This paper studies the numerical failure mechanism of the solder joints in the ball grid array (BGA) package under thermal reliability process. The package consists of the silicon die, the Flame Retardant 4 (FR-4) substrate and the FR-4 printed circuit board (PCB). A total of 64 95.5Sn-4.0Ag-0.5Cu (SAC405) solder joints with a diameter of 0.46 mm are arranged together in area array fashion with a pitch distance of 0.8 mm. Only a quarter-model of the package is simulated since all the geometry, loading and boundary conditions (BC) is symmetry at the centre of the package. The package is exposed with thermal loading, initially at the liquidus temperature of 220°C to room temperature (25°C). Then, it follows with 3 additional thermal cycles between 125°C and -40°C with a ramp rate of 11°C/min and 15 minutes dwell time, respectively. Unified inelastic strain model (Anand model) was used to compute the inelastic behaviour of the solder joints. Results show that the stress level at the critical solder joints and the corresponding inelastic strain are 39.91 MPa of 0.2083%, respectively after the end of the solder reflow cooling process. As predicted, the inelastic strains accumulate continuously in the solder joint throughout the temperature cycles. Additionally, in the critical solder joint, both high stress and inelastic strain gradients are localized near to the solder-IMC interfaces. Prolong the thermal cycles can extensively accumulate the inelastic strains which lead to fatigue crack and subsequently crack propagation in the solder joints. After the end of the FE simulation, the highest stress and inelastic strain predicted are 57.96 MPa and 0.5781%, respectively.
Total hip replacements (THR) is a surgical operation to replace defect bone at the hip joints. The rate of succession of THR post-operative still debatable as complication and failure rate of the prosthesis still exists. Edge-loading, dislocation, fracture and longevity are among the concerned issues with many studies were conducted via software analysis. This study aims to simulate the difference of anatomical and simplified modelling in finite element analysis (FEA) and investigate edge-loading effect at different inclination angle in both modelling conditions. A CT scan hemi-pelvic model was reshaped and converted into 3D model in SolidWorks and the next step, FEA was conducted in ANSYS Workbench V16 at different inclination angle. Anatomical and simplified model were run in ANSYS Workbench and the results were recorded. The anatomical modelling produced less contact pressure range 26% to 51% compared with simplified modelling at four inclination angle conditions. Von Mises stress and total deformation in anatomical also produced reduction of more than 65%. Both modelling conditions shows agreement that elevated inclination angle had induced higher contact pressure at superior region of acetabular cup. The inclusion of hemi-pelvic model gives lower value recorded in FEA as contact stress dispersed into the bone that already integrated with the implant given statistically significant (p<0.05). Noteworthy to include bone integration into implant during FEA study to produce unambiguous contact mechanics studies.
Dislocation and edge loading are significant issues highlighted due to the acetabular component orientation during total hip replacement(THR). This study aims to define the optimum acetabular cup orientation with the most suitable femoral ball size, thus eliminating the possible issue that may arise during postoperative surgery. A numerical approach by creating a single function that enables the calculation of the cup inclination (α) and the cup anteversion (β) with respect to range of motion are developed by using a programming language namely Matlab®. Three separate studies were done by having a head neck ratio of 2.33, 2.67 and 3.0, respectively. From these data, it is clear that the size of femoral head affects the area under range of motion at the bearing surfaces. A wide area under the graph resulted in a better and greater number combination of acetabular cup thus reducing the risk of dislocation and edge loading.
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