FPC coils are thinner and smaller in size but have larger resistance and reduced efficiency.
In 2017, the iPhone uses FPC coils with 7.5W fast charge, considering the factors such as efficiency loss. The charging speed is actually slightly slower than the 5W wired charging. Because the FPC resistance is large, even if you want to achieve fast charging, the power should not be too high to avoid overheating. Apple chooses 7.5W, which is actually trying to achieve the same level as wired charging. Speed, and can not have overheating, but also want to consider the RX module thin and light.
The copper wire coil would be thicker but allow for higher power and better charging efficiency.
According to industry sources, the cost of the copper wire coil is lower than that of the FPC. Since high power and high efficiency are the trend of wireless charging, it is expected that at least one of the three iPhones in 2018 will abandon the FPC to adopt a copper coil solution to achieve the above goal, and because the copper wire coil resistance is small. It can also offset the thermal effects generated by the increase in power.
Apple is widely expected to unveil its new iPhones this September. You can follow iClarified on Twitter, Facebook, Google+, or RSS for updates.