"In this high-temperature process, plastic is injected into precisely milled channels in the aluminum enclosure where it bonds to micro-pores in the aluminum surface," the document reads. "After the plastic cools, the entire enclosure is finished with a precision CNC machining operation, yielding a seamless integration of plastic and aluminum into a single, strong enclosure."
The process leads to the formation of small vertical bands or "splits" in the sides of the iPad and turns parts of the enclosure into cellular antennas. Apple explains that these splits, coupled with the new tablets' straight edges -- previous versions, as you know, have more rounded ones -- may create "subtle deviations in flatness" that are only visible from certain angles. Cupertino stressed that these slight bends are imperceptible during normal use and they don't affect the enclosure's strength or the tablet's performance. Plus, it said slight bends will not change over time, which hopefully means that they won't get worse
Here, Cupertino also reiterated that it "allows for no more than 400 microns of deviation across the length of any side." That's less than one millimeter of variance allowed for the gadget's flatness. It's encouraging customers who believe their devices don't meet that standard to contact Apple Support.