No abstract

No 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.

No abstract

There is an increasing necessity to record the deformation characteristics of microelements often consisting of freestanding foils and wires. The data required are either mechanical or thermal such as Young`s moduli, stress-strain values, fatigue-and thermal strain data, but the nominal strength of a structure changes by scaling its size. Due to this size effect, material data cannot be taken from macrospecimens, thus special testing procedures were introduced. Laseroptical sensors based on the speckle correlation method were applied to determine non-contacting strain values with high strain resolution. For the mechanical properties tensile tests were used for the freestanding foils and wires. For thermal strain measurements a laser speckle based dilatometer was designed. A short outline of applicability of the testing equipment is given. The following materials data are presented and discussed: Young`s modulus, mechanical and thermomechanical and thermal strain data of various Cu foils and wires with varying grain sizes, thickness and defined texture. A thickness effect was detected and is interpreted in terms of a "thickness to grain size ratio" approach.