Guest
[Entry]
"A lot of questions here and few answers. Here's my take after gauging the repair community and doing some screen replacements myself in our store:
FACT 1: the home button has an embedded chip on the backside of the button. To use simple words, this chip stores the key that allows the board to recognize it. Thus if you use a different home button, whether original or aftermarket, the board will not recognize the home button.
As a result, the non-native home button will not be able to scan the finger print and will not react to any input. The phone will act as if it's missing the home button completely. A message will also appear ""Touch ID cannot be activated."" The only way to have the home button function in this case is by using the assistive touch aka virtual on-screen home button. And the only way to wake the phone would be by using the power button or raise to wake.
FACT 2: Apple - and only in an Apple owned Apple Store, but starting to show up at some AASPs as I write this - can replace the screen and home button and reprogram the new home button and pair it with the board/phone. If a third party repair shop or DIYer damage the home button during repair, or the owner breaks it somehow, or it fails, the only way to have a home button function restored at this date is to take it to an Apple Store or one of those AASPs that are starting to receive the pairing machine.
FACT 3: Apple did nothing to prevent replacing screens with OEM or aftermarket parts. If you replace the screen and transfer the home button without damaging it, everything will work normally. But expect cheap parts to perform poorly. So invest in good quality parts from reputable vendors. Replacement screens should be as close as possible to Apple screens in terms of : color fidelity, backlight, touch, force touch, durability, frame lifting, frame finishing.
FACT 4: many replacement screens have a defective home button interconnect cable. When the home button works with the original screen but not the replacement screen, it is a bad screen and you need to warranty it or replace it. And yes a whole batch can be defective.
However, sometimes while disassembling the iPhone, you damage the home button extension cable on the broken screen, then you try to fit a bad replacement part. Now home button doesn't work on neither the old nor the new screen, and you assume the home button itself has failed. Well no, sometimes it hasn't.
FACT 5: you may damage the home button and completely lose all functions, specially if you tear the home button cable. Some very patient people resolder the pieces together. I would rather fit an original broken screen together with the damaged home button and send them to an Apple Store for complete screen assembly replacement and pairing (see FACT 2). The cost of the new screen from Apple is comparable in price to the cost of stitiching the broken home button back together in my opinion.
FACT 6: in some instances, a chip (other than the one in FACT 1) present on the home button is damaged (specially during transfer of home button from broken to new screen). When damaged and failing, this chip will prevent home button function from working such as to exit an app and go back to home screen. But the finger print scanner would still be working and you are able to wake/unlock the screen with your finger/fingerprint and use reachability. This chip is accessible (contrary to the fingerprint scanner chip in FACT 1 which is practically unreachable) can be replaced and the issue can be fixed. Sometimes a partial tear to the home button cable can cause the same failure. It is also repairable by some people with the right tools, skill, and patient mindset.
EDIT: New Fact (7)
FACT 7: some repair techs noticed that a damaged front cam assembly can interfere with the functioning of the Home Button/Touch ID. To rule out this possibility, test the Home Button + Touch ID functions after disconnecting the front camera flex cable. BUT, starting with iOS 11, front cam assembly may need to be present/connected for the iPhone to boot. So may be try a different/known good one.
EDIT: iOS 11.0.0-11.0.3
FACT 8: after the release if iOS 11, and up till iOS 11.0.3, we noticed that some iPhone 7 devices cannot boot completely or may boot-loop if home button is missing or damaged (as well as front cam assembly). [Not verified yet: a fellow tech observed that some i7 would boot without home button attached. His theory is that the board version that has a certain Intel chip would boot without the home button while the board version with a Qualcomm chip requires the home button to be installed to boot].
Hope this will be of any help and feel free to message me for additional info or clarifications. I'll be happy to share."
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