Kevin, The answer is obvious---take my workshops (see www.engelmaier.com); a less preferred option (from my perspective) is to get a copy of IPC-D-279. Werner -----Original Message----- From: Kevin Glidden <[log in to unmask]> To: [log in to unmask] Sent: Fri, 24 Apr 2009 9:12 pm Subject: Re: [TN] solder fatigue analysis for slowly changing thermal environment I apologize to all for the thread hi-jack, but it seem's pertinent: So where ould someone less experienced look to learn more about redicting/calculating SJ life due to fatigue/creep etc via thermal cycling? Thanks, Kevin Glidden uminescent Systems Inc. ----Original Message----- rom: Werner Engelmaier /* [mailto:[log in to unmask]] ent: Friday, April 24, 2009 9:50 AM o: [log in to unmask] ubject: Re: [TN] solder fatigue analysis for slowly changing thermal nvironment Hi John, ou need to consider that solder creep-fatigue is not a stress issue but a train issue; and that creep is a time-dependent process. Thus, the slower he transition the more complete the creep process the larger the fatigue amage. our worst case scenario are cycles of -50 to +50 giving you a maximum 100C elta-T; anything else will give you longer life/higher reliability. he easiest way to deal with all of this is calculate the the mean fatigue ives for all the cycles involved; that tells you if you have a problem eliability-wise in 50 cycles of any of them---you would realy have to have very large CTE-mismatch for 50 cycles to be a probem. Werner -----Original Message----- rom: Nieznansk i, John A - SSD <[log in to unmask]> o: [log in to unmask] <[log in to unmask]>; [log in to unmask] [log in to unmask]> ent: Thu, 23 Apr 2009 6:51 pm ubject: RE: [TN] solder fatigue analysis for slowly changing thermal nvironment i Werner, hanks for responding. Sorry for the confusion. I’ll try to clarify further. 1] and [2] are the limiting cases: i.e., [1] = HOT case = +50C Heat Sink, 2] = COLD case = -50C Heat Sink.. They do not occur sequentially as implied y [4]. The daily heat sink temperature drift [3] = 10C is a worst case alue. ssume when the part is OFF it is at the heat sink temperature and when ON t is 20C above the heat sink temperature. or the example20given, there are only 50 operational cycles in total. An perational cycle is defined as 30 minutes ON + 30 minutes OFF at some teady-state heat sink temperature between [1] = HOT case and [2] = COLD ase. he 50 operational cycles do not occur periodically or at predictable emperatures or time intervals, but can be separated in both time and emperature. In between operational cycles, the system is OFF but can slowly rift in temperature <=10C per day. So going from the HOT case heat sink to he COLD case heat sink will take a minimum of 100C delta / 10C per day = 10 ays. ith this much variability, I want to try to bound the upper/lower fatigue amage calculations and perhaps estimate the expected fatigue (if ossible). t seems a reasonable high damage estimate can be calculated assuming 50 onsecutive operational cycles in the HOT case: hold heat sink steady at 50C, complete 50 operational cycles (each operational cycle = 30 minutes ON 30 minutes OFF), and ignore the 10C daily temperature drifts. Do you gree? A variant here which will be more damaging yet is to allow more OFF ime between operational cycles while in the HOT case (perhaps days). Do ou agree? t seems a reasonable low damage estimate can be calculated assuming 50 onsecutive operational cycles in the COLD case: hold heat sink steady at 50C, complete 50 operational cycles (each operational cycle = 30 minutes ON 30 minutes OFF) , and ignore the 10C daily temperature drifts. Do you gree? A variant here which will be more damaging yet is to allow more OFF ime between operational cycles while in the COLD case (perhaps days). Do ou agree? think the other case of interest from a fatigue analysis standpoint is as ollows: The system starts out at the upper temperature limit, runs ONE perational cycle (30 minutes ON + 30 minutes OFF) while heat sink is OT=+50C, shuts off, cools down over 10 days to the lower temperature limit, uns ONE operational cycle (30 minutes ON + 30 minutes OFF) while heat sink s COLD=-50C, heats up over 10 days to the upper temperature limit where he cycle repeats. This would give me a total of 25 cycles while heat sink s HOT and 25 cycles while heat sink is COLD. o there are quite a20few variables here to consider. Any confirmation or epudiation of these ideas or other insights you can offer up are greatly ppreciated. I recognize that the +50C/-50C range is in the realm of “Large emperature Excursions” where additional damage mechanisms may apply. hanks again. ohn Nieznanski From: [log in to unmask] [mailto:[log in to unmask]] ent: Thursday, April 23, 2009 2:44 PM To: [log in to unmask]; ieznanski, John A - SSD Subject: Re: [TN] solder fatigue analysis for slowly changing thermal nvironment i John, 0 Form your email it is not clear [at least to me] what is happening. How many cycles [1.]? How many cycles[2.]? How does your assembly go from 1.] to [2.]? ycle [1.] is much more damaging than cycle [2.] because of the higher mean yclic temperature. The cycle described in [4.] is even more damaging because of the much larger elta-T. Fatigue analysis is based on the assumption [and there is very strong vidence that it is correct—Palmgren-Miner's Rule] that fatigue damage ccurring at a given cycles is additive to any damage occurring at other ycles. So, in order to analyze the fatigue life of anything including solder oints, you first must determine the cyclic loading history to be expected, alculate the fraction of life consumed for each cycle type, and add it up. Regards, Werner Engelmaier Engelmaier Associates, L.C. Electronic Packaging, Interconnection and Reliability Consulting 7 Jasmine Run Ormond Beach, L 32174 SA Phone:=2 0386-437-8747, Cell: 386-316-5904 E-mail: [log in to unmask], Website: www.engelmaier.com ----Original Message----- From: Nieznanski, John A - SSD <[log in to unmask]> To: [log in to unmask] Sent: Wed, 22 Apr 2009 2:11 pm Subject: [TN] solder fatigue analysis for slowly changing thermal nvironment ello TechNet Gurus, Using the classical IPC-D-279 methods, how would you determine SMT solder oint atigue for the following situation? 1. SMT part turns on at upper system temperature limit (Thi= +50C), runs or 0 minutes at Thi+ = +70C, shuts off, part stabilizes at Thi= +50C for 30 inutes. 2. SMT part turns on at lower system temperature limit (Tlo= -50C), runs or 0 minutes at Tlo+ = -30C, shuts off, part stabilizes at Tlo= -50C for 30 inutes. 3. And now the twist, the system temperature can slowly vary between these limits as much as 10C in a 24-hour period. 4. How much fatigue develops after 50 thermal cycles between T-hi and -lo? Can I claim that the upper limit on fatigue can be calculated simply by unning 0 operational cycles from the upper temperature limit (Thi= +50C to Thi+ = 70C)? Can I claim that the lower limit on fatigue can be calculated simply by unning 0 operational cycles from the lower temperature limit (Tlo= -50C to Tlo+ = 30C)? Can I claim that the actual fatigue is somewher e between these two limiting ases (worst case, best case)? ohn This e-mail and any files transmitted with it may be proprietary and are ntended solely for the use of the individual or entity to whom they are ddressed. If you have received this e-mail in error please notify the ender. 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