Water-borne coatings often contain nanofillers to enhance their mechanical or optical properties. The aggregation of these fillers may, however, lead to undesired effects such as brittle and opaque coatings, reducing their performance and lifetime. By controlling the distribution and structural arrangement of the nanofillers in the coatings and inserting reversible chemical bonds, both the elasticity and strength of the coatings may be effectively improved, while healing properties, via the reversible chemistry, extend the coating’s lifetime. Aqueous dispersions of polymer-core/silica-corona supracolloidal particles were used to prepare water-borne coatings. Polymer and silica nanoparticles were prefunctionalized with thiol/disulfide groups during the supracolloid assembly. Disulfide bridges were further established between a cross-linker and the supracolloids during drying and coating formation. The supracolloidal nanocomposite coatings were submitted to intentional (physical) damages, i.e., blunt and sharp surface scratches or cut through into two pieces, and subsequently UV irradiated to induce the recovery of the damage(s). The viscoelasticity and healing properties of the coatings were examined by dynamic, static, and surface mechanical analyses. The nanocomposite coatings showed a great extent of interfacial restoration of cut damage and surface scratches. The healing properties are strongly related to the coating’s viscoelasticity and interfacial (re)activation of the disulfide bridges. Nanocomposite coatings with silica concentrations below their critical volume fraction show higher in situ healing efficiency, as compared to coatings with higher silica concentration. This work provides insights into the control of nanofillers distribution in water-borne coatings and strategies to increase the coating lifetime via mechanical damage recovery.

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The risk of corrosion poses a challenge to meet the stringent reliability requirements of microelectronic devices that are used in harsh environments. Microelectronic devices are often encapsulated in polymer packaging materials, which protect them from corrosion. These polymers are, however, not completely hermetic and thus allow small amounts of ions and moisture to reach the device, which might cause corrosion of the microelectronic circuitry. To improve and predict the reliability of the device, it is important to quantify the ion diffusivity in these materials. Previously reported values for the ion diffusivity vary by multiple orders of magnitude for a single class of material. Here, we investigate the causes for this discrepancy using three experimental methods: (i) saltwater immersion, (ii) diffusion cell measurements, and (iii) transient electric current measurements. Several materials, such as silicone, epoxy, and polyamide, were tested to cover the broad spectrum of polymers used by the microelectronics industry. We found that the discrepancies are likely due to the strong dependence of the ion diffusivity on both the moisture content within the polymers, as well as on the salt concentration and pH of the solutes. Furthermore, we found that the very low ion diffusivity causes long measuring times, and thus a large risk for errors from contamination, leakage, or minor defects in the samples.

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Epoxy Mold Compounds (EMC) are used to protect integrated circuits (IC) from environmental influences, with one of these influences being moisture ingress, causing corrosion. To obtain the needed thermal and mechanical properties EMCs require a high loading of (silica) fillers, introducing a large amount of interface. While silane coupling agents promote good binding, they have shown to introduce an interphase volume that exhibits a faster moisture transport between epoxy and SiO₂ in glass fiber filled epoxy. In this work, we investigate if such an interphase volume is also introduced by the filler particles in EMC and if it influences the moisture diffusion coefficient of the composite. We compare moisture uptake measurements performed by dynamic vapor sorption (DVS) with predictions from effective medium theory, as well as with numerical simulations based on micro-CT scans of our samples for a model epoxy system containing different filler levels and commercial EMC samples with two different filler levels. From the measured DVS data, we observe an effective diffusion coefficient, that is higher than predicted for an absence of any interphase for both the EMC and the model system. This suggests that an interphase layer should be present.

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In general, packaging materials which encapsulate light emitting diodes (LEDs) and microelectronic devices offer barrier protection against several environmental hazards such as water and ionic contaminants. However, these encapsulants may provide pathways for water and ionic contaminants to reach the metal/polymer interfaces and provoke local corrosion of electronics, which is a major reliability concern for polymer encapsulated LEDs and microelectronics. As the water and corrosive constituents play a crucial role in their reliability, water uptake kinetics, interfacial ion transport and delamination behaviour of silicone coated copper model system, mimicking a typical microelectronics packaging system, is explored in the present work. Electrochemical impedance spectroscopy (EIS) integrated with attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy studies revealed that water diffusion inside the silicone network is Fickian in nature and the evolution of the observed time constants are related to the diffusion and interfacial reactions. A decrease of impedance magnitude with time was observed in EIS measurements concurrently with water absorption bands shifting towards lower wavenumber in ATR-FTIR measurements, implying the growth of strong hydrogen bonding between water molecules and the silicone network. The estimated diffusion constant of water using the capacitance method was in the order of 7 × 10-12 m2 s−1 and the water absorption volume fraction was in the range of 0% to 0.30%. Scanning Kelvin probe studies elucidated the ion transport process occurring at the silicone/copper interface in a humid atmosphere. The interfacial ion transport process is controlled by the interfacial electrochemical reactions at the cathodic delamination front and the estimated average delamination rate is 0.43 mm h-1/2. This work demonstrates that exploring ion and water transport in the silicone coating and along the silicone/copper interface is of pivotal importance as part of a detailed reliability assessment of the polymer encapsulated LEDs and microelectronics.@en

The reliability of LEDs decreases in moist environments. One potential gateway of moisture ingress, reducing the product lifetime is the lens. In white LEDs, phosphor particles are embedded into the optical silicone of the lens to convert the blue light emitted by the diode down in frequency and achieve a light output that appears white. In this study, the influence of these phosphor particles on the moisture sorption, permeation and diffusion in optical silicones is investigated by comparing two silicone resins that are commonly used in LEDs, both with and without the addition of phosphor particles. The results of two methods are compared: the wet-cup method and a gravimetric approach of dynamic vapour sorption (DVS). Diffusion coefficients between 20 and 75 °C are reported as well as sorption isotherms, activation energy and sorption enthalpy. It is concluded that the addition of phosphor particles only has a very small impact on the moisture transport properties of the silicones.@en

Tarnishing of the reflective silver layer in LED packages is an important failure mechanism, leading to both a decrease in luminous flux by up to 75% and a change in color spectrum.

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