2021 22nd International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE)
The integrity of the solder joint is critical to ensure long-term reliability of power-LEDs under... more The integrity of the solder joint is critical to ensure long-term reliability of power-LEDs under harsh environmental conditions. Many studies have focused on prediction of the lifetime for different lead-free solder joints in temperature cycling tests especially Ball Grid Arrays (BGA), flip chip, SMD, etc [1]. However, physics-of-failure (PoF) based solder fatigue modelling is an on-going struggle for microelectronics and microsystems industry since it heavily depends on the geometry of the solder solder (i.e. package type and therefore, correct implementation of the thermo-mechanical response) and, precise knowledge of valid process dependent material properties, above all for the solder material. Further, a comparison of lifetime data between different package types depends on a stringent definition of a suitable failure criterion and evaluation of the local failure parameter. This makes it challenging to establish a reliable and universal lifetime model for a specific solder material across package types. In LEDs L2 bonding by solder attach, due to thermal management requirements the use of Insulated Material Substrates (IMS) is compulsory. The combination of Metal-Core-PCB boards and the ceramic substrate in LEDs introduces a complexity factor caused by the large E-modulus and CTE mismatch which must be considered.In this paper, a model is developed to predict the lifetime of SAC305 solder joint in a LED on board setup using accelerated tests and finite element modelling where crack length is the failure criterion and the accumulated creep strain is the computational failure parameter to quantify damage. Moreover, influence of geometrical factors on reliability of LED is investigated. Moreover, it was observed that process uncertainties such as void could largely impact the lifetime which leads us to dive further in robustness evaluation within a physics of failure reliability paradigm.
A multi-fluid model for gas stirred gas/liquid/liquid reac- tors with mass transfer between the t... more A multi-fluid model for gas stirred gas/liquid/liquid reac- tors with mass transfer between the two liquid phases has been developed within a commercial CFD code. Using the CFD model a scale up study of a gas/metal/slag reactor in which an unwanted impurity element is transferred from the metal to the slag phase has been carried out. Reactors of two different sizes and with four different gas-stirring rates have been simulated. The results show that scale up of the smaller reactor increases the metal productivity signifi- cantly, and that the refining rate increases significantly with increasing gas rate.
ABSTRACT In this letter the existence of non-axisymmetric states, as well as symmetric ones, for ... more ABSTRACT In this letter the existence of non-axisymmetric states, as well as symmetric ones, for the same operating conditions, in a symmetric Chemical Vapor Deposition reactor is revisited. Of particular interest here, is the actual effect of the non-axisymmetric flow patterns on the deposited solid film. Assessment of the film quality in terms of uniformity and symmetry over a wide range of operating conditions is made possible with detailed three-dimensional computational models. The results indicate that the predominance of non-axisymmetric flow patterns in symmetric reactor set-ups leads to films with unfavorable characteristics, especially in operating conditions that yield high deposition rates.
Multi-crystalline silicon ingot casting using directional crystallisation is the most costeffecti... more Multi-crystalline silicon ingot casting using directional crystallisation is the most costeffective technique for the production of Si for the photovoltaic industry. Non-uniform cooling conditions and a non-planarity of the solidification front result, however, in the build-up of stresses and viscoplastic deformation. Known defects, such as dislocations and residual stresses, can then occur and reduce the quality of the produced material. Numerical simulation, combined with experimental investigation, is therefore a key tool for understanding the crystallisation process, and optimizing it. The purpose of the present work is to present an experimental furnace for directional crystallisation of silicon, and its analysis by means of numerical simulation. The complete casting procedure, i.e., including both the crystallisation phase and the subsequent ingot cooling, is simulated. The thermal field has been computed by a CFD tool, taking into account important phenomena such as radiation and convection in the melt. The transient thermal field is used as input for a thermo-elasto-viscoplastic model for the analysis of stress build-up and viscoplastic deformation during the process. Numerical analysis is employed to identify process phases where further optimisation is needed in order to reduce generated defects.
