People all over the world mail their broken iPhones to microsoldering specialist Jessa Jones. Aided by powerful microscopes and precision soldering irons, experts like Jessa pluck tiny chips off logic boards, swap them for new ones, and resurrect devices over which AppleÂ’s Genius Bar would say a eulogy.Jessa can fix practically anything. But these days, she spends most of her time fixing just one thing. Because every single month, more and more iPhone 6 and (especially) 6 Plus devices show up at her shop, iPad Rehab, with the same problem: a gray, flickering bar at the top of the display...