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

Abstract

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.

Designing Safer Solvents to Replace Methylene Chloride for Liquid Chromatography Applications Using Thin-Layer Chromatography as a Screening Tool

“…For each glass vial and dissolution time, the solubility performance of each solvent was labeled as "Dissolved" if the API was fully dissolved or "Undissolved" if the API was not fully dissolved. This protocol was modified from a prior study measuring the solubility of a conformal coating in various solvents [10].…”

“…The Hansen Solubility Parameters (HSP) theory was used to determine the solubility of the tested APIs. HSP theory can be used to predict which solvents may be able to dissolve target solutes and is an efficient method to rapidly identify safer and effective alternatives to toxic solvents [10,12,21]. The HSP approach is based on three distinctive forms of inter-molecular force: Dispersion forces (D), Polar forces (P), and Hydrogen bond forces (H).…”

“…Solubility parameters are numerical values that represent the degree of solubility for a specific solvent. The Kamlet-Taft parameters, Hansen solubility parameters (HSP), and the Schneider solubility triangle are three such systems that have been used to evaluate the solubility of organic molecules such as APIs [10][11][12]. The Kamlet-Taft parameters utilize Solvatochromic data based on Solvatochromism, a phenomenon where specific compounds (probes) adsorb different wavelengths of light and thus show different colors [13].…”

“…With an extensive database of thousands of solvents, the system allows for the quick identification of many potential solvent alternatives for testing. HSP theory has previously been used to identify effective solvents for the dissolution of polymeric materials including polystyrene, polycarbonate, and styrene acrylonitrile [10]. For example, Lu et al (2021) used the HSP theory to find alternative solvent replacements for DCM to dissolve acrylic coatings on electronics [10].…”

“…HSP theory has previously been used to identify effective solvents for the dissolution of polymeric materials including polystyrene, polycarbonate, and styrene acrylonitrile [10]. For example, Lu et al (2021) used the HSP theory to find alternative solvent replacements for DCM to dissolve acrylic coatings on electronics [10]. It has also been used to identify the miscibility between a pharmaceutical and coformer for indications of cocrystal formulation [16].…”