Novel Testing Instrument for Lead-Free Solder Characterization (original) (raw)
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IEEE 70th Electronic Components and Technology Conference (ECTC), 2020
In electronic packages, solder joints are frequently exposed to thermal cycling environment where temperature variations occur from very low to high temperature. These exposures can occur in real life applications as well as in accelerated thermal cycling tests used for the characterization of thermal-mechanical fatigue behavior. Due to temperature variations and CTE mismatches of the assembly materials, cyclic temperature leads to damage accumulation due to shear fatigue and material property evolves in the solder joints. In addition, the thermal cycling dwell periods at the high temperature extremes will cause thermal aging phenomena in the solder material. This leads to microstructural evolution and material property degradation. Further aging effects can occur during the ramp periods between the low and high temperature extremes of the cycling. While changes in solder materials during aging have been examined in detail in prior studies, there have been limited studies examining material evolution occurring during thermal cycling. In a previous study of the authors, mechanical behavior evolutions of SAC305 lead-free solder material under several different thermal cycling profiles have been reported. The results demonstrated severe degradations in the mechanical properties, especially for thermal cycles with the long ramp and dwell periods. In our other recent work, evolution of the mechanical behavior of real solder joints has been investigated. In the current investigation, these prior studies have been extended. In particular, the mechanical behavior evolutions in both bulk SAC305 solder samples and SAC305 solder joints have been investigated under the same slow thermal cycling profile, and then the results were compared. In the first part of this study, miniature bulk solder uniaxial test specimens were prepared by reflowing solder in rectangular cross-section glass tubes with a controlled temperature profile. After reflow solidification, the samples were placed into the environmental chamber and thermally cycled between-40 C to +125 o C under a stress-free condition (no load). The thermal cycle consisted of 150 minutes cycles with 45 minutes ramps and 30 minutes dwells. The test specimens were separated into groups that were subjected to various durations of cycling (e.g. 0, 10, 50, 100, 250 cycles, etc.). After the environmental exposures, stress-strain curves of the cycled uniaxial samples were recorded, and then the mechanical properties were measured including the effective elastic modulus (E), yield stress (YS), ultimate tensile strength (UTS). The evolutions of the mechanical properties were characterized as a function of number of applied thermal cycles. In the second part of this study, the evolution of the mechanical behavior in thermally cycled BGA solder joints was studied using nanoindentation. PBGA solder joint strip specimens were first prepared by cross sectioning BGA assemblies followed by surface polishing to facilitate nanoindentation testing. Single grain solder joints were tested since they had large regions of solder material with equivalent mechanical behavior, which could then be indented several times after various durations of cycling. After preparation, the solder joint strip samples were thermally cycled using the same thermal cycling profile as the bulk samples. At various points in the cycling, the package was taken out from the chamber, and nanoindentation was performed to obtain the modulus and hardness. This allowed for investigation of the evolution of the mechanical properties of the SAC305 solder joints with the duration of thermal cycling. The results for the thermally cycled bulk samples showed that the detrimental effects of aging are accelerated in a thermal cycling environment. Similar degradations were found in the BGA solder joints subjected to thermal cycling. The degradation for both bulk samples and solder joints showed exponential variation with number of cycles. However, the degradation rates were higher in the bulk solder samples relative to those in the real solder joints. For example, the effective elastic modulus and yield stress reduced by 69% and 43%, respectively, for the bulk samples; whereas for the real solder joints, these values both reduced by 26%.
