Phase Stability, Phase Transformations, and Reactive Phase Formation in Electronic Materials XVI: Pb-free Soldering & UBM
Sponsored by: TMS Functional Materials Division, TMS: Alloy Phases Committee
Program Organizers: Shih-kang Lin, National Cheng Kung University; Chao-hong Wang, National Chung Cheng University; Jae-Ho Lee, Hongik University; Ikuo Ohnuma, National Institute for Materials Science (NIMS); Chih-Ming Chen, National Chung Hsing University; Thomas Reichmann, Karlsruhe Institute of Technology; Yu Zhong, Florida International University; Shijo Nagao, Osaka University; Shien Ping Tony Feng, The University of Hong Kong; Yee-wen Yen, National Taiwan Univ of Science & Tech

Wednesday 2:00 PM
March 1, 2017
Room: 25A
Location: San Diego Convention Ctr

Session Chair: Yee-wen Yen, National Taiwan University of Science and Technology; Cheng-En Ho, Yuan Ze University

2:00 PM  
One-step Electrodeposition of Gold Dendrites in Aminosilane-contained Electrolyte and Their Applications: Hau Nga Yu1; Shien Ping Feng1; 1The University of Hong Kong
    Nanotechnology brings up many breakthroughs in scientific development. For instance, catalytic ability of gold was neglected before the appearance and analysis of gold nanostructures in the 80s. Because of its large compatibility in catalysis, molecular sensing and also more other prospective fields, shape-controlled gold nanostructures has been catching much attention in this decade. In this talk, a templateless method is introduced to fabricate anisotropic grown gold nano-dendrites by one-step electrodeposition in (3-Aminopropyl)trimethoxysilane (APTS)-contained electrolyte. Growing direction of branch and trunk of the dendrites are controlled to provide specific shape and morphology that can enhance their catalytic ability. These shape-controlled gold dendrites present satisfying catalytic performance in selective oxidation of glucose and methanol, which can be promoted to biomedical sensors and methanol fuel cell production.

2:20 PM  
Development of Sn-free and Sn-containing Low Melting Solder Alloys: Chih-Hao Chen1; Albert T. Wu1; BoonHo Lee2; HsiangChuan Chen2; ChangMeng Wang2; 1National Central University; 2SHENMAO Technology Inc.
    In recent decades, diverse products emerge with various requirements for manufacturing and reliability. In some products, such as light emitting diodes (LEDs), biosensor, and molded interconnect device (MID) plastics, soldering temperature is one of the most difficult challenges in the manufacturing processes. High temperature packaging process reduces the total life time and also degrades the yield of the products. New solder alloy has to be developed for low temperature applications. In this study, tin-containing and tin-free low melting solder with melting point at 82 oC and 95 oC are developed. The morphology of the intermetallic compounds (IMC) at the interfaces and in the solders are reported. The alloys were assembled to flip chip test vehicles for ball shear test, drop test, and thermal cycling test to evaluate the possible applications in real devices.

2:40 PM  
A Colorful Titanium Foil as a Photoanode Substrate for Dye-sensitized Solar Cells under Back-side Illumination: Chih-Hsiang Huang1; Chih-Ming Chen1; 1National Chung Hsing University
    Titanium (Ti) foil is widely employed as a flexible photo-anode substrate in dye-sensitized solar cells (DSSCs). To increase the specific surface area of the Ti substrate, the Ti surface was etched to form a porous titanium dioxide (TiO2) layer through anodizing oxidation technology (AOT). The surface TiO2 film showed a high color variety with various AOT voltage which was attributable to the light refraction and scattering capability of the porous TiO2 structures. With the porous TiO2 structure, the electrical contact between screen-printed TiO2 nanoparticle film and the Ti substrate was improved. The porous TiO2 structure also suppressed the charge back-reaction on the photo-anode substrate based on the impedance analysis of electrochemical impedance spectroscopy (EIS). A higher power conversion efficiency (PCE) of DSSC based on the porous TiO2 structure was achieved and the contribution was mainly due to increased short-circuit current density (JSC).

3:00 PM  
Solderability of Ultrathin-Ni(P)-type Au/Pd(P)/Ni(P)/Cu Pad: P Content Effect of the Pd(P) Film: Ying-Syuan Wu1; Pei-Tzu Lee1; Ming-Kai Lu1; Tsai-Tung Kuo2; Cheng-En Ho1; 1Yuan Ze University; 2Uyemura Limited Company
    Recently, a great deal of attention has been focused on an ultrathin Ni(P) surface finish (less than 0.3 μm in thickness) over the Cu pads because of its lower dB loss at high frequencies and better suitability of fine-pitch packaging applications than a thick Ni(P) film. The effect of Ni(P) thickness on the solderability has been recently investigated; however, information regarding the P content effect of the Pd(P) film is still seriously lacking to date. The focus of this study is to investigate the soldering reaction between a Sn-3Ag-0.5Cu alloy and an ultrathin-Ni(P)-type Au/Pd(P)/Ni(P)/Cu metallization pad, where the Pd(P) film possessed various P contents in the range of 0–4 wt.%. Additionally, the mechanical properties of Sn-3Ag-0.5Cu/Au/Pd(P)/Ni(P)/Cu were examined via a high-speed ball shear test. Optimization of the P content in the Pd(P) film for this ultrathin-Ni(P)-type Au/Pd(P)/Ni(P)/Cu metallization pad will be made in this study.

