Quote Originally Posted by Kiske View Post
I worked as an repair engineer at a big international company and worked with motherboard sized circuit boards that has up to 16 layers (normal motherboards has 4-6).

Bad solder balls generally dont really impact the working performance gradually but more like a on/off switch. It either works or not.
I can also say that bad solderballs is by far the most common problems on modern circuit boards.
16 layers? that sounds like it would have to be both "very specific" and very complex to design.