PCB007 Magazine

PCB007-Aug2018

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AUGUST 2018 I PCB007 MAGAZINE 47 • Some components exhibited a moderate probability of self-mitigation within the range of 0.6 to 0.9 • One component exhibited a very low probability of self-mitigation (0612 chip) • XRF is an effective technique for evaluation of self-mitigation • Aging of parts to 14 months did not compromise self-mitigation but aging to five years did • There is a difference in self-mitigation depending on reflow process and peak oven temperature • Lead geometry affects self-mitigation probability of QFNs The afternoon presenta- tions started with "Solder Interconnect Challenge and Modeling for High Performance Electronics" by Dr. Michael Osterman of CALCE-University of Maryland. Osterman gave a compelling lecture on the physics of failure (PoF) for complex electronics units, including: • Microelectronic components • Conductive filament formation • Dendritic growth • PFH barrel cracking • Trace fracture • Solder fatigue • Lead wire fracture He explained the PoF simulation-based life assessment with models and FEA demonstra- tions. Lead-free solders were a focus with re- view of their history from the first generation to the present third generation solders. He concluded with the effect of underfilling components and the important role simulation of the modeling life under complex temperature cy- cles has to life predictions. The next talk was "As- sembly Tests for Solder Joint Reliability" by Jim Wilcox of Universal Instru- ments. Jim is a member of Table 5: The settings for the seven reflow conditions used in the DOE matrix for Tin Whisker Mitigation study. (Source: Raytheon) Setting Process A Process B Process C Process D Process E Process F Process G Reflowtype Vapor phase Convection oven Convection oven Convection oven Convection oven Convection oven Convection oven Flux ROL0 ROL0 ORM0 63/37 ROL0 Sn62RMA No-clean No-clean No-clean Stencil thickness 5 mil 5 mil 5 mil 4 mil Laser 5 mil 5 mil 5 mil Stencil aperture 1:1 1:1 1:1 1:1 1:1 1:1 1:1 Time above liquidus 90 s 60-75s 66 s 90 s 45 s 60 s 70 s Peak temperature 218 °C 215 °C 220 °C 225 °C 220 °C 213 °C 220 °C Atmosphere Air Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen Number of reflow cycles 1 1 1 1 1 1 2 Rework None None None None None None Yes Jim Wilcox Dr. Michael Osterman

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