There were several articles around that... It was a very special manufacturing procedure, something that is hard to copy without the special hardware. And App

There were several articles around that... It was a very special manufacturing procedure, something that is hard to copy without the special hardware. And Apple bought all that supply. You couldn't get the production line to do it... (IIRC, bit my memory may fail me on that. Please Google it, I would be interested in rereading it!)