bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Systematic Study of Fan-Out Wafer Warpage Using Analytical, Numerical and Experimental Methods
Authors: Gadhiya Ghanshyam , Rzepka Sven , Otto Thomas , Kersjes Sebastiaan , Fernandes Felandorio 
Published: December 2020

Abstract
Low-Density Fan-Out (LDFO) (or fan-out wafer-level packaging) technologies are getting significant attention for heterogeneous system integration in many applications. Despite many studies, excessive wafer warpage is still a challenge for many process steps in these technologies. Therefore, the systematic study is carried out to understand the physics of wafer warpage focusing on the interactions between the silicon (Si) and the epoxy molding compound (EMC). The study started with analytical calculations and finite element (FE) analyses of simple mold/Si bilayer wafer bow for the initial benchmarking. The actual 8″ mold/Si wafer warpage measurements are performed using a newly developed measurement system featuring a 3-point support and an in-situ temperature measurement platform. The finite element model is calibrated with respect to measured wafer warpage showing bifurcation behavior by incorporating the cure shrinkage, mold layer thickness variation, perturbation force, gravity and the actual mold material properties measured by dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA). Also, the FE models with and without rigid contact support are validated showing a good match with measured wafer bow for different silicon thicknesses. Next, the study was further widened to realistic 12″ reconstituted wafers using the validated FE analysis approach. Interestingly, these wafers also exhibit the bifurcation effect and the bifurcation region is analyzed for the relevant range of die and overmold thicknesses for two mold materials. A virtual design of experiments (DOE) quantified these influences for different die and mold thicknesses, die occupation rate and mold materials. These studies provide good practical guidance for the optimal LDFO design to avoid excessive warpage.
Electromigration Analysis of Solder Joints for Power Modules Using an Electrical-Thermal-Stress Coupled Model
Authors: Kato Mitsuaki , Omori Takahiro , Goryu Akihiro , Fumikura Tomoya , Hirohata Kenji 
Published: December 2020

Abstract
Power modules are being developed with the aim of increasing power output. Achieving this aim requires increased current density in power modules. However, at high current densities, power modules can degrade as a result of electromigration, which is a phenomenon where atoms move due to momentum transfer between conducting electrons and metal atoms. In addition, atoms are also moved by mechanical stress gradients and temperature gradients, so it is necessary to consider the combined effects of electrical, thermal, and mechanical stress.
This report describes an electromigration analysis of solder joints for power modules. First, we validated our numerical implementation and showed that it could reproduce the distributions of vacancy concentrations and hydrostatic stress that were almost the same as those in previous studies. We then describe the effects of electromigration in a single solder joint. Due to the appearance of plastic and creep strains, the rate of increase in vacancy concentration was very slow and inelastic strain grew at an increasing rate. This result indicates that inelastic properties may strongly affect electromigration-induced degradation. Next, we present results for the solder joint with a SiC device and substrate. A current crowding appeared at the edge of the solder joint, and a vacancy concentration gradient was generated in not only the thickness direction but also the longitudinal direction. The absolute value of vacancy concentration increased significantly at the edge and did not reach a steady state even after a long time. These results indicate that peripheral components may strongly affect the electromigration-induced degradation. In addition, we modeled the behavior of metal atoms passing through the interface of the solder joint and simulated the growth of the intermetallic layer by electromigration.
Additive Fabricated Compliant Interconnects: Design, Fabrication and Reliability Effects
Authors: Olatunji Tumininu , Huitink David 
Published: December 2020

