We've got some PCB's in receiving inspection that has these little nodules in plating inside all of the barrels. These are microwave PCB's and have almost all of the surface area on both sides covered with with solid metal planes, and no solder mask.
Is this a normal appearance? The plating inside the barrels look to be a much lighter color than the plating on the surface planes on the PCB...almost silver looking.
I don't know for sure what I'm looking at, maybe someone could help me. Could it be electro-plated Tin? I'm being asked if this is okay...I don't know if it is or not. I know that nodules per se' aren't rejectable unless it reduces the hole diameter. But the surface appearance of the plating is something I've not seen before.