Printed Circuit Design & Fab - January 2008 - (Page 26)

PAUL REID, PWB INTERCONNECT SOLUTIONS 50 % Failed 25 10 5 2 12 10 200 6 6 % Failed 6 6 6 6 PAUL REID, PWB INTERCONNECT SOLUTIONS 90 75 30% 6 6 FR-4 PCB-PTVs, =13.5 mils [0.34 mm], h =100 mils [2.54 mm], Grid: 50 mils [1.3 mm] 10 layers, non-functional pads, ATC: -55 125°C 6 Assembly simulation: 5 x reflow @ 215°C, = 4.1 No assembly simulation, = 3.7 5,000 10 4 90 75 50 25 10 5 33% 2 12 10 6 50% 6 6 6 6 FR-4 PCB-PTVs, =13.5 mils [0.34 mm], h =102 mils [2.60 mm], Grid: 50 mils [1.3 mm] 10 layers, non-functional pads, IST: +25 150°C 6 Assembly simulation: 3 x reflow @ 230°C, = 2.3 No assembly simulation, = 5.1 10 3 500 2,000 5,000 10 4 Cycles-to-Failure 10 3 500 2,000 Cycles-to-Failure 200 FIGURE 9. Weibull plots of failure data of plated-through hole barrels by SnPb-solder assembly simulation (with and without pre-conditioning). These data show about a 30% loss of life resulting from the five simulated reflow cycles. FIGURE 10. Weibull plots of failure data of plated-through hole barrels by lead-free solder assembly simulation (with and without pre-conditioning). These data show up to a 50% loss of life resulting from only three simulated reflow cycles. Microvias-DMA Method, The Institute for ” Interconnecting and Packaging Electronic Circuits, Northbrook, IL, November 1998. 6. IPC-Test Methods Manual, IPC-TM-650, 2.4.24.6, “Decomposition Temperature Td of Laminate Material Using TGA, The Insti” tute for Interconnecting and Packaging Electronic Circuits, Northbrook, IL, April 2006. 7. IPC-Test Methods Manual, IPC-TM-650, 2.4.41, “Coefficient of Linear Thermal Expansion of Electrical Insulating Boards, ” The Institute for Interconnecting and Packaging Electronic Circuits, Northbrook, IL, March 1986. 8. IPC-Test Methods Manual, IPC-TM-650, 2.4.24.1, “Time to Delamination (TMA Method), The Institute for Interconnecting ” and Packaging Electronic Circuits, Northbrook, IL, December 1994. 9. Bhandarkar, S. M., A. Dasgupta, D. Barker, M. Pecht, and W. Engelmaier, “ThermoMechanical Stress Analysis of Plated Through Hole Structures, ASME J. Elec” tronic Packaging, Vol. 114, No. 1, March 1992, pp. 8-13. 10. Engelmaier, W., “Interconnect Failures and Design for Reliability for Plated-Through Holes/Vias (PTHs/PTVs), Workshop Notes, Engelmaier Associates, L.C., 2007. 11. IPC-Test Methods Manual, IPC-TM-650, 2.6.26, “DC Current Induced Thermal Cycling Test, The Institute for Intercon” necting and Packaging Electronic Circuits, Northbrook, IL, May 2001. 12. IPC-Test Methods Manual, IPC-TM-650, 2.6.7.2B, “Thermal Shock, Continuity and Microsection, Printed Board, The Institute ” for Interconnecting and Packaging Electronic Circuits, Northbrook, IL, May 2004. in terms of operational conditions. Preconditioning, such as subjecting a PCB to 5 or 6 cycles of solder reflow or vapor phase exposure up to the maximum soldering temperature could reveal possible damage resulting from the high lead-free soldering environment. Such preconditioning shows that temperature excursions to solder reflow temperatures can reduce the PCB long-term reliability by as much as 50%, as illustrated in FIGURES 9 and 10. The difference in the samples in Figures 9 and 10 is the increase in preconditioning temperature, which is still not at the level expected for lead-free reflow soldering. PCD&F 2. 3. 4. REFERENCES 1. Engelmaier, W., “Recommendations for PCB FAB Notes and Specifications in Printed Circuit Board Drawings for SnPb 5. and Lead-Free Soldering Assemblies, the Qualification of PCB Shops and Activities to Assure Continued Quality, v.07, White ” Paper/Multi-Client Study, Engelmaier Associates, L.C., February 2007. IPC-4101 “Laminate/Prepreg Materials Standard for Printed Boards, The Institute ” for Interconnecting and Packaging Electronic Circuits, Bannockburn, IL, Rev. B June 2006. IPC-Test Methods Manual, IPC-TM-650, 2.4.24C, “Glass Transition Temperature and Cure Factor by DSC, The Institute for ” Interconnecting and Packaging Electronic Circuits, Northbrook, IL, December 1994. IPC-Test Methods Manual, IPC-TM-650, 2.4.25C, “Glass Transition Temperature and Z-Axis Thermal Expansion by TMA, The ” Institute for Interconnecting and Packaging Electronic Circuits, Northbrook, IL, December 1994. IPC-Test Methods Manual, IPC-TM-650, 2.4.24.4, “Glass Transition Temperature and Thermal Expansion of Materials Used In High Density Interconnection (HDI) and WERNER ENGELMAIER, known as “Mr. Reliability” in the industry, is president of Engelmaier Associates, L.C., (engelmaier.com), a firm providing consulting services on reliability, manufacturing and processing aspects of electronic packaging and interconnection technology; engelmaier@aol.com. 26 PRINTED CIRCUIT DESIGN & FAB JANUARY 2008 http://www.pcb-pool.com http://www.free-pcb-software.com http://www.pcb-pool.com

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Printed Circuit Design & Fab - January 2008 Contents Our Line Market Watch Around the World Happenings ROI PTH Reliability: Designing to Improve PTH Reliability EMC for the Real World PTH Reliability: The Survival and Long-Term Reliability of Lead-Free PCBs iNEMI's Emerging Technologies: Research Priorities for the Electronics Industry Printed Circuit Design & Fab Annual Buyers Guide Special Suppliers Section Guide to Products and Services Off the Shelf: Designcon Preview Marketplace Ad Index BGA Bulletin

Printed Circuit Design & Fab - January 2008

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