Combined loading and failure analysis of lead-free solder joints due to creep and fatigue phenomena
Soldering & Surface Mount Technology, 2014
Purpose -The aim of this work is the use of specially designed, authoring device to evaluate the strength of solder alloys commonly used in all kinds of electronic and electrical devices that are used in various fields of economic and industrial development to shorten the testing period. By obtaining answers to pervade science questions on how to properly investigate the reliability of solder joints can increase lifespan (uptime) of all electronic devices, and especially those that are used in the process submitted severe external conditions (dust, humidity air, heat, mechanical stress). Design/methodology/approach -The basic demand for performing the experimental tests is to measure small displacements (order of fractions of micrometers or of single microns) occurring within the sample. The analysis of the displacement values in various environmental conditions (temperature, humidity, current flow) allows estimating how a given material behaves also in a longer time, under normal operating conditions. Unlike a commonly used method, based on measuring the time-to-failure, at which the item is damaged due to accelerated aging, a behaviour of the sample is being tested for the selected duration time and the given loading conditions. Findings -The theoretical analysis and performed numerical simulations of ATC tests based on developed failure and reliability investigation system (FRIS) imply proposed here combined loading approach a promising and affective method for accelerated reliability tests. Both indentation and FRIS techniques by numerous possibilities of loading conditions seem to be appropriate in order to study the creep and fatigue behaviour. That kind of behaviours can be used by different models which characterize separately the mechanical properties under creep or fatigue tests. In case of creep mode, the displacement is expressed as a function of time where different parameters can be used to represent the creep sensibility. Originality/value -New device can provide both creep and fatigue phenomena simultaneously and perform tests in digital controlled environmental conditions. That approach enables faster method for testing reliability of solder joints.
A General Methodology to Predict Fatigue Life in Lead-Free Solder Alloy Interconnects
Journal of Electronic Packaging, 2009
The ubiquitous eutectic tin-lead (Sn-Pb) solder alloys are soon to be replaced with lead-free alternatives. In light of this transition, new computational tools for predicting the fatigue life of lead-free solders are required. A fatigue life prediction methodology was developed, based upon stress-strain, creep and isothermal fatigue data; the later generated using a double lap-shear (DLS) test assembly. The proposed fatigue life prediction methodology builds on current practices in fatigue prediction for solder alloys, particularly the concepts of un-partitioned energy methods in finite element analysis (FEA) and continuum damage mechanics. As such, the current state of these fields is briefly discussed. Next, global and local FEA simulations of the DLS test assembly are detailed. A correlation is then made between the empirical data and the FEA simulations. A general fatigue life prediction methodology is next described in detail.
Reliability of the Aging Lead Free Solder Joint
56th Electronic Components and Technology Conference 2006, 2006
Solder materials demonstrate evolving microstructure and mechanical behavior that changes significantly with environmental exposures such as isothermal aging and thermal cycling. These aging effects are greatly exacerbated at higher temperatures typical of thermal cycling qualification tests for harsh environment electronic packaging. In the current study, mechanical measurements of thermal aging effects and material behavior evolution of lead free solders have been performed. Extreme care has been taken so that the fabricated solder uniaxial test specimens accurately reflect the solder materials present in actual lead free solder joints. A novel specimen preparation procedure has been developed where the solder uniaxial test specimens are formed in high precision rectangular cross-section glass tubes using a vacuum suction process. The tubes are then sent through a SMT reflow to re-melt the solder in the tubes and subject them to any desired temperature profile (i.e. same as actual solder joints).
Reliability of Lead-Free Solder Joints Under a Wide Range of Thermal Cycling Conditions
2011
In this paper, we report a comprehensive set of accelerated thermal cycling (ATC) tests that were performed on test vehicles with different package types, sizes, pitches, and solder joint alloy metallurgies using four different thermal cycling profiles: 0 to 100, -40 to 125, -55 to 125, and -60 to 150°C. Samples from the tests were analyzed for their failure modes, and failure rates were calculated by using Weibull statistics. The characterized life for each test condition was determined and analyzed. The impact of solder alloy metallurgies, package types, sizes, and pitches on acceleration factors of the ATC tests to fatigue life was also analyzed and discussed. The quantified discrepancies among several acceleration factors from different studies compared to the experimental data presented in this paper are illustrated. The results provide valuable guidance on the effects of package types, size, pitches, and solder joints alloy metallurgies on various ATC test conditions. In addition, failure analysis was performed at different stages of the tests for each thermal cycling condition. Dramatic failure mode shifts at extreme ATC conditions were observed. The significance and the long-term impact of the failure modes and failure mechanism shift between various ATC test conditions to the life prediction of lead-free solders are extensively discussed.
