Emerging Interconnect and Pb-free Materials for Advanced Packaging Technology: Transient Liquid Phase Bonding and Nanosolder
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

Thursday 8:30 AM
March 2, 2017
Room: 30E
Location: San Diego Convention Ctr

Session Chair: Fan-Yi Ouyang, National Tsing Hua University; Tae-Kyu Lee, Portland State University

8:30 AM  
Transient Liquid Phase Processing of Sn-Cu Alloys for Soldering Applications: Stuart McDonald1; Syeda Mehreen1; Flora Somidin1; Arif Mohd Salleh1; Kazuhiro Nogita1; 1Nihon Superior Centre for the Manufacture of Electronic Materials
    In tin-rich Sn-Cu alloys with a copper concentration in excess of 7.6 wt%, solidification commences with the nucleation and growth of the Cu3Sn phase. The equilibrium phase diagram predicts that on further cooling this Cu3Sn will undergo a peritectic reaction with the remaining liquid to form Cu6Sn5. This research investigates this solidification sequence using real-time synchrotron X-ray analysis including the effect of ternary nickel additions. It was found that the extent of the peritectic reaction is highly dependent on the nickel concentration and the formation of Cu3Sn can be completely suppressed after a critical concentration is exceeded . The results of this study were used as the rationale to develop a high-temperature solder alloy for use in transient liquid phase (TLP) processing. The reaction sequence of the TLP alloy during reflow soldering on a copper substrate is described.

8:50 AM  Cancelled
Low Thickness Au-In TLP Hermetic Encapsulation: Eyup Can Demir1; Oguzhan Temel2; Tayfun Akin2; Eren Kalay1; 1METU; 2METU MEMS
    As the detectors are operated under vacuum to obtain high performance, the electronic packaging a crucial step to convert the MEMS based uncooled IR detectors into real commercial products. In this respect, this paper presents fabrication and characterization of gold-indium wafer level hermetic bonding with a thickness of less than 2.5 microns for MEMS applications. We have studied Au-In TLP bonding using e-beam evaporation and sputter processes. The TLP bonding has several advantages over conventional bondings in terms of bonding and re-melts temperatures and good hermetic properties. Hermeticity of the packages was controlled by deflection method. Bonding was performed at 200ᵒC and the corresponding achieved hermeticity does not break up in the subsequent heat-treatment at 400ᵒC for 15 minutes. The average shear strength was measured to be 36 MPa over 15 dies. The details of the encapsulation process will be discussed based on structural, electronic and thermal analyses.

9:10 AM  
Microstructural Evolution and Mechanical Performance of High-Bi, Sn-Bi Transient Liquid Phase Bonds: John Holaday1; Carol Handwerker1; 1Purdue University
    Transient Liquid Phase Bonding (TLPB) technologies are being developed as alternative die attach, interconnect, and thermal interface materials not only to replace high-Pb solders but to provide improved performance and reliability. TLPB differs from other bonding methods involving liquid phases, such as liquid phase sintering or soldering, in that a low-melting temperature phase (LTP) melts and reacts completely with the high-melting temperature substrate (and sometimes with an added particulate phase) to form intermetallic compounds (IMC) with higher melting points than the original LTP. In our previous work, we identified composition and temperature ranges for Cu-Sn-Bi TLPB that avoids the pitfalls associated with a eutectic Sn-Bi LTP. Specifically, melting point of Cu-Sn-Bi TLP bonds were increased from 200C to 271C. In this presentation, we will address microstructural evolution including crystallographic orientation relationships during aging and relate these outcomes to mechanical performance for bonds assembled using a Bi-Sn LTP.

9:30 AM  
Microstructure and Thermomechanical Properties of Nanoparticle-added Sn-Ag-Cu Solder Paste: Kyoung-Ho Kim1; Jung-Hwan Bang1; Junichi Koike2; Jonghyuk Yoon3; Songhee Yim3; Bum-Gyu Baek3; Jae-Pil Jung4; Sehoon Yoo1; 1Korea Institute of Industrial Technology; 2Tohoku University; 3KD One; 4University of Seoul
    The microstructure and thermomechanical reliabilities of a La2O3-nanoparticle-added Sn-3.0wt%Ag-0.5wt%Cu (SAC305) nano-composite solder paste were investigated in this study. The nano-composite solder paste was printed on a PCB and was reflowed with a peak temperature of 250C. The thermomechanical reliability was evaluated with a thermal shock test with temperature range of -40C - 125C. After the thermal shock test, the mechanical properties were measured with a high speed shear test and a lead-pull test. The growth rate of intermetallic compound (IMC) for the nano-composite solder showed lower than that for the conventional solder. The nano-composite solder possessed higher shear strength and toughness than conventional solder after thermal shock test. After 2000 cycles of thermal shock test, the nanocomposite solder did not show any crack formation at the solder joints while crack propagation were observed for the conventional solder joint.

9:50 AM Break

10:10 AM  
Effect of Lead-free Nanosolder Additions on the IMC Formation and Growth of Solder Paste on Cu Substrate: Evan Wernicki1; Zhiyong Gu1; 1University of Massachusetts Lowell
    Nanomaterials have been added to many materials in order to reinforce or alter the material properties, with much success. Similarly, metal nanoparticle additions to solder pastes have been shown to affect the resulting solder joints. However, little focus has been placed on lead-free nanosolder additions to lead-free solder pastes to form a more homogeneous composition. This study showed the effect of nanosolder particles on the intermetallic compound (IMC) formation and growth of solder pastes, and its relationship to the solder joint mechanical properties. Herein, Sn/Ag and Sn/Ag/Cu nanoparticles were synthesized using a chemical reduction method that resulted in spherical nanosolders between 20 – 30 nm. Pastes containing varying nanosolder additions (0.1 - 5 wt%) were prepared, printed and subjected to a reflow process to form the solder joints. The interface was observed for intermetallic compounds formed, before and after thermal aging, for relationships to the resulting solder joint reliability.

10:30 AM  
Nano Solder Interconnections by Low Temperature Soldering of Cu6Sn5: Ying Zhong1; Sungho Jin2; Chunqing Wang3; 1University of California, San Diego, and Harbin Institute of Technology, China; 2University of California, San Diego; 3Harbin Institute of Technology, China
    Modern electronic packaging with smaller size solder bonding for higher device density increases the burden of having to carry significantly larger current density. In order to enhance the resistance to the electromigration/thermomigration and fatigue failures in Pb-free solders, mechanically and thermally more stable solder materials are desirable. We report on a novel concept of utilizing nanosized Cu6Sn5 intermetallics as low-temperature solderble interconnects. By utilizing 10 nm size regime nanoparticles of Cu6Sn5 intermetallics with nano-induced suppressed melting point, a solder bonding at ~200oC was successfully accomplished. A Pb-free solder bonding using such intermetallics having 415oC melting temperature can be beneficial for reduced electromigration/thermomigration during service. Microstructural analysis indicates a ductile dimple type fracture upon mechanical deformation, indicating an improved fracture toughness via nanograined microstructure. Effects of various materials parameters and processing variables on solder synthesis, structure as well as mechanical, thermal and electrical properties will be discussed.