Advanced Microelectronic Packaging, Emerging Interconnection Technology and Pb-free Solder: Pb-free Solder Alloys I
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
Tuesday 8:30 AM
February 25, 2020
Room: Palomar
Location: Marriott Marquis Hotel
Session Chair: Mike Wolverton, Raytheon Company
8:30 AM Invited
The Relation Between the Microstructure and Properties of SnAgCu/SnBiAg Mixed Assemblies, and Thermal History: Eric Cotts1; Mohammed Genanu1; Faramarz Hadian1; 1Binghamton University
Pb-free solders containing solid substitutional elements (e.g. Bi) offer promise for more stable solder joint strength and better reliability performance. Mixed assembly SAC/Bi-Sn solder joints (e.g., SAC305/Sn57Bi1Ag) provide lower temperature assembly for a wide range of conditions. The changes in microstructure of these mixed assemblies during reflow (140oC to 215oC) depend upon the peak temperature, TP, and on the initial ratio of the volume of the SnBiAg paste to the volume of the SnAgCu solder ball. In fact, the final volume ratio between the volumes of the SnAgCu and SnBiAg phases can be predicted as a function of the peak reflow temperature, as can the Ag and Bi distributions in the resulting solder joints. These calculations are reported, and compared to results from investigations of microstructure, and to measurements of mechanical properties (such as shear strength) as a function of peak reflow temperature and of initial volume ratio.
8:50 AM
A Model Study of Bi Diffusion and Intermetallic Growth in Sn-Bi Low Temperature Soldering Systems: Yaohui Fan1; Yifan Wu1; John Blendell1; Nilesh Badwe2; Carol Handwerker1; 1Purdue University; 2Intel Corporation
A new low temperature interconnect technology based on Sn-Bi alloys is being considered for attaching Sn-Ag-Cu (SAC) solder BGAs to circuit boards at temperatures significantly lower than for homogeneous SAC joints. Microstructure development studies of reflow and annealing, including Bi diffusion and precipitation, are important in understanding mechanical reliability and failure paths in the resulting heterogeneous joints. Experiments in several SAC-SnBi geometries revealed that Bi concentration profiles deviate from local equilibrium expected from the phase diagram, with much higher local concentrations and lower volume fractions of liquid than expected during short-time high temperature anneals in the two-phase region. A preliminary model based on Bi interface segregation model was constructed for predicting Bi diffusion and distribution characteristics in Sn during annealing. Rapid (Ni,Au)Sn4 intermetallic growth was also observed at Ni-Sn interface during solid-state annealing in SnBi-ENIG assemblies but is reduced if silver is added to Sn-Bi eutectic.
9:10 AM
Reliability Behavior of Surface Mount Devices Assembled with Bismuth Bearing Low-melt Solder Pastes: Luke Wentlent1; Michael Meilunas1; Jim Wilcox1; 1Universal Instruments Corp.
As the electronics industry continues to evolve in complexity, a concerted effort has developed to implement lower melting point solders. While several exist, one of the most popular has been the SnBi eutectic alloy. Although the process procedures required to create such assemblies is straight-forward, the reliability performance of the bismuth bearing alloys is not well documented and requires significant study before the materials can be adopted by the industry. This concern is compounded by the fact that the microstructural characteristics of the bismuth based alloys are highly dependent upon processing parameters such as time and temperature when assembled in a “mixed” alloy system (i.e. combined with Tin-Silver-Copper) and it is theorized that such microstructural variability may result in significant thermo-mechanical reliability variations. Accordingly, BGA and LGA components were assembled using SnBi paste and subjected to thermo-mechanical cycling. Upon failure, the package reliability and interconnect failure mechanisms were studied.
9:30 AM
Influence of Indium Addition on Microstructural Properties of Sn-rich Solder Joints: Amey Luktuke1; Kumar Ankit1; Nikhilesh Chawla1; 1Arizona State University
Composition of alloying elements in Sn-rich solder joints play a pivotal role in determining the microstructure, interfacial intermetallic (IMC) layer formation and the damage associated with thermal and electromigration stressing. Alloying of Indium and Sn can contribute to superior ductility, wettability, and fatigue resistance as opposed to conventional solders. However, the effects of Sn-In composition on the microstructure are not well understood. In order to study the effect of Indium content in Sn-rich solder, sandwich solder samples were fabricated with solder composition of Sn-2, 4, 6, 10 wt.% In. The samples were analyzed using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDS). The combination of these characterization techniques provided unique insights into the influence of Indium content on the solidification process after reflowing, the morphology of microstructure, interfacial IMC formation, grain size and the correlation between the grain boundaries and segregation of Indium.
9:50 AM Break
10:10 AM Invited
Achieving Collapse-free Joint in 3D-package by Hybrid Solder Alloy with Reducing Thermal Budget Usage: Tzu-Ting Chou1; Yu-Ching Wang1; Jenq-Gong Duh1; Rui Wen Song1; 1National Tsing Hua University
The hybrid solder with the improved infrastructure of Sn-Ag-Cu/Sn-Bi was introduced to solve the concern of overweight of stacked dies in 3D-package. Through combining Sn-3.0Ag-0.5Cu and Sn-58Bi solder with two different melting points, the reflow temperature was successfully reduced to 185℃ as compared to 260℃ of traditional Sn-3.0Ag-0.5Cu solder. Such a low bonding temperature could not only reduce the thermal expansion but also result in lower thermal budget during reflowing process. Furthermore, hybrid solder would diminish the issue of infrastructure collapse in 3D-package. As Sn-Ag-Cu part of hybrid solder was allowed to maintain solid when reflowing, the solid portion could serve as spacer to support the weight of stacked dies. In Sn-Ag-Cu/Sn-Bi/Cu joints, the large amounts of potential harmful Ag3Sn particles were observed to form along the interfacial Cu6Sn5 layer at the Sn-Bi/Cu interface. However, by using Sn-Ag-Cu-Ni/Sn-Bi solder, these interfacial Ag3Sn particles were effectively suppressed.
10:30 AM
Development of Low Temperature Sn-Bi based Solder Alloys: Mehran Maalekian1; Aranav Das1; Ludo Krassenburg1; Co van Veen1; Mo Biglari1; 1Mat-Tech
The eutectic or near eutectic Sn-Bi alloys are common lead-free solder alloys for low temperature soldering application in electronic industry. Poor formability and low ductility of this alloy system has limited its widespread application. To improve the formability the effects of In and Sb additions on the mechanical and soldering properties of Sn-Bi based solder alloy is investigated. In order to understand to what extent alloying additions can improve ductility of Sn-Bi solder while maintaining the melting temperature within an acceptable range, wetting contact angle, hardness, and microstructure evolution of the alloys are studied and compared against the reference Sn-Bi alloy.