Sessions Index

Bio:

M.S., Chemical Engineering, National Tsing Hua University
Ph.D., Materials Science, National Chiao Tung University

Abstract:

Types and Applications of Advanced Packaging Materials
 - Key materials: Substrates, RDL dielectric materials, molding films, underfills, and thermal interface materials (TIMs)
 - Functional and technical requirements evolving with heterogeneous integration and high-frequency, high-speed applications
The Role of Substrate Technologies in Advanced Packaging
 - Applications of high-density substrates in CoWoS, InFO, FOPLP platforms
 - Challenges in fine-pitch design, substrate thinning, multilayer structuring, and panel-level scaling
Technical Challenges and Innovation Opportunities in Molding Films
 - Key issues: Flow control, stress management, and long-term reliability
 - Innovation directions: Low-temperature curing, filler dispersion, and ultra-thin film design
Key Entry Points and Strategies for Material Localization
 - Current dependency status of Taiwan’s material supply chain
 - Potential entry points and opportunities for local suppliers
 - Strategic pathways to build a resilient domestic supply chain through partnerships and innovation

 

Bio:
Shubhayan Mukherjee is a senior Ph.D. candidate at the Department of Materials Science and Engineering, National Cheng Kung University (NCKU), Taiwan. His research centers on understanding the fundamental mechanisms governing phase stability, lattice deformation, and defect evolution in intermetallic compounds and metallic systems under electric fields. Using in-situ synchrotron-based techniques such as SR-XRD and SR-XND, he investigates early-stage structural instabilities driven by electric current, aiming to decouple thermal and field-induced effects at the atomic scale. His work spans FCC metals like Cu and Au, as well as intermetallic phases, contributing to a deeper physical understanding of electromigration and current-induced plasticity beyond conventional reliability studies.

Abstract:
In advanced packaging platforms designed for AI acceleration, high-frequency computing, and high-power PCB systems, the structural integrity of metallic interconnects under extreme current density is a critical reliability concern. Subtle lattice-level instabilities can emerge long before visible failure, demanding advanced characterization tools for early detection. Electromigration (EM) in Cu, Ag, Au, and Al interconnects has been extensively studied. Classical work by Huntington and Grone first established the mechanism, showing that momentum transfer from conducting electrons drives directional atomic diffusion and void formation [1]. Blech later demonstrated that such mass transport induces stress accumulation in thin films [2], while Conrad and co-workers found that electric current pulses can reduce flow stress and alter dislocation behavior, providing evidence of electroplastic (EP) effects [3,4]. More recently, Liu et al. employed synchrotron radiation-based characterization to probe current-induced lattice deformation in Cu and Al interconnects, revealing strain evolution prior to morphological failure [5,6]. However, the onset of irreversible lattice deformation in Au interconnects under comparable electrical stress remains largely unexplored. Owing to its exceptional conductivity and corrosion resistance, Au is widely used in high-density PCBs and wire bonding and is increasingly deployed in fine-pitch substrates and embedded power modules for high-performance computing systems, making its structural stability under high current density a pressing concern for next-generation packaging technologies.
We conducted in-situ synchrotron radiation-based X-ray diffraction (SR-XRD) measurements on pre-annealed FCC Au strips (3 μm × 16 μm × 2 cm) to investigate their structural response under electric current stressing (ECS). Experiments were performed at beamline TLS BL17B1 (NSRRC), where samples were subjected to electric current densities ranging from 4.2 × 105 A/cm2 to 1.25 × 106 A/cm2 for 30 min. Diffraction peak tracking during stressing enabled high-resolution monitoring of lattice parameter evolution. For comparison, control heating experiments up to 190 °C, as observed during ECS due to the Joule heating effect, were carried out at both TLS BL17B1 and BL01C2 under identical thermal profiles but without current.
A distinct threshold was identified near ~1.04 × 106 A/cm2, beyond which the (111) reflection exhibited irreversible lattice expansion as shown in Fig. 1. In contrast, thermal-only experiments revealed no such peak shifts, confirming that the observed lattice deformation originated from the electron wind force rather than Joule heating. The d-spacing increase was crystallographically anisotropic, indicating directional stress accumulation along specific lattice planes. Furthermore, the d-spacing shift persisted even after post-stressing thermal recovery, a condition representative of high-cycle thermal loading in AI and server environments, indicating irreversible lattice distortion instead of purely elastic strain.
These results are consistent with our previous studies on Cu and Al, where a critical lattice strain (~0.008) correlated with the onset of electromigration-induced plasticity [6]. However, unlike Cu, which demonstrated twinning and slip deformation under elevated current density [5], the Au strips showed no evidence of phase transformation or surface hillocking throughout the measurement period. This highlights the distinct structural response of Au interconnects under high current stress.
By effectively decoupling thermal and electric field effects, the present methodology establishes a direct route to quantify early-stage lattice instability in metallic conductors. These findings support a generalized framework in which current-induced lattice strain, rather than observable damage, enables early-stage identification of sub-critical deformation in FCC metals, providing valuable insight for the design of thermally and electrically robust interconnect materials in next-generation AI, HPC, and 3D-IC packaging systems.

