Advanced Microelectronic Packaging, Emerging Interconnection Technology and Pb-free Solder: 3D Microelectronic Packaging and Emerging Interconnects II
Sponsored by: TMS Functional Materials Division, TMS: Electronic Packaging and Interconnection Materials Committee
Program Organizers: Christopher Gourlay, Imperial College London; Kazuhiro Nogita, University of Queensland; David Yan, San Jose State University; Mike Wolverton; Babak Arfaei, Ford Motor Company; Andre Delhaise; Mehran Maalekian, Mat-Tech; Mohd Arif Salleh, Universiti Malaysia Perlis
Wednesday 2:00 PM
February 26, 2020
Room: Palomar
Location: Marriott Marquis Hotel
Session Chair: Chris Gourlay, Imperial College London; Tianhong Gu, Imperial College London
2:00 PM Invited
Mechanisms of Electromigration in Bicrystal Sn Solder Joint by Correlative X-ray Tomography and Microscopy: Marion Branch Kelly1; Nikhilesh Chawla1; 1Arizona State University
Electromigration-driven void and intermetallic growth are critical reliability concerns for solder joints in microelectronic devices. Grain orientation and grain boundary density play an important role in determining the rate of damage evolution due to the anisotropic diffusion of copper in tin. However, little attention has been paid to determining the effect of grain boundary character on intermetallic growth. In this study, a bicrystal solder joint with two grain boundary types, twins and high angle boundaries, was studied during interrupted electromigration testing. Microstructure and grain orientation were characterized using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). X-ray microtomography scanning facilitated the quantification of intermetallic and void growth rates. The interrupted tomography scans captured the complex intermetallic and void evolution. SEM and EBSD analysis in parallel with tomography contributed to unique insight into the relationships between grain orientation, grain boundaries, and intermetallic growth and morphology.
2:20 PM
Effect of Solder Joint Geometry on Electromigration Failure Mechanism in Micro Solder Joint: Hossein Madanipour1; Yi Ram Kim1; Allison Osmonson1; Choong-Un Kim1; 1University of Texas, Arlington
Electromigration failure mechanisms impacted by microsolder joints with differing joint geometry, specifically a comparison of various solder joint aspect ratios (length to height), is investigated in this research. Unlike in large scale solder joints, like those used in a ball grid array (BGA), electromigration in microsolder joints competes with the diffusion induced conversion of Sn to IMC phases. In such cases, electromigration failure does not necessarily follow the known kinetic mechanism and instead exhibits a much more complex dependence on the current and temperature. Our study, using ~20um thick solder with 2 different geometries under varying electromigration test conditions, shows that the mechanisms behind electromigration failure are related to Sn self-diffusion, intermetallic compound conversion and also surface diffusion which is more active in joints having lower aspect ratios. Our result produces evidence supporting that electromigration failure can be inhibited under some conditions due to rapid conversion of Sn into IMCs.
2:40 PM
Modeling and Simulation of Pore Electromigration in Tin Solders: Zachary Morgan1; Yongmei Jin1; Vahid Attari2; Raymundo Arroyave2; 1Michigan Technological University; 2Texas A&M University
Migration of pores in solder interconnects is a significant reliability concern for electronic devices. With dimensional shrinking of solder joints, anisotropic properties of solder materials play increasingly important roles in electromigration processes. Effects of property anisotropies on pore migration are investigated using phase field modeling and simulation of beta-tin polycrystals. The model accounts for mass diffusion due to charge conduction and stress gradient solving microscopic Ohm’s law and microelasticity equations. Simulations show pore velocity and path are not only impacted by local crystal orientation with respect to applied electric field, but also depend on property mismatches across grain boundaries and grain structure. Details of pore-pore interactions and pore-grain boundary interactions are also revealed in the simulations. Results are analyzed in terms of the microstructure-dependent internal electric field and stress gradient. Findings provide insight into the roles of anisotropic properties and grain microstructures in performance and degradation of tin solder alloys.
