Size and Constraining Effects in Lead‐Free Solder Joints

Abstract

Because of the tremendous developments in advanced processing technologies, the dimensions of contemporary electronic devices and interconnections have become smaller and smaller, while the density of heat generation is progressively reaching the limits of traditional cooling techniques. This situation is responsible for higher and higher temperature gradient in electronic packages and, in the same way, for an always increasing range of thermal-induced mechanical loads, which, combined with temperature-dependant material properties, has lead to severe reliability issues. Moreover, in recent electronic designs, like SMT and BGA, the solder joints may not only be electrical interconnections but plays also a dominant role in the mechanical stability of the package. In the case of transportation, mobile or automotive electronics, a high survivability under complex thermo-mechanical dynamic loads, like power-cycling, impacts or vibrations, is required. Nowadays to ensure the reliability of the future products, numerical simulation and optimization methods appears to be the most efficient tools, but, in turn, these techniques require a precise knowledge of thermo-mechanical loads and very accurate material models to predict the lifetime of solder joints. From this point of view, the recent progress of the numerical simulation capabilities has lead to an important increase of the demand for highly detailed 3D constitutive material models that can accurately represent the behaviour of complex materials in a large range of thermomechanical conditions. Lead-free soldering materials have shown very complex elasto-visco-plastic behaviours [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] with strong dependencies on time, strain history and temperature, as well as other geometric and processing parameters that affect their microstructure. Due to these strong influences of geometrical constraints, [20][21][22][23] processing parameters and possible size effects, the macroscopic stress-strain constitutive law of lead-free solder materials should therefore be determined in the most geometrically and physically realistic conditions.In the most cases, solder joints are constituted of only a thin layer or a small ball of lead-free soldering alloy, with a typical size of less than 100 lm, confined between two relatively rigid substrates. Testing material properties at this length scale is a difficult task as it requires a very sensitive and accurate measurement of both applied forces and displacements with typical values in the order of 1 N and 0.1 lm respectively. Optical strain measurement techniques, like Electronic Speckle Pattern Interferometry (ESPI), Moiré Interferometry or Digital Image Correlation (DIC), [31][32][33][34] are the best candidates to achieve the required displacement and spatial resolutions. By combining standard optical microscopy observation, high-resolution CCD image recording and DIC image post-processing, a versatile high resolution strain measurement technique can be developed to charac...

Viscoplastic Creep Response and Microstructure of As-Fabricated Microscale Sn-3.0Ag-0.5Cu Solder Interconnects

“…[31][32][33][34] The literature on microscale SAC solder behavior is limited compared with the literature on their bulk behavior. Sn-3.5Ag solders are also discussed because their microstructure and properties are similar to those of SAC solders.…”

Mechanical Size Effects in Miniaturized Lead-Free Solder Joints

“…6 Simultaneously with our investigation 17 experimental results were described by means of finite-element analysis (FEA), indicating an inverse relationship (using a power-law description) between the tensile strength and gap size. 18 Although these efforts were very successful for the description of the specific specimen under investigation, it seems useful to reintroduce some of the pre-existing models into this discussion. There is a lack of description of the principle amount of the constraint effects occurring at the lower and upper boundaries related to the simple mechanical parameters of the base and solder material.…”

Poroviscoelastic characterization of particle-reinforced gelatin gels using indentation and homogenization

“…The specimen was discretized using eightnode elements with biquadratic displacement interpolation, bilinear pore pressure interpolation, and reduced integration. The FE model was integrated in the identification procedure previously developed by the authors (Cugnoni et al, 2006), which is based on the non-linear least-squares optimization routine provided in MATLAB R ⃝ Optimization Toolbox TM (Version 7.4, The MathWorks, Natick, MA, USA) and whose use in the context of material property identification and indentation is reported in the literature Szeri and Lei, 2007;Liu et al, 2009;Wang and Ovaert, 2009). The identification was carried out using the average experimental creep curve for each case.…”