For high temperature interconnection sintered silver can be used, however, it induces new demands on the thermo-mechanical design. That issue requires knowledge on the thermo-mechanical reliability of silver sintered devices, the subject of this paper. Material characteristics of the sinter layers are needed for simulation, which are addressed in the first part of the paper. Based on material properties of pure silver, for sintered silver with different porosities effective material characteristics have been derived by use of a micromechanical cell model. Shear loadings with in-situ deformation analyses have also been made to investigate sintered silver behavior. A complicated dependence on processing, temperature, and deformation rate is seen. Based on different effective constitutive models for the sintered interconnects, stress loadings are studied for a power module, an IGBT on DCB substrate, for passive and active thermal cycling. For the passive cycle complex interactions of the different layers of the stack are observed, which are not seen in a module with soft solder bonding. This result can be attributed to the missing decoupling by the soft soldering layer. Failure risks are evaluated by both conventional FEA and cohesive zone modeling. A quite different stress situation is depicted for active power cycling. The situation is even more complex and it is obvious from the simulations, that active power cycling can induce failure modes different from passive cycling

Packages for high pin counts using the ball grid array technology or its miniaturized version, the chip scale package, inherently require reliability concepts as an integral part of their development. This is especially true for the latter packages, if they are combined with the flip chip technology. Accordingly, thermal fatigue of the solder balls is frequently investigated by means of the finite element method. Various modeling assumptions and simplifications are common to restrict the calculation effort. Some of them, like geometric modeling assumptions, assumptions concerning the homogeneity of the cyclic temperature fields, simplified creep characterization of solder, and the related application of Manson-Coffin failure criteria, are discussed in the paper. The packages chosen for detailed analyses are a PBGA 272 and a FC-CSP 230.

Lead-free solder for electronic assemblies and systems is fast becoming a reality primarily because of market driven forces. While the industry has identified possible alternatives to SnPb solder, much work still needs to be done, especially in the following areas: solder materials characterization (temperature and stress dependent inelastic behavior creep and stress relaxation, bulk versus joint behavior), failure mechanisms related to the solder joints of the new alloys (will creep deformation still play a dominant role for e.g. thermally induced low cycle fatigue?), temperature cycle data, for instance, on real components (acceleration factors may depend on accelerated test conditions and solder alloys, and field conditions may be much more benign than accelerated test conditions), life prediction models (models have to incorporate time and temperature dependent behavior of solders, implementation of constitutive equation in FEA software is one of the keys, isothermal fatigue data should not be useful for life prediction model development), solder-surface interactions (solder reacts with metallization to form interfacial intermetallics, intermetallics grow with time and temperature, metallization consumption by intermetallic growth, intermetallics within the solder, thermo-mechanical properties of the intermetallics), and assembly process development. The impact of some of these issues on the reliability assessment of lead-free solder interconnects through experiments and FE calculations is discussed in the paper, shown on examples like SMD-components and Flip-Chips

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Theoretical analyses on the thermo-mechanical behavior of power modules designed in a new buildup and interconnection technology based on silver sintering and electroplated copper interconnects have been made. The characteristic difference to other technologies can be seen in the replacement of bonding wires by planar copper interconnects and the high voltage applicability of the resulting modules. A high voltage and temperature resistant polymeric foil provides the insulation in this high voltage planar interconnect technology. Electrical connection is made by structured electro-deposited copper structures, which allow additional heat spreading from top of the dies. This interconnection technology is raising new questions concerning the constitutive behavior of the materials involved in the power stack as well as the closely linked questions concerning their thermo-mechanical reliability. Investigations on characteristics of dielectric materials and copper plated interconnects are reported. For the latter, a significant dependence on microstructure is seen. FE-analyses were made to study the thermal and mechanical loadings. Both passive and power cycling were investigated for a prototype converter module substrate designed by HVPT. Transient power cycling induced loading was studied using electric-thermal-mechanical coupling. Significant change in the potential failure modes of such an assembly are to be expected, in particular metallization delamination failure at different interfaces can occur