The biggest hurdle has reportedly been the flexible printed circuit board (FPCB) for the antenna due to its increased complexity.
Special materials, recipes, design, processes, equipments and tests are required for antenna FPCB, as the specifications for iPhone X antenna (supplied by Amphenol (US)) are higher than those of iPhone 8 and only Murata (JP) and Career Tech (6153 TT, NT$30.1, NR) can meet Apple's requirements. Murata (originally with a 60% order allocation or higher) won't be able to resolve its issues before 2Q18, and thus has been fully replaced by second supplier Career. We believe Career will ramp up in November, as capacity expansion takes time, and its materials, recipes, design, processes, equipments and tests are different from those of Murata.
Another bottleneck is said to have been the FPCB for the wide angle rear camera lens. Unlike dual camera phones from Samsung and Huawei, the iPhone X uses separate PCBs for the wide angle and telephoto lenses. Supplier Interflex has apparently struggled with quality issues on the part.
Finally, a third bottleneck was the TrueDepth camera's infrared dot projector, known as the 'Romeo' component. Kuo says that previous design issues have been addressed and the 'worst is behind us'.
KGI is cutting iPhone X shipment estimates for the fourth quarter to 25-30 million units, down from 30-35 million. Shipments are expected to 'pick up markedly' in the first quarter of 2018.