Role of Process and Microstructural Parameters on Mixed Mode Fracture of Sn-Ag-Cu Solder Joints Under Dynamic Loading Conditions

Electronic packages in mobile devices are often subjected to drops, leading to impact loading. Since solder joints, which serve as mechanical and electrical interconnects in a package, are particularly prone to failure during a drop, the fracture behavior of solders at high strain rates is a critical design parameter for building robust packages. Here we report on a methodology for measuring mixed-mode fracture toughness of Sn3.5Ag0.7Ag (SAC387) solder joints under dynamic loading conditions (at strain rates up to 100s−1), and use this method to investigate the role of solder microstructure and interfacial intermetallic compound (IMC) layer thickness on the joint fracture toughness at different mode-mixities and strain rates. Modified compact mixed mode (CMM) samples with adhesive solder joints between Cu plates and a thin film interfacial starter crack were used for the measurements. The interfacial IMC layer thickness was adjusted by controlling the dwell time during reflow, while the solder microstructure was controlled via the post-reflow cooling rate and subsequent thermal aging. The critical strain energy release rate (Gc) was measured as a function of these microstructural and loading variables, and these data were correlated with the associated crack path, details of which were elicited through fractography as well as crack-profile observations. The crack profile studies were based on samples with double interfacial starter cracks, one of which propagated only partially. Associated with the alteration of the joint microstructure, transitions in the fracture behavior were noted. In all cases, the cracks remained confined to the interfacial region, although the details of the crack propagation path and its interaction with interfacial IMCs, the adjacent solder and the pad surface finish varied significantly. Fracture toughness decreased with an increase in the strain rate and decreased with increasing mode-mixity. A thicker/coarser interfacial IMC layer (due to high dwell times) decreased toughness, while coarser solder microstructures (due to slow cooling during reflow or post-reflow aging) increased toughness. Correlations between joint microstructure and the observed deformation and fracture mechanisms will be highlighted, and a qualitative model based explanation for the inter-play between solder and IMC, and the associated interfaces will be presented.

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Evaluation of size effect on mixed-mode fracture behavior of epoxy/silica nanocomposites

The Journal of Strain Analysis for Engineering Design ◽

10.1177/0309324717703491 ◽

2017 ◽

Vol 52 (4) ◽

pp. 239-248 ◽

Cited By ~ 3

Author(s):

Ahmad Ghasemi-Ghalebahman ◽

Javad Akbardoost ◽

Yaser Ghaffari

Keyword(s):

Fracture Toughness ◽

Tangential Stress ◽

Mixed Mode ◽

Fracture Behavior ◽

Process Zone ◽

Maximum Tangential Stress ◽

Mixed Mode Fracture ◽

Mode Fracture ◽

Stress Criterion ◽

Maximum Tangential Stress Criterion

The aim of this study was to examine the effect of size on the mixed-mode fracture toughness of quasi-brittle nanocomposites with the help of modified maximum tangential stress criterion. The literature reveals that the effect of size on mixed-mode fracture behavior of brittle nanocomposites has not been well investigated previously using modified maximum tangential stress criterion. The studied nanocomposites were made of epoxy resin reinforced with 7 wt%, 20–30 nm nanosilica. The accuracy of the method was assessed by taking into account the high-order terms of Williams series expansion along with finite element over-deterministic method. To investigate the effect of size on fracture toughness, a number of three-point semi-circular bending tests with different radii and four angles of edge–crack orientation were conducted and subjected to mixed-mode loading. The size of fracture process zone and apparent fracture toughness ( Kc) were also evaluated as a function of sample size. Experimental results showed that the proposed approach can accurately predict the fracture behavior of studied nanocomposites.

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High Strain Rate Fracture Behavior of Sn-Ag-Cu Solder Joints on Cu Substrates

ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, MEMS and NEMS: Volume 2 ◽

10.1115/ipack2011-52220 ◽

2011 ◽

Author(s):

Z. Huang ◽

P. Kumar ◽

I. Dutta ◽

J. H. L. Pang ◽

R. Sidhu ◽

...

Keyword(s):

Fracture Toughness ◽

Yield Strength ◽

Strain Rate ◽

Fracture Mechanism ◽

Fracture Behavior ◽

Solder Joints ◽

High Strain ◽

Effective Thickness ◽

Strain Rates ◽

Cu Substrates

During service, micro-cracks form inside solder joints, making a microelectronic package prone to failure particularly during a drop. Hence, the understanding of the fracture behavior of solder joints under drop conditions, synonymously at high strain rates and in mixed mode, is critically important. This study reports: (i) the effects of processing conditions (reflow parameters and aging) on the microstructure and fracture behavior of Sn-3.8%Ag-0.7%Cu (SAC387) solder joints attached to Cu substrates, and (ii) the effects of the loading conditions (strain rate and loading angle) on the fracture toughness of these joints, especially at high strain rates. A methodology for calculating critical energy release rate, GC, was employed to quantify the fracture toughness of the joints. Two parameters, (i) effective thickness of the interfacial intermetallic compounds (IMC) layer, which is proportional to the product of the thickness and the roughness of the IMC layer, and (ii) yield strength of the solder, which depends on the solder microstructure and the loading rate, were identified as the dominant quantities affecting the fracture behavior of the solder joints. The fracture toughness of the solder joint decreased with an increase in the effective thickness of the IMC layer and the yield strength of the solder. A 2-dimensional fracture mechanism map with the effective thickness of the IMC layer and the yield strength of the solder as two axes and the fracture toughness as well as the fraction of different fracture paths as contour-lines was prepared. Trends in the fracture toughness of the solder joints and their correlation with the fracture modes are explained using the fracture mechanism map.

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Biaxial Fracture Behavior of Polycrystalline Alumina

Materials Science Forum ◽

10.4028/www.scientific.net/msf.475-479.1329 ◽

2005 ◽

Vol 475-479 ◽

pp. 1329-1332

Author(s):

Masayuki Tsukada ◽

Eiichi Sato ◽

Kazuhiko Kuribayashi

Keyword(s):

Fracture Toughness ◽

Mixed Mode ◽

Fracture Behavior ◽

Mixed Mode Fracture ◽

Polycrystalline Alumina ◽

Mode Fracture ◽

Multiaxial Stress State ◽

Four Point Bending ◽

Biaxial Tests ◽

Fracture Tests

Fracture behavior under multiaxial stress state of polycrystalline alumina was studied from the view point of an artificial crack propagation and fracture from a natural flaw. The former was studied by mixed-mode fracture toughness tests; asymmetric four-point bending and diametral compression techniques were carried out using precracked and notched specimens. The latter was studied by biaxial fracture tests in compression and torsion loading; multiaxial fracture statistics was applied to the measured fracture envelope. The ratio KIIC/KIC obtained from the biaxial tests was higher than that obtained by the mixed-mode fracture toughness tests. It revealed that the fracture from an artificial flaw does not simulate the fracture from a naturall flaw in polycrystalline ceramics.

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