As mentioned above, a coating is not particularly helpful, but it is better than nothing. The problem is also that no one really knows how whiskers are formed and the mechanism, so it is a lot of trial and error as to what promotes and what prohibits them. If you have chemically deposited tin, you have to remelt it to reduce the risk of whiskers. In addition, components are often only tin-plated with pure tin, they are re-alloyed in a tin-lead pot, even the leads of components are always re-tinned. In addition, the gold must be removed from the soldering surfaces.
More details are often a bit proprietary