One of the reasons Shenzhen is iPhone assembly city is because there are so many little ancillary providers around for all the surface mount components that are

One of the reasons Shenzhen is iPhone assembly city is because there are so many little ancillary providers around for all the surface mount components that are common on PCBs. If I'm running a PCB assembly line and my primary supplier of surface mount capacitors is the only guy within 50 miles, where do I get replacements from if something happens like there's a fire in his factory and it goes offline? In Shenzhen you go to the next guy down the street who's selling the exact same part. So instead of being down for three days while finding a way to get an additional supplies airlifted in you can have probably have another supplier up and going before you run out of what's left in the lean manufacturing pipeline. Before making the move to any labor market concerns like those have to be addressed or at least the risks mitigated. That takes time and costs serious money. As the SMT industry ramps up in more locations it'll be easier to diversify assembly locations.