ISOTHERMAL MECHANICAL AND THERMO-MECHANICAL DURABILITY CHARACTERIZATION OF SELECTED PB-FREE SOLDERS

Due to the hazards of Pb in the environment and its effect on humans and marketing competition from Japanese electronics manufacturers, the conversion to Pb-free solders in the electronics industry appears imminent. As major mechanical, thermal, and electrical interconnects between the component and the PWB, solder joints are crucial for the reliability of the most electronic packages. There is an urgent need for constitutive properties, mechanical durability and thermo-mechanical durability of Pb-free solders. A partitioned constitutive model consisting of elastic, plastic, primary creep and secondary creep models is obtained for the Sn3.9Ag0.6Cu solder and the baseline Sn37Pb solder from comprehensive monotonic and creep tests conducted on Thermo-Mechanical-Microscale (TMM) setup. The comparison between two solders shows that Sn3.9Ag0.6Cu has much better creep resistance than Sn37Pb at the low and medium stresses. The isothermal mechanical durability of three NEMI recommended Pb-free solders, Sn3.9Ag0.6Cu, Sn3.5Ag, Sn0.7Cu, is tested on the TMM setup under low creep and high creep test conditions. The damage propagation rate is also analyzed from the test data. The generic Energy-Partitioning (E-P) durability model is obtained for three Pb-free solders by using the incremental analytic model developed for TMM tests. The scatter of the test results from the prediction by these E-P durability model constants is small. The thermo-mechanical durability of the Pb-free Sn3.8Ag0.7Cu solder is investigated by a systematic approach combining comprehensive thermal cycling tests and finite element modeling. The effects of mixed solder systems, device types, and underfill are addressed in the tests. Thermal cycling results show that Sn3.8Ag0.7Cu marginally outperforms SnPb for four different components under the studied test condition. The extensive detailed three-dimensional viscoplastic FE stress and damage analysis is conducted for five different thermal cycling tests of both Sn3.8Ag0.7Cu and Sn37Pb solders. Power law thermo-mechanical durability models of both Sn3.8Ag0.7Cu and Sn3Pb are obtained from thermal cycling test data and stress and damage analysis. The energy-partitioning durability models of two solders are also obtained. It is found that the slopes of the plastic and creep curves in the E-P damage model of Pb-free solders for thermal cycling are steeper than those for mechanical cycling and those of Sn37Pb solders

The influence of microstructure on the mechanical properties of solder

Solder joints in microelectronics devices consist of low-melting solder compositions that wet and join metal contacts and are, ordinarily, used at high homologous temperatures in the as-solidified condition. Differences in solidification rate and substrate interactions have the consequence that even solder joints of similar compositions exhibit a wide range of microstructures. The variation in microstructure causes a variation in properties; in particular, the high-temperature creep properties that govern much of the mechanical behavior of the solder may differ significantly from joint to joint. The present paper reviews the varieties of microstructure that are found in common solder joints, and describes some of the ways in which microstructural changes affect mechanical properties and joint reliability

Size, Temperature, and Strain-Rate Dependence on Tensile Mechanical Behaviors of Ni 3

This study focuses on exploring the mechanical properties and nonlinear stress-strain behaviors of monoclinic Ni3Sn4 single crystals under uniaxial tensile test and also their size, temperature, and strain-rate dependence through constant temperature molecular dynamics (MD) simulation using Berendsen thermostat. The deformation evolution of the Ni3Sn4 atomic nanostructure during the tensile test is observed. In addition, the tensile yield strains of various Ni3Sn4 single crystals at different strain rates and temperatures are characterized through unloading process. At last, by way of linear regression analysis, the corresponding normal elastic stiffness constants are approximated and then compared with the literature theoretical data. The radial distribution function analysis shows that Ni3Sn4 single crystal in a one-dimensional nanowire configuration would become a highly disordered structure after thermal equilibration, thereby possessing amorphous-like mechanical behaviors and properties. The initial elastic deformation of Ni3Sn4 single crystal is governed by the reconfiguration of surface atoms, and its deformation evolution after further uniaxial tensile straining is characterized by Ni=Sn bond straightening, bond breakage, inner atomic distortion, cross-section shrinking, and rupture. The calculated normal elastic constants of Ni3Sn4 single crystal are found to be consistent with the literature theoretical data

Intermetallic Compound And Reliability Study Of Sac And Snbi Lead Free Solders

Due to the environmental concern for lead toxicity, the use of lead-free solder has been widespread in electronic packaging industries. In order for lead-free solder to replace the current lead solder, lead-free solder should have as close melting point as lead solder (1830C) and also has good wettability, excellent physical and mechanical properties. This thesis is devoted to the research and development of lead-free Sn-Bi and SAC based solder alloy for microelectronic packaging applications. A systematic study was conducted on the solders characteristics, wetting behavior, the interfacial reaction, mechanical properties and growth kinetics of solders on Cu and Ni-P substrate

Creep And Isothermal Fatigue Behaviour Of Eutectic SnPb, SnBi And SnZn Solders For Microelectronic Packaging At Mildly Elevated Temperatures

Interconnect materials are used to connect surface mounting components and other passive and discrete circuit components on to copper pads or lands, and in holes on the printed circuit boards. Presently, the industrial practice is using thermal cycling as a method for reliability testing of circuit boards with assembled components. Bulk specimens of 63Sn37Pn solder alloy were subjected to isothermal fatigue at three mildly elevated temperatures (30, 40 and 50oC), loading frequencies (6, 60 and 600 CPM) and at different applied peak stresses (ranging from 8.75 to 33.25 MPa)

Design and Analysis of the Slider Shear Test System Using Nested GR&R Measurement System