Abstract
Electronics packaging development is greatly dependent on the magnitude of interconnect and on-chip stress that ultimately limits the reliability of electronic components. Thermomechanical strains occur because of the coefficient of thermal expansion mismatch from different conjoined materials being assembled to manufacture a device. To curb the effect of thermal expansion mismatch, studies have been done in integrating compliant structures between dies, solder balls, and substrates. Initial studies have enabled the design and manufacturing of these structures using a photolithography approach which involves an increased number of fabrication steps depending on the complexity of the structures. This current study involves the fabrication of these structures using a different approach, utilizing additive manufacturing that reduces the number of fabrication steps required to obtain compliant geometries, while also providing a platform for unique compliant structures. This paper discusses the method of fabrication and analyzes the properties and effects of these interconnect structures on a die. Structural finite element thermal cycling simulations between −40 to 125°C show about a 115% increase in the solder joint fatigue life. Additionally, fabricated test structures created directly on a PCB were experimentally characterized for compliance using a micro-indenter tester, showing a mechanical compliance range of 265.95 to 656.78 μ/N for selected design parameters to be integrated into a test vehicle.
Thermal Model of the Package Integrated Cyclone COoler (PICCO): Achieving High Thermal Conductance Using Swirled Two-Phase Flow
Authors: Miorini Rinaldo L. , Sharar Darin J. , deBock Peter 
Published: December 2020

Abstract
The demand for high power density, therefore high heat dissipation, power electronics modules is propelled by applications such as hybrid transportation and asynchronous power generation, among others. Besides a low thermal resistance, these applications require high thermal capacitance to manage transient operations.
The Package Integrated Cyclone COoler (PICCO) is an additively manufactured, thermal energy storing cooler codesigned by GE Research (GRC) in collaboration with the US Army Research Lab (ARL). The key aspect of PICCO is its capability to swirl a two-phase coolant, i.e. liquid-gas. The centrifugal field creates a radial pressure gradient inducing buoyancy. The strong radial acceleration to which the fluid is subject forces relatively cold flow outward to reach the hot wall, thus boosting the heat transfer, while hot flow and bubbles migrate inward and the two-phase system is nearly isothermal (thermal storage).
The proposed study models the swirled flow in terms of liquid film heat conductance and critical heat flux predictions. The resulting heat transfer coefficient can be applied to the walls of the cyclone and used as a boundary condition for the heat conduction problem through the cyclone wall and the module layers.
Surface Engineering Through Atomic Layer Deposition on Three-Dimensionally Structured Materials
Authors: Quach Nhi V. , Pham Quang N. , Han Ju-Hwan , Suh Youngjoon , Park Jin-Seong , Won Yoonjin 
Published: December 2020

Abstract
Atomic layer deposition (ALD) is effective in depositing conformal thin films, which is highly favorable for coating various patterned surfaces. These coatings serve as barrier layers in addition to surface modifications to improve wettability of porous structures, such as meshes and membrane channels. However, it has been challenging to conformally deposit hydrophilic thin films on three-dimensionally (3D) designed, more complicated architectures. To understand the effect of surface modifications on 3D structures’ surface properties, we deposit thin silica films via ALD on hydrophobic porous media, which is nickel inverse opal structures in this case. The silica thin film is used to improve hydrophilicity without modifying the geometries of the microporous structure such as porosity, pore size, and metal type. We study the consequences of applying silica coatings to the 3D structure in comparison to flat surface counterpart. The hydrophilicity effects of ALD coating on porous structures and flat nickel surfaces are approximately the same with a result of decreasing apparent static contact angle of approximately 30°. In relation, the Fowkes method reveals the surface energy of the ALD silica samples increases by a factor of 1.3. Thermal stability of the coating is tested, revealing a relative degradation with increasing thermal cycling, most likely associated with the adsorption species on the thin film surface. The droplet spreading rate is analyzed in addition to droplet volume loss to estimate the liquid penetration rate into the structure, if any. Condensation rate and condensate growth show that despite having lower droplet nucleation in comparison to a flat surface, the droplet area growth on inverse opal regions is larger. These findings showcase potential improvements to 3D microporous structures by employing ALD coating for fluid transport through the porous media.
PHM Features for Large Circuit Boards to Be Implemented Into Electric Drivetrain Applications
Authors: Otto A. , Kaulfersch E. , Singh P. , Romano C. , Hildebrandt M. , Rzepka S. 
Published: December 2020

