A Study on Strain Concentration Around V Notch in Lead Free Solder Material and the Low Cycle Fatigue Life

2015 ◽  
Author(s):  
Takashi Kawakami ◽  
Takahiro Kinoshita ◽  
Hirokazu Oriyama
Keyword(s):  
Fatigue Life ◽  
Solder Joints ◽  
Low Cycle Fatigue ◽  
Lead Free ◽  
Design Rule ◽  
Lead Free Solder ◽  
Cycle Fatigue ◽  
Stress Strain ◽  
Test Pieces ◽  
Free Solder

Solder joints are sometimes opened under thermal cyclic loads as low cycle fatigue phenomena. The fatigue crack is usually initiated around the edge of the interface where stress and strain very severely concentrate, having stress strain singularity. In this study, Sn-3.0Ag-0.5Cu test pieces with V shape notch were supplied to low cycle fatigue tests at 100°C. And inelastic stress strain simulations, which were based on time-dependent non-unified material model, were carried out under several cyclic load levels to obtain strain distributions around the bottom of the V notch. By results of fatigue test and inelastic simulation, the depth from the bottom of the V notch, where the strain range agrees with the prediction of the fatigue life based on smooth test pieces on Coffin-Manson rule, was investigated as the mechanical design rule for lead free solder joints.

Low-Cycle Fatigue Reliability Evaluation for Lead-Free Solders in Vehicle Electronics Devices

2007 ◽  
Author(s):  
Qiang Yu ◽  
Tadahiro Shibutani ◽  
Akifumi Tanaka ◽  
Takahiro Koyama ◽  
Masaki Shiratori
Keyword(s):  
Fatigue Life ◽  
Crack Propagation ◽  
Low Cycle Fatigue ◽  
Strain Range ◽  
Reliability Evaluation ◽  
Lead Free ◽  
Generation Process ◽  
Lead Free Solder ◽  
Cycle Fatigue ◽  
Free Solder

The changeover from eutectic Sn-Pb solder to lead-free solder (Sn-Ag-Cu) has been driven by environmental concerns in the last few years. In this study, in order to obtain the low-cycle fatigue characteristic of Sn-Ag-Cu lead-free solder joints, an isothermal mechanical fatigue test with a large strain range, which can clarify the crack generation process and shorten the examination time, was carried out. FEM analysis was also performed in order to evaluate the relationship between the inelastic strain range and the low-cycle fatigue life. As a result, compared with fatigue life longer than 1000 cycles, the scatter of the fatigue cycles from 100 to several hundred cycles becomes larger. So, it seems that it is necessary to carefully evaluate the low-cycle fatigue life in the reliability evaluation. Moreover, in large chip components, not only crack initiation, but also crack propagation, affects the failure life. Thus, the crack path was simulated and the failure cycle of the large chip was evaluated based on Miner’s rule, and reliability of including the fatigue crack propagation can be evaluated by the analytical approach.

Tensile and Fatigue Properties of Miniature Size Specimen of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge Lead-Free Solder

2018 ◽  
Vol 941 ◽  
pp. 2081-2086
Author(s):  
Masaki Yokoi ◽  
Tatsuya Kobayashi ◽  
Ikuo Shohji
Keyword(s):  
Tensile Strength ◽  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Ternary Eutectic ◽  
Lead Free ◽  
Fatigue Properties ◽  
Lead Free Solder ◽  
Cycle Fatigue ◽  
Proof Stress ◽  
Free Solder

Tensile and low cycle fatigue properties of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge (mass%) lead-free solder were investigated using miniature size specimens and obtained data were compared to those of Sn-3.0Ag-0.5Cu (mass%). The microstructure of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge consists of dendritic β-Sn phases and ternary eutectic phases surrounding them which are composed of β-Sn, (Cu,Ni)6Sn5 and Ag3Sn. Tensile strength and 0.1% proof stress of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge are superior to those of Sn-3.0Ag-0.5Cu at 25°C and 150°C. However, elongation of it is inferior to that of Sn-3.0Ag-0.5Cu at both temperatures. Fatigue lives of both alloys obey the Manson-Coffin equation and are analogous at 25°C. Although fatigue lives of both alloys decrease at 150°C, the fatigue life of Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge is inferior to that of Sn-3.0Ag-0.5Cu. At 150°C, the crack mainly progresses at grain boundaries of recrystallized grains. Sn-3.5Ag-0.5Cu-0.07Ni-0.01Ge has several grain boundaies which can be the origin of the crack so that fatigue lives degrade at 150°C.

