Effect of Encapsulation on Electrolyte Leakage in Aluminum Electrolytic Capacitors Under Constant Thermal and Electrical Loading

This study focuses on the influence of encapsulation (with silicone elastomer potting compound) on electrolyte leakage in aluminum electrolytic capacitors. Experiments were conducted on potted capacitors at constant elevated temperature and rated DC voltage, and results were compared to those from a control batch of unpotted capacitors. The weight, ESR and capacitance were periodically monitored. Encapsulation was found to decelerate electrolyte loss rate and ESR degradation. There was an increasingly discernible deceleration of capacitance degradation but the magnitude did not reach statistically significant thresholds within the test period. A simplified axisymmetric finite element model was constructed for theoretical understanding of the electrolyte loss process. The experimental measurements were used to guide the selection of the material properties in the model. The model addresses several possible sources of non-uniformities in the mass flux density in the test specimen: (i) radial nonuniformity of mass transport properties of the rubber seal; and (ii) delamination between the potting compound and the capacitor leads. This model was then used: (i) to conduct parametric investigation of the effect of mass transport properties of the potting compound; and (ii) in conjunction with the experimental results to estimate the electrolyte mass loss from the capacitor through the rubber seal

Numerical Parametric Study of the Thermomechanical Effect of Encapsulation on a Welded Beam Lead Component

Encapsulation of components and assemblies has become widespread in the design of electronic products, providing protection from the environment and enhancing reliability. In this thesis, computational simulations are used to parametrically investigate the thermomechanical role played by the encapsulant when a beam-lead component is welded to slender copper busbars, encapsulated in a polymeric encapsulant, and subjected to temperature cycling. The parametric studies are conducted in two phases, using simplified two-dimensional finite element models. In the first phase, a parametric design space is generated to systematically vary the encapsulant's thermomechanical properties, namely the Young's modulus and Coefficient of Thermal Expansion. A gull wing geometry is introduced into the lead of the component as a stress relief feature. In this case, a ramp thermal loading profile is used to understand the physics of this design and to provide relative comparisons between different combinations of the encapsulant's material properties within the design space. Response surface models are generated over the design space. In the second phase, a Taguchi Design of Experiments (DOE) approach, based on orthogonal arrays, is used to analyze the effects of multiple design parameters under cyclic thermal loading. This includes encapsulant properties (a subset of the properties investigated in the first phase), encapsulant dimensions, lead geometry and dimensions, and busbar dimensions. Lead geometry is considered with and without stress relief features. The loading used in this phase is three temperature cycles between -40oC and 90oC. The primary areas of concern (response variables) in both studies are the component lead and interconnect regions. Deformation and stress states in these critical regions are compared. Main factor effects and selected parameter interactions are computed in accordance with the Taguchi orthogonal arrays, to understand the dominant parameters and parameter interactions for cyclic thermomechanical stresses in this encapsulated assembly

Characterization of Non-linear Polymer Properties to Predict Process Induced Warpage and Residual Stress of Electronic Packages

Nonlinear thermo-mechanical properties of advanced polymers are crucial to accurate prediction of the process induced warpage and residual stress of electronics packages. The Fiber Bragg grating (FBG) sensor based method is advanced and implemented to determine temperature and time dependent nonlinear properties. The FBG sensor is embedded in the center of the cylindrical specimen, which deforms together with the specimen. The strains of the specimen at different loading conditions are monitored by the FBG sensor. Two main sources of the warpage are considered: curing induced warpage and coefficient of thermal expansion (CTE) mismatch induced warpage. The effective chemical shrinkage and the equilibrium modulus are needed for the curing induced warpage prediction. Considering various polymeric materials used in microelectronic packages, unique curing setups and procedures are developed for elastomers (extremely low modulus, medium viscosity, room temperature curing), underfill materials (medium modulus, low viscosity, high temperature curing), and epoxy molding compound (EMC: high modulus, high viscosity, high temperature pressure curing), most notably, (1) zero-constraint mold for elastomers; (2) a two-stage curing procedure for underfill materials and (3) an air-cylinder based novel setup for EMC. For the CTE mismatch induced warpage, the temperature dependent CTE and the comprehensive viscoelastic properties are measured. The cured cylindrical specimen with a FBG sensor embedded in the center is further used for viscoelastic property measurements. A uni-axial compressive loading is applied to the specimen to measure the time dependent Young’s modulus. The test is repeated from room temperature to the reflow temperature to capture the time-temperature dependent Young’s modulus. A separate high pressure system is developed for the bulk modulus measurement. The time temperature dependent bulk modulus is measured at the same temperatures as the Young’s modulus. The master curve of the Young’s modulus and bulk modulus of the EMC is created and a single set of the shift factors is determined from the time temperature superposition. The supplementary experiments are conducted to verify the validity of the assumptions associated with the linear viscoelasticity. The measured time-temperature dependent properties are further verified by a shadow moiré and Twyman/Green test

TAO Conceptual Design Report: A Precision Measurement of the Reactor Antineutrino Spectrum with Sub-percent Energy Resolution