The plunging jet in tapping of steel from converters or electric arc furnaces entrains gas into t... more The plunging jet in tapping of steel from converters or electric arc furnaces entrains gas into the steel bath contained in a ladle. Gas entrainment rate and the effect of the gas on the flow pattern in the ladle are studied by means of Computational Fluid Dynamics CFD. The work focuses on the mathematical modeling. Two numerical methods, one for free-surface flows and one for dispersed multiphase flow are combined. A transport equation for the average bubble diameter that incorporates the effect of coalescence and breakup is presented. Results from computations for one ladle and tapping configuration are shown. Our findings indicate that the gas entrainment rate is affected by the material properties of the liquid in the sense that the material properties determine the shape of the jet. Moreover, bubble sizes in the range of two-orders of magnitude are predicted in the ladle. The dispersed diameter model seems to work well. It showed the expected response to material parameters and...
The spontaneous bubble formation in a narrow uniformly gas-fluidized bed was simulated over 5 rea... more The spontaneous bubble formation in a narrow uniformly gas-fluidized bed was simulated over 5 real time seconds using a two-fluid model and a new solution technique for dispersed two-phase flow.
Scandinavian Journal of Metallurgy - SCAND J METALL, 2000
Alloying of steel during tapping from BOF and EAF furnaces has been studied by computational flui... more Alloying of steel during tapping from BOF and EAF furnaces has been studied by computational fluid dynamics (CFD) in a recent publication (Berg et al. 1999, accepted for publication in Ironmaking and Steelmaking). The original paper has focused on the results of a comprehensive parameter study where alloy type, size, addition time, and other parameters were varied. The present work focuses on the CFD methodology that has been used to simulate the alloying process. In short, the CFD analysis of the dissolution process in the ladle combines a single-phase turbulent flow field computation with the tracking of 1000 stochastic particle paths. In the original paper the analysis was conducted in two-dimensional axisymmetric models of the ladle geometries, however, in the present work the numerical analysis is extended to three dimensions. Comparisons are made between results for three and two-dimensional computations. It is shown that the analysis can be conducted in two dimensions with on...
Proceedings of the Int. Symp. on the Reliable …, 1999
... Stein Tore Johansen and Harald Laux Flow Technology SINTEF Materials Technology, N-7034 Trond... more ... Stein Tore Johansen and Harald Laux Flow Technology SINTEF Materials Technology, N-7034 Trondheim, Norway ... These models were later improved and adapted to practical flow situations like flows in bins and inclined chute flows (Walton [3],[4] ). A good review of the state ...
2021 22nd International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE)
The integrity of the solder joint is critical to ensure long-term reliability of power-LEDs under... more The integrity of the solder joint is critical to ensure long-term reliability of power-LEDs under harsh environmental conditions. Many studies have focused on prediction of the lifetime for different lead-free solder joints in temperature cycling tests especially Ball Grid Arrays (BGA), flip chip, SMD, etc [1]. However, physics-of-failure (PoF) based solder fatigue modelling is an on-going struggle for microelectronics and microsystems industry since it heavily depends on the geometry of the solder solder (i.e. package type and therefore, correct implementation of the thermo-mechanical response) and, precise knowledge of valid process dependent material properties, above all for the solder material. Further, a comparison of lifetime data between different package types depends on a stringent definition of a suitable failure criterion and evaluation of the local failure parameter. This makes it challenging to establish a reliable and universal lifetime model for a specific solder material across package types. In LEDs L2 bonding by solder attach, due to thermal management requirements the use of Insulated Material Substrates (IMS) is compulsory. The combination of Metal-Core-PCB boards and the ceramic substrate in LEDs introduces a complexity factor caused by the large E-modulus and CTE mismatch which must be considered.In this paper, a model is developed to predict the lifetime of SAC305 solder joint in a LED on board setup using accelerated tests and finite element modelling where crack length is the failure criterion and the accumulated creep strain is the computational failure parameter to quantify damage. Moreover, influence of geometrical factors on reliability of LED is investigated. Moreover, it was observed that process uncertainties such as void could largely impact the lifetime which leads us to dive further in robustness evaluation within a physics of failure reliability paradigm.
A multi-fluid model for gas stirred gas/liquid/liquid reac- tors with mass transfer between the t... more A multi-fluid model for gas stirred gas/liquid/liquid reac- tors with mass transfer between the two liquid phases has been developed within a commercial CFD code. Using the CFD model a scale up study of a gas/metal/slag reactor in which an unwanted impurity element is transferred from the metal to the slag phase has been carried out. Reactors of two different sizes and with four different gas-stirring rates have been simulated. The results show that scale up of the smaller reactor increases the metal productivity signifi- cantly, and that the refining rate increases significantly with increasing gas rate.