Abstract
Canary structures being used as early warning indicators represent an important tool for condition and health monitoring of electronic components and systems. In this paper, printed circuit boards with canary structures based on SMD 2512 ceramic chip resistors with reduced solder pad sizes were studied. Focus of these investigations was set on thermo-mechanical and mechanical stresses caused by passive thermal cycling as well as by vibrational loads. For this purpose, experimental methods such as deformation analysis and accelerated ageing tests as well as finite element based methods were applied. In addition, an outlook on the implementation of these canary structures into dual inverter electronic control boards for electrical powertrain applications will be given.
Investigation Regarding Thermal Resistance of Surface Mount Type Discrete Power Semiconductor Package
Authors: Nishi Koji 
Published: December 2020

Abstract
Power electronics is becoming more important than before with motor application expansion. For size reduction of inverter integrated motor design, accurate temperature prediction of power devices is becoming critical. For up to several hundred-watt motor system, inverter is designed with discrete power devices with standard package. This paper investigates package thermal resistance of a DPAK package as an example. Firstly, three-dimensional heat conduction simulation only with DPAK package model is conducted. It is found that its package thermal resistance changes by ∼6.2°C/W due to boundary condition variation. After that, simulation not only with DPAK package but also with PCB is conducted to understand package thermal resistance of a real system implementation case. It is found that package thermal resistance varies drastically by copper trace size. “Smallest” case with minimum copper traces shows ∼0.9 °C/W higher value than larger copper trace case and shows ∼1.5 °C/W higher value than the case that copper trace fully covers PCB top surface, in the case that horizontal PCB size is 50 × 50 mm.
After that, two types of test boards with different trace size for of n-channel MOSFET with DPAK package are prepared. Measurements are conducted to know package thermal resistance variation by copper trace size. Transient thermal impedance curve is obtained from measurement result and is converted to a cumulative Rth-Cth curve to know and discuss the difference by copper trace size of these two test boards. The difference is also discussed with and compared to that of simulation results.
Lasered Roughness to Increase Wicking Rates in Pin-Fin Microstructure
Authors: Hazra Sougata , Liu Tanya , Asheghi Mehdi , Goodson Kenneth 
Published: December 2020

Abstract
In this study, we demonstrate an inexpensive and fast method of creating hybrid microstructures for enhancement of capillary wicking by using UV laser ablation. We have also experimentally observed that capillary wicking rates are greatly increased by laser-machining induced surface roughness in pin-fin microstructures, and in one case the amount of enhancement was as large as 116%. The capillary wicking enhancement is a strong function of the geometry of the largescale pin-fin microstructures as well as the surface roughness of the flat areas. This study will help lead to the better understanding of capillary wicking in hybrid structures that in turn can assist with more informed designing and optimization processes of evaporator wicks in vapor chambers.
Twist Reliability Assessment of Flexible Battery in Wearable Applications
Authors: Lall Pradeep , Jang Hyesoo , Miller Scott 
Published: December 2020

Abstract
Survivability of thinner power sources such as flexible Li-ion batteries (LIB) when exposed to repeated charge-discharge cycles at different operating temperatures along with small mechanical twisting loads encountered in human body applications is relatively unknown. With the advancements in portable and densely packaged electronics, thin power sources, which are reliable and are needed to sustain the daily stresses of motion. The ability of thin form factors to operate reliably in presence of loads such twisting while simultaneously being exposed to different ambient temperatures is the major concern. Development of meaningful test protocols for reliability of the battery requires the replication of human body motion. A twisting test-stand capable of replicating the stresses of daily motion in a lab-environment has been developed for the test. The battery state assessment analyzer comprises of programmable source meter and electronic load, a multi-channel data acquisition system, LabVIEW user interface. A mechanical bending actuator controlled via microcontroller was used for subjecting the LIBs to bending loads. The microcontroller was programmed in a way such that 60 twisting cycles were performed during every discharge phase. A total of 150 charge-discharge cycles are conducted during the life cycle tests where each cycle is comprised of discharging to full depth, bending during discharging, and charging back to full voltage. The degradation of the batteries has been studied. FEM model has been developed for life prediction of the battery and for assessment of acceleration factors between test conditions and use conditions.
Creep Behavior of Various Materials Within PBGA Packages Subjected to Thermal Cycling Loading
Authors: Fahim Abdullah , Hasan Kamrul , Suhling Jeffrey C. , Lall Pradeep 
Published: December 2020

