Phase Stability, Phase Transformations, and Reactive Phase Formation in Electronic Materials XVI: Electrochemistry & Pb-free Soldering
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 8:30 AM
March 1, 2017
Room: 25A
Location: San Diego Convention Ctr

Session Chair: Shien Ping Tony Feng, The University of Hong Kong; Jae-Ho Lee, Hongik University

8:30 AM  
Effects of Pretreatments on the Adhesion of Cu/Non-conductive Substrates in Electroless Copper Plating: Ju-Seok Kang1; Jinuk Lee2; Hyun-Woo Kwon2; Jae-Ho Lee1; 1Hongik University; 2Samsung Electro-Mechanics
    Electroless copper plating has been used extensively in PCB industries. The processes were well known and established. In the normal process, the PCB substrates were chemically etched before electroless copper plating for the better adhesion between copper/substrate. The elecroless copper layers under DFR were etched out after copper line fabrication in PCB. In this procedure the electroless copper layers were over etched to remove the copper completely on the etched surface. During this procedure, the copper lines were also attacked and partially etched out, and then the credibility of line width was not guaranteed especially in narrow line/space. In this research, the electroless copper plating on the substrates without chemical etching was studied. The effects of pretreatments on the Pd seedings were investigated. Ultrasonic was used to enhance the adhesion of copper on the non-conductive substrates.

8:50 AM  
Etching Behaviors of Copper and Invar in via Hole of Copper-Invar-Copper Clad Substrate: Jong-Chan Choi1; Jinuk Lee2; Hyun-Woo Kwon2; Jae-Ho Lee1; 1Hongik University; 2Samsung Electro-Mechanics
    Copper-invar-copper clad has a high electric conductivity with low thermal expansion coefficient and CIC is regarded as the future substrate to replace PCB. Similar to the conventional PCB, via hole was formed through etching process. However the difference of etching rate of CIC clad make uniform hole difficult. In this research, the etching behaviors of copper and invar at different etchants were investigated. Ferric chloride and cupric chloride were used the main etching chemicals. The etching rate is dependent on the mass flow rate as well as the concentration of etchants. OCV of each etchant was measured and compared. The etching mechanism of CIC was proposed and finally the optimum condition for the CIC via hole was obtained.

9:10 AM  
Sulfurization Effect on the Ag and Ag-Pd Reflectors: Erh-Ju Lin1; Yan-Hao Chen1; Cheng-Yi Liu1; 1National Central University
    In this study, we found that the Ag reflector would be seriously tarnished by the sulfurization, and the reflectivity of the sulfurized Ag reflector drops significantly over 52%. However, if the Pd is alloyed into the Ag layer and forms a Ag-Pd alloy reflector, and the minimum reduction rate (around 20%) occurs at the Ag-Pd reflector with a Pd content of 3.72 at.%. Above, two effects of Pd alloying atoms on the sulfurization of the surface Ag atoms have been drawn, which are (1) chemical-state change effect and (2) surface microstructure effect. We found the chemical-state change effect retards the sulfurization of the surface Ag atoms, but the surface microstructure effect promotes the sulfurization of the surface Ag atoms. Here, we believe that these two opposite effects explain that there is an optimal Pd content on the Ag-Pd surface for the resistance of the sulfurization on the Ag surface.

9:30 AM  
Interfacial Characterizations of an Electroless Nickel Layer on a Polyimide Film: Pei-Yu Wu1; Chih-Ming Chen1; 1National Chung Hsing University
    Polyimide (PI) is promising as the substrate in the application of portable and flexible electronic products due to superior thermal stability and chemical resistance. Metallization of Ni on a polyimide film through surface modification and chemical deposition has been successfully developed in which the Ni nanoparticles formed in an potassium salts of poly(amic acid) (PAA) sublayer were used as the catalyst for electroless deposition of Ni. For high frequency application, the interfacial characterizations of a Ni layer on a PI film need more attention. In this study, the stability of Ni at the Ni/PI interface and in the PAA sublayer was investigated by heating the Ni/PI samples at 260 oC and 200 oC to simulate the reflow and thermal aging conditions, respectively. Transmission electron microscopy (TEM) and X-ray photoelectron spectrometry (XPS) were used to examine the atomic diffusion behavior of Ni at the Ni/PI interface.

9:50 AM  
Strong Effect of Cu Electroplating Formulas on the Electroplated-Cu/Sn Interfacial Reactions: Hsuan Lee1; Chih-Ming Chen1; 1National Chung Hsing University
    Electrochemical deposition is a technique widely used in the microelectronic industry and Cu is the most common material used for deposition. Various formulas of Cu electroplating are proposed with the addition of specific additives to overcome the deposition difficulty resulted from the geometrical variety of the substrate. In this study, we demonstrate that the Cu electroplating formulas also have a remarkable effect on the interfacial reactions between Sn and electroplated Cu substrate. The impurity residues originated from the additives were incorporated in the Cu deposits during electroplating, aggregated to the Sn/Cu interface during thermal annealing, and resulted in the formation of voids and some Cu-impurity complexes. The effect of impurity residues showed a strong dependence upon the formula and concentration of the additives.

