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Reliability assessment of flip-chip assemblies with lead-free solder joints

: Schubert, A.; Dudek, R.; Walter, H.; Jung, E.; Gollhardt, A.; Michel, B.; Reichl, H.


IEEE Components, Packaging, and Manufacturing Technology Society; Electronic Components, Assemblies, and Materials Association:
52nd Electronic Components & Technology Conference 2002. Proceedings : San Diego, California, USA, May 28 - 31, 2002
Piscataway, NJ: IEEE Order Department, 2002
ISBN: 0-7803-7430-4
ISBN: 0-7803-7431-2
Electronic Components and Technology Conference (ECTC) <52, 2002, San Diego/Calif.>
Fraunhofer IZM ()
reliability assessment; lead-free solder joint; Environmental Awareness; health hazard; Sn-Ag lead-free solder; reliability; thermal fatigue resistance; solder interconnect; SnAg solder alloy; SnPb lead-containing solder; mechanical property; physical properties; coefficient of thermal expansion; stress strain curve; microstructural appearance; mechanical behaviour; thermomechanical behavior; TMA; DTMA; tensile test; constant-load creep test; test temperature; steady-state strain-rate; flip chip assembly; underfill material; solder bump; thermal cycling; electrical resistance; SEM; material parameter; finite element analysis; microelectronic package; lead-free solder interconnect

Due to environmental awareness, and the health hazards involved in using lead in solders, large efforts to develop lead-free soldering have been made in recent years. Sn-Ag alloys are expected to be one of the best candidate lead-free solders. Furthermore, from a reliability viewpoint, there has been interest in improved thermal fatigue resistance of solder interconnects. In this study, two lead-free solder alloys (Sn96.5Ag3.5, Sn95.5Ag3.8Cu0.7) were investigated in comparison to lead-containing solder alloys (Sn63Pb37, Sn59Pb40Ag1). These investigations were focused on mechanical and physical properties (coefficient of thermal expansion, stress-strain curves at different strain-rates) as well as on the microstructural appearance of the solders. The mechanical and thermomechanical behavior of the solders were examined by TMA, DTMA, tensile tests, and creep tests. Constant-load creep tests were performed on the specimens at temperatures from 20 degrees C to 150 degrees C. Steady-state strain rates spanned seven orders of magnitude ranging from 10/sup -11/ s/sup -1/ to 10/sup -4/ s/sup -1/. The second step is a reliability study of flip-chip assemblies on FR-4 (high T/sub g/ material) with three different underfill materials and with Sn63Pb37, Sn96.5Ag3.5, and Sn95.5Ag4.0Cu0.5 bumps, undergoing thermal cycles from - 55 degrees C to 125 degrees C and -55 degrees C to 150 degrees C. The deterioration (characterized by electrical resistance and SEM) are described. Furthermore, it is shown that the material parameters obtained from the tests will increase the precision of finite-element analysis for reliability studies of microelectronic packages with lead- free solder interconnects.