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0 pointskalleboo9y ago0 comments

> Fundamentally a long flat thin object is going to be bendy or brittle

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.

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pjc509y ago

Doable, and might even be a good idea for long thin PCBs, but it messes with both your routing and placement and therefore consumes PCB area. Also upsets your controlled-impedance traces. And adds an extra assembly step. To estimate doing this, take the PCB image and Paint and try to clear a 3mm gap in it. How many components do you have to move? Do you have to make the whole thing 3mm longer? Aren't most of them decoupling capacitors that must be kept right next to their corresponding IC?

(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.

kallebooOP9y ago

And after all this discussion I'd bet Apple already fixed this with the 6s by simply stiffening the actual case...

pilsetnieks9y ago

They did, they even said in the keynote that they're using a new aluminum alloy[1], and it's mentioned on the website as well[2]

[1] http://www.theverge.com/2015/9/12/9315471/iphone-6s-new-alum...

[2] https://www.apple.com/iphone-6s/design/

yincrash9y ago

In the article, it's mentioned that in the 6S, the chip location has moved to where it's not near the most flexed area.

Retric9y ago

Alternatively, let the case flex slightly and have the board float in a gap attaching to the center as apposed to the edges. You still need to connect the buttons to the main board, but that's not a major issue. basically: [---|--|---] with [ ] as edge, -- as board and | as attachment points.

This is not going to be as flat as possible, but it let's you play with some flex vs thin and completely stiff.

Waterluvian9y ago

But you'd have to make the hundreds of broken connections between the boards you split. So isn't that a really delicate ribbon cable?

talsit9y ago

Not really, you do the split according to functionality, not just a straight split. CPU/memory on one side, WiFi/BT/Baseband on the other.

quantumhobbit9y ago

So something like Google's project Aria that they just cancelled with separate modules for each function. Only not user serviceable.

mikeash9y ago

Like any phone. They all have separate components and boards connected with ribbon cables. You can see the iPhone 6+'s various ones here:

https://d3nevzfk7ii3be.cloudfront.net/igi/DSCkX6EfcARJYOHa.h...

The proposal is just to do a little more of that.

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