Foxconn Electronics, the world’s largest contract manufacturer of consumer electronics, has already admitted that Apple’s iPhone and iPad are very hard to assemble because of extremely dense design. However, even previous-gen products from Apple are incomparable to the new iPhone 5, as the latter is the most complex device that Foxconn has ever made, the company said.

“The iPhone 5 is the most difficult device that Foxconn has ever assembled. To make it light and thin, the design is very complicated. It takes time to learn how to make this new device. Practice makes perfect. Our productivity has been improving day by day,” said a representative for Foxconn, who declined to be named, in an interview with the Wall Street Journal.

The demand for Apple iPhone 5 is very high and while Foxconn is the only company in the world that can produce such a complex device in tens of millions of units per quarter, it is not enough to fulfill demand, partly because of the fact that yields early in the lifecycle of any gadget are usually lower than desired. This is not the first time when Foxconn publicly or semi-publicly complains about yields of new Apple products early in the lifecycle.

After consumers discovered that the black version of Apple iPhone 5 can come with damages or scratches on the case, Foxconn and Apple imposed new quality-related requirements so that to ensure that the end-user gets smartphones without scrapes. After stricter quality requirements were imposed, Foxconn faced strikes at select facilities. Unfortunately, since there is a global issue with the black coating, consumers will easily damage their iPhones themselves.

“It is always hard to satisfy both aesthetic needs and practical needs,” said the rep for the contract maker.

Foxconn currently assembles the iPhone 5 for Apple at its plants in Zhengzhou, central China, and in Guan Lan, in southern China.

Tags: Apple, iPhone, Foxconn, Hon Hai