The Taishan Antineutrino Observatory (TAO, also known as JUNO-TAO) is a satellite experiment of the Jiangmen Underground Neutrino Observatory (JUNO). A ton-level liquid scintillator detector will be placed at about 30 m from a core of the Taishan Nuclear Power Plant. The reactor antineutrino spectrum will be measured with sub-percent energy resolution, to provide a reference spectrum for future reactor neutrino experiments, and to provide a benchmark measurement to test nuclear databases. A spherical acrylic vessel containing 2.8 ton gadolinium-doped liquid scintillator will be viewed by 10 m^2 Silicon Photomultipliers (SiPMs) of >50% photon detection efficiency with almost full coverage. The photoelectron yield is about 4500 per MeV, an order higher than any existing large-scale liquid scintillator detectors. The detector operates at -50 degree C to lower the dark noise of SiPMs to an acceptable level. The detector will measure about 2000 reactor antineutrinos per day, and is designed to be well shielded from cosmogenic backgrounds and ambient radioactivities to have about 10% background-to-signal ratio. The experiment is expected to start operation in 2022

Long-Baseline Neutrino Experiment (LBNE)Conceptual Design ReportThe LBNE Water Cherenkov DetectorApril 13 2012

Conceptual Design Report (CDR) developed for the Water Cherekov Detector (WCD) option for the far detector of the Long Baseline Neutrino Experiment (LBNE

Full Proceedings, 2018

Full conference proceedings for the 2018 International Building Physics Association Conference hosted at Syracuse University

Flex Cracking and Temperature-Humidity-Bias Effects on Reliability of Multilayer Ceramic Capacitors

Multilayer ceramic capacitors (MLCCs) are known to be susceptible to cracking when subjected to excessive printed circuit board (PCB) flexure, which is called "flex cracking". The bending of the printed circuit board causes stresses to be transmitted through the solder fillets to the surface mount capacitors. These stresses are the highest at the bottom of the capacitor, where the termination bands end. In order to reduce the amount of stress that is transmitted to the brittle ceramic body of MLCCs through end terminations, a flexible termination system which incorporates a silver-loaded epoxy in end-terminations was developed by some MLCC manufacturers. With the transition to lead-free materials in the electronics industry there is a concern that MLCCs assembled on PCBs with lead-free solder have different susceptibility to flex cracking than those assembled with eutectic tin-lead solder. In this study, the flex cracking of MLCCs assembled with lead-free solder (Sn3.0Ag0.5Cu) was compared with those assembled with eutectic tin-lead (Sn37Pb) solder and differences in the results were explained in terms of solder mechanical properties and solder solidification temperature. Tin-silver-copper lead-free solders and eutectic tin-lead solder have different mechanical properties, which affect the stresses that are transmitted to the ceramic body of the capacitor through the solder fillet. The higher solidification temperature for lead-free solder leads to increased residual compressive stresses after the reflow cool-down process for MLCCs assembled with lead-free solder compared with those assembled with tin-lead solder. In this work, the effects of dielectric material, capacitor size, solder assembly process, solder material, and end-termination type on flex cracking of MLCCs were determined for MLCCs from different manufacturers. Since some flexible- and standard-termination MLCCs are made with precious metal electrodes (silver-palladium), there is a possibility of electrochemical silver migration under bias and humidity. In this study, the effects of temperature-humidity-bias on electrical parameters of flexible-termination MLCCs were characterized and compared with standard-termination MLCCs. In addition, the effect of temperature-humidity-bias on electrical parameters of MLCCs with base metal electrodes was compared to that for precious metal electrode capacitors

Design and reliability of polymeric packages for high voltage power semiconductors

This thesis focuses on the development of a novel polymer based housing for power thyristor devices typically used in long distance high voltage direct current (HVDC) transmission. Power thyristor devices used in HVDC power conversion stations are typically packaged in a hermetically sealed ceramic housing and have demonstrated an excellent history of reliability and performance. However, to avoid increasing the number of thyristors in future higher powered HVDC schemes thyristors having higher power ratings at 8.5 kV and sizes at 125 mm and 150 mm diameters are sought for implementation to achieve higher transmission ratings of, for example, 4000 A at +/- 800 kV. The main disadvantages of such large ceramic-based packages are higher processing cost and weight whilst robustness is also a concern. To overcome these issues, replacing the current ceramic housing with a polymeric material has been investigated in this project. The advantages it is anticipated such packages will provide include lower cost, less weight, robustness, recyclability, etc. However, some challenges it will also offer are: non-hermeticity i.e. polymers are moisture and gas permeable, potentially more complex manufacturing routes, and different electrical, mechanical and thermal properties compared to ceramic materials. The work presented in this thesis was part of a larger project where these challenges have been addressed by developing and testing a prototype polymeric thyristor housing. The prototype is aimed at demonstrating that polymer packages can deliver performance and reliability comparable to, if not better than, current ceramic packages. In this thesis, it is the package development and reliability related studies that are discussed. Because the housings will experience severe electrical stresses and various thermal excursions during their service life, the electrical and thermo-mechanical behaviour of the polymer housing was studied using finite element analysis to gain an understanding of the effects of various design variables and materials properties on performance and the tradeoffs between performance and manufacturability. From these modelling studies, design guidelines have been established for the future development of polymer housings. On the other hand, to identify the physics-of-failure of the prototype that was manufactured as part of the project, accelerated life tests were performed to study its reliability. The knowledge gained from the polymer prototype development was then applied to the design of a larger 125 mm diameter housing using the Taguchi method of experimental design