Uniaxial and cyclic stress-strain behavior of lead-free solders at nanoscale

2021 ◽  
Author(s):  
Afnan Mostafa ◽  
Mohammad Motalab ◽  
Ahmad Rasheeq Faiyaz ◽  
Ratul Paul
Keyword(s):  
Cyclic Stress ◽  
Lead Free ◽  
Stress Strain ◽  
Strain Behavior ◽  
Lead Free Solders

Effects of Test Temperature and Prior Aging on the Cyclic Stress-Strain Behavior of Lead Free Solders

2019 ◽  
Author(s):  
Mohammad Ashraful Haq ◽  
Mohd Aminul Hoque ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Strain Range ◽  
Peak Stress ◽  
Cyclic Stress ◽  
Lead Free ◽  
Stress Strain ◽  
Plastic Strain Range ◽  
Strain Behavior ◽  
Loop Area ◽  
Prior Aging ◽  
Lead Free Solders

Abstract In temperature changing environments, solder joints often experience fatigue failure due to cyclic mechanical stresses and strains induced by mismatches in the coefficients of thermal expansion. These stresses and strains lead to damage accumulation and contribute to the crack initiation, crack propagation, and eventually to failure. In this study, we have investigated the cyclic stress-strain behavior of SAC305 and SAC_Q reflowed lead free solders that occur at various testing temperatures and with various prior aging conditions. Lead free solder uniaxial test specimens with circular cross-section have been prepared using vacuum suction method and then were aged for 0 to 20 days at 125 °C. The samples were then subjected to cyclic stress-strain loading using a Micro-mechanical tester at different testing temperatures from T = 25 C to T = 100 C. The evolution of hysteresis loops with duration of prior aging was characterized by measuring the strain energy density dissipated per cycle (loop area), peak stress, and plastic strain range. It was observed that aging degrades the mechanical fatigue properties due to microstructural coarsening. At elevated temperatures, a drop in the loop area and peak stress and an increase in the plastic strain range for both lead free reflowed solder materials were obtained. In addition, SAC_Q samples had a higher loop area and peak stress compared to SAC305.

The Effects of Aging of the Cyclic Stress-Strain and Fatigue Behaviors of Lead Free Solders

2013 ◽  
Author(s):  
Muhannad Mustafa ◽  
Jordan C. Roberts ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Cyclic Loading ◽  
Damage Accumulation ◽  
Solder Joints ◽  
Peak Load ◽  
Cyclic Stress ◽  
Lead Free ◽  
Failure Behavior ◽  
Stress Strain ◽  
Effects Of Aging ◽  
Lead Free Solders

Solder joints in electronic assemblies are typically subjected to thermal cycling, either in actual application or in accelerated life testing used for qualification. Mismatches in the thermal expansion coefficients of the assembly materials cause the solder joints to be subjected to cyclic (positive and negative) mechanical strains and stresses. This cyclic loading leads to thermomechanical fatigue damage that involves damage accumulation, crack initiation, crack propagation, and failure. In addition, the microstructure, mechanical response, and failure behavior of lead free solder joints in electronic assemblies are constantly evolving when exposed to isothermal aging and/or thermal cycling environments. While the effects of aging on solder constitutive behavior (stress-strain and creep) have been examined in some detail, there have been no prior studies on the effects of aging on solder failure and fatigue behavior. Aging leads to both grain and phase coarsening, and can cause recrystallization at Sn grain boundaries. Such changes are closely tied to the damage that occurs during cyclic mechanical loading. In this investigation, we have examined the effects of aging on the cyclic stress-strain behavior and fatigue life of lead free solders. Uniaxial solder test specimens (SAC105 and SAC305) have been prepared and subjected to cyclic stress/strain loading at different aging conditions. A four-parameter hyperbolic tangent empirical model has been used to fit the entire cyclic stress-strain curve and the hysteresis loop size (area) was calculated using definite integration for a given strain limit. This area represents the energy dissipated per cycle, which is correlated to the damage accumulation in the joint. Using the recorded cyclic stress-strain curves, the evolution of the solder hysteresis loops with aging have been characterized and empirically modeled. Similar to solder stress-strain and creep behavior, there is a strong effect of aging on the hysteresis loop size (and thus the rate of damage accumulation) in the solder specimens. Fatigue experiments were also performed, where the uniaxial specimens were subjected to cyclic loading over a particular strain range until failure. Fatigue failure in the experiments was defined to occur when there was a 50% peak load drop during mechanical cycling. Prior to testing, the specimens were aged (preconditioned) at 125 °C for various aging times, and then the samples were subjected to cyclic loading at room temperature (25 °C). It was found that aging decreased the mechanical fatigue life, and the effects of aging on the peak load drop have been studied. It has also been observed that degradations in the fatigue/failure behavior of the lead free solders with aging are highly accelerated for lower silver content alloys (e.g., SAC105). Various empirical failure criteria such as the Coffin-Manson model and the Morrow model have been used to fit the measured data, and the parameters in the models have been determined as a function of the aging conditions.

