Removing Acrylic Conformal Coating with Safer Solvents for Re-Manufacturing Electronics

Conformal coating is typically composed of polymeric film and is used to protect delicate electronic components such as printed-circuit boards. Without removing conformal coating, it would be difficult to repair these complicated electronics. Methylene chloride, also called dichloromethane (DCM), has a widespread usage in conformal coating stripper products. The high toxicity of DCM increases human health risk when workers are exposed to DCM during the conformal coating removal processes. Therefore, the replacement of DCM would be beneficial to greatly improve the overall safety profile for workers in the electronics and coating industries. This research identified and evaluated alternative chemicals for replacing DCM used in acrylic conformal coating stripping operations. The solubility of an acrylic conformal coating was measured and characterized using Hansen solubility parameters (HSP) theory. Coating dwell time tests using various solvent blends verified the accuracy of the created HSP solubility sphere. A data processing method was also developed to identify and screen potential alternative solvent blends in terms of safety, toxicity, and cost-effectiveness. The identified safer solvent blends were demonstrated to provide equivalent stripping performance as compared to DCM based coating strippers within an acceptable cost range. The results of this research will be of value to other types of conformal coatings, such as silicone and polyurethane, where DCM is commonly used in similar coating stripping operations. By safely removing conformal coating, delicate electronics would be available for re-manufacturing, enabling a circular economy.

Narrowband transmission filters based on resonant waveguide gratings and conformal dielectric-plasmonic coatings

Nanostructured filter arrays on image sensors are promising for miniature spectrometers and spectral imagers. In this work, we report on resonant waveguide gratings fabricated by UV nanoimprint lithography and conformal dielectric-plasmonic coatings. Optical measurements in accordance with numerical simulations report on a resonance bandwidth of 20 nm in transmission in the visible range. The impact of cladding thickness and filter lateral size on the resonance properties is investigated with the help of numerical calculations. Finally, it is shown that the proposed geometry based on conformal coatings has a very efficient blocking rate compared to other nanostructured filter approaches.

A Coating Strategy for Coevolving Photocatalysis to Stabilise Visible-Light Absorbing Semiconductors

Semiconductors of narrow bandgaps and high quantum efficiency have not been successfully utilised for coevolving photocatalysis despite the widely demonstrated protective coating schemes. Herein, we showcase a general strategy of using conformal coatings and cocatalysts energetic properties to transform CdS powders and GaInP2 films into stable and efficient photocatalysts for coevolution of H2 and reversible redox couples. A scalable redox-mediated solar water-splitting reactor was constructed, regenerating the redox mediators while evolving O2 in a separate compartment. Distinct from the single direction of charge transfer found with conventional photoelectrode stabilisation, the coating herein allows both photo-excited electrons and holes to spatially separate and inject simultaneously to the respective reductive and oxidative sites. With TiO2 stabilisation, CdS particles produced H2 continuously for 150 hours. Under simulated sunlight, solar-to-hydrogen (STH) efficiency of 5.9% and 9.4% can be achieved for the CdS and GaInP2 panels, respectively, by stacking multiple panels and matching the rate of redox regeneration to that of H2 production.

A New Halogen-Free Parylene for High Performance and Reliability of Microelectronics in Harsh Environments

The rapid growth and adoption of microelectronics around the world has resulted in an increased awareness of potential environmental issues related to their use and disposal. Halogens, which have had various uses in microelectronics over the years, are known to emit toxic and corrosive gases during the disposal of electronic waste. Many organizations have applied pressure to the electronics industry to eliminate halogens completely (e.g., fluorine, chlorine, and bromine) from their products. Among the various efforts toward environmentally friendly products, making electronics completely halogen-free has gained significant attention, particularly in Asia and Europe. This initiative even impacts conformal coatings worldwide, on which most electronics rely for their long-term protection, reliability, and high performance against water and other corrosive harsh environments. Among the various coating options, the parylene family of conformal coatings offers beneficial properties to the microelectronics, improved over many properties offered by common epoxies, acrylics, urethanes, and silicones. Although parylene N is the only commercially available parylene that does not contain any halogens, its barrier performance against moisture and other corrosive chemicals is not quite as robust as the other parylenes. To meet the industry’s current and future requirements, a new halogen-free parylene, ParyFree®, has been developed. This study introduces a new parylene type to the microelectronics industry and shares the characterization and qualification results of ParyFree® parylene conformal coating for the protection, reliability, and robust performance of microelectronics. Testing on the new coating includes IPX water resistance, corrosion resistance, and qualification per IPC-CC-830B.