10:10 AM Break

10:25 AM  
Electrochemical Fabrication of Functional Ag Nanocrystals with Highly Electrocatalytic Activity: Shien Ping Feng1; Ya-Heui Chang1; Chang Liu1; 1The University of Hong Kong
    We present a new electrochemical approach to convert a bulk thin Ag film into japonica-like Ag flowers by using a combination of 3-mercaptopropyl-trimethoxysilane (MPS) layer and cyclic sweeping potential (CSP). An intact bulk Ag layer is electroplated on MPS-grafted substrate, and then a CSP treatment is applied to the Ag-coated substrate in a weak alkaline electrolyte of CH3COONa, NiSO4, and Na2SO4. The flower-like Ag nanocrystals can be effectively produced via manipulation of potential waveform and scan rate of CSP. This method is readily extended to other metals or bimetallic system, such as Cu and Ag-Cu. This finding may open up a new route to effectively synthesize metal and bimetallic NCs with various shapes and versatile functionalities. In this work, the flower-like Ag NCs are chosen to demonstrate as high-sensitive electrode in the application of noninvasive/non-enzymatic electrochemical glucose biosensors, achieving a record low detection limit of 0.1 nM.

10:45 AM  
Controlling Interfacial IMC Phase via Modifying Bi Composition in Low Temperature Bi-33In/Cu Solder Joint: Rui-Wen Song1; Jenq-Gong Duh1; 1National Tsing Hua University
    With the trend of developing wearable and flexible electronic devices, low temperature soldering process is preferred due to the temperature sensitivity of unconventional polymer-based substrates or other low heat budget material. On account of an adequate reflow temperature around 130C, Bi-33In solder with 109C eutectic melting temperature is a candidate with application potential on flexible electronic devices using PET as substrate. The Bi content successfully reduced reflow temperature of In-based solder and only dense layer-type Cu2In phase was revealed in Bi-33In/Cu solder joints. Cu2In, compared to Cu11In9 IMCs forming at In/Cu joints, is intrinsically more ductile and has a higher shear strength. Although no Bi-based IMCs were observed, Bi content altered the thermodynamic and kinetic properties of the solder joints. In addition, the advantageous layer-type morphology of Cu2In in Bi-33In/Cu alleviates stress concentration and acts as a diffusion barrier, as compared to the scallop-type Cu11In9 in In/Cu joints.

11:05 AM  
High-speed Cu Electrodeposition and Its Solid-state Reaction with Sn-3Ag-0.5Cu: Pei-Tzu Lee1; Ying-Syuan Wu1; Cheng-Hsien Yang1; Hung-Cheng Liu2; Cheng-En Ho1; 1Yuan Ze Univeristy; 2Kinsus Interconnect Technology Corp.
    Cu pillar bumps become an important joint configuration of the chip-to-substrate and chip-to-chip interconnections in 3D microelectronic packaging applications. Fabrication of Cu pillars via traditional electroplating (current density j ≈ 2 A/dm2) is a time-consuming process, it is necessary to improve throughput of this process through using high j (alternatively termed high-speed Cu electrodeposition). In the literature, data regarding the j effects on the microstructure of the solderability of various Cu platings is still quite lacking to date. The objective of this study is to explore the solid-solid reaction between Sn-3Ag-0.5Cu and electroplating Cu deposited via various j (2–10 A/dm2). The knowledge advances our understanding of the current density effect on the solderability and the thermal reliability of Cu pillars in packaging applications.

11:25 AM  
Crystallization Kinetics of Amorphous Chalcogenide-based Phase Change Materials and Elemental Semiconductors and Studied with Multi-frame, Nanosecond-scale Dynamic TEM: Mark Winseck1; Huai-Yu Cheng2; Geoffrey Campbell3; Melissa Santala1; 1Oregon State Unviersity; 2Macronix International Co., Ltd.; 3Lawrence Livermore National Laboratory
    Multi-frame, nanosecond-scale dynamic transmission electron microscopy (DTEM) is used to study crystallization of amorphous chalcogenide-based phase change materials (PCMs) and semi-conductors under very highly driven conditions. Nine-frame bright-field DTEM movies are captured during laser-crystallization of the amorphous thin films. Individual images have time resolution as low as 17.5 ns and interframe times are as low as 75 ns, enabling crystal growth to be tracked even when the growth front velocity exceeds 10 m/s. Recent DTEM results with GeSb6Te and other Sb-rich PCMs, that are candidates for memory applications, will be described, with focus on the connections between crystal growth kinetics and growth mechanisms revealed with in-situ imaging. The crystallization of GeSb6Te is found to be reminiscent of explosive crystallization of elemental semiconductors, such as Ge, both in the magnitude of the growth rate (>10 m/s) and in the resulting crystalline microstructures.