ABSTRACT In this letter the existence of non-axisymmetric states, as well as symmetric ones, for ... more ABSTRACT In this letter the existence of non-axisymmetric states, as well as symmetric ones, for the same operating conditions, in a symmetric Chemical Vapor Deposition reactor is revisited. Of particular interest here, is the actual effect of the non-axisymmetric flow patterns on the deposited solid film. Assessment of the film quality in terms of uniformity and symmetry over a wide range of operating conditions is made possible with detailed three-dimensional computational models. The results indicate that the predominance of non-axisymmetric flow patterns in symmetric reactor set-ups leads to films with unfavorable characteristics, especially in operating conditions that yield high deposition rates.
Multi-crystalline silicon ingot casting using directional crystallisation is the most costeffecti... more Multi-crystalline silicon ingot casting using directional crystallisation is the most costeffective technique for the production of Si for the photovoltaic industry. Non-uniform cooling conditions and a non-planarity of the solidification front result, however, in the build-up of stresses and viscoplastic deformation. Known defects, such as dislocations and residual stresses, can then occur and reduce the quality of the produced material. Numerical simulation, combined with experimental investigation, is therefore a key tool for understanding the crystallisation process, and optimizing it. The purpose of the present work is to present an experimental furnace for directional crystallisation of silicon, and its analysis by means of numerical simulation. The complete casting procedure, i.e., including both the crystallisation phase and the subsequent ingot cooling, is simulated. The thermal field has been computed by a CFD tool, taking into account important phenomena such as radiation and convection in the melt. The transient thermal field is used as input for a thermo-elasto-viscoplastic model for the analysis of stress build-up and viscoplastic deformation during the process. Numerical analysis is employed to identify process phases where further optimisation is needed in order to reduce generated defects.
The plunging jet in tapping of steel from converters or electric arc furnaces entrains gas into t... more The plunging jet in tapping of steel from converters or electric arc furnaces entrains gas into the steel bath contained in a ladle. Gas entrainment rate and the effect of the gas on the flow pattern in the ladle are studied by means of Computational Fluid Dynamics CFD. The work focuses on the mathematical modeling. Two numerical methods, one for free-surface flows and one for dispersed multiphase flow are combined. A transport equation for the average bubble diameter that incorporates the effect of coalescence and breakup is presented. Results from computations for one ladle and tapping configuration are shown. Our findings indicate that the gas entrainment rate is affected by the material properties of the liquid in the sense that the material properties determine the shape of the jet. Moreover, bubble sizes in the range of two-orders of magnitude are predicted in the ladle. The dispersed diameter model seems to work well. It showed the expected response to material parameters and...
The spontaneous bubble formation in a narrow uniformly gas-fluidized bed was simulated over 5 rea... more The spontaneous bubble formation in a narrow uniformly gas-fluidized bed was simulated over 5 real time seconds using a two-fluid model and a new solution technique for dispersed two-phase flow.
Scandinavian Journal of Metallurgy - SCAND J METALL, 2000
Alloying of steel during tapping from BOF and EAF furnaces has been studied by computational flui... more Alloying of steel during tapping from BOF and EAF furnaces has been studied by computational fluid dynamics (CFD) in a recent publication (Berg et al. 1999, accepted for publication in Ironmaking and Steelmaking). The original paper has focused on the results of a comprehensive parameter study where alloy type, size, addition time, and other parameters were varied. The present work focuses on the CFD methodology that has been used to simulate the alloying process. In short, the CFD analysis of the dissolution process in the ladle combines a single-phase turbulent flow field computation with the tracking of 1000 stochastic particle paths. In the original paper the analysis was conducted in two-dimensional axisymmetric models of the ladle geometries, however, in the present work the numerical analysis is extended to three dimensions. Comparisons are made between results for three and two-dimensional computations. It is shown that the analysis can be conducted in two dimensions with on...
Proceedings of the Int. Symp. on the Reliable …, 1999
... Stein Tore Johansen and Harald Laux Flow Technology SINTEF Materials Technology, N-7034 Trond... more ... Stein Tore Johansen and Harald Laux Flow Technology SINTEF Materials Technology, N-7034 Trondheim, Norway ... These models were later improved and adapted to practical flow situations like flows in bins and inclined chute flows (Walton [3],[4] ). A good review of the state ...
Uploads
Papers by Harald Laux