Characterization of the Effects of Silver Content on the Aging Resistance of SAC Solder Joints

2015 ◽  
Author(s):  
Md Hasnine ◽  
Jeffrey C. Suhling ◽  
Barton C. Prorok ◽  
Michael J. Bozack ◽  
Pradeep Lall
Keyword(s):  
Creep Rate ◽  
Crystal Orientation ◽  
Solder Joints ◽  
Silver Content ◽  
Test Results ◽  
Aging Effects ◽  
Creep Properties ◽  
Single Grain ◽  
Sac Solder

In the current study, we have extended our previous work on nanoindentation of joints to examine a full test matrix of SAC solder alloys. The effects of silver content on SAC solder aging has been evaluated by testing joints from SACN05 (SAC105, SAC205, SAC305, and SAC405) test boards assembled with the same reflow profile. In all cases, the tested joints were extracted from 14 × 14 mm PBGA assemblies (0.8 mm ball pitch, 0.46 mm ball diameter) that are part of the iNEMI Characterization of Pb-Free Alloy Alternatives Project (16 different solder joint alloys available). After extraction, the joints were subjected to various aging conditions (0 to 12 months of aging at T = 125 C), and then tested via nanoindentation techniques to evaluate the stress-strain and creep behavior of the four aged SAC solder alloy materials at the joint scale. The observed aging effects in the SACN05 solder joints have been quantified and correlated with the magnitudes observed in tensile testing of miniature bulk specimens performed in prior studies. The results show that the aging induced degradations of the mechanical properties (modulus, hardness) in the SAC joints were of similar order (30–40%) as those seen previously in the testing of larger “bulk” uniaxial solder specimens. The creep rates of the various tested SACN05 joints were found to increase by 8–50X due to aging. These degradations, while significant, were much less than those observed in larger bulk solder uniaxial tensile specimens with several hundred grains, where the increases ranged from 200X to 10000X for the various SACN05 alloys. Additional testing has been performed on very small tensile specimens with approximately 10 grains, and the aging-induced creep rate degradations found in these specimens were on the same order of magnitude as those observed in the single grain joints. Thus, the lack of the grain boundary sliding creep mechanism in the single grain joints is an important factor in avoiding the extremely large creep rate degradations (up to 10,000X) occurring in larger bulk SAC samples. All of the aging effects observed in the SACN05 joints were found to be exacerbated as the silver content in the alloy was reduced. In addition, the test results for all of the alloys show that the elastic, plastic, and creep properties of the solder joints and their sensitivities to aging are highly dependent on the crystal orientation. Due to the variety of crystal orientations realized during solidification, it was important to identify the grain structure and crystal orientations in the tested joints. Cross-polarized light microscopy and Electron Back Scattered Diffraction (EBSD) techniques have been utilized for this purpose. The test results show that the elastic, plastic, and creep properties of the solder joints and their sensitivities to aging are highly dependent on the crystal orientation. In addition, an approach has been developed to predict tensile creep strain rates for low stress levels using nanoindentation creep data measured at very high compressive stress levels.

Nanomechanical Characterization of Aging Effects in Solder Joints in Microelectronic Packaging

2013 ◽  
Author(s):  
Mohammad Hasnine ◽  
Muhannad Mustafa ◽  
Jing Zou ◽  
Jeffrey C. Suhling ◽  
Barton C. Prorok ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Solder Joints ◽  
Bulk Solder ◽  
Lead Free ◽  
Lead Free Solder ◽  
Aging Effects ◽  
Single Grain ◽  
Free Solder ◽  
Aging Phenomena ◽  
Sac Solder

The mechanical properties of a lead free solder are strongly influenced by its microstructure, which is controlled by its thermal history including solidification rate and thermal aging after solidification. Due to aging phenomena, the microstructure, mechanical response, and failure behavior of lead free solder joints in electronic assemblies are constantly evolving when exposed to isothermal and/or thermal cycling environments. Through uniaxial testing of miniature bulk solder tensile specimens, we have previously demonstrated that large changes occur in the stress-strain and creep behaviors of lead free solder alloys with aging. Complementary studies by other research groups have verified aging induced degradations of SAC mechanical properties. In those investigations, mechanical testing was performed on a variety of sample geometries including lap shear specimens, Iosipescu shear specimens, and custom solder ball array shear specimens. While there are clearly aging effects in SAC solder materials, there have been limited prior mechanical loading studies on aging effects in actual solder joints extracted from area array assemblies (e.g. PBGA or flip chip). This is due to the extremely small size of the individual joints, and the difficulty in gripping them and applying controlled loadings (tension, compression, or shear). In the current work, we have explored aging phenomena in actual solder joints by nano-mechanical testing of single SAC305 lead free solder joints extracted from PBGA assemblies. Using nanoindentation techniques, the stress-strain and creep behavior of the SAC solder materials have been explored at the joint scale for various aging conditions. Mechanical properties characterized as a function of aging include the elastic modulus, hardness, and yield stress. Using a constant force at max indentation, the creep response of the aged and non-aged solder joint materials has also been measured as a function of the applied stress level. With these approaches, aging effects in solder joints were quantified and correlated to the magnitudes of those observed in testing of miniature bulk specimens. Our results show that the aging induced degradations of the mechanical properties (modulus, hardness) of single grain SAC305 joints were similar to those seen previously by testing of larger “bulk” solder specimens. However, due to the single grain nature of the joints considered in this study, the degradations of the creep responses were significantly less in the solder joints relative to those in larger uniaxial tensile specimens. The magnitude of aging effects in multi-grain lead free solder joints remains to be quantified. Due to the variety of crystal orientations realized during solidification, it was important to identify the grain structure and crystal orientations in the tested joints. Polarized light microscopy and Electron Back Scattered Diffraction (EBSD) techniques have been utilized for this purpose. The test results show that the elastic, plastic, and creep properties of the solder joints and their sensitivities to aging are highly dependent on the crystal orientation. In addition, an approach has been developed to predict tensile creep strain rates for low stress levels using nanoindentation creep data measured at very high compressive stress levels.

