If you don't want to remove components and go through sandpaper-wash-scan process using Cheap (~$500 off ebay), used dental x-ray machine with film pressed to the PCB (~$30 box of Fujifilm). Developed film should have low granularity and can be scanned and magnified to great extent later. Some people tried to use SLR cameras with these dental machines, but I think film gives better results especially with those cheap x-ray machines. I guess I don't have to mention that you should pint machine down and be like 5meters away in another room when you push the button (they usually come with remote).
With sanding it is easy to go wrong and remove just a bit too much and it is very dusty and hard to remove layers of PCB evenly.