Low Cycle Fatigue Behavior and Surface Feature by Image Processing of Sn-0.7Cu Lead-Free Solder

2006 ◽  
Vol 306-308 ◽  
pp. 115-120 ◽  
Author(s):  
Takehiko Takahashi ◽  
Susumu Hioki ◽  
Ikuo Shohji ◽  
Osamu Kamiya
Keyword(s):  
Fatigue Life ◽  
Fatigue Test ◽  
Surface Deformation ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Surface Feature ◽  
Lead Free ◽  
Lead Free Solder ◽  
Cycle Fatigue ◽  
Free Solder

The low-cycle fatigue behavior on Sn-0.7Cu lead-free solder as-cast and Sn-Pb eutectic solder as-cast were investigated at a strain rate 0.1%/s under various temperatures of 25, 80 and 120oC. In addition, the relationships between the surface feature in the low-cycle fatigue test and low-cycle fatigue life of those solders at 25oC were investigated by image processing. The low-cycle fatigue life of Sn-0.7Cu decreased when the temperature increased. And the fatigue life of Sn-0.7Cu was better than that of the Sn-Pb eutectic solder at the temperatures of 25 and 80oC. The low-cycle fatigue behavior on the solders investigated followed Coffin-Manson equation. The fatigue ductility coefficient of Sn-0.7Cu was found to be affected by the temperature. The surface deformation as fine meshes in the low-cycle fatigue test of Sn-0.7Cu did not appear until 10% of the fatigue life. Although it was over 10% of the fatigue life, the surface deformation that was caused by micro cracks and coalesces occurred with the increasing number of cycles. The relationships between the surface feature in the low-cycle fatigue test and the low-cycle fatigue life on Sn-0.7Cu and Sn-37Pb solders were discussed.

Effect of Micro Structure on Fatigue Characteristics of Lead Free Solder Joints

2011 ◽  
Author(s):  
Takahiro Akutsu ◽  
Qiang Yu
Keyword(s):  
Grain Size ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Solder Joint ◽  
Crack Propagation ◽  
Solder Joints ◽  
Lead Free ◽  
Lead Free Solder ◽  
Micro Structure ◽  
Free Solder

This paper presents the influence of the micro structure on the crack propagation in lead free solder joint. The author’s group have studied the Manson-Coffin’s law for lead free solder joint by using the isothermal fatigue test and FEM analytical approaches to establish the practicable evaluation of thermal fatigue life of solder joints, for example, for the Sn-Cu-Ni solder, because this solder is attracted from the aspect of the decrease of solder leach in the flow process and material cost. However, even if the same loading is given to the solder joints of BGA test piece, there was a large dispersion in the fatigue life. Even though the effect of the shape difference has been considered, the range of the dispersion could not been explained sufficiently. In the study, the fatigue crack propagation modes in the solder joints were investigated, and an internal fatigue crack mode and an interfacial fatigue crack mode were confirmed. And the tendency of a shorter on fatigue life in the interfacial fatigue mode was confirmed. To clarify the mechanism of these fatigue crack modes, the crystal grain size in the solder joints was investigated before the fatigue test and also after the test. Furthermore, the verification of the mechanism using FEM models considering the crystal grain size was carried out. First of all, each element in FEM models matching to the average crystal grain size was made. Second, the inelastic strain ranges in each FEM models were studied. As a result, it was shown that the influence of the crude density of the crystal grain to the fatigue crack progress can be evaluated. In addition, the micro structure of the solder joint of large-scale electronic devices is observed, and FEM model was made based on the observation result. As a result, it was shown that the influence of the directionality with the crystal grain to the fatigue crack progress can be evaluated.

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