Characterization of Hysteresis Loop Evolution in Aged Lead Free Solders

2011 ◽  
Author(s):  
Muhannad Mustafa ◽  
Zijie Cai ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Cyclic Loading ◽  
Hysteresis Loop ◽  
Solder Alloy ◽  
Damage Accumulation ◽  
Cyclic Stress ◽  
Lead Free ◽  
Stress Strain ◽  
Effects Of Aging ◽  
Lead Free Solders ◽  
Control Constant

Solder joints in electronic assemblies are typically subjected to thermal cycling, either in actual application or in accelerated life testing used for qualification. Mismatches in the thermal expansion coefficients of the assembly materials leads to the solder joints being subjected to cyclic (positive/negative) mechanical strains and stresses. This cyclic loading leads to thermomechanical fatigue damage that involves damage accumulation, crack initiation, crack propagation, and failure. While the effects of aging on solder constitutive behavior (stress-strain and creep) have been examined in some detail, there have been no prior studies on the effects of aging on solder failure and fatigue behavior. In this investigation, we have examined the effects of aging on the cyclic stress-strain behavior of lead free solders. Uniaxial SAC lead free solder specimens were subjected to cyclic (tension/compression) mechanical loading. Samples were cyclically loaded under both strain control (constant positive and negative strain limits) and stress control (constant positive and negative stress limits). The hysteresis loop size (area) was calculated from the measured cyclic stress-strain curves for a given solder alloy and temperature. This area represents the strain energy density dissipated per cycle, which can be typically correlated to the damage accumulation in the joint. The tests in this investigation were performed with SAC105 solder alloy. Prior to cyclic loading, the specimens in this study were aged (preconditioned) at 125 °C for various aging times (0–6 months). From the recorded cyclic stress-strain curves, we have been able to characterize and empirically model the evolution of the solder hysteresis loops with aging. Similar to solder stress-strain and creep behaviors, there is a strong effect of aging on the hysteresis loop size (and thus the rate of damage accumulation) in the solder specimens. The observed degradations in the fatigue/cyclic behavior of the lead free solders are highly accelerated for lower silver content alloys (e.g., SAC105), and for aging and testing at higher temperatures. In our current work, we are also subjecting aged solder samples to cyclic loading until failure occurs. Our ultimate goal is to understand the effects of aging on the thermomechanical fatigue life.

Cyclic Stress-Strain Behavior of Reinforcing Steel Including Effect of Buckling

1999 ◽  
Vol 125 (6) ◽  
pp. 605-612 ◽  
Author(s):  
Mario E. Rodriguez ◽  
Juan C. Botero ◽  
Jaime Villa
Keyword(s):  
Cyclic Stress ◽  
Reinforcing Steel ◽  
Stress Strain ◽  
Strain Behavior
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