Hi Werner On the purely technical point of view you may be (usually are) right ; on the practical it worked slightly differently : 1 The reduction of life has been calculated and accepted , on base of major reduction of early failures , influencing as you can imagine the warranties ( 1-2-3 years ) . Therefore , commercially , little emphasis is on the longevity of the product ; technology and depreciation laws currently being changed to reflect the realistic pace do also encourage this short term focus. Even simple burn in gives results , and the say 10% cycling did screen early faults quite effectively , once the short occurred and interrupted the continuity (switched tested unit off) ; it's been established . Obviously without this closed mode of observation ; the "visual" inspection is more than less useless ; as you said . It is likely that due to the commercial, perhaps disputable ethics of the "designed" life character, not many folks will be responding . 2 When we did on the telecomm products the vibration tests, in various designed frequencies , simulating rail transport ( droning ), etc., we found that more than the joints we tested componentry, = the components , still very much mixed even today , failed long before we got to see anything on the joints . It has been good indicator of what should be tied down , or poured over with epoxy ; but poor indicator of the whole board early faults status . The mix is just too diverse , unless you make SIMM cards only , and cap's notoriously disintegrate for all different reasons than joint far too quickly . Or, take a MQFP , you can vibrate all the legs to oblivion ; with one dry not being fazed at all ; the body will support it , while cycled under load it will show up . To sum it up, for example on that IPC-SM-785 you helped us to get going ; if on page 20 you take the telecomm category on leadless with 4700 cycles and establish whatever part of infant mortality (pages 6-7) eradication on precycling you sacrifice from the length of the 7 years life ; considering you'll have likely new telephone within 5 years ; you are still ahead , happy OEM , with less warranty problems for you AND the customer . Thanks for all the help Werner paul ; ResMed ; >---------- >From: Engelmaier[SMTP:[log in to unmask]] >Sent: Thursday, 16 April 1998 10:48 >To: [log in to unmask] >Subject: Re: [TN] temp cycling of soldered assemblies > >Hi Sheila, >You did not say what kind of temperature cycling nor for how many cycles this >"temperature cycling after solder rework" would involve. But from a purely >technical point of view, temperature cycling of product to be shipped to the >customer is silly. It is not a very effective ESS techique for full >assemblies, because if it were carried out to be effective it would do more >damage to good solder joints than finding bad ones. Any temperature cycling >of >full assemblies will accumulate some fatigue damage and therefore reduce the >life. Whether this is significant or not will depend on the severity and >number of temperature cycles as well as the design parameters of the >assembly. >To find bad-improperly wetted, other so-called defects rarely make a >difference-solder joints one would be well advised to use vibration, >preferably at -40 degrees C. Good solder joints are not damaged, bad ones >fall >apart. > >Werner Engelmaier >Engelmaier Associates, L.C. >Electronic Packaging, Interconnection and Reliability Consulting >7 Jasmine Run >Ormond Beach, FL 32174 USA >Phone: 904-437-8747, Fax: 904-437-8737 >E-mail: [log in to unmask] > > >################################################################ >TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c >################################################################ >To subscribe/unsubscribe, send a message to [log in to unmask] with following >text in the body: >To subscribe: SUBSCRIBE TechNet <your full name> >To unsubscribe: SIGNOFF TechNet >################################################################ >Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional >information. >For the technical support contact Dmitriy Sklyar at [log in to unmask] or >847-509-9700 ext.311 >################################################################ > ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################