Characterization of aging effects in lead free solder joints using nanoindentation

2013 ◽  
Author(s):  
Mohammad Hasnine ◽  
Muhannad Mustafa ◽  
Jeffrey C. Suhling ◽  
Barton C. Prorok ◽  
Michael J. Bozack ◽  
...  
Keyword(s):  
Solder Joints ◽  
Lead Free ◽  
Lead Free Solder ◽  
Aging Effects ◽  
Free Solder

Nanoindentation Testing of SAC305 Solder Joints Subjected to Thermal Cycling Loading

2019 ◽  
Author(s):  
Abdullah Fahim ◽  
S. M. Kamrul Hasan ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Mechanical Properties ◽  
Solder Joint ◽  
Thermal Cycling ◽  
Creep Behavior ◽  
Solder Joints ◽  
Test Results ◽  
Sac305 Solder ◽  
Nanoindentation Testing ◽  
Single Grain ◽  
Cycling Loading

Abstract Solder joints in electronic packages are frequently exposed to thermal cycling environment. Such exposures can occur in real life application as well as in accelerated thermal cycling tests used for the fatigue behavior characterization. Because of temperature variations and CTE mismatches of the assembly materials, cyclic temperature leads to damage accumulation and material property evolution in the solder joints. This eventually results in crack initiation, and subsequent crack growth and failure. In this study, the nanoindentation technique was used to understand the evolution of mechanical properties (modulus, hardness and creep behavior) of SAC305 BGA solder joints and Cu pad subjected to thermal cycling loading for various durations. In addition, microstructural changes in those joints that occur during thermal cycling were observed using both SEM and optical microscopy. BGA solder joint strip specimens were first prepared by cross sectioning BGA assemblies followed by surface polishing to facilitate SEM imaging and nanoindentation testing. The strip specimens were chosen to contain several single grain solder joints. This enabled 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 from T = −40 to 125 °C in an environmental chamber. At various points in the cycling (e.g. after 0, 50, 100, and 250 cycles), the package was taken out from the chamber, and nanoindentation was performed on each single grain joint and joint Cu pads to obtain the modulus, hardness, and creep behavior at 25 °C. This allowed the evolution of the mechanical properties with the duration of thermal cycling to be determined. Moreover, microstructural changes were also observed after various durations of cycling using optical microscopy. From the nanoindentation test results, it was found that the modulus and hardness of the SAC305 solder joints dropped significantly with thermal cycling. However, the Cu pad did not show any change in the mechanical behavior during cycling. Moreover, the nanoindentation creep test results showed significant increases in the creep deformation for solder joints whereas Cu pad did now show any significant changes in creep behavior when both of them were subjected to thermal cycling up to 250 cycles.

scholarly journals Grain-Scale Anisotropic Analysis of Steady-State Creep in Oligocrystalline SAC Solder Joints

Materials ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 5973
Author(s):  
Qian Jiang ◽  
Abhishek Nitin Deshpande ◽  
Abhijit Dasgupta
Keyword(s):  
Solder Joints ◽  
Thermomechanical Behavior ◽  
Steady State Creep ◽  
Heterogeneous Integration ◽  
Test Results ◽  
Cohesive Elements ◽  
Statistical Homogeneity ◽  
Scale Modeling ◽  
Assembly Performance ◽  
Sac Solder

Heterogeneous integration is leading to unprecedented miniaturization of solder joints, often with thousands of joints within a single package. The thermomechanical behavior of such SAC solder joints is critically important to assembly performance and reliability, but can be difficult to predict due to the significant joint-to-joint variability caused by the stochastic variability of the arrangement of a few highly-anisotropic grains in each joint. This study relies on grain-scale testing to characterize the mechanical behavior of such oligocrystalline solder joints, while a grain-scale modeling approach has been developed to assess the effect of microstructure that lacks statistical homogeneity. The contribution of the grain boundaries is modeled with isotropic cohesive elements and identified by an inverse iterative method that extracts material properties by comparing simulation with experimental measurements. The properties are extracted from the results of one test and validated by verifying reasonable agreement with test results from a different specimen. Equivalent creep strain heterogeneity within the same specimen and between different specimens are compared to assess typical variability due to the variability of microstructure.

Elaboration and Characterization of the Properties of Refractory Cr Base Alloys

2010 ◽  
Vol 72 ◽  
pp. 46-52 ◽  
Author(s):  
Laurent Royer ◽  
Stéphane Mathieu ◽  
Christophe Liebaut ◽  
Pierre Steinmetz
Keyword(s):  
Mechanical Properties ◽  
Melting Point ◽  
Molten Glass ◽  
Energy Production ◽  
Creep Properties ◽  
Refractory Alloys ◽  
Industrial Use ◽  
Kinetics Of ◽  
Selection Of

For energy production and also for the glass industry, finding new refractory alloys which could permit to increase the process temperatures to 1200°C or more is a permanent challenge. Chromium base alloys can be good candidates, considering the melting point of Cr itself, and also its low corrosion rate in molten glass. Two families of alloys have been studied for this purpose, Cr-Mo-W and Cr-Ta-X alloys (X= Mo, Si..). A finer selection of compositions has been done, to optimize their chemical and mechanical properties. Kinetics of HT oxidation by air, of corrosion by molten glass and also creep properties of several alloys have been measured up to 1250°C. The results obtained with the best alloys (Cr-Ta base) give positive indications as regards the possibility of their industrial use.

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