Accelerated testing is a complex subject. Much confusion exists in the industry, because many tests, that have quite different purposes, are called 'accelerated tests'. The main differentiation in purpose is between product screens and testing of prototypes/test vehicles. In a previous TechNet discourse I wrote: Product Screens: Burn-In: Is a functional test for some time (typically 8 to 24 hours) involving perhaps worst case but still realistic operational environments. Environmental Stress Screening (ESS): A screening procedure involving environmental stresses of limited duration, such as thermal cycling, thermal shock, vibration, mechanical shock, etc., designed to precipitate 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 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. Higher acceleration means higher stress levels which can translate into causing significant damage to good product. Accelerated Tests for Test Vehicles: Accelerated Reliability Test: This is 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. HALT (Highly Accelerated Life Testing): This is 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. HAST (Highly Accelerated Stress Testing): This is a test on product prototypes to cause failures with very high stress regimens which show the least robust portions of a design. By beefing up the observed failure sites (often successively) a more robust product is arrived at. 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. >From your question, I assume that you are primarily interested in Accelerated Reliability Testing, where the results can be related via some acceleration transform yielding an acceIeration factor to some equivalent life at actual operating conditions. For this purpose, accelerated testing requires: (1) that, in fact, the same damage mechanism active during product operation is dominant during accelerated testing, (2) that the acceleration of this damage mechanism by some appropriate change in the operating conditions to the test conditions can be expressed in an acceleration transform, which is known. Both of these requirements are frequently not present. However, IPC-SM-785, 'Guidelines for Accelerated Reliability Testing of Surface Mount Solder Attachments' does provide in Table 2 equivalent test cycles for a variety of service lives. The equations to generate equivalent service lives and test durations for other conditions are stated. Temperature cycling -55 to 125oC is appropriate for bare boards to accelerate the failures of PTHs, but not for assemblies, because these test conditions generate dominant failure mechanisms absent in most field operations. For the temperature/humidity test conditions that you stated, you need to differentiate between SIR and CAF failures. There are some acceleration transforms available for SIR, but experimental activation energies observed vary significantly. For CAF, difficulties in finding a correlation from failures at high humidity conditions to typical failure conditions, has led to the postulation of some threshold condition. Thus, there can not really be a satisfactory answer to your question. I would, however, suggest a look at Engelmaier, W., and L. Turbini, "Design for Reliability in Advanced Electronic Packaging," Proc. Surface Mount International Conf., San Jose, CA, August 1995, pp. 844-879, which deals with the underlying issues. Werner Engelmaier Engelmaier Associates, Inc. Electronic Packaging, Interconnection and Reliability Consulting 23 Gunther Street Mendham, NJ 07945 USA Phone & Fax: 201-543-2747 E-mail: [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] * ***************************************************************************