Computer simulation of the reliability of wire bonds and ribbon bonds in power electronics modules

Aluminium wires are widely used in power electronics modules to connect power semiconductor devices and other parts of the module electrically. Recently, other interconnect techniques have been proposed such as ribbon bond to improve the reliability, performance and reduce costs of power modules. The reliability of ribbon bond technique for an IGBT power module under power cycling is compared with that of conventional wire bond in this study using electro-thermal nonlinear Finite Element Analysis. The results showed that a single ribbon of 2000μm x 200μm will replace three wire bonds of 400μm in diameter to achieve a similar module temperature distribution under same power load. Using the equivalent plastic strain increment per cycle, it is seen that the ribbon bond is more reliable than the wire bonds. The impact of neglecting joule heat in the wire/ribbon bonds during power cycling simulation has also been investigated

An analysis of the reliability and design optimization of aluminium ribbon bonds in power electronics modules using computer simulation method

Ribbon bonding technique has recently been used as an alternative to wire bonding in order to improve the reliability, performance and reduce cost of power modules. In this work, the reliability of aluminium and copper ribbon bonds for an Insulated Gate Bipolar Transistors (IGBT) power module under power cycling is compared with that of wire bonds under power and thermal cycling loading conditions. The results show that a single ribbon with a cross section of 2000 μm × 200 μm can be used to replace three wire bonds of 400 μm in diameter to achieve similar module temperature distribution under the same power loading and ribbon bonds have longer lifetime than wire bonds under cyclic power and thermal cycling conditions. In order to find the optimal ribbon bond design for both power cycling and thermal cycling conditions, multi-objective optimization method has been used and the Pareto optimal solutions have been obtained for trade off analysis

Investigating the accuracy of digital image correlation in monitoring strain fields across historical tapestries

Finite element generated synthetic image deformation is used to assess factors affecting the reliability and accuracy of strain fields measured by the DIC technique, when using the inherent historical tapestry image to track deformations. Compared with direct correlation with the reference image, incremental correlation is found to introduce accumulated error and is less suitable for DIC analysis under low strains. Image quality, for example, variation in resolution, is demonstrated to strongly affect DIC performance. Finally, it is recommended that an iterative approach is required to determine the optimum subset and strain filter size for effective DIC analysis using inherent tapestry patterns, especially at low strain levels

Investigating the accuracy of digital image correlation in monitoring strain fields across historical tapestries

Finite element generated synthetic image deformation is used to assess factors affecting the reliability and accuracy of strain fields measured by the DIC technique, when using the inherent historical tapestry image to track deformations. Compared with direct correlation with the reference image, incremental correlation is found to introduce accumulated error and is less suitable for DIC analysis under low strains. Image quality, for example, variation in resolution, is demonstrated to strongly affect DIC performance. Finally, it is recommended that an iterative approach is required to determine the optimum subset and strain filter size for effective DIC analysis using inherent tapestry patterns, especially at low strain levels

An approximate numerical method for the prediction of plastic strain in layered structures

A simple and fast approximate numerical method has been developed using the total deformation theory of plasticity and strength of material relationship to predict stress and strain in layered structures that are common in power electronics and other electronics components. As an application example, the method has been used to estimate the fatigue life of wire bonds in IGBT modules. The method has been compared with Finite Element Analysis method and the results show that the predicted trends are similar for a range of design and loading parameters. Therefore, the approximate method can be used for design optimization of layered structures

Numerical simulation of the junction temperature, the coolant flow rate and the reliability of an IGBT module

By increasing coolant flow rate, the junction temperature of IGBT power modules can be reduced but this is accompanied by undesirable increase in pressure and pumping power. In this paper, numerical simulation and multi-objective optimization methods have been used to obtain a trade-off relationship between reducing IGBT junction temperature and the increase in pressure drop due to increased coolant flow-rate. It is found that the pressure drop increases more than 100% for a 10% reduction in IGBT maximum junction temperature due to the increased coolant flow rate. The impact of the IGBT junction temperature on the power module lifetime has also been investigated. Moreover, an effective and efficient work-flow in integrating numerical methods software results for performing thermo-mechanical analysis under power cycling conditions has been explored

Using FloTHERM XT and ANSYS workbench to perform Thermo-Mechanical analysis

Thermally induced stress in electronic products is a growing concern for electronic package designers. These stresses result in material degradation of the package, and lead to a wear-out mechanism known as fatigue. Depending on the magnitude of these stresses, fatigue can result in premature loss of performance and hence reliability of the overall product. This impact of fatigue is governed by (i) system design (ii) non-uniform temperature distribution during operation and (iii) mismatch in materials properties (e.g. co-efficient of thermal expansion (CTE). Accurately predicting the magnitude of stress requires a coupled thermo-mechanical analysis. First, the nonuniform temperature distribution across the system needs to be predicted, taking into account the relevant heat sources and heat transfer mechanisms. Secondly, the resulting deformation, strain (including creep) and stress distributions across the package needs to be predicted. Best-in-class analysis tools used by electronic product designers treat thermal and mechanical (Stress) design separately. In particular, CFD tools are used for thermal analysis and FEA tools are used for mechanical design. Although thermo-mechanical analysis, using FEA tools, is not new, the majority of reported work assumes that temperature changes across the package/system are constant. Of course, in reality, this is not the case. Current trends in both micro and power electronics packaging include the use of 3D-ICs, Through Silicon Vias, WaferLevel Packaging, Higher switching frequency, etc, and operating in higher temperature environments. Hence there is an increasing need to enable thermal and mechanical design engineers to work collaboratively using best-in-class analysis tools