Research 2020-2021

The IEEC values research as a means to create connections and to open future possibilities in the area of electronics packaging.

  

Pooled Research Projects

Every year, we provide what we call "seed-funding," to propel research opportunities in the direction of capacity building and problem-solving for faculty members in academia.

Skilled researchers partner with industry members to meet real-time project needs of companies. That is, whether you are a chemist, physicist, or mechanical engineer, to name a few, members of all fields carry expertise that is integral in catapulting the metrics of success for projects to reach new heights.

Below are the abstracts of the selected 2020-2021 Pooled Research Projects-a partnership between faculty and mentor companies.

2020-2021 Pooled Research Projects

• Fabrication of 3-dimensional Integrated Photonic Devices via Femtosecond Laser Micromachining - Bonggu Shim
  In this proposed research, we will first investigate the optimal parameters for femtosecond laser micromachining of waveguides both in rigid and flexible glass substrates. Second, we will implement fully 3-dimensional laser micromachining setup which will be used for manufacturing integrated photonic devices. Third, we will utilize our 3-dimensional fabrication capability to manufacture spatial light multiplexers called photonic lanterns.
• Modeling Temperature-Dependent Properties of Solder Interfaces - Manuel Smeu

  Building on our recent computational work investigating the temperature-dependent elastic properties of materials, we will now extend our efforts towards interfaces of solder assemblies.

  We will use a combination of density functional theory (DFT) and ab initio molecular dynamics (AIMD) to investigate the elastic moduli, Poisson’s and Pugh ratios of solder interfaces as a function of temperature. With these data we will also analyse the hardness, Debye temperature, elastic wave velocity, and coefficient of thermal conductivity as a function of temperature.

  In addition, we will also use the volume-energy relationship, coupled with the Vinet equation of state to calculate the temperature-dependent coefficient of thermal expansion of these materials.

  We are particularly interested in the Sn-Bi solder joint as well as other lowtemperature solders. With the combination of these computational efforts we aim to identifying potential weak spots and failure mechanisms in these junctions.

• Inorganic Composite Phase Change Materials forPassive Thermal Management - Hao Liu

  This proposal aims to develop high-energy-density inorganic salt hydrate/carbon foam composite phase change materials for passive thermal cooling in electronics.

  This work is expected to yield a form-stable carbon foam Ba(OH)2·8H2O composite phase change material with four times as much thermal energy storage density as the existing paraffin wax.

  The proposed project will optimize the critical wetting property between carbon foam and Ba(OH)2·8H2O through a systemic investigation of strategies for hydrophilic modification of carbon foam.

• Multi-Material Additive Manufacturing of Non-Planar Flexible Substrates with Conformally Conductive Traces for Integrated Electronics - Fuda Ning

  Current additive manufacturing (AM) processes lack the ability to construct integrated electronics with non-planar, conformally patterned features during a single build. In this proposed research, we present a novel multi-axis multi-head AM approach for one-step fabrication of non-planar flexible electronics.

  The objective is to advance fundamental understanding of this innovative multi-material printing of electronics while integrating direct ink writing, fused filament fabrication, and machining processes.

  The underlying materialprocess-structure-performance connection will be deciphered through numerical and experimental investigations. The curve-shaped PET substrate with tailored surface roughness will be created with the subsequent depositions of Cu and/or Ag traces and their geometrical, structural, and electrical effectiveness will be assessed.

  In addition, the interfacial adhesion and failure mechanisms will be elucidated by finite element analysis and mechanical testing including peeling/shear tests and tension/bending fatigue tests.

  Finally, we will fabricate 3D integrated circuits by multi-layer deposition to offer the embedded solutions that maximize the functional capability for 3D integration/packaging.

• Cyber-Physical and Intelligent Edge Computing Platform for Smart Connected Manufacturing - Wenfeng Zhao

  The aim of this proposal is to develop KcASE (Figure 1, blue), a cyber-physical and intelligent edge computing hardware platform for connected and intelligent industrial 4.0 paradigm. In particular, we consider one use case for the state-of-the-art SMT (surface mount technologies) inline manufacturing (Figure 1, gray) and real-time quality inspection (Figure 1, green).

  We plan to accomplish two specific tasks to achieve the connectivity and intelligence extension to the entire product line. First, we will develop a communication module with versatile interfaces (COM, Ethernet, etc.,) that can be used for bidirectional communication among KcASE, 3rd-party equipment and Koh Young Inspection machines. Second, we will integrate the communication module with the latest embedded AI computing hardware and study efficient, distributed edgenode inference.

  Upon the success of this project, we envision that KcASE can pave the way for comprehensive AI-driven, closed-loop process optimization strategies in SMT inline production. KcASE can also be regarded as a feasibility exploration effort toward a potential future product, i.e., an edge extension to KBOX for cost-effective industrial 4.0 deployment solutions.

• Automated Integration with Micro/Nanowire based Fine-pitch Interconnects for 3D Packaging - Kaiyan Yu

  This project aims to create novel micro or nanowire-based fine-pitch interconnects for 3D packaging using precisely controlled micro or nanowires. An automated, precise 3D manipulation scheme is proposed to assemble multiple micro and nanowires in fluid suspension under electrical field. A solution-based approach is designed fabricating interconnects using vertically aligned and horizontally patterned micro or nanowires.

  This project addresses important challenges regarding the precise and scalable assembly for high density interconnects in 3D packaging.

