I think GPs idea was to make the PCB no longer long, but have two smaller PCBs with flat flex between them. Then when the phone bends, the PCBs wont bend but let the flat flex take the stress instead.
> (To see the problem, place a coin on a credit card and bend the card - note that the coin no longer touches across its whole surface)
Now cut the card in half and connect it with half a cm of tape and bend it - the two halves will be flat and you'll get a V shape instead. Put the coin on one side and no problem.
I guess it depends on how much open space is in the phone or if the whole PCB is completely flush with the bent casing.
(Look at the smallest .04 x .02 resistors on there!)
More cynically, the PCB only needs to be made as bend-resistant as the display: you don't care about your BGAs if you've cracked the screen.
The article does mention a fix the repairers have been applying, involving the "sticker shield" - not shown in the hero image, it's the metal casing that's been removed and you can see the edges of. That's a few mils off the surface of the PCB and evidently stiffens it enough (on the I-beam principle of operation) to avert the problem.
[1] http://www.theverge.com/2015/9/12/9315471/iphone-6s-new-alum...
This is not going to be as flat as possible, but it let's you play with some flex vs thin and completely stiff.
https://d3nevzfk7ii3be.cloudfront.net/igi/DSCkX6EfcARJYOHa.h...
The proposal is just to do a little more of that.
There are already polymer glue solder alternatives. They are nowhere near as good as solder, however.
The normal solution is to make the PCB stiffer... Fundamentally a long flat thin object is going to be bendy or brittle
What about changing the layout, such that you can introduce many, many voids in the circuit board? If you can divide up the board into many separate "compartments" then each individual segment can be proportionally stiffer and less flexy. (Long, thin things are "bendy" because the material can act as a lever against itself, so many short stubby things can be very stiff locally.)
(To see the problem, place a coin on a credit card and bend the card - note that the coin no longer touches across its whole surface)
The normal solution is to make the PCB stiffer (thicker, or invent something better than FR4), or to make the overall casing stiffer. Either by changing materials or changing the aspect ratio. Fundamentally a long flat thin object is going to be bendy or brittle. The older iPhones that were smaller with glass front and back were an extremely good design from this point of view.