 

Bio:
Ph. D Program of Mechanical and Aeronautical Engineering, Feng Chia University, Taichung, Taiwan

Abstract:
Substrate materials play a critical role in influencing the warpage behavior, thermal performance, electrical characteristics, and overall reliability of power modules [1–6]. Among these factors, warpage is particularly critical, as it directly impacts alignment accuracy, manufacturing yield, and long-term reliability [7–10]. Among the various ceramic substrates, active metal brazed (AMB) types are widely employed in high-power packaging applications due to their excellent reliability and bonding strength. However, the annealed copper (Cu) layers (ACLs) in AMB substrates are susceptible to significant plastic deformation, primarily due to recrystallization that occurs during high-temperature bonding. This process leads to grain growth and increased slip activity, resulting in reduced yield strength and enhanced ductility [11–12].
While previous studies have examined various structural and thermal effects, the influence of ACLs plasticity in AMB ceramic substrates on the process-induced warpage of power modules remains underexplored [13–16]. To address this gap, this study investigates the plastic deformation effect of ACLs in AMB substrate on the warpage behavior of a three-phase, full-bridge silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) power module during manufacturing, using nonlinear numerical modeling and experimental validation. A three-dimensional (3D) process modeling methodology is developed to accurately characterize the process-induced warpage. This approach incorporates ANSYS element birth–death technique and a nonlinear finite element analysis (FEA) model, explicitly accounting for the nonlinear plastic deformation of the ACLs and geometric nonlinearities. Furthermore, the effect of vacuum suction during the wire bonding process is included. The effectiveness of the proposed process modeling methodology is confirmed through in-line warpage measurements taken at key process steps. At last, comparative analysis is conducted to evaluate differences in warpage behavior with and without ACLs plasticity modeling.
The three-phase, full-bridge SiC MOSFET power module under investigation is shown in Figure 1, and the corresponding FEA model used for process modeling is presented in Figure 2. The stress–strain curves applied to the ACLs are illustrated in Figure 3 [16]. The measured and simulated warpage values before and after the die bonding process, after wire bonding, and after heat sink attachment are shown in Figures 4(a) and 4(b), respectively. It should be noted that all results, except those after heat sink attachment, represent the warpage distribution across the AMB substrates. Once the heat sink is attached to the AMB substrate, the measured and simulated warpage data reflect the combined deformation across both the heat sink and the AMB substrate. It is evident that the simulated warpage results closely match the experimental data, both in trend and in magnitude, demonstrating the validity of the proposed process modeling methodology.
Figure 5 exhibits the measured and simulated warpages of the AMB substrate with and without the plasticity effect during the die bonding (i.e., Steps 0–3) and wire bonding (i.e., Steps 3–6) processes. As noted earlier, the warpage results after heat sink attachment are not included in this figure due to the difficulty in isolating the warpage contributions of the AMB substrate and the heat sink. The simulation results reveal a noticeable difference in warpage behavior depending on whether the plasticity of the ACLs is considered. Incorporating the plasticity effect of the ACLs turns out to significantly improve prediction accuracy, underscoring the importance of accounting for their post-annealing mechanical response in reliable warpage modeling.

 

Bio:
Masahiro Inoue is an associate professor at the Graduate School of Science and Technology, Gunma University, Japan. His current research focuses on characterizing and applying novel electrically and thermally conductive pastes. He also develops novel human/machine interfaces using stretchable wiring technology.