The shear strength of the adhesive bonding between slider and suspension is a vital characteristic for head gimbal assembly. The current shear test method has shown improper failure modes; therefore, a new system has been designed to improve the slider shear test. Six sigma framework was applied to redesign the slider shear test system. The finite element method confirms that new design concept is acceptable because it can yield the correct failure mode of shear test. Next, the measurement errors of the new shear test system are assessed using nested gage repeatability and reproducibility (NGR&R). NGR&R of new shear test system is less than 10% which is an adequate gage. Then, the results of simulation also confirm that decreasing of measurement error can significantly reduce the over reject rate. In conclusion, new shear test system can be effectively used to reflect the real product quality and to obtain more accurate process capability resulting from the correct failure mode of testing

Technology of Welding and Joining

In this book, you will find information on new materials and new welding technologies. Problems related to the welding of difficult-to-weld materials are considered and solved. The latest welding technologies and processes are presented. This book provides an opportunity to learn about the latest trends and developments in the welding industry. Enjoy reading

COMPARISON OF INTERCONNECT FAILURES OF ELECTRONIC COMPONENTS MOUNTED ON FR-4 BOARDS WITH SN37PB AND SN3.0AG0.5CU SOLDERS UNDER RAPID LOADING CONDITIONS.

Electronic circuit boards can experience rapid loading through shock or vibration events during their lives; these events can happen in transportation, manufacture, or in field conditions. Due to the lead-free migration, it is necessary to evaluate how this rapid loading affects the durability of a leading lead free solder alternative (Sn3.0Ag0.5Cu) assemblies as compared with traditional eutectic lead based solder Sn37Pb assemblies. A literature review showed that there is little agreement on the fatigue behavior of Sn37Pb solder assemblies and Sn3.0Ag0.5Cu solder assemblies subjected to rapid loading. To evaluate the failure behavior of Sn37Pb and Sn3.0Ag0.5Cu solder assemblies under rapid loading conditions, leadless chip resistors (LCR), ball grid arrays (BGA), small outline integrated circuits (SOIC), and small outline transistors (SOT) were subjected to four point bend tests via a servo-hydraulic testing machine at printed wiring board (PWB) strain rates greater than 0.1/s. The PWB strain was the metric used to evaluate the failures. The PBGAs and LCRs were examined with both Sn37Pb and Sn3.0Ag0.5Cu solders. There was no significant difference found in the resulting test data for the behavior of the two solder assembly types in the high cycle fatigue regime. PBGA assemblies with both solders were also evaluated at a higher strain rate, approximately 1/s, using drop testing. There was no discernable difference found between the assemblies as well as no difference in the failure rate of the PBGAs at this higher strain rate. The PWB strain was converted to an equivalent solder stress index using finite element analysis. This equivalent stress index value was used to compare the results from the LCR and BGA testing for Sn37Pb and Sn3.0Ag0.5Cu. Independently generated BGA data that differed with respect to many testing variables was adjusted and incorporated to this comparison. The resulting plot did not show any significant differences between the behaviors of the two solder assemblies under rapid loading outside of the ultra low cycle fatigue regime, where the assemblies with Sn37Pb solder outperformed the assemblies with SnAgCu solder

Mechanical behaviour and reliability of Sn3.8AgO.7Cu solder for a surface mount assembly

The demands for compact, light weight and Iow cost electronic products have resulted in the miniaturisation of solder interconnects to a sub-millimetre scale. With such a reduction in size, the solder joints cannot be assumed to behave in the same way as bulk solder in terms of reliability due to the fact that their material behaviours are influenced by the joint size and microstructure. The complexity of their reliability assessment is furthermore compounded by the demand for the replacement of traditional SnPb solder alloys with lead-free alloys, due to the presence of the toxic and health hazardous element (Pb) in the former alloy. However, these new lead-free alloys have much less history of industrial applications, and their material and reliability data is not as well developed as traditional lead-based alloys. In addition, most previous reliability assessments using finite element analysis have assumed a uniform distribution of temperature within the electronic assembly, which conflicts the actual temperature conditions during circuit operation. Therefore, this research was undertaken to analyse the effect of solder joint size on solder material properties from which material models were developed, and to determine the effect of an actual (nonuniform) temperature distribution in an electronic assembly on the reliability of its solder joints. Following a review of lead-free solders and potential lead-free alloys, lead-free solder microstructures, and the reliability issues and factors affecting the reliability of solder joints, the practical aspects of this research were carried out in two main parts. The first part consisted of substantial work on the experimental determination of the temperature distribution in a typical surface mount chip resistor assembly for power cycling conditions, and the stress-strain and creep behaviour for both Sn3.8AgO.7Cu solder joints and reflowed bulk solder. This also included building material models based on the experimental data for the solder joints tested and comparison with that for bulk solder. Based on the comparison of the material properties, two extreme material models were selected for the reliability study. Size and microstructure effects on the solder material properties were also discussed in this part. The second part comprised of extensive finite element analysis of a surface mount chip resistor assembly and reliability assessment of its solder joints. The simulation began with elasto-plastic analysis for 2D and 3D chip resistor assemblies to decide upon the kind of formulation to be used when the full complexity of both plasticity and creep is considered. The simulation was carried out considering the determined non-uniform temperature distribution and idealized or traditional uniform temperature condition. The solder joint's material properties were modelled using the two material models determined from the experimental results. The effect of temperature distribution during thermal cycling and of the selected material models on the solder joint reliability was demonstrated using finite element analysis and subsequent fatigue life estimation. In summary, this research has concluded that the material behaviour of the solder joint is different from that of bulk solder due to the effect of its size and microstructure. The anisotropic behaviour of the solder joint cannot be ignored in reliability studies, since it has a significant effect on the solder joint's fatigue life. The research also showed the significant effect of an actual (non-uniform) temperature distribution in the electronic assembly on the solder joint fatigue life