100 um Fine Pitch Flip Chip/ 10-20 um Microbumps Issues 100 um Flip Chip Geometry and Assembly Methodology IMC Growth with Thermal Aging: 00 um to 0.5 mm Pitch Components Introduction Intermetallic Compounds and Reliability Microstructure Evolution in Lead-Free Solder: BGAs and Flip Chips Justin Chow, Ye Tian, Suresh K. Sitaraman School of Mechanical Engineering, Georgia Institute of Technology and other institutions. Reliability of lead-based solders is well understood. In the past decade however, lead-free solder alloys are being used due to environmental and health considerations. National Electronics Manufacturing Initiative (NEMI, 2007) has recommended Sn4.0Ag0.5Cu (SAC405) alloy and Japan Electronic Industry Development Association (JEIDA) has recommended Sn3.0Ag0.5Cu (SAC305) alloy. With the change in solder material the reliability of lead free solder alloys needs to be understood. A layer of Inter-Metallic Compounds (IMC’s) form at the copper/solder interface during reflow and subsequent aging. • IMC’s are more brittle than bulk solder • Joints tend to fail at IMC region What variables are important for growth? Labie, R., et al. Electronic System-Integration Technology Conference 2010: IEEE. Copper Pad Bulk Solder Cu 6 Sn 5 Cu 3 Sn BGA SAC Alloy Characterization Experiments Characterize IMC Growth as a function of: • Aging Time (12 hr, 24 hr, 1 week, 4 weeks) • Temperature (25 C, 70 C, 100 C, 150C) • Solder Metallurgy (SAC 105, 305, SnAg, SnPb) • Surface Finishes (Ni, OSP) • Geometry (Pitch, Size) Phase 1: Unassembled Packages Phase 2: Assembled Packages Phase 3: Ex-situ Aging With technologies and form factors constantly getting smaller, solder joints and pitches are concurrently shrinking. At these smaller scales, the atomic diffusion paths are shortened, increasing the interfacial chip/substrate interaction. Additionally, the IMC volume proportion increases dramatically. These changes in microstructure have an important effect on the reliability. With small stand off heights, the entire solder joint can become an intermetallic. Ex-Situ 1 Day: 3.94 um 1 Week: 4.77 um 4 Weeks: 5.87 um y = 0.0912x + 3.5296 R² = 0.997 0 1 2 3 4 5 6 7 0 5 10 15 20 25 30 Thickness Microns Time(hours) 1/2 0.5 mm Pitch BGA IMC Growth 100 um Pitch Flip Chip Cross-Sections After Reflow 100 Hours at 150 C