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The thermomechanical fatigue of solder joints on the system level is more complex to predict than on the board level. The damage of the solder joints of an electronic device in an ECU (electronic control unit) depends on the thermal expansion mismatch between the materials of the device and the PCB (printed circuit board), so called local mismatch, as well as on the global deformation of the PCB induced...
The board level drop test is intended to evaluate and compare the drop performance of surface mount electronic components. The JEDEC standardize for board level drop test address test board construction, design, material, component locations and test conditions etc. However, in actual drop test conditions, continued drops usually loosen up the mounting screw, which is not considered in JEDEC. This...
One of the driving factors for a steady reduction in wafer and cell thickness is the present shortage of polysilicon feedstock combined with the need to reduce manufacturing costs in photovoltaic module production. Therefore materials and manufacturing processes must adapt to maintain acceptable mechanical yields and module reliability. The soldering of solar cell strings is a critical step in the...
The lifetime of a solder joint is mainly determined by its creep behaviour. Creep arises from the stresses inside the solder joints as a consequence of the thermomechanical mismatch of the board and the substrate. The stress state is heavily influenced by the anisotropy of tin. To understand the damage process in solder joints, the influence of the anisotropic microstructure must be understood. In...
Considerable scientific efforts were made in the past decade, to come up with reliable and predictive analyses for lead-free solder interconnects, in view of their obligatory introduction a few years ago. This paper concentrates on a number of physical, computational and experimental multi-scale aspects, based on the analyses of the instabilities that occur in a Sn-Ag-Cu (SAC) alloy. Particular attention...
This paper investigates the degradation behaviour of lead-free Sn96.5Ag3.0Cu0.5 solder. A series of isothermal mechanical cycling tests under different conditions has been conducted. The tests were monitored in-situ with a high magnification camera system. Optical observations are presented from selected tests, showing the surface morphology during testing. In addition to the optical investigation,...
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...
Due to environmental consciousness and legislative regulations, Pb-free solders have been increasingly used for replacement of conventional SnPb solders in the microelectronic industry. However, during the transition period from SnPb to Pb-free solders, some products will potentially consist of mixtures of Pb-free with SnPb solders. This paper presents the results of microstructural analysis of mixed...
The simulation results show that larger contact opening may not benefit on relieving current crowding effect in the flip-chip solder joints. For the solder joints with a 10-mum thick Cu UBM, the diameter of the contact opening for the lowest current crowding effect is 60 mum. It means that using larger or smaller diameter will increase the current density in the solder bumps. In addition, the optima...
This paper presents a study of the probabilistic effects that act in addition to deterministic (mechanistic) effects to reduce the thermal cycling durability of ball grid array (BGA) interconnects as the component I/O count increases. The mechanistic drivers include increasing thermal expansion mismatch with increasing package size and increasing stress levels with decreasing solder joint size. The...
In this paper, a wrist device conception was selected to study the reliability of flexible devices by drop test simulation. In the conception device, all of the components cannot be made flexible immediately. Some of them are still rigid, such as the ball grid array (BGA), the connector, and some other big components like the vibrator. The reliability of the device, where such rigid components are...
In this paper we discuss the influence of solder joint geometry on the lifetime of a flip chip assembly. Geometry variations caused by variations of solder volume, pad configuration, and pad size on the printed circuit board (PCB) were taken into account. Typically these parameters vary due to technological fabrication tolerances. Consequently, the influence of such design aspects on system reliability...
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