• The Electromigration Behavior of Pb Free Solder Joints Containing Bi: High Melt - Low Melt Solder Interconnect Structures for SMT Applications - Eric Cotts

  We will study the materials science of SAC/BiSn solder joints (e.g., SAC305/Bi42Sn, Fig. 1a) and on such mixed assemblies when both board and component are bumped (Fig. 1b), which promise to provide lower temperature assembly for a wide range of conditions. The eutectic Bi42Sn solder alloy enables process temperatures as low as 150C (Fig. 2) and is widely available in paste form (the Bi42Sn1Ag is a popular variant intended to improve interfacial toughness in drop shock loading).

  We propose to examine the properties of mixed solder alloy joints with combinations of SAC305 or SAC405 solder balls, and Bi42Sn or Bi42Sn1Ag solder paste (Fig.1). Key parameters will include the thickness (volume) of the near eutectic BiSn paste, the peak reflow temperature and reflow time, and fabrication parameters (in particular, variation of geometry from that of Fig. 1a to that of Fig. 1b).

  We will examine microstructures of final joints, determining grain sizes and orientations, as well as composition throughout the joints (including Bi concentration). Mechanical characterization will include hardness and shear characteristics of individual and mixed assembly solder joints. Furthermore, characterizations of the current density limits of such SnBi mixed assemblies will be conducted over a range of current densities, temperatures, and geometries, with focus on the newer geometry illustrated in Fig. 1b. Fabrication of such samples will be by conventional means.

  Building an understanding of the materials science of these new solder joints will provide for reliable product design capability.

• “Understanding and Preventing Voiding in Small Ni-Sn Joints Through Design and Process Control - Nikolay Dimitrov

  This proposal addresses defects in Sn or solder based joints at scales ranging from BGA to ultra-fine flip chip assemblies. Microjoints in 2.5/3D assembly are commonly formed by small Sn or solder caps between opposing Cu or Ni surfaces. Ongoing work funded by the IEEC is leading to a systematic characterization of the strongly enhanced risk of Kirkendall voiding within the intermetallic bonds in microjoints on Cu surfaces. This problem is found to be associated with the quality of the electroplated Cu and guidelines will be offered as to how to minimize the risk.

  An alternative is the use of Ni or Ni/Au coated pillars or pads. Very small Sn thicknesses and repeated reflows, like in stacking of chips, and/or subsequent exposure to elevated temperatures may however lead the intermetallic layers from opposing surfaces to meet. Alternatively, this may be done on purpose to provide for solid support in repeated thermocompression bonding when stacking die or to eliminate concerns with respect to electromigration and thermomigration through unfortunately oriented Sn grains. In either case, collision between the highly irregular intermetallic surfaces tends to lead to the entrapment of a row of Sn ‘pockets’ which are finally drained of Sn, leaving severe voiding. Another concern with slightly larger Ni based joints is the formation of large voids between the Ni3Sn4 intermetallic surface and the solder. Several research groups suggest that the formation of such voids is inevitable once the intermetallic thickness starts to exceed 5µm.

  It is proposed to characterize the effects of interactions between design, electroplating process chemistry and parameters, assembly process parameters, and subsequent thermomechanical history on either of these phenomena. The goal is to establish practical guidelines for how to minimize or, preferably, entirely eliminate the voiding.

• Machine Learning Application for Controlling SMT Reflow Oven - Jia Deng & Sangwon Yoon

  Research Problem: Thermal interface materials are a bottleneck to heat flow, and limit performance as performance increases.

  Research Objective: The goal is to develop an alternative solution for thermal interface materials by metal additive manufacturing which provides lower thermal resistance and enables packages with heat fluxes up to ~1,000 W/cm2.

  Technical Approach: We will develop the process parameters to additively fabricate Cu and/or AlSi10Mg structures on a die (CPU, GPU etc.) using Sn3Ag4Ti interlayer alloy by selective laser melting. The structures can be micro-channels, heat pipes or vapor chamber evaporators. Furthermore, we will look at the interface microstructure and composition of Si-interlayer alloy and Cu and/or AlSi10Mg-interlayer alloy by scanning electron microscopy (SE2, EDS, BEI) and transmission electron microscopy (SAED, BF, DF, EDS).

  Vibratory polishing, focused ion beam (FIB) and Argon beam ion milling will be used along conventional polishing techniques for sample preparation. We will evaluate the strength of the interfacial bonding by mechanical testing such as ball shear tests and finite element analysis simulations. Thermal properties of the fabricated heat sink structures will be experimentally measured using Frequency-Domain Thermoreflectance (FDTR) analysis across the interface. Finally, the performance of the additively fabricated heat sink will be evaluated experimentally and numerically in single phase and two-phase scenarios. 

  Anticipated Outcome: We will develop a process to additively fabricate thermal management devices onto the chip without using conventional thermal management solutions which lead to lower thermal resistance in the package.

  Industry Impact: Current thermal interface materials will not be able to keep up with Moore’s Law, whereas our alternative solution will enable 10X increase in heat fluxes (~1,000 W/cm2). By our calculations, chips can run 10-20 °C cooler under heat fluxes of 100 W/cm2 in current microprocessors.

• Nano-crystalline Planar Magnetic Components for High Power Density Solid State Transformer in AC-DC Power Converters used for Integration of Li-ion Batteries to AC Systems - Pritam Das & Scott Schiffres

  Current power conversion is only 90% efficient, primarily due to losses in the magnetic components. This power conversion is increasingly important for the power grid, vehicles, aerospace and defense.

  This proposal seeks a 3D printed enhanced magnetic component that can reduce transformer losses, while maintaining a compact design.

  Our goal is to develop technologies that will create a transformer with an efficiency of greater than 95%, a 50% reduction in losses compared to today’s standards. 3D printed cores with varying processing conditions will be manufactured and the effect of the processing on microstructure and magnetic properties will be investigated. This proposal will be leveraged into larger future proposals.

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