3:00 PM
A Comprehensive Approach on Understanding Electromigration Failure Kinetics with Varying UBM Thickness and Joint Geometry in WCSP Solder Interconnects: Allison Osmanson1; Yi Ram Kim1; Hossein Madanipour1; Choong-Un Kim1; Patrick Thompson2; Qiao Chen2; 1University of Texas at Arlington; 2Texas Instruments
Electromigration (EM) induces failure due to factors such as joule heating, current crowding, and ensuing competing failure kinetics such as heterogeneous nucleation and void growth. Some industries approach this problem by introducing alloying elements and changing the joint geometry to reduce the intermetallic nucleation rate and void formation rate while further allowing the joint to resist failure by EM kinetics. Using rectangular shaped joints while also increasing the under-bump metallization (UBM) thickness has become a promising method in reducing the effects of EM. Wafer-level chip scale package (WCSP) specimens with varying joint size and shape and UBM thickness were subjected to EM failure while assessing the failure rate and completing subsequent failure analysis. Further, finite element method (FEM) was used to analyze the transient stress development in the device under test (DUT) resulting from current density and joule heating with varying UBM thickness and progressing void formation size.
3:20 PM Break
3:40 PM
Study on the UBM Thickness and Current Flow Configuration Effects on Electromigration Failure Mechanism in Solder Interconnects: Yi Ram Kim1; Allison Osmanson1; Hossein Madanipour1; Choong-Un Kim1; Patrick Thompson2; Qiao Chen2; 1University of Texas at Arlington; 2Texas Instruments, Inc.
This study reports the results of our investigation of the electromigration (EM) failure mechanism in solder interconnects with varying under bump metallization (UBM) thickness and two different current flow configurations, asymmetry and symmetry. This study is motivated to investigate the mechanism by which the EM kinetics is affected by the Cu UBM thickness and/or current flow configuration. For a comparative study, we conduct EM testing of three different UBM thickness samples under different current flow configurations. Surprisingly, we find that EM failure kinetics is affected by UBM thickness in a more complicated manner. The failure is not linearly scaled with UBM thickness. An optimum UBM thickness for the most beneficial effect exists. While the mechanism is currently not so clear, we believe that it has to do with the balance between the delayed void nucleation by supply of Cu and the delay in the void growth by thermal stress.
4:00 PM
Microstructure Evolution and Interfacial Growth of Intermetallic Compound for Cu/In/Cu Structure under Thermomigration: Chen-Wei Lee1; Jou Hsuan Lee1; Fan-Yi Ouyang; 1National Tsing Hua University
In response to the scaling and higher performance of integrated circuit, electronic industry is introducing the so-called 3D IC technology. In order to reduce the thermal damage during high-temperature fabrication in 3D ICs, solid-liquid interdiffusion bonding and hot pressing in low-temperature bonding technology have gradually attracted attention. Because the diameter of microbumps in 3D IC is usually below 20 um, it is easy to establish a large temperature gradient, and induces the intermetallic compound to grow asymmetrically during the reflow process. In addition, Indium has been used well as a bonding solder because of its low melting point. Therefore, in this study, a copper/indium/copper symmetrical structure was used to understand the copper-indium interfacial reaction and the growth of copper-indium intermetallic compounds during reflow at 220 °C and to understand the diffusion behavior caused by the temperature gradient and the related dynamic mechanism
4:20 PM
Role of Grain Boundaries in Electromigration and Thermomigration Related Failure : A Phase Field Simulation Study: Supriyo Chakraborty1; Praveen Kumar2; Abhik Choudhury2; 1Ohio State University; 2Indian Institute of Science
Grain-boundary migration, void formation as well as associated hillock formation are important mechanisms which lead to the failure of interconnects in the microelectronic packages. An understanding of the underlying physics of each of the phenomena can allow better design of interconnects. We formulate a phase-field model for studying the phenomena of grain-boundary grooving under the combined influence of pure diffusion controlled transport, electric current and thermal gradient. We separately investigate the contributions of each of the stimuli towards the process of grain-boundary migration and hillock formation, by performing phase field simulations as well as comparing with analytical theories. Additionally, we qualitatively reproduce the phenomena observed in experiments on polycrystalline metals, wherein electromigration and thermomigration may act in unison or against each other towards their contributions in grooving,hillocking and void growth.