Abstract
Electronic packages are frequently exposed to a thermal cycling environment in real life applications. Particularly, the plastic ball grid array (PBGA) is one of the most widely used electronic package, and consists of various component materials, e.g. solder joint, silicon die, die attachment adhesive, mold compound, solder mask, etc. All of these materials play a significant role on the reliability of the overall package. Failure under creep deformation is one of the significant failure mode for electronic packages. Hence, it is important to study their creep behavior and evolution under the thermal cycling environment. These changes must be evaluated in order to understand and predict their failure behavior due to creep damage in operation.
In our previous study, evolution of mechanical properties of SAC305 solder joints in a PBGA package up to 250 thermal cycles was evaluated using the nanoindentation technique. In this work, nanoindentation technique was utilized to understand the evolution of creep behavior of the SAC305 solder joint, die attachment adhesive, silicon die, and solder mask material for various durations of thermal cycling. Test specimens were first prepared by cross sectioning a PBGA package to reveal the different materials, followed by surface polishing to facilitate SEM imaging and nanoindentation testing. After preparation, the package samples were thermally cycled from T = −40 to 125 °C in an environmental chamber. At various points in the cycling (e.g. after 0, 50, 100, 250 and 500 cycles), the package was taken out from the chamber, and nanoindentation was performed on above mentioned materials to obtain creep behavior at room temperature (25 °C). From the nanoindentation test data, it was found that creep deformation of SAC305 increased upto 500 cycles. Die attachment and solder mask materials showed initial decrease in creep deformation up to 250 cycles and then increased value at 500 cycles. As expected, the silicon die material does not show any significant change in creep deformation behavior upto 500 cycles.
High Strain Rate Low Temperature Properties for SAC-R After Exposure to Isothermal Aging
Authors: Lall Pradeep , Saha Mrinmoy , Suhling Jeff , Blecker Ken 
Published: December 2020

Abstract
Electronic parts in military, automotive, avionics and space applications may be subjected to sustained operation at high temperature in addition to high strain-rate loads. Parts may be stored in non-climate-controlled enclosures prior to deployment. Earlier studies on undoped SAC alloys have shown that the material properties evolve after prolonged period of storage at even modest temperatures. In order to mitigate the aging effects, a number of alloy formulation have been proposed. Data of the mechanical properties of lead-free solder alloys which is used for interconnection in the electronic packaging at high strain rates and at high storage temperature is very essential for design optimization of electronic package sustainability at extreme temperature environment because the SAC solders have shown to have degradation in mechanical properties at prolonged exposure to storage temperature. Industries have come up with a solution to reduce the degradation using dopants in SAC solder. In this study, a doped SAC solder called SAC-R has been subjected to high strain rate testing after extended storage at temperature of 50°C for 1 month, 2 months and 3 months. Samples with no aging and aged samples for up to 3-months have been subjected to uniaxial tensile tests to measure the mechanical properties of SAC-R for High and Low operating temperature ranging from −65°C to +200°C. The material data has been used to compute the constants for the Anand Visco-Plasticity model. The ability of the model to represent the material constitutive behavior has been quantified by comparing the model predictions of the uniaxial tensile test with the experimental data.
High Strain Rate Mechanical Properties of SAC-Q Between -65°C and +200°C After Exposure to Isothermal Aging
Authors: Lall Pradeep , Mehta Vishal , Suhling Jeff , Blecker Ken 
Published: December 2020

