Mechanical Size Effects in Miniaturized Lead-Free Solder Joints

Abstract

Future reliability and quality control of microelectronics will greatly depend on a detailed understanding of the complex mechanical and thermal properties of miniaturized lead-free solder joints. Therefore, the question of the occurrence of size effects or dimensionally induced constraints, which could change the mechanical properties of solder joints in small dimensions dramatically, has become the focus of investigation. In this study we investigated the influence of decreasing gap size on the tensile, shear, and stress relaxation behavior of solder joints to investigate the occurrence of size effects and dimensionally induced constraints, which could change the mechanical properties of solder joints significantly in micrometer dimensions. Residual stresses might remain in the solder joints during high-temperature dwell in thermomechanical fatigue. Model solder joints (Sn3.5Ag/Cu) of rectangular shape with gap sizes varying between 25 lm and 850 lm were prepared by reflow soldering to achieve near-industrial soldering processing. Scanning electron microscopy was used for analyzing the microstructure and the complex modes of fracture and crack propagation in the solder interconnect. The observed tensile behavior can be interpreted in terms of an existing theory for brazed joints to complement finite-element analysis that is usually used for a description of these phenomena.

The effect of undercooling on the microstructure and tensile properties of hypoeutectic Sn–6.5Zn–xCu Pb-free solders

“…However, as can be seen from Sn-Zn binary diagram, the peak around 200.6°C is due to the second-phase formation in solder matrix, while the b-Sn primary phase melts at 214.6°C. Actually, these results completely agree with that reported by El-Daly et al [11,12], where the same effect …”

“…Such samples are usually manufactured from standard bar-solder, which is melted and solidified in a steel mold. In order to obtain relevant constitutive data for real interconnections, specimens had to be scaled down to a typical solder joint size if one considers the extremely small solder volumes in modern microelectronic industry [12,13]. Therefore, the design optimization of solder joints could be conducted with different geometries to investigate the tensile behavior.…”

Microstructural modifications and properties of low-Ag-content Sn–Ag–Cu solder joints induced by Zn alloying

“…In previous related studies, characterization of constitutive alloy behavior is usually done through tensile tests using standard specimens. To obtain a relevant constitutive data for real interconnections, the specimens had to be scaled down to a typical solder joint size if one considers the extremely small solder volumes in modern microelectronic industry [11,12]. Therefore, the design optimization of solder joints could be conducted with different geometries to investigate the tensile behavior.…”

Geometry effect on mechanical performance and fracture behavior of micro-scale ball grid array structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints

“…Compared with the ball shear tests, lap-shear tests can exert a similar stress concentration occurring close to the attachment interface at both ends of the joints and reflect the mechanical behavior of BGA solder joint more accurately. By using lap-shear tests, Chawla et al [9][10][11][12][13] found that the testing and geometrical parameters have profound effects on the mechanical behavior and fracture location of rectangular solder joints.…”