Question: We have some RF components that are “bottom only” and the castellations are gold. Is there anything we can do about the 75% gold removal rule?
Answer: If you check J-STD-002, you will see the methods to check for solderability of those components. Basically they have to be introduced to the solder pot at an angle and then removed from the solder with a sweeping motion to prevent icicles from forming on the termination pad. This can be a very time consuming process if there is a large quantity of components.
I would suggest finding a company that tins components as their business as they would automate this process and provide you with the results you are looking for on those bottom only terminations and castellations.