Abstract
In many industries, such as automotive, oil and gas, aerospace, medical technologies, electronic parts can often be exposed to high strain loads during shocks, vibrations and drop-impact conditions. Such electronic parts can often be subjected to extreme low and high temperatures ranging from −65°C to 200°C. Also, these electronic devices can be subjected to strain rates of 1 to 100 per second in the critical environment. Recently, many doped SAC solder alloys are being introduced in the electronic component including SAC-Q, SAC-R, Innolot. SAC-Q is made with addition of Bi in Sn-Ag-Cu composition. Mechanical characteristic results and data for lead-free solder alloys are extremely important for optimizing electronic package reliability, at high temperature storage and elevated strain rates. Furthermore, the mechanical properties of solder alloys can be changed significantly due to a thermal aging, which is causing modification of microstructure. Data for the SAC-Q solder alloy with a high temp aging and testing at extreme low to high operating temperatures are not available. SAC-Q material was tested and analyzed for this study at range of operating temperatures of −65°C to 200°C and at a strain rate up to 75 per second. After the specimens were manufactured and reflowed, specimens were stored at 100°C for the isothermal aging for up to 90 days, before tensile tests were carried out at different operating temperatures. For the wide range of strain rates and test temperatures, stress-strain curves are established. In addition, the measured experimental results and data were fitted to the Anand viscoplasticity model and the Anand constants were calculated by estimating the stress-strain behavior measured in the wide range of operating temperatures and strain rates.
Correlation of Microstructural Evolution With the Dynamic-Mechanical Viscoelastic Properties of Underfill Under Sustained High Temperature Operation
Authors: Lall Pradeep , Kasturi Madhu , Wu Haotian , Davis Ed , Suhling Jeff 
Published: December 2020

Abstract
Automotive underhood electronics are subjected to high operating temperatures in the neighborhood of 150 to 200°C for prolonged periods in the neighborhood of 10-years. Consumer grade off-the shelf electronics are designed to operate at 55 to 85 °C with a lower use-life of 3 to 5 years. Underfill materials are used to provide supplemental restraint to fine-pitch area array electronics and meet the reliability requirements. In this paper, a number of different underfill materials are subjected to automotive underhood temperatures to study the effect of long time isothermal exposure on microstructure and dynamic-mechanical properties. It has been shown that isothermal aging oxidizes the underfill, which can change the mechanical properties of the material significantly. The oxidation of underfill was studied experimentally by measuring oxidation layer thickness using polarized optical microscope. The effect on the mechanical properties was studied using the dynamic mechanical properties of underfill with DMA (Dynamic Mechanical Analyzer). Two different underfill materials were subjected to three different isothermal exposure, which are below, near and above the glass transition temperature of the underfills. The dynamic mechanical viscoelastic properties like storage modulus, loss modulus, tan delta and their respective glass transition temperatures were investigated. Three point bending mode was used in the DMA with a frequency of 1 Hz operating at 3 °C/min.
Reliability Assessment of Cu-Al WB Under High Temperature and High Voltage Bias Application
Authors: Lall Pradeep , Jung Sungmo 
Published: December 2020

Abstract
Electronics in automotive underhood environments may be subjected to high temperature in the range of 125–200°C. Transition to electric vehicles has resulted in need for electronics capable of operation under high voltage bias. Automotive electronics has simultaneously transitioned to copper wire-bond from gold wire-bond for first-level interconnections. Copper has a smaller process window and a higher propensity for corrosion in comparison with gold wire bonds. There is scarce information on the reliability of copper wire bonds in presence of high voltage bias under operation at high temperature. In this paper, a multiphysics model for micro galvanic corrosion in the presence of chlorine is introduced. The diffusion cell is used to measure the diffusivity of chlorine in different pH values and different temperatures. Diffusivity measurements are incorporated into the 3D ionic transport model to study the effect of different environmental factors on the transport rate of chlorine. The tafel parameters for copper, aluminum and intermetallics have been extracted through measurements of the polarization curves. The multiple physics of ionic transport in presence of concentration gradient, potential gradient is coupled with the galvanic corrosion.