date posted: Mon Mar 5 15:08:51 US/Eastern 2007 Subject: Failure Rate Estimation of Rubber Diaphragm Message: Hi. Where can I find failure rate estimates for a nitrile diaphram that will be used in a pressure compensator? Thanks in advance.
Posted by: Ananya Date posted: Tue Oct 4 10:29:58 US/Eastern 2005 Subject: Why failure rate of a capacitor is higher for non-operating vs operating condition Message: Hi, In RAC Prism, if you calculate the failure rate of a system which contains 1 capacitor; at (negative) -10C, 100% duty cycle, GS operating environment, Military Ground operating profile, relative humidity 40, vibration level 0, cycling rate 1, year of manufacture 2005, capacitance 0.1uF, operating volatge 0.001V and rated voltage 50V; you get 0.001131 fpmh. This is the "operating condition". If you calculate the failure rate of a system which contains 1 capacitor; at (negative) -10C, 0% duty cycle, GS operating environment, Military Ground operating profile, relative humidity 40, vibration level 0, cycling rate 0, year of manufacture 2005, capacitance 0.1uF, operating volatge 0.001V and rated voltage 50V; you get 0.002333 fpmh. This is the "non-operating condition", with 0% duty cycle and 0 cycling rate. Why is the failure rate under non-operating (dormant) condition higher than the failure rate under the operating condition? Shouldn't it be the other way around? Thanks for your help in advance.
Posted by: Uma Date posted: Fri Sep 30 15:40:47 US/Eastern 2005 Subject: Qualifying suppliers Message: Hi, Does anybody have an example of a supplier questionnaire that we can use to qualify the devices we are buying? For eg. questions like "what is the predicted reliability of the device?" "How was it derived?" "Has this been tested?" "How accurately does your field returns mimic this prediction"? "What is done to assure reliability during the design process? etc etc Is there a standard that can be used? Thanks for your help in advance.
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