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JULY 2021 I SMT007 MAGAZINE 81 Figure 11 summarizes the corrosion rates of bare (uncoated) copper and silver serpentine thin films and the corrosion rates of thin films coated with acrylic or silicone. Atomic level deposition (ALD) coated thin film corrosion rates were not included because their corro- sion rates were within the limits of the experi- mental error. Discussion Figure 11 summarizes the corrosion rates of copper and silver serpentine thin films coated with acrylic or silicone and compares them to corrosion rates of bare (uncoated) cop- per and silver films. Atomic level deposition (ALD) coated thin film corrosion rates were not included because their corrosion rates were too low; they were within the limits of the experimental error. Acrylic coating protected copper thin films from corrosion to some extent. In 40°C FoS environment, the corrosion rate of acrylic- coated copper was two orders of magni- tude less compared to bare copper. Increas- ing the FoS environment temperature to 50°C increased the acrylic coated copper thin film corrosion rate by approximately an order of magnitude. Of the three humidity test condi- tions (15, 31 and 75%), the highest corrosion rate of acrylic-coated copper was at 75% rela- tive humidity. Acrylic coating did not protect the underlying silver thin films. An increase in temperature from 40 to 50°C did increase the silver corrosion rate somewhat. Silicone coating provided no corrosion pro- tection to the underlying copper thin films. At 40°C and 15% relative humidity, silicone coating provided some corrosion protection to silver thin films. At 50°C, silicone coating provided no corrosion protection to the under- lying silver thin film, over the whole range of relative humidity tested. Figure 12 gives visual qualitative evidence of the extent of the underlying metal corro- sion in agreement with the metal corrosion rates plotted in Figure 11. e ALD coat- ings clearly provided excellent corrosion pro- tection to the underlying Cu and Ag films. Acrylic coating protected copper but not sil- ver, in agreement with Figure 11. Silicone did not protect Cu or Ag films, again in agreement with Figure 11. Another interesting observa- tion is that Ag 2 S whiskers grew on the bare silver thin films and that these whiskers were prevented from growing by the three confor- mal coatings. Figure 12: Photographs of serpentine thin films after the 5.32-day test at 50°C and 31% relative humidity.