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The continuous push for smaller bump pitch interconnection in line with smaller Cu/low-k technology nodes demands the substrate technology to support finer interconnection. However, the conventional organic buildup substrate is facing a bottleneck in fine-pitch wiring due to its technology limitation, and the cost of fabricating finer pitch organic substrate is higher. To address these needs, Si interposer...
Thus far, there is a severe lack of understanding about interfacial fracture and impact behavior of the microscale lead-free solder interconnects. In this study, the finite element simulation and analytical method were used to characterize the interfacial fracture and impact behavior at the interfaces of the microscale Sn-Ag-Cu solder joints. The intersection of a linear microcrack tip upon Sn-Ag-Cu...
Wafer level Chip Scale Package (WLCSP) fulfills the demand for small, light, and portable handheld electronic devices, and it is one of the most advanced packaging concepts. When the WLCSP was assembled on board level, the connection, i.e. solder joints are generally the critical and challenging issue for the whole device's reliability. In addition to the shape and material of solder joints, the material...
Cracking along the intermetallic compound (IMC) interface in solder joints is the most important failure mechanism in electronics packages. In order to understand the failure mechanism well, a 2D solder/IMC interface model is used to examine the stress around the interface. Three solder materials, Sn37Pb, Sn3.5Ag and Sn3.0Ag0.5Cu, and various IMC thicknesses, which represent different growth stages...
Cure Induced Micro-Anomaly (CIMA) are worm like hollow microstructures found within resin rich region of underfill after curing within a BGA package with combination of copper die bumps and Sn-Ag substrate bumps. CIMA leads to solder extrusion during secondary reflow. Root cause of CIMA has been identified to be from thermal mechanical stress induced by the stiffness of the joints formed between the...
In this paper, the investigation focuses on the copper stud bump solder joint thermal-mechanical reliability. The copper stud bump processing is simulated by FEM software Ansys/Ls-dyna, and then the relationship between the copper stud bump and processing parameters (bonding force, ultrasonic power, bonding time and bonding temperature) is studied. Based on the simulation result, the dimension of...
Solder joints are subjected to a complex combined loading condition of tensile and shear deformation. The fracture behavior of solder joints is different when it is subjected to pure-tensile, pure shear or varying combination of mixed-mode tension and shear loading combinations. The observed failure modes can vary from brittle intermetallic (IMC) layer failure to ductile bulk solder shear failure...
A complete halogen-free test vehicle was achieved by assembling five ball grid array (BGA) components with daisy-chain on an 8-layer high density interconnection (HDI) printed circuit board with a low-halide Sn1.0Ag0.5Cu (SAC105) Pb-free solder pastes for reducing the formation of Ag3Sn. Afterward a board-level cyclic bending test was enforced on the as-reflowed assemblies according to the JESD22-B113...
In this paper, a new application of 4-point cyclic bending test for the solder joint reliability evaluation is discussed. In light of the long cycle time of thermal cycle testing, the industry has been searching for a more cost-effective and time-effective way to achieve the evaluation task. The 4-point cyclic bending test is considered a good candidate in this study. The thermal cycle test and 4-point...
Understanding of interface fracture behavior of the solder joints has long been significant in reliability evaluation of electronic components and packages. The experimental and finite element methods were employed to characterize the fracture performance of "Cu wire/solder/Cu wire" sandwich structured butt microscale solder joints with different sizes (75 to 425 mum in thickness and 200...
In this paper, steady-state creep behavior of lead free 80Au-20Sn solder was investigated at three different temperatures (i.e. 25degC, 75degC and 125degC) and a range of stress levels. Hyperbolic-Sine model was employed to characterize the creep properties of the lead free solder, constants in the model were determined through data fitting and were compared with that of other lead free solders.
Most accelerated temperature cycling (ATC) tests reported the observations that SnAgCu (SAC) solders have better thermal fatigue reliability than SnPb solders due to their lower creep strain rate. But material studies revealed that this is true only when stress level is below a certain level. When the stress level in the solder increases, eventually the creep strain rate of SAC solder may outgrow...
Properties of body-centered tetragonal beta-Sn are highly anisotropic. The crystal orientation of the beta-Sn has a marked effect on the stress state in the SnAgCu solder joints. A finite element analysis has been performed of the thermal cycling of the SnAgCu solder and solder joints. Significant amounts of stresses at the solder/Cu interface and in the plane of the grain boundary was found. The...
BGAs packaging offer high pin counts and lower interconnecting space, and are suitable for high density packaging. However, it is difficult to inspect individual solder joints on BGA assembly by conventional visual methods and need a complicated practice on rework. Ball impact test is a useful method to estimate the reliability of BGA solder joint. In this study, the three-dimensional explicit finite...
PbSnAg solder was widely used in die attachment for high power chip packaging, and the thermal-mechanical reliability of PbSnAg solder layer is a key factor to evaluate the quality of high power devices packaging. Viscoplastic finite-element simulation methodologies were utilized to predict Pb92.5Sn5Ag2.5 solder joint reliability for die attachment under accelerated temperature cycling conditions...
The transition from tin-lead to lead free soldering in the electronics manufacturing industry has been in progress for the past 10 years. In the interim period before lead free assemblies are uniformly accepted, mixed formulation solder joints are becoming commonplace in electronic assemblies. For example, area array components (BGA/CSP) are frequently available only with lead free Sn-Ag-Cu (SAC)...
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. In our prior work on aging effects, we have demonstrated that the observed material behavior variations of Sn-Ag-Cu (SAC) lead free solders during room temperature aging (25degC) and elevated...
Continuous increase in demand for product miniaturization, high package density, high performance and integration of different functional chips has lead to the development of three dimensional packaging technologies. Face-to-face silicon (Si) dies stacking is one of the three dimensional (3D) packaging technologies to form a high density module. In this work, a chip level stacked module was demonstrated...
This paper presents a reliability model for wafer level chip scale packages (WLCSP) assembled with Sn4%Ag 0.5%Cu (SAC 405) solder. The reliability model is based on a creep constitutive model that takes into consideration the dimensions of the solder joints and a thermo-mechanical fatigue crack growth model. The creep constitutive model was derived from over 250 constant load creep tests performed...
Reliability of SnAgCu solder joints under mechanical stress is not proven, in particular for Aeronautic and High Performance (AHP) products. They are subjected to high temperatures, severe mechanical stresses and long-term mission profiles. This work is comprehended within a larger study, which has as objective the characterization of the SnAgCu alloys mechanical behaviour at the solder joint scale...
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