3:20 PM  
Niobium Pentoxide Hole-blocking Layer for Perovskite Solar Cell: Rui Cheng1; Yu Ting Huang1; Shien Ping Feng1; 1The University of Hong Kong
    Recently perovskite, a low cost hybrid material with both organic and inorganic components, has been used as absorption material for solar cell and achieved 22.1% power conversion efficiency (PCE). A uniform and pinhole-free hole-blocking layer (HBL) is necessary for high-performance perovskite solar cell (PSC). Until now, many effective materials and intelligent ways for fabricating HBL has been reported by former researchers. Different from the wide-adopted methods like spin-coating, spray pyrolysis, ALD and sputtering, this research introduces ekectrophosis Nb2O5 HBL. Nb2O5 nano-particles was synthesized through a series of chemical reactions and then deposited on FTO surface by electrophoresis to form a compact HBL. It significantly reduces the effect of charge-hole recombination and avoid current leakage. An optimized PCE of 13.9% for mesoporous PSC and 15.8% for planar PSC was demonstrated, with fill factor (FF) of 0.72 and 0.78.

3:40 PM Break

3:55 PM  
Thermal Capacitive Electrochemical Cycle on Supercapacitor: Xun Wang1; Shien Ping Feng1; 1The University of Hong Kong
    Low-grade thermal energy is abundantly available in industry, power plant, combustion engines and also solar and geothermal heat. However, it is still a great challenge to convert low grade heat into electric energy in an efficient way. Thermal charging and cycle on electrochemical system are newly proposed as an attractive method for efficient temperature thermal-electrical energy conversion. Here we applied a four-step thermal electrochemical cycle to commercial supercapacitor. Molecular dynamic simulation was performed on supercapacitor in different temperature and electrostatic potential. The structure of tetraethylammoinum tetrafluoroborate in acetonitrile electrolyte near graphene electrode was investigated to explore temperature effect on electrostatic cell potential, which explains how heat boosting ions moved, and further distributed to achieve a thermo-electrochemical cycle.

4:15 PM  
Analysis of Electrochemical Impedance Spectroscopy of Dye-sensitized Solar Cells with a Blocking Layer: Yen-Chiao Chen1; Chih-Ming Chen1; 1National Chung Hsing University
    The photovoltaic performance of dye-sensitized solar cells (DSSCs) is limited by the recombination reaction of the electrons from the fluorine-doped tin oxide (FTO) substrate back into the electrolyte. In order to reduce the electron recombination at the FTO/electrolyte interface, a blocking layer which can prevent the electrolyte from direct contact with the FTO substrate is deposited on the FTO to improve the cell performance. Based on the analysis results of transmission line model and electrochemical impedance spectroscopy (EIS), the blocking layer can promote the cell power conversion efficiency (PCE) by increasing the electron recombination resistance. The suppression effect of the blocking layer on the electron recombination under different light intensity was investigated. The suppression effect became stronger under low-light condition, indicating that the blocking layer played a more important role in the indoor or low-level outdoor lighting applications.

4:35 PM  
Pulse Pb-UPD to Achieve a High Gap-filling of Cu Film Deposited on Trenched Ru/p-SiOCH/Si Substrate: Jhih-Yan Wong1; Jai-Lin Wu1; Jau-Shiung Fang1; 1National Formosa University
    This paper reports the formation and properties of Cu film deposited on Ru/p-SiCOH/Si substrates with high aspect ratio trench using electrochemical atomic layer deposition (ECALD). The conformability and step coverage of the deposited Cu film were elucidated to reach high gap fill capability as Cu interconnects for microelectronics. ECALD can be used to fabricate Cu metallized film by combining underpotential deposition (UPD) and surface-limited redox replacement (SLRR). Consequently, this work elucidates the effect of a fixed Pb-UPD potential and pulse Pb-UPD potential on the gap-filling capability and electrical properties of resulting Cu film on the substrate. Layer-by-layer deposition of Cu film formed at a Pb-UPD of -443 mV exhibited higher conformability, and step coverage, and (111) texture. The results of this study suggested that the ECALD can used for fabricating Cu interconnects.

4:55 PM  
Thermomigration of Cu-Sn and Ni-Sn Intermetallic Compounds during Reliability Test in SnAg Solder Joints: Po-Ning Hsu1; 1National Chiao Tung University
    In this study will study the thermomigration behavior in three different solder joints. The joints were placed on a hotplate maintained at 200 C for 1000 hours. In order to create a large temperature gradient, we stacked three silicon chips and one heat sink on the top to increase the thermal gradient. Simulations were performed to determine the migration induced material transport and the resulting mass flux divergences in finite element analysis (FEA) models of the different high height of micro-bumps. We found that the nickel layer in solder exhibits the ability to inhibit the dissolution of Cu at the hot end and the formation of IMCs at the cold end. The detailed results will be presented in the conference.

5:15 PM  
Using Sn-Bi-Zn Solder Layer as the LED Die-attach Material by Controlling Position of Zn in the Solder Layer: Yue Kai Tang1; Chengyi Liu1; 1National Central University
    Generally, Au-Sn solder is the most commonly die-attach material for LED package. However, the high melting point is the big problems. High processing temperature would also generate the residual stress and degrades the LED performance and the reliabilities. We had successfully used Sn-Bi-xZn-Sn solder layer as the LED die-attach material by controlling Bi-Zn alloy compositions. The brittle Bi phase is found to be trapped in the intermetallic compound phases at the interface. This unique interfacial microstructure could provide a good reliability performance. To further understand the details about the effect of Bi and Zn on the bonding system, the position and sequence of Bi and Zn solder layers are studied in this work. Interestingly, we find that the die strength will be influenced and improved by varying the position of the Zn layer in the solder bonding layer structure. The detail mechanism will be discussed in this talk.