If it weren't for the redesigned Home button and larger flash, the iPhone 5S and iPhone 5 would look like identical twins, at least on the outside. Take the new 5S apart, however, and the differences are more apparent -- even if only slightly so. And although it isn't the easiest phone to repair, with the right tools and a little patience, it is possible.
Cracking Open observations
Opening the phone still requires special tools: With the iPhone 5, Apple ditched the twin-glass panels in favor of a wraparound metal case and single, front glass panel. This change. The iPhone 5S shares this same basic design. Unfortunately, it also has the same tamper-resistant screws along the bottom edge. You'll need a special pentalobe screwdriver to remove them.
Once you've removed the outer screws, you can lift off the front panel. I used both a suction cup and several plastic tools to pop it loose. Interestingly, I found the iPhone 5S' front glass more difficult to remove than the iPhone 5's panel. The pair of metal clips hold the right side of my iPhone 5S' panel to the case were extremely tight. And it took me nearly 20 minutes to remove the front panel.
Beware the Home button's new wire: The iPhone 5's Home button was connected to the phone's internal circuitry with a simple pressure contact. The iPhone 5S' new fingerprint-scanning Home button uses a thin ribbon cable. When removing the front panel, you must be extremely careful not to damage this cable. And you'll need to disconnect it before completely removing the front glass.
Familiar internal hardware layout: The iPhone 5 and 5S share the same basic internal hardware layout. There's a speaker and docking connector assembly at the bottom, battery along the left side, motherboard along the right, and the rear camera and flash at the top. Attached to the front panel are the display, front camera and sensors, earpiece speaker, and the Home button.
Home button can be removed: Despite the new Home button being able to scan fingerprints, it can still be removed and replaced.
Slightly higher-capacity battery: The iPhone 5S has a 3.8V, 5.92Wh, 1,560mAh battery compared to the iPhone 5's 3.8V, 5.45Wh, 1,440mAh unit.
No battery removal pull tab: Unlike the iPhone 5, there's no pull tab mechanism under the iPhone 5S' battery. You'll need to pry the battery away from the case with a thin tool, being extremely careful not to puncture the cell in the process.
iSight camera covered with rubber flap: The new rear-facing, iSight camera is covered with a very thin, rubber flap. This flexible strap is new to the iPhone 5S. It is secured to the right side of the camera's mounting bracket and when it's folded over the camera and attached to the bracket's left side, it appears to help hold the camera in place. It's also possible that it helps cushion the camera or dampen vibrations, I don't know for sure.
Main board shields soldered in place: As on the iPhone 5, the EMI/RFI shields that cover the iPhone 5S' motherboard are soldered to the board. As I wanted to put this phone back together in working order, I refrained from breaking out the soldering iron and snips.
Case components are held in place with screws/adhesive: The phone's vibration motor, speaker assembly, headphone jack, Lightning connector, and lots of connector cables are attached to the case with either screws, adhesive, or both. If any of these components were damaged, removing and replacing them wouldn't be difficult. But I didn't want to risk damaging them during removal. So, I left them in place.
Two simple design changes would simplify repairs
With its new 64-bit A7 processor, M7 motion coprocessor, improved camera, and fingerprint-reading Home button, the iPhone 5S is a solid upgrade to the line. And I'm glad that Apple didn't make the phone any more difficult to crack open than its predecessor. Unfortunately, the iPhone is still one of the most difficult-to-repair flagship smartphones on the market.
If Apple engineers wanted to make the iPhone more DIY repair-friendly, which I doubt they really do, they should take a few cues from Samsung's Galaxy S4 and Galaxy Mega. First, stop using tamper-resistant screws on the outside and settle on a single length for the screws on the inside. Second, stop gluing nearly every ribbon cable and internal component to the case. A little adhesive is fine, but not everything needs to be glued in place.
Perhaps Apple will take my suggestions to heart and include them in next year's iPhone 6 -- along with a larger screen.