Abstract:
INTRODUCTION
Flexible hybrid electronics (FHE) are expected to be a valuable technology for realizing advanced electronic devices in the Internet of Things (IoT) society. The research and development of advanced FHE devices have expanded the concept of “flexibility” to include stretchability beyond conventional bendability. The constituent elements, such as substrates, wires, and electrodes, must exhibit extensive stretchability to achieve stretchable devices; therefore, material development and reliability assessment for stretchable electric circuits are essential to establishing the electronics packaging technology for FHE devices.
Among the packaging techniques for preparing stretchable wires and electrodes, printing methods using elastomer-based electrically conductive pastes have several advantages from the viewpoint of High-mix, low-volume production with low cost. However, the wires and electrodes exhibit severe problems with electrical reliability when they undergo mechanical deformation. Because the conduction paths in the wires and electrodes printed with the conductive pastes are formed in a network of fillers, conducting contacts between fillers are easily deformed to increase their electrical resistivity. Thus, improving electrical reliability is a crucial issue for the widespread adoption of this fabrication process.
Since the problems in the electrical reliability of the wires are caused by their deformation, this work focuses on analyzing the electrical behavior of the stretchable wires during a uniaxial cyclic tensile test to improve the stability of electrical conductivity. In this work, the material design of conductive pastes for printing on substrates with extremely low hardness is discussed. One of the proposed design concepts aims to stabilize electrical conductivity by controlling viscoelasticity in the wires.
MATERIALS AND METHODS
Silver flakes and micro-particles (Fukuda Metal Foil & Powder Co., Ltd., Kyoto, Japan) were mixed with polyhydroxyurethane (Dainichiseika Color & Chemicals Mfg. Co., Ltd., Tokyo, Japan) at up to 80 wt% to prepare pastes for printing stretchable wires. The wire samples, with dimensions of 5 mm × 40 mm × 30 μm, were printed on polyurethane-based substrates with an Asker hardness (C) of 15. After printing, the specimens were cured at 100 °C for 1200 s.
A uniaxial cyclic tensile test with 10 % strain amplitude of the wire samples was performed for 100 cycles at a strain rate of 2.5 × 10-1 or 2.5 × 10-3 s-1. Subsequently, a stress relaxation test was conducted after the cyclic tensions. Variation in the electrical resistivity of the wires was simultaneously measured during the tensile test.　After the tensile test, the samples were post-annealed at 100 °C. Subsequently, the electrical resistivity of the post-annealed samples was measured.
RESULTS
The sample printed on a 15-hardness substrate exhibited a specific electrical behavior when an appropriate level of viscoelasticity was imparted to the wire sample. The electrical resistivity initially increased and decreased in the first loading step. However, increased electrical resistivity was suppressed in the subsequent unloading step. Furthermore, the electrical resistivity decreased, approaching a constant range as the number of cycles increased.
The electrical behavior observed in the sample printed on the 15-hardness substrate suggests that the sample's viscous relaxation plays a crucial role in suppressing the increased electrical resistivity during the unloading steps. The mechanism of this electrical behavior remains unclear. However, this suggests that the conducting filler network (conduction paths) in stretchable wires can be stabilized by mechanical deformation under specific conditions, thereby improving their electrical reliability. Based on the experimental results, stretchable wires that exhibit little variation in electrical resistivity have been successfully developed.

 

Bio:
1. Major in Chemical Engineering & Materials Science at Yuan Ze University. 2. Research expertise: mmWave antenna, 3D electromagnetic simulation. 3. Y. H. Chang, Y. C. Chiang, C. C. Huang, C. C. Huang, C. H. Chou, and C. E. Ho, Comparative Study between Single and Array Antenna Characteristic with Different Surface Finishes, Proceeding of the 19th International Microsystems, Packaging, Assembly and Circuits Technology Conference (IMPACT 2024), Taipei, pp. 299–302, Oct. 23–24, 2024.

Abstract:
Millimeter-wave (mmWave) antennas are now being widely used in automotive radar system, low earth orbit (LEO) satellites, and wireless data center due to their capability for higher bandwidth, lower latency, and better spatial resolution. Several critical factors must be taken into account in the mmWave antennas design, which includes signal characteristic, lightweight, low-cost fabrication and so on. The microstrip structure, consisting of two parallel conducting layers separated by a dielectric substrate with the upper conductor patterned on the substrate surface for radiation, can appropriately meet the above requirements, therefore promoting its widespread adoption in mmWave antenna design. However, a portion of Cu traces in the microstrip structure are inevitably exposed to the ambient environment during operation and the Cu constituent easily reacts with atmospheric oxygen.

