Emerging Interconnect and Pb-free Materials for Advanced Packaging Technology: Alloying and Doping of Pb-free Materials
Sponsored by: TMS Functional Materials Division, TMS: Electronic Packaging and Interconnection Materials Committee
Program Organizers: Fan-Yi Ouyang, National Tsing Hua University; C. Robert Kao, National Taiwan University; Albert T Wu, National Central University; Fay Hua, Intel Corporation; Yan Li, Intel Corporation; Babak Arfaei, Binghamton University; Kazuhiro Nogita, The University of Queensland

Tuesday 2:00 PM
February 28, 2017
Room: 30E
Location: San Diego Convention Ctr

Session Chair: Chih Chen, National Chiao Tung University; Albert T. Wu, National central University

2:00 PM  
Effects of Cobalt on the Nucleation, Grain Refinement and Orientations of Sn-3Ag-0.5Cu Solder: Christopher Gourlay1; Sergey Belyakov1; Zhaolong Ma1; 1Imperial College London
    We show that cobalt-microalloying causes significant grain refinement in large samples (60 g) of Sn-3Ag-0.5Cu solder. Nucleation occurs on the (100) facet of CoSn3 crystals with a reproducible orientation relationship of (100)Sn // (100)CoSn3 with [001]Sn // [001]CoSn3, which has a planar lattice mismatch of ~4%. In 550 um solder joints on Cu substrates, Co microalloying alters the Sn nucleation location to an CoSn3 particle in the bulk liquid and increases the number of Sn nucleation events when the cooling rate is higher than ~5 K/s. However, Co-microalloying caused only weak grain refinement in sample volumes relevant to solder joints.

2:20 PM  
Influence of Bi on Microstructure and Properties of Sn-Cu-Ni Based BGAs on Cu Metallization: Sergey Belyakov1; Christopher Gourlay1; Takatoshi Nishimura2; Keith Sweatman2; 1Imperial College London; 2Nihon Superior Co., Ltd.
    There has been significant interest in the addition of Bi to Pb-free solders as Bi has been demonstrated to lower melting temperature, to improve solder wetting performance and, more importantly, to improve mechanical properties of solder joints. In this study we investigate the influence of Bi additions on microstructure formation of Sn-Cu-Ni solders during reflow on Cu substrates as well as its evolution during storage at elevated temperatures. The focus is on (i) influence of Bi on nucleation and growth of tin in BGA joints and (ii) influence of Bi on solder microstructural stability during ageing. The second part of the talk will discuss the influence of Bi additions on thermal cycling and shear impact properties of BGA solder joints with a focus on their failure mechanisms.

2:40 PM  
The Effect of Bi on the Behaviour and Properties of Sn-0.7Cu Based Alloys: Keith Sweatman1; Selena Smith2; Arif Salleh3; Stuart McDonald2; Takatoshi Nishimura1; Kazuhiro Nogita2; 1Nihon Superior Co., Ltd.; 2University of Queensland; 3University of Malaysia Perlis
    With Pb contamination no longer a significant risk Bi is being used increasingly as a beneficial addition to Pb-free solder alloys. The solid solution strengthening effect that Bi provides to the β-Sn matrix has the significant advantage over the particle strengthening effect of Ag of being stable during extended ageing. However the effects of Bi on phase equilibria and mechanical properties of established Pb-free solder alloy systems such as Sn-Cu and Sn-Cu-Ni are not yet well understood. In this paper the authors will report some of the results emerging from systematic studies of the effect of Bi on β-Sn lattice parameters, wetting and IMC formation on substrates, on hardness, elastic modulus and the accumulation of strain in solder alloys based on Sn-0.7Cu. These observations will be related to the results of high speed ball shear testing in which a Sn-Cu-Ni alloy with a Bi addition outperforms SAC alloys.

3:00 PM  
Effect of Ni on Mechanical Properties and Microstructure of Sn-0.7Cu and SAC307 Solder Alloys: Mehran Maalekian1; Karl Seelig1; 1AIM Metals & Alloys
    In this paper the effects of micro-alloying Ni on Sn-0.7Cu and Sn-3Ag-0.7Cu (wt%) alloys and solder joints are studied. Using mechanical testing and scanning electron microscopy a comprehensive understanding on the influence of Ni micro-alloying on the interfacial reactions and mechanical properties of solder alloys is provided. It is demonstrated that Ni does not influence much the compressive strength or hardness of the alloys; however, it reduces the growth kinetics of intermetallic compound (IMC) layer for Sn-Cu in a short aging time. But Ni in Sn-Ag-Cu solder is effective to reduce the IMC thickness in both short and long aging times. It is also shown that addition of Ni makes the morphology of IMC layer smoother in the as-soldered condition and prevents the formation of thick Cu3Sn IMC for both Sn-Cu and SAC alloys.

3:20 PM Break

3:40 PM  
Long Term Isothermal Aging Effect on Reliability of Doped Lead-Free Solder Joint: Cong Zhao1; John Evans1; Jeffrey Suhling1; Michael Bozack1; 1Auburn university
    This study is to evaluate effect of long-term isothermal aging and thermal cycling on reliability of doped lead-free solder mixes. Twelve doped solder pastes supplied by eight companies, as well as SAC105 and SAC305 solder balls together with three board platings of OSP, ImAg and ENIG are being tested. Package sizes ranges from 15mm, 0.8mm pitch to 6mm, 0.5mm pitch BGA, and QFN and 2512 Resistor were tested. Aging condition is 125℃ with 12 months. Subsequently, specimens were thermally cycled from -40℃ to 125℃ with 15 minutes dwell time. Failure modes of solder joints will be investigated using SEM. IMC layers thickness will be measured. EDX will be employed to analyze the chemical characterization of IMC layer for SAC/ImAg, SAC/OPS and SAC/ENIG systems. Data analysis will be performed to show the characteristic life degradation for different solder pastes under different conditions.

4:00 PM  
Physico-mechanical Properties and Microstructure of Sn3.0Ag0.5Cu Solder Ribbons Doped with Ni and Ni-Sn Nanoparticles: Andriy Yakymovych1; Peter Svec Sr.2; Pavel Sebo2; Martin Nosko2; Herbert Ipser1; 1University of Vienna; 2Slovak Academy of Sciences
    The Ni and Ni-Sn nanoparticles were synthesized using a chemical reduction method. The morphology and particle size of the as-synthesized nanopowders were analyzed using transmission electron microscopy (TEM). The nano-composite solder alloys were prepared by mechanical mixing of Sn3.0Ag0.5Cu powder with nano Ni and Ni-Sn powders, while ribbons were fabricated using the conventional planar flow casting method. The electrical resistivity of doped (Sn3.0Ag0.5Cu)100 x(nanoNi)x and (Sn3.0Ag0.5Cu)100-x(nanoNi-Sn)x ribbons was measured by the standard four-points method. Furthermore, scanning electron microscopy was used to characterize the microstructure and morphology of intermetallic compounds at the interface solder/Cu. Afterwards, the shear strength and microhardness of the solder joints were investigated. It could be shown that nanosized additions led to minor changes in the electrical resistivity of Sn3.0Ag0.5Cu solder ribbons, while the minor Ni and Ni-Sn nanoinclusions resulted in a reinforced microstructure accompanied by an enhancement of the shear strength and microhardness of the solder joints.