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74 SMT007 MAGAZINE I JULY 2021 and humid environments [8,9] . Effective con- formal coatings protect the underlying metal well. e paper gives a detailed description of the proposed test method for characteriz- ing conformal coatings. e test method was evaluated at four temperature-humidity condi- tions on three different coatings (acrylic, sili- cone and ALD). A somewhat modified version of the iNEMI flowers of sulfur (FoS) chamber was used as the environmental chamber [10-13] . Experimental Procedure and Results e test vehicle used for evaluating confor- mal coatings consisted of a serpentine thin film of copper or silver, 800 nm thick, sputtered on oxidized silicon die 15x15 mm. e die was glued to a prototype printed circuit board (PCB). One end of each of four L-shaped con- nector pins were soldered to the PCB and the other ends were joined using silver epoxy to 4-point contact pads of the serpentine thin film. e silver epoxy we chose required 140°C bake for one hour in flowing nitrogen gas. Nitrogen gas blanket avoids oxidation of the metal thin film. e L-shaped pins soldered ends were further connected to a receptable connector also soldered to the PCB. A sche- matic cross section of the serpentine thin-film test vehicle is shown in Figure 1 along with a photograph of the thin-film setup. e thin-film setups were conformally coated with the coatings under test. Fine wire, 50 mm-diameter, T-type thermocouples were by forming low resistance bridges (electri- cal short circuits) when the relative humidity in the air is above the DRH of the particulate matter. As data centers proliferate worldwide into geographies with high levels of pollution and high relative humidity, the use of confor- mal coatings becomes necessary especially for mission-critical and military hardware [1-5] . Another factor making conformal coat- ings necessary is the decreasing feature sizes of components. With decreasing feature gaps that dust particles and corrosion product par- ticles can more readily bridge, conformal coat- ings need serious design considerations. Commercially available conformal coatings cover a wide range of price, ease of application, and effectiveness in protecting the underlying metal from corrosion. e industry standard means of evaluating conformal coatings is to apply them to the actual hardware and deter- mine the mean time to failure of the coated hardware. is means of testing is very incon- venient and slow. Even where the corrosion of the coated components can be monitored, such as in the case of surface-mount resistors, it can take more than a year to evaluate a coat- ing and that too under very limited conditions of temperature, humidity and environmental corrosivity [5-7] . A convenient way of evaluating conformal coatings is to coat thin films of copper and sil- ver and to monitor the corrosion rates of the coated thin films while subjected to corrosive Figure 1: a) Serpentine thin-film setup. In earlier works the bottom thin films were to heat the top film; b) In this work the bottom films were not used. a) b)