SWRU553A September 2019 – February 2020 AWR1243 , AWR2243
All of the 77-81GHz RF and 20 GHz LO transmission-line and antenna structures on this design have been left exposed on the top soldermask layer. An immersion silver finish is applied to these solder-mask free regions to protect the underlying copper. The immersion silver finish provides the RF structures with a more simple and controlled high-frequency finish compared to solder mask.
However, the immersion silver finish is also prone to oxidation in an open atmosphere environment. This oxidation causes the surface around the antenna region to blacken or tarnish as a layer of silver-oxide forms. To avoid this effect, store the PCB in an ESD cover and keep it at controlled room temperature with low humidity conditions. It should be noted though that transmission lines and antenna which are tarnished will not experience RF performance degredation.
All ESD precautions must be taken while using and handling the EVM.