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Testing and inverse modelling for solder joint reliability assessment

Testing and inverse modelling for solder joint reliability assessment

Kamara, Elisha Tingha (2013) Testing and inverse modelling for solder joint reliability assessment. PhD thesis, University of Greenwich.

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As the trends in green manufacturing, miniaturization, and enhanced functionality of electronics devices continue without any sign of slowing down, the reliability of lead free solder joints with diminishing size has become more and more a challenge to the design engineers and the electronics manufacturing industry. In order to predict the reliability of solder joints accurately, it is necessary to develop test techniques to test solder joints efficiently under conditions that are comparable to those in application environment. In this day and age when computer simulation has become an indispensable tool in many areas, it is also very important that suitable material models are available for solder materials so that virtual design tools can be used to predict device reliability performance accurately.

In this work, the aim was to develop vibration and cyclic shear test methods and equipment, and to use computer modelling techniques in the analysis of lead free solder joints in microelectronics devices, and to develop an inverse Finite Element technique and experimental data to obtain constitutive laws for lead-free solder alloys. In the development of the vibration test machine, a prototype test machine that uses piezoelectric cell as actuators for the loading was modelled using the Finite Element Analysis method, and the behaviours of the test specimen which is similar to a BGA solder joint in dimensions was analysed. The static and dynamic response of the equipment was modelled and compared with experimental results. A novel multi-joint test specimen in which the solder deformation is similar to that in solder joints of BGAs that are under thermal loading was analysed so that test results can be interpreted and the specimens and loading conditions can be improved. The response of the joints reinforced the understanding that the interface of the solder and the copper or printed circuit board is the mostly likely region for crack growth and hence failure of the package. In the inverse Finite Element Analysis of solder joints, cyclic shear test data and Finite Element Analysis methods were used to improve the Anand's visco-plastic constitutive law for the SAC solder specimens under the test conditions. To reduce the possibility of spurious experimental data skewing the entire analysis, a technique was employed that uses limited experimental datasets in determining the material parameters. Simulation results using the new constitutive law showed significant improvement in accuracy.

The main contribution of this research work to the manufacturing, testing and virtual design of solder joints can be summarised as follows: (1) A unique dedicated high cycle fatigue test equipment that is especially suited for testing very small solder joints and other surface mounted technologies under vibration conditions has been successfully designed, and manufactured. This is expected to enhance the capability of the industry in solder joint tests. (2) The behaviours of individual solder joints in a BGA-like multi-joint test specimen under isothermal cyclic loading condition have been characterised making the prediction of solder properties more accurate and efficient. (3) A novel procedure that is based on inverse Finite Element Analysis to obtain nonlinear creep parameters of, for example, Anand’s model, has been proposed and demonstrated. This method reduces the effect of spurious dataset, the high reliance of the skill of the individuals who perform the analysis and makes it possible for small institutions with limited resources to obtain the necessary model parameters for virtual product design and reliability analysis.

Item Type: Thesis (PhD)
Additional Information:
Uncontrolled Keywords: computer modelling, device reliability prediction, device reliability performance, device reliability testing, lead free solder joints testing, virtual design tools,
Subjects: Q Science > QA Mathematics > QA75 Electronic computers. Computer science
T Technology > TK Electrical engineering. Electronics Nuclear engineering
Faculty / School / Research Centre / Research Group: Faculty of Liberal Arts & Sciences
Last Modified: 14 Oct 2016 09:28

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