which has a=0Aconstant failure rate for some reason. That is essentially = the assumption=0Aunderlying the MIL-HBK-217, which has been shown to be i= nadequate for=0Aelectronic assemblies, because electronic products contai= n wearout failure=0Amechanisms which cause a continuously increasing fail= ure rate with time, and=0Athus render the MTBF concept meaningless. For c= onstant failure rates you can=0Aexpress the reliability in FITs (1 FIT = =3D 1 failure/10**9 device-hours), a=0Aconcept developed way-back by Bell= Labs. But both FITs and MBTF are purely=0Astatistcal concepts and do not= take into account the physics-of-failure of the=0Amachanisms and loading= conditions the actually cause failures. At Bell Labs,=0Awe tried to get = around this by using iFITs (time-dependent instantaneous FITs)=0Ato accou= nt for changing failure rates=97while it works within the FIT frame=0Awor= k, it is cumbersome and really does not answer the basic question of the= =0Aexpected system reliability.=0AIn IPC-D-279, 'Design Guidelines for Re= liable Surface Mount Technology Printed=0ABoard Assemblies', equations ar= e given allowing you to get a cumulative=0Afailure probability for all th= e SM solder joints in a system.=0A=0AWerner Engelmaier=0AEngelmaier Assoc= iates, L.C.=0AElectronic Packaging, Interconnection and Reliability Consu= lting=0A7 Jasmine Run=0AOrmond Beach, FL 32174 USA=0APhone: 904-437-874= 7, Fax: 904-437-8737=0AE-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 ################################################################ ################################################################ 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 ################################################################