Predicting the reliability of power electronic modules

This paper discusses the reliability of an IGBT power electronics module. This work is part of a major UK funded initiative into the design, packaging and reliability of power electronic modules. The predictive methodology combines numerical modeling techniques with experimentation and accelerated testing to identify failure modes and mechanisms for these type of power electronic module structures. The paper details results for solder joint failure substrate solder. Finite element method modeling techniques have been used to predict the stress and strain distribution within the module structures. Together with accelerated life testing, these results have provided a failure model for these joints which has been used to predict reliability of a rail traction application

Study of the thermal stress in a Pb-free half-bump solder joint under current stressing

The thermal stress in a Sn3.5Ag1Cu half-bump solder joint under a 3.82×108 A/m2 current stressing was analyzed using a coupled-field simulation. Substantial thermal stress accumulated around the Al-to-solder interface, especially in the Ni+(Ni,Cu)3Sn4 layer, where a maximal stress of 138 MPa was identified. The stress gradient in the Ni layer was about 1.67×1013 Pa/m, resulting in a stress migration force of 1.82×10-16 N, which is comparable to the electromigration force, 2.82×10-16 N. Dissolution of the Ni+(Ni,Cu)3Sn4 layer, void formation with cracks at the anode side, and extrusions at the cathode side were observed

Fracture mechanics analysis of cracks in solder joint intermetallic compounds

The trend towards miniaturization of electronic products leads to the need for very small sized solder joints. Therefore, there is a higher reliability risk that too large a fraction of solder joints will transform into Intermetallic Compounds (IMCs) at the solder interface. In this paper, fracture mechanics study of the IMC layer for SnPb and Pb-free solder joints was carried out using finite element numerical computer modelling method. It is assumed that only one crack is present in the IMC layer. Linear Elastic Fracture Mechanics (LEFM) approach is used for parametric study of the Stress Intensity Factors (SIF, KI and KII), at the predefined crack in the IMC layer of solder butt joint tensile sample. Contrary to intuition, it is revealed that a thicker IMC layer in fact increases the reliability of solder joint for a cracked IMC. Value of KI and KII are found to decrease with the location of the crack further away from the solder interfaces while other parameters are constant. Solder thickness and strain rate were also found to have a significant influence on the SIF values. It has been found that soft solder matrix generates non-uniform plastic deformation across the solder-IMC interface near the crack tip that is responsible to obtain higher KI and KII.

Joint ownership and beneficial entitlement: Stack v Dowden.

Explores the issue of the share of beneficial entitlement to the family home where the legal title is jointly owned, but where there has not been an express declaration of a beneficial joint tenancy. Discusses the House of Lords judgment in Stack v Dowden which addressed this point. Explains how the judges moved the focus away from the court imposing its own sense of fairness on the parties or imputing an intention based on the circumstances to one where the concentration will be on the parties' relevant conduct. Outlines three other points of interest referred to in the judgment: (1) whether an indirect financial contribution could support a constructive trust; (2) whether proprietary estoppel and common intention constructive trusts should be assimilated; and (3) whether a mortgage liability is equivalent to a financial contribution.

Resulting trusts, joint borrowers and beneficial share

Reviews case law illustrating the courts' approach to beneficial ownership of property purchased in joint name by means of a joint mortgage but without any declaration of beneficial interest, the resulting trust and joint beneficial interest presumptions. Contrast the approach adopted in cases where one party made no contribution to the mortgage payments with those where both parties made a contribution. Highlights the courts' treatment of the right to buy discount afforded tenant purchasers and property purchased as a commercial venture rather than a home.

The role of joint training in practitioner development for learning disability services

The presentation explores and evaluates an innovation in education and training in which two different professional trainings (nursing and social work) are integrated to produce jointly qualified specialist practitioners.