Electronic Packaging and Interconnections 2021: Pb-free Solder Alloys I
Sponsored by: TMS Functional Materials Division, TMS: Electronic Packaging and Interconnection Materials Committee
Program Organizers: Mehran Maalekian, Materials & Metallurgy Expertise; Christopher Gourlay, Imperial College London; Babak Arfaei, Ford Motor Company; Praveen Kumar, Indian Institute of Science; Sai Vadlamani, Intel Corporation; Kazuhiro Nogita, University of Queensland; David Yan, San Jose State University
Monday 8:30 AM
March 15, 2021
Room: RM 22
Location: TMS2021 Virtual
Session Chair: Mehran Maalekian, Mat-Tech; Amir Hossein Nobari, 5NPlus
8:30 AM Invited
Nucleation and Growth Kinetics of Sn Whiskers Under Applied Pressure: Eric Chason1; Piyush Jagtap1; Nupur Jain1; Allan Bower1; 1Brown University
Sn whiskers grow spontaneously out of coatings on electronic components and pose risks for system failure. Numerous studies suggest that whisker growth is driven by stress in the film, yet many aspects of their nucleation and growth are still not understood. This can be attributed, in part, to the fact that the stress is difficult to characterize or control. We have performed experiments using an apparatus that applies controlled pressure to a region of the film’s surface. This apparatus was designed to be small enough to fit into a scanning electron microscope so that the resulting whiskers could be monitored periodically without removing the applied pressure. This enabled the number density and growth rate of individual whiskers to be measured in real-time. A finite element analysis model is used to relate the stress to the observed nucleation and growth kinetics.
8:50 AM
Development of Near Room Temperature Solder Alloys and Soldering Processes in Microelectronics: Shiqian Liu1; Stuart McDonald1; Tetsuro Nishimura2; Kazuhiro Nogita1; 1University of Queensland; 2Nihon Superior Co., Ltd
New and emerging applications involving temperature-sensitive or flexible electronics have created a need for low process temperatures during electronics assembly. Ga and some of its alloys have a range of properties that offer the possibility of near room temperature soldering processes. This study develops a fundamental and comprehensive understanding of interfacial reactions between Ga and Cu-Ni substrates at near room temperature. Microstructure development and key properties of the interfacial intermetallics were investigated. These results are reported in the context of recent advances in the understanding of solder alloys and intermetallics and builds on current knowledge in the broader field of metal joining. A case is made for the commercial applications of non-toxic Ga and Ga-based alloys for joining materials in electronics manufacturing.
9:10 AM Invited
Comparison of Corrosion for Ni- and Co-based Surface Finishes: Albert T. Wu1; Si-Wei Lin1; Shu-Chi Ku2; Nico Li2; 1National Central University; 2Taiwan Uyemura Co., Ltd
Surface finishes are used on device substrates to prevent oxidation and enhance joint strength. If the surface finishing layer cannot sustain corrosion when operating the device in high humidity ambient with corroding sulfur-containing atmosphere, corrosion products grow on the surface and damage the device. Cu atoms from the substrate diffuse to the surface when the surface finishing layer cannot act as an effective diffusion barrier due to corrosion. This study compares different corrosion behavior and diffusion barrier capability between Ni- and Co-based surface finishes. Samples are placed in SO2 chamber for different duration of time. Surface morphology, cross-sectional observation and electrochemical measurement are used for comparing the anti-corrosion mechanism.
9:30 AM Invited
Microstructural Evolution in Low-temperature Pb-free Solders: Nikhilesh Chawla1; 1Purdue University
With the increasing miniaturization and shift to heterogeneous integration in electronic packaging, a lot of attention is being paid to lower temperature solder alloys. In this talk, we discuss the microstructure evolution of Sn-Bi and Sn-In low temperature solder alloys. The evolution of the bulk solder microstructure as well as the Cu6Sn5 intermetallic layer during thermal aging and electromigration was studied. Coarsening of the microstructures was studied by correlative microscopy techniques, including x-ray micro and nanotomography, EBSD, and scanning electron microscopy. Mechanisms for coarsening, microstructure evolution, and their effect on electrical and mechanical properties were elucidated and will be discussed.
9:50 AM
Tailoring βSn Grain Orientations in Electronic Interconnections via Manipulating Textures of Interfacial Intermetallics: Zhaolong Ma1; Ce Li1; Xingwang Cheng1; Suyuan Yang1; 1Beijing Institute of Technology
Many reliability issues of electronic interconnections such as electromigration and thermomechanical fatigue are governed by βSn grain orientations. Here, we demonstrated that using single-crystal Cobalt substrates can effectively control βSn grain orientations through tailoring textures of interfacial αCoSn3 intermetallics. On (0001)Co, (11-20)Co, (10-10)Co, and (1-102)Co, interfacial αCoSn3 exhibited 2-5 symmetric orientations related to Co with reproducible orientation relationships (ORs). The orientation selection of αCoSn3 was understood by exploring i) thermodynamic stabilities of interfaces indicated by interfacial atomic matches and work of adhesion and interfacial energies calculated based on density functional theory (DFT) and ii) crystal growth kinetics indicated by the angle between (100)CoSn3 and the substrate plane. On (11-20)Co, total βSn orientations including twinned grains were reduced to 20, and on (10-10)Co, the βSn orientation featuring c-axis perpendicular to the substrate (i.e. parallel with the electron flow direction) was predicted to eliminate, which should improve the reliability of solder joints.
10:10 AM
Reliability Evaluation of Ag Sinter-joining Die Attach under a Harsh Thermal Cycling Test: Zheng Zhang1; Chuantong Chen1; Suetake Aiji1; Ming-Chun Hsieh1; Iwaki Aya1; Katsuaki Suganuma1; 1Osaka University/ISIR
Ag sinter joining is an ideal connection technique for next-generation power electronics packaging due to its excellent high-temperature stability. In this work, we applied Ag sinter joining to die attach of power electronics and focused reliability of Ag sinter joining under a harsh thermal cycling condition. The thermal cycling test was conducted at a temperature range from -50 °C to 250 °C. The bonding quality of as-sintered die attach had a shear strength of over 40 MPa and remained over 25 MPa after a 500-cycle test. However, the shear strength drastically degraded to less than 10 MPa due to a failure of metallization layer detachment after 500 cycles. Meanwhile, thermal resistance changes of die attach during the thermal cycling test were also evaluated by a T3ster. The investigation suggests that the Ag sinter joining is capable of withstanding a severe operating condition of power electronics.
10:30 AM
Modeling Effect of Copper Solute on Electromigration Induced Stress Generation in Al-based Interconnects: Kieran Cavanagh1; Ping-Chuan Wang1; 1SUNY New Paltz
Electromigration as a degradation mechanism in microelectronics has been extensively studied for decades due to its reliability implications and the underlying materials science. It is well known that the addition of copper solute significantly improves the electromigration lifetime of Al interconnects. It has been observed that preferential Cu electromigration occurs near the cathode initially, followed by Al electromigration restricted within the Cu depleted region, inducing a localized mechanical stress gradient. The interaction between Cu and Al diffusion, as well as the evolution of the stress distribution, have been of great scientific interest. In this study, a numerical model is established to simulate such interaction in an Al (0.25 at% Cu) interconnect during electromigration. The model parameters and assumptions will be calibrated with experimental data from synchrotron-based x-ray microbeam techniques. Critical timescales involved in Al(Cu) electromigration failure will also be discussed.