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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...
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...
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...
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...
A systematic study of the effect of Ag, Cu and Zn alloying elements on the EM performance of Sn-rich Pb-free solder is reported. EM performance was found to strongly depend on the types of UBMs, alloying elements, compositions, and microstructures in solder. While leaded solders were found to be more robust than Pb-free solders, SnAg solders, in general, has better EM performance than SnCu solders...
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...
The properties of lead-free solders such as Sn3.8Ag0.7Cu are less understood than traditional Sn-Pb solders, as well as the factors affecting these material properties. Therefore, the present paper focuses on determination of stress-strain properties for both small-scale solder joints and for bulk solder for three different strain rates. The paper also analyses the obtained experimental results, and...
A thorough understanding of the mechanics of lead-free solder joint in a ball grid array (BGA) assembly under expected operating conditions is essential in developing reliable life prediction models. In this respect, accurate deformation response of Sn-4Ag-0.5Cu (SAC405) solder under varying temperature cycles and straining rates is established using unified inelastic strain theory. The mechanics...
Drop/impact causes high strain rate deformation in solder joints of microelectronics package. It is important to understand mechanical behavior of solder joints under high strain rate for reliability design of products. In this paper mechanical behaviors of two lead-free solder alloys, Sn3.5Ag and Sn3.0Ag0.5Cu, were investigated by quasi-static tests and the split Hopkinson tension/pressure bar testing...
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