Reliability of lead-free interconnections under consecutive thermal and mechanical loadings

• Published in: Journal of electronic materials Vol. 35; no. 2; pp. 250 - 256
• Main Authors: MATTILA, T. T, KIVILAHTI, J. K
• Format: Journal Article
• Language: English
• Published: New York, NY Institute of Electrical and Electronics Engineers 01.02.2006; Springer Nature B.V
• Subjects: Applied sciences; Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization; Cold working, work hardening; annealing, quenching, tempering, recovery, and recrystallization; textures; Cross-disciplinary physics: materials science; rheology; Electronics; Exact sciences and technology; Materials science; Metallization, contacts, interconnects; device isolation; Microelectronic fabrication (materials and surfaces technology); Physics; Product reliability; Product testing; Semiconductor annealing; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Simulation; Thermal cycling; Treatment of materials and its effects on microstructure and properties; Ternary alloy; chip-scale packed (CSP); Tin alloy; Thermal cycle; Metallizing; Fracture; BGA technology; Chip scale packaging; Under bump metallization; drop test; Inorganic compound; Stress effects; Void; Copper alloy; Annealing; Experimental study; Loading test; Dispersion; thermal cycling; Transition metal alloy; Interconnection; Silver alloy; Recrystallization; Numerical simulation; JESD22-B111; isothermal annealing; Reliability; lead-free; Crack
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/BF02692443

To simulate more realistically the effects of strains and stresses on the reliability of portable electronic products, lead-free test assemblies were thermally cycled (-45°C/+125°C, 15-min. dwell time, 750 cycles) or isothermally annealed (125°C, 500 h) before the standard drop test. The average number of drops to failure increased when the thermal cycling was performed before the drop test (1,500 G deceleration, 0.5 ms half-sine pulse). However, the difference was not statistically significant due to the large dispersion in the number of drops to failure of the assemblies drop tested after the thermal cycling. On the other hand, the average number of drops to failure decreased significantly when the isothermal annealing was carried out before the drop test. The failure analysis revealed four different failure modes: (1) cracking of the reaction layers on either side of the interconnections, (2) cracking of the bulk solder, (3) mixed mode of component-side intermetallic and bulk solder cracking, and (4) void-assisted cracking of the component-side Cu^sub 3^Sn layer. The assemblies that were not thermally cycled or annealed exhibited only type (1) failure mode. The interconnections that were thermally cycled before the drop test failed by mode (2) or mode (3). The drop test reliability of the thermally cycled interconnections was found to depend on the extent of recrystallization generated during the thermal cycling. This also explains the observed wide dispersion in the number of drops to failure. On the other hand, the test boards that were isothermally annealed before the drop testing failed by mode (4). [PUBLICATION ABSTRACT]