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Presuming that manufacturers aren't about to stop trying to make thinner and thinner devices... Is this class of issues correctable (to a degree) with a change

by Mtinie 10y ago

Presuming that manufacturers aren't about to stop trying to make thinner and thinner devices... Is this class of issues correctable (to a degree) with a change in the design of those components -- for example, proactively splitting the board at the point that the fissure is likely to appear and coupling it in a flexible way -- or is this a materials science concern where we need to find new methods to build the components' substrates so they are innately flexible?

pjc50 10y ago
You can't split the board, it's the solder joints on the surface that are the problem. So far as I know there is no flexible soldering technology, and creating one would be pretty extreme materials science. (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.
- kalleboo 10y ago
  > 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.
  - Waterluvian 10y 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?
    - talsit 10y 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.
      - quantumhobbit 10y ago
        So something like Google's project Aria that they just cancelled with separate modules for each function. Only not user serviceable.
        mikeash 10y 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.huge https://d3nevzfk7ii3be.cloudfront.net/igi/DSCkX6EfcARJYOHa.h... The proposal is just to do a little more of that.
  - pjc50 10y 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.
- snowwrestler 10y ago
  Simply making the cross section of the iPhone rectangular again would go a long way toward stiffening it up. The curved edges are beautiful to see and great to hold, but they're quite a bit weaker as beams.
- Retr0spectrum 10y ago
  It would probably be very hard/expensive to manufacture, but you could have something like an LGA socket, with the springy contacts soldered to both the IC and the PCB. Thay way, the board can flex all it wants without overly stressing the solder joints.
- zaroth 10y ago
  Do they add any flexibility around the mounting points? So the PCB can continue to lay flat, while the case flexes ~1mm around it?
- stcredzero 10y ago
  So far as I know there is no flexible soldering technology, and creating one would be pretty extreme materials science. 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.)

by Mtinie 10y ago

pjc50 10y ago

You can't split the board, it's the solder joints on the surface that are the problem. So far as I know there is no flexible soldering technology, and creating one would be pretty extreme materials science. (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.

kalleboo 10y ago
> 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.
- Waterluvian 10y 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?
  - talsit 10y 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.
    - quantumhobbit 10y ago
      So something like Google's project Aria that they just cancelled with separate modules for each function. Only not user serviceable.
      - mikeash 10y 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.huge https://d3nevzfk7ii3be.cloudfront.net/igi/DSCkX6EfcARJYOHa.h... The proposal is just to do a little more of that.
- pjc50 10y 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.
snowwrestler 10y ago
Simply making the cross section of the iPhone rectangular again would go a long way toward stiffening it up. The curved edges are beautiful to see and great to hold, but they're quite a bit weaker as beams.
Retr0spectrum 10y ago
It would probably be very hard/expensive to manufacture, but you could have something like an LGA socket, with the springy contacts soldered to both the IC and the PCB. Thay way, the board can flex all it wants without overly stressing the solder joints.
zaroth 10y ago
Do they add any flexibility around the mounting points? So the PCB can continue to lay flat, while the case flexes ~1mm around it?
stcredzero 10y ago
So far as I know there is no flexible soldering technology, and creating one would be pretty extreme materials science. 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.)