Apparently it’s not easy to assemble one of the world’s thinnest and lightest smartphones. Who would have guessed?

The iPhone 5 is almost 20 percent thinner than iPhone 4, at just 7.6 mm or .3 inches, and it’s 20 percent lighter than the previous model as well. Plus, those diamond-cut chamfered (sloping) angles and glass inlays are not easy to get just exactly perfect.

That’s why Foxconn execs are calling the iPhone 5 “the most difficult device” that the company has ever assembled. And that’s the key reason why today, a month after its initial introduction to the market, iPhone 5 is still in limited supply.

iPhone 5 launched in late September, selling two million in 24 hours, and five million in its first weekend, and continuing to sell briskly. Shipping delays on Apple’s website today are between three and four weeks, meaning that supply is still significantly constrained.

Foxconn did say that the company was improving every day, getting better and faster.

One of the challenges has been build quality. iPhone 5 is partially made of aluminum, which — though it’s lighter — is also softer than the steel in the iPhone 4 and 4S. That’s caused some issues in brand-new phones, especially black models, with some reports saying that half of all phones were scratched out of box, or shortly thereafter. According to Apple exec Phil Schiller, that was “normal.”

When it was just launched, Schiller called iPhone 5 “the most beautiful consumer device that we’ve ever created,” and a “jewel-like device.”

Jewels, apparently, take time to manufacture.

photo credit: LJR.MIKE via photopin cc