Production of Apple's next iPhone, commonly referred to be the iPhone 5S and is scheduled to be unveiled on September 10, could reach only 3-4 million units in the third quarter of 2013 compared to 10 million units as originally planned due to a delay in production of fingerprint sensors needed for the iPhone 5S, according to industry sources.

　　Mass production of the fingerprint sensors was originally scheduled to begin in May at Taiwan Semiconductor Manufacturing Company (TSMC) and then to be packaged at Xintec, a TSMC subsidiary, the sources indicated.

　　However, the production of the sensors has been delayed due to issues related to integration between iOS 7 and fingerprint chips, as well as a low yield rate at packaging firm Xintec, the sources revealed.

　　An engineering team composed of engineers from Apple and TSMC has been dispatched to Xintec recently to help ramp up the yield rate for the packaging of fingerprint sensors, revealed the sources, adding that the supply chain will be able to start volume production of fingerprint chips at the end of August.

　　Production of the iPhone 5S are likely to ramp up to 28-30 million units in the fourth quarter of 2013 thanks to sufficient supplies of fingerprint chips, the sources noted.