Investigation of moisture diffusion in cross-linked epoxy moulding compound by molecular dynamics simulation

Effects of Moisture Diffusion on a System-in-Package Module by Moisture-Thermal-Mechanical-Coupled Finite Element Modeling

Epoxy molding compounds (EMCs) are commonly used in electronic products for chip encapsulation, but the moisture absorption of EMC can induce significant reliability challenges. In this study, the effects of hygrothermal conditions and structure parameters on moisture diffusion and the consequent influences (such as moisture content on die surfaces and stress distribution) on a system-in-package module have been systematically investigated by moisture-thermal-mechanical-coupled modeling. Hygroscopic tests were carried out on a new commercial EMC at 60 °C/60% RH and 85 °C/85% RH, followed by evaluations of diffusion coefficients by Fick's law. It was found that the moisture diffusion coefficients and saturation concentrations at 85 °C/85% RH were higher than those at 60 °C/60% RH. From the modeling, it was found that the consequent maximum out-of-plane deformation and stress of the module at 85 °C/85% RH were both higher than those at 60 °C/60% RH. Influences of thicknesses of EMC and PCB on the moisture diffusion behavior have also been studied for design optimization. It was found that the maximum moisture concentration on die surfaces and resultant stress increased notably with thinner PCB, whereas the effects of EMC thickness were limited. This can be attributed to the comparison between the thicknesses of EMC and PCB and the shortest existing diffusion path within the module. These findings can provide helpful insights to the design optimization of electronic modules for hygrothermal conditions.

Exploring secondary interactions and the role of temperature in moisture-contaminated polymer networks through molecular simulations

Leveraging the state of absorbed moisture within a polymer network to identify physical and chemical features of the host material is predicated upon a clear understanding of the interaction between the polymer and a penetrant water molecule; an understanding that has remained elusive. Recent work has revealed that a novel damage detection method that exploits the very low baseline levels of water typically found in polymer matrix composites (PMC) may be a valuable tool in the composite NDE arsenal, provided that a clear understanding of polymer-water interaction can be obtained. Precise detection, location, and possible quantification of the extent of damage can be performed by characterizing the physical and chemical states of moisture present in an in-service PMC. Composite structures have a locally elevated dielectric constant near the damage sites due to a higher fraction of bulk ("free") water, which has a higher dielectric constant when compared to water molecules bound to the polymer network through secondary bonding interactions. In this study, we aim to get a clear atomistic scale picture of the interactions which drive the dielectric signature variations necessary for tracking damage. Molecular Dynamics (MD) simulations were used to explore the effect of temperature on the state of moisture in two epoxy matrices with identical chemical constituents but different morphologies. The motivation was to understand whether higher polarity binds a greater fraction of moisture even at higher temperatures, leading to suppressed dielectric activity. Consequently, the influence of secondary bonding interactions was investigated to understand the impact of temperature on the absorbed water molecules in a composite epoxy matrix.

Biomimetic and Superelastic Silica Nanofibrous Aerogels with Rechargeable Bactericidal Function for Antifouling Water Disinfection

Disinfecting drinking water in a reliable, sustainable, and affordable manner is a great challenge, especially for water contaminated with pathogenic microbes, and traditional water disinfection strategies still suffer from biofouling, irreversible depletion of disinfectants, and energy consumption. In this study, we developed biomimetic and superelastic skeletal-structured silica nanofibrous aerogels (SNAs) with rechargeable bactericidal and antifouling property via the combination of electrospun silica nanofibers and a functional Si-O-Si bonding network. The premise for our design is that the Si-O-Si network comprising rechargeable N-halamine moieties can provide the aerogels with structural stability yet durable bactericidal activity. The resulting aerogels exhibit intriguing properties of high porosity, superhydrophilicity, superelasticity, rechargeable chlorination capability (>4800 ppm), and exceptional bactericidal activity (99.9999%), enabling the aerogels to effectively disinfect the bacteria-contaminated water with ultrahigh flux (57 600 L m^-2 h^-1) and antifouling function. The synthesis of the SNAs opens pathways for exploring antibacterial and antifouling materials in a renewable and nanofibrous form.

Molecular dynamics study on the tensile deformation of cross-linking epoxy resin

Various epoxy resins are used in the electronic industry as encapsulants, adhesive, printed wiring boards, electronic packagings, and so on. In this study, molecular dynamics method is employed to simulate the tensile deformation of the typical electronic epoxy resin. An efficient cross-linking procedure is developed to build the molecular model. Based on the cross-linking algorithm, the effects of moisture content, cross-linking conversion, strain rate, and temperature on the mechanical properties of epoxy resins are investigated. The stress-strain curves are plotted. Also the Young's modulus and Poisson ratio are calculated. The simulation results are compared with existing experimental data. Good agreements are observed. The results show that mechanical properties of epoxy resin decrease obviously with increasing moisture content and temperature. However the high cross-linking conversion and strain rate enhance the mechanical properties of resin. This study is significant to understanding the mechanical properties of cross-linking epoxies in high temperature and high humidity.