The presence and change of thermal stresses in solders, which are used for mounting microelectronic packages on PC-boards, will eventually lead to material fatigue. The number of cycles to failure can be predicted from empirical relations of the Coffin-Manson type provided the increments of creep strains and/or energy densities are known, for example, from (rather extensive) FE-simulations. A special problem arises for newly developed solders for which the Coffin-Manson equations are not known yet and need to be established first from a combination of FE and costly reliability experiments. In any case the goal of the industry and research institutions is to replace experiments as much as possible by reliable predictive simulations. However, FE calculations, which are widely used to perform this task, can-as indicated-be rather time-consuming, due to the huge effort involved for component meshing, and due to the various non-linear constitutive equations required for the description of creep in solders and other package materials. In a previous paper (Müller and Hauck in Mech Adv Mater Struct, 15(6):485-489, (2008)) a simple analytical 1D-model was presented that allows computing characteristic damage quantities, such as creep strain and creep energy density, for different solder materials and different temperature profiles in a very efficient manner, provided a creep law is known. In this paper the proposed procedure is validated by comparison with results from detailed FE-simulations.
Fabrication of modern microelectronic components requires miscellaneous solder materials for joining. In order to guarantee the quality of the manufacturing process and the reliability of the resulting solder joint it is necessary to know the material properties of the joining parts and of the solder materials. In particular Young's modulus, yield stress, and the hardness are of great interest. Moreover, a complete stress-strain curve is important for a detailed material characterization and simulation of a component, e.g., by Finite Elements (FE). The miniaturization of modern electronic products with small solder joints allows only fabrication of very small-sized specimens. Because of this miniature tests are used for measuring the mechanical properties of the solders in the experimental investigations of this paper. More specifically two miniature tests are presented and discussed, a mini-uniaxial-tension-test and a nanoindenter experiment. In the tensile test the axial loading is prescribed, the corresponding extension of the specimen length is recorded, both of which determines the stress-strain-curve directly. The stress-strain curves are then mathematically analyzed by assuming a non-linear relationship between stress and strain of the Ramberg-Osgood type and fitting the corresponding parameters to the experimental data by means of an optimization routine. For a detailed analysis of very local mechanical properties nanoindentation is used, resulting primarily in load vs. indentation-depth data. According to the procedure of Pharr and Oliver this data can be used to obtain hardness and Young's modulus but not a complete stressstrain curve, at least not directly. In order to obtain such a stress-strain-curve, the nanoindentation experiment is combined with FE and the coefficients involved in the corresponding constitutive equation for stress and strain are obtained by means of the inverse method. Finally in this paper, the stress-strain curves from nanoindentation and tensile tests are compared for two materials, namely aluminum and steel and differences are explained in terms of the locality of the measured properties.
Nanoindentation is quite a common method for local material characterization. Values for hardness and Young's modulus can be determined directly from the recorded data. Essential for the correct determination of the material parameters is the precise measurement of the actual indentation depth of the indenter. The indenter measures the current depth by means of a Wheatstone bridge which correlates the indentation depth to a change in voltage. A possible tool for the verification of the recorded indentation depths is Atomic Force Microscopy (AFM). AFM is able to scan an area of indents for almost any surface. The deflection of the tip is measured by a laser spot reflected from the surface of the cantilever. The difference in height between the surface and the indent can directly be read off from the plotted image. However, using an AFM only allows us to measure the depth of the permanent indentation depth after unloading the indenter. Nevertheless, correlation between the remaining indentation depths measured by the explained methods allows for a first assessment of the correctness of the online recorded depth-data by the nanoindenter.
The continuous effort of modern electronic industry is the miniaturization of microelectronic components. In order to guarantee the reliability of the joining process, the quantitative knowledge of the solder material properties is very important, especially the values of Young's modulus, Nanoindentation hardness and yield stress. However, small‐sized microelectronic devices require the fabrication of small sized specimens and the use of corresponding miniature material tests. At the Technische Universität Berlin nanoindentation tests are applied. Moreover the material properties at elevated temperature are of particular interest in order to characterize the solder materials more detailed. This work describes the setup and the elevation of high‐temperature nanoindentation tests in context with first results for selected materials. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.