2011 IEEE 61st Electronic Components and Technology Conference (ECTC), 2011
Solder joints in electronic assemblies are typically subjected to thermal cycling, either in actual application or in accelerated life testing used for qualification. Mismatches in the thermal expansion coefficients of the assembly materials leads to the solder joints being subjected to cyclic (positive/negative) mechanical strains and stresses. This cyclic loading leads to thermomechanical fatigue damage that involves damage accumulation, crack initiation, crack propagation, and failure. While the effects of aging on solder constitutive behavior (stress-strain and creep) have been examined in some detail, there have been no prior studies on the effects of aging on solder failure and fatigue behavior.
Size and Constraining Effects in Lead-Free Solder Joints
Advanced Engineering Materials, 2006
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 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, 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.
2006
Predicting the fatigue life of solder interconnections is a challenge due to the complex nonlinear behavior of solder alloys and the load history. Long experience with Sn-Pb solder alloys together with empirical fatigue life models such as the Coffin-Manson rule have helped us identify reliable choices among package design alternatives. However, for the currently popular Pb-free choice of SnAgCu solder joints, designing accelerated thermal cycling tests and estimating the fatigue life are challenged by the significantly different creep behavior relative to Sn-Pb alloys. This study is divided into two parts: In the first part, a hybrid fatigue modeling approach inspired by nonlinear fracture mechanics is discussed. The hybrid fatigue model has been shown to predict the crack trajectory and fatigue life of a Sn-Pb solder interconnection subjected to both isothermal accelerated thermal and anisothermal power cycling conditions. In the second part, results of experimental characterization via fatigue testing of microelectronic packages with SnAgCu solder interconnections subjected to anisothermal power cycling conditions are described. Packages of different geometries were tested to study the effects of these variations on the estimation of fatigue life. The aforementioned hybrid model relies on the estimation of two fracture parameters which are to be determined experimentally. In this study, a novel technique involving tracking crack fronts in solder interconnections as a function of number of fatigue cycles is proposed to estimate these fracture parameters that can be then used to model fatigue crack growth using the hybrid modeling technique
Fatigue analysis of miniaturized lead-free solder contacts based on a novel test concept
Microelectronics Reliability, 2007
The paper presents the method of generating lifetime-prediction-laws on special prepared very stiff specimen. The combination of thin-and thick-film technology allows building up test samples on ceramic very similar to electronic packages including the measurement issues. Influences of pad surface metallurgy, microstructure of solder, ineutectic solder alloys and assembly process parameter are regarded now. The investigation objects provide monitoring of electrical and mechanical damage process of SnAgCu solder bump. Different thermo-mechanical loads will be applied in temperature ranges of 0 to +80°C, À40 to +125°C and À50 to +150°C, where the temperature gradient and cycle frequency also vary. A Variation of four different chip sizes allows the determination of fatigue laws for each temperature profile, to be able to compare in between them. The results of these tests will give universal lifetime-prediction laws for SnAgCu base solder joints. Main goals are to find coefficients for lifetime prediction models such as Coffin-Manson-or Norris-Landzberg-relation, which are transferable in between different electronic packages.
Micro-mechanical characterization of lead-free solder joints in power electronics
Fourteenth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm), 2014
The following study is motivated by the need to capture the elasto-viscoplastic behavior of a "real" industrial power module lead-free solder joint. In this work, we carried out a numerical design of experiments in order to forecast the ability of an experimental bending system to identify the specimen material properties. As a proof of principle, the micromechanical elastic behavior of power module copper substrates was then characterized thanks to the development of an innovative in-situ micro-mechanical bending test under an optical profilometer. An inverse Finite-Element Method has been applied in order to identify the material properties of test specimens designed directly out of industrial assemblies and not from bulk solder for good representativity. The results show that identified copper Young's modulus values are lower than that of a bulk material. It will be defined as such in the next identificatio n step targeting the solder joint.