Re: How long to burn in a circuit board

Leslie: Product screens and tests of prototypes and test vehicles should be tailored for the specific goal and product. I caution your use of equations and test condition information without specific use environments and design conditions.

Lawyer: "Mr. Bob, regarding the equipment manufactured by your company that was on the plane when it went down over Manhattan, did you do reliability testing?" Mr. Bob: "Yes (proudly), we do extensive reliability testing on all the equipment we manufacture." Lawyer: "Mr. Bob, tell us about reliability testing. Help us understand what�s involved in reliability testing." Mr. Bob: "Well, it�s very involved. We use only the finest equipment for this. You have to hook the unit up to the flammer valve with the sculler screws and bla bla bla. Then , you put the whole thing into an environmental test chamber. An environmental test chamber bla bla bla. Then, the environmental test chamber subjects the assemblies to the following thermal cycling process: Starting at room temperature, ramp the temperature at bla, bla, bla" Lawyer: "Mr. Bob, please tell the court, the jury, grieving family members, and maimed children and once cute fuzzy pets; how you determined the parameters of this thermal cycling process." Mr. Bob: "Oooooo, that�s easy. We used a generic test sequence that I found on a chat room on the internet." Loud buzzer goes off, Mr. Bob is smacked on the head with a large wooden mallet, and Mr. Bob�s boss climbs the railing and lunges at the witness chair, but he�s tackled by the bailiff, a retired linebacker from the Jets with a bum knee. Fast forward to ... "Abba-dabba-do, who wants to open the bidding on this environmental test chamber?"

Reliability testing is either testing of product to be shipped (actually screening) or testing of prototypes and test vehicles. 1 Product Screens: � Burn-In: A functional test to screen products for some time (typically 8 to 24 hours) involving perhaps worst case, but still realistic operational environments. � Environmental Stress Screening (ESS): A product screening procedure involving environmental stresses of limited duration, such as thermal cycling, thermal shock, vibration, mechanical shock, etc., designed to speed specific suspected "latent defects" or product weaknesses to failure (so these failures can be detected) without causing significant damage to good product. � Highly Accelerated Stress Screening (HASS): A more aggressive product screening procedure involving environmental stresses, such as thermal cycling, thermal shock, vibration, mechanical shock, etc., designed to precipitate specific suspected "latent defects" or product weaknesses to failure more quickly than ESS. Here, higher acceleration means higher stress levels, potentially damaging good product. 2 Tests For Prototypes And Test Vehicles: � Accelerated Reliability Test: A test on test vehicles designed to produce failures with the same damage mechanism product would experience in the field on an accelerated basis. The purpose is to create a data base from which product reliability in the field can be estimated. � Highly Accelerated Life Testing (HALT): A test on product prototypes to cause failures with very high stress regimens, but somehow still related to the operational environment of the product. The damage mechanisms employed in HALT, and thus the failures, may or may not have any connection of the experiences of product in the field. This is an attempt to do an accelerated reliability test quickly, which is can lead in many cases to misleading information, because the high acceleration has brought about damage mechanisms and/or material behavior that are not pertinent for product reliability. � Highly Accelerated Stress Testing (HAST): A test on product prototypes to cause failures with very high stress regimens which show the least robust portions of a design. With HAST, a more robust product is developed at by beefing up the observed failure sites (often successively). The damage mechanisms employed in HAST, and thus the failures, may or may not have any connection of the experiences of product in the field. Consider industry documents that deal, at least in part, with reliability testing: � IPC-SM-785, "Guidelines for Accelerated Reliability Testing of Surface Mount Solder Attachments" � IPC-D-279, "Design Guidelines for Reliable Surface Mount Technology Printed Board Assemblies" Consider a workshop at NEPCON West or APEX.

My2�

Dave F

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