In high-frequency signal transmission, electromagnetic losses may cause temperature rise, which further accelerates the Cu oxidation process, leading to the formation of cuprous oxide (Cu2O) and copper oxide (CuO) layers over the Cu surface. In this study, the XPS depth profiling of the microstrip Cu traces revealed noticeable oxidation after annealing at 150 °C for 24 h and 48 h under 1 atm. The predominant oxide formed was identified as Cu2O, with oxide layer thicknesses exceeding approximately 200 nm and 1000 nm after 24 h and 48 h of aging, respectively, based on the Cu 2p and O 1s signals. The 2D radiation patterns (77 GHz) of a mmWave antenna after annealing at 150 oC for 0 h (initial), 24 h, and 48 h. Obviously, the gain value of mmWave antenna gradually decreased from 10.1 dBi (0 h), to 8.8 dBi (24 h), and then to 7.7 dBi (48 h) in the yz-plane. The degrdation in the antenna’s gain value can be attributed to its lower bulk conductivity (10⁻²–10⁻³ S/m) than Cu (5.87 × 107 S/m). Our preliminarily results revealed that the Cu oxidation is an important factor of antenna performance, and an appropriate surface finish coating might be required in order to enhance the thermal/transmission reliability of mmWave antennas.

 

Bio:
Professor Nogita graduated as an Engineer in Japan in 1990 and worked in the nuclear power industry with Hitachi Ltd. He was awarded a PhD from Kyushu University in 1997. He migrated to Australia in 1999 after accepting a position at the University of Queensland, where he became the founding director of the Nihon Superior Centre for the Manufacture of Electronic Materials (NS CMEM) in 2012 as well as project manager of the University of Queensland – Kyushu University Oceania project (UQ-KU project) at the School of Mechanical and Mining Engineering. He is also an invited Professor at Kyushu University and a Research Adviser at the University of Malaysia Perlis. His research is in three major areas, namely lead-free solders and interconnect materials, energy materials such as hydrogen-storage alloys, and structural and coating alloy development. He holds 20 international patents and has authored over 250 refereed scientific papers. He is a deputy chair for the Electronic Packaging and Interconnection Materials (EPIM) Committee (since 2022), and Leading organiser (2019 and 2023) and Co-organiser of the “Emerging interconnect and Pb-free materials for advanced packaging technology” symposium at TMS in the USA, from 2015 to the current date. He is the recipient of the TMS Research to Industrial Practice Award in 2021.

Abstract:
This paper provides an overview of how advanced characterisation approaches, such as Synchrotron X-ray radiation facilities and state-of-the-art electron microscopy, can be used to optimise and develop Pb-free solder alloys and associated intermetallics that form between the solder alloys and substrates of electronic interconnects. The following two practical/experimental advanced approaches will be discussed, along with their use in international collaborative projects, (1) Synchrotron X-ray imaging at the SPring-8 synchrotron, and (2) State-of-the-art electron microscopy at The University of Queensland and Kyushu University.

 

Bio:
Department of Materials Science and Engineering, National Chung Hsing University, Taichung 402, Taiwan

Abstract:
Direct Cu-to-Cu bonding applied in 3D IC packaging exhibits many advantages, such as higher I/O density, better thermal dissipation and faster signal transportation. It also contributes to low electrical resistance and low insertion loss as well, which are beneficial to electrical performance for packages. This study applies ensemble learning, which is one of the machine learning techniques, to develop a predictive model for bonding strength. By integrating experimental data such as oxide layer thickness and constitutional phases, the modeldeveloped enables accurate prediction of shear strength of Cu-to-Cu joints under various oxidation conditions, and can be further utilized for rapid screening of process parameters and evaluation of joint reliability.To provide high-quality experimental data and enhance the generalizability of the model, oxide layer data generated from various processing methods, including thermal annealing and vacuum ultraviolet (VUV) exposure, were incorporated into the training set. The measurement of oxide thicknesses and also phase identification were performed using coulometric reduction.

Keywords: Cu-to-Cu direct bonding, pre-treatment, machine learning