Behavior Of Lead Free Solders Research Articles

Effect of the Angle Between Sn Grain c-Axis and Electron Flow Direction on Cu-Reinforced Composite Solder Joints Under Current Stressing

With a body-centered tetragonal crystal structure, Sn grains were demonstrated to have highly anisotropic behaviors in various properties. The electromigration behavior of lead-free solder was impacted by the grain orientations. In this paper, the angle between the c-axis and the electron flow direction in composite solder joints (angle θ) was proven to be an important factor during electromigration. The effects of angle θ on the electromigration of composite solder joints were investigated in this paper. Cu particle-reinforced Sn3.5Ag solder joints were stressed under a current density of 104 A/cm2 at room temperature. After 336 h current stressing time, different electromigration phenomena occurred at the two sides of the grain boundary in the composite solder joint which contained two Sn grains with different angle θ. The Sn grains with the larger angle θ had a smaller growth rate of Cu6Sn5. In addition, a composite solder joint with a single Sn grain was set as the contrast and its angle θ was smaller than that of the composite solder joint with two Sn grains. The growth rate of Cu6Sn5 in the composite solder joint with a single grain was faster than that of the composite solder joint with two Sn grains.

Solder wetting behavior enhancement via laser-textured surface microcosmic topography

In order to reduce or even replace the use of Sn-Pb solder in electronics industry, the laser-textured surface microstructures were used to enhance the wetting behavior of lead free solder during soldering. According to wetting theory and Sn-Ag-Cu lead free solder performance, we calculated and designed four microcosmic structures with the similar shape and different sizes to control the wetting behavior of lead free solder. The micro-structured surfaces with different dimensions were processed on copper plates by fiber femtosecond laser, and the effect of microstructures on wetting behavior was verified experimentally. The results showed that the wetting angle of Sn-Ag-Cu solder on the copper plate with microstructures decreased effectively compared with that on the smooth copper plate. The wetting angles had a sound fit with the theoretical values calculated by wetting model. The novel method provided a feasible route for adjusting the wetting behavior of solders and optimizing solders system.

Damage Mechanics of Solder Joints under High Current Density

In this paper, Moiré interferometry technique is used to measure the in-situ displacement evolution of lead-free solder joints under high density (104A/cm2). An electromigration constitutive model is developed to simulate deformation of lead-free solder joint under current stressing. The simulation predicts Moiré interferometry measurements in both spatial distribution and time history evolution, which indicates that the model is reasonably good for predicting the mechanical behavior of lead-free solder joints under electric current stressing.

Behavior of Lead-Free Solder Under Thermomechanical Loading

This paper presents an investigation of lead-free Sn-Ag base alloy, 95.5Sn-3.9Ag-0.6Cu, both experimentally and analytically. Experimentally, the deformation behavior of the material was measured for different temperatures (25°C and 1000°C) over a range of strain rates (10−5 to 10−3/s) under isothermal and thermomechanical conditions. Development of a unified viscoplastic constitutive model followed, taking into account the effects of the measured strain rate and temperature changes. The temperature rate effects are considered in the evolution equation of back stress. In order to include material degradation in the solder, the theory of damage mechanics is applied by introducing two damage variables in the viscoplastic constitutive model. Finally, the constitutive model is coded into a general-purpose finite element computer program (ABAQUS) through its user-defined material subroutine (UMAT). The damage-coupled finite element analysis (FEA) is then employed to monitor the condition of failure of a notched component. The predicted and measured maximum loads have been compared and found to be satisfactory. In addition, the calculated damage distribution contours enable the identification of potential failure site for failure analysis.

Resonant vibration behavior of lead-free solders

This study investigated the resonant vibration-fatigue characteristics of some potential lead-free solders, including Sn-Zn, Sn-Ag Sn-Cu, and Sn-Bi alloys. Results show that, under a fixed vibration force, the damping capacity and vibration-fracture resistance of Sn-Cu and Sn-Ag eutectic alloys with an off-eutectic structure are higher than Sn-Pb and are also higher than Sn-Bi and Sn-Zn. This is closely related to the vibration-deformed structure and crack-propagation morphology associated with the microstructural features of the materials. Also, the striated deformation in the Sn-rich phase can be regarded as an effective mechanism in absorbing vibration energy. Moreover, microstructural modification of the Sn-Zn eutectic alloy can be achieved through Ag addition, and thus, the damping capacity and vibration-fracture resistance can be significantly improved.

517 環境適合型鉛フリーはんだの擬弾性挙動

517 環境適合型鉛フリーはんだの擬弾性挙動

Microthermomechanical Analysis of Lead-Free SN-3.9AG-0.6CU Alloys; Part I : Viscoplastic Constitutive Properties

ABSTRACTThis is part I of a two-part paper on the mechanical behavior of lead-free solders. The constitutive properties of Sn3.9Ag0.6Cu lead-free alloy are presented and compared against baseline data from eutectic Sn63Pb37 solder. Monotonic, displacement-controlled and load-controlled tests are performed over various temperatures, strain rates and stresses using the thermo-mechanical-microstructural (TMM) test system. It is shown that the lead-free alloy exhibits creep strain rates that are from one to five orders of magnitude lower than the eutectic SnPb alloy, depending on the stress level and the homologous temperature.