Quantification of creep strain distribution in small crept lead-free in-situ composite and non composite solder joints

In this study, local creep of lead-free solder SnAg3.8Cu0.7 has been investigated for the first time by using surface markers prepared by focused ion beam (FIB). The test setup was optimized with respect to the applied shear stresses. Two different microstructures have been investigated at 30°C, 50°C, and 80°C, respectively. A high sensitivity of the steady-state creep rate to the microstructure has been demonstrated. The shear deformation was observed to be inhomogeneous and concentrated in specific areas. Local dislocation bands dominate the solder deformation.

Section: Local Creepmentioning

confidence: 84%

Local creep in SnAg3.8Cu0.7 lead-free solder

Jud

Grossmann

Sennhauser

et al. 2005

“…4 The creep properties of SnAgCu solder joints have been studied to some extent. [5][6][7][8] However, detailed information of the effect of microstructure on the creep properties, and especially on the failure mechanism during creep, has been scarce. Studies of failure mechanisms in other kinds of tests, like pull or shear tests, have shown that the failure mechanism is strongly dependent on the test method, the geometry of the solder joint, and the temperature.…”

Section: Introductionmentioning

confidence: 99%

Microstructure, creep properties, and failure mechanism of SnAgCu solder joints

Sundelin

Nurmi

Lepistö

et al. 2006

The effect of microstructure on the creep properties and the failure mechanism of SnAgCu solder joints was studied. Single overlap shear specimens made of FR-4 printed circuit boards (PCBs) with organic solderability preservative (OSP), NiAu, and immersion Sn surface finish were reflow-soldered with hypoeutectic, eutectic, and hypereutectic SnAgCu solder paste. Creep tests of the solder joints were performed at 85°C and 105°C under constant load. The effect of microstructure on the creep behavior of the joints was studied by examining the fracture surfaces and cross-sectional samples of the tested joints. Results show that the intermetallic compound at the interface between the PCB and solder affects the fracture behavior of SnAgCu solder joints, thus creating a significant difference in the creep properties of solder joints on different surface finishes. Composition of SnAgCu solder was also found to affect the creep properties of the joints.

“…[9][10][11][12][13][14][15][16][17] Reinforcing the solder matrix with a small volume fraction of second phase reinforcement particles (such as Cu/Cu 6 Sn 5 /Cu 3 Sn, Ni/ Ni 3 Sn 4 , Fe/FeSn/FeSn 2 , or Ni-coated graphite) has been found to enhance strength, as well as creep and fatigue resistance, [9][10][11][12] particularly under stresscontrolled fatigue, 9 and low strain-rate TMC conditions. 11,12 However, in microelectronic applications, TMC is strain-controlled, and under these conditions, hard/stiff reinforcements appear to decrease fatigue life and creep resistance by promoting void nucleation at the particle-matrix interfaces.…”

Section: Introductionmentioning

confidence: 99%

Role of shape-memory alloy reinforcements on strain evolution in lead-free solder joints

Dutta

Pan

et al. 2006

Microelectronic solder joints are exposed to aggressive thermomechanical cycling (TMC) during service, resulting in strain localization near solder/bondpad interfaces, which eventually leads to low-cycle fatigue (LCF) failure of the joint. In order to mitigate these strain concentrations, a ''smart solder'' reinforced with a martensitic NiTi-based shape-memory alloy (SMA) has been proposed before. In the present work, the role of NiTi particles on strain evolution in composite solders was studied using a combination of experimental and numerical means. Finite element modeling showed that NiTi pariculate reinforcements can reduce inelastic strain levels in the solder via shape recovery associated with the B199 / B2 transformation. In situ TMC studies in the scanning electron microscope (SEM), in conjunction with strain analysis via digital image correlation (DIC), showed evidence of reverse deformation in the solder commensurate with the NiTi phase transformation, demonstrating the conceptual viability of the smart solder approach. The SEM-DIC experiments also suggested that the presence of particulates mitigates shear localization, which is commonly observed in monolithic solder joints close to joint/bond-pad interfaces. Finally, TMC experiments on monolithic solder and NiTi/solder single-fiber composite joints highlighted the beneficial effect of shape-memory transformation in reducing inelastic strain range of solders.