iPhone 6 won’t turn on after cellular antenna replacement

I never even touched the battery. Since the cellular antena part is on the top left corner of the phone, I carefully disconnected the screen and replaced that small part and when I connected the screen back it no turned on. I forgot to mention that the phone did have a problem before and that was that the back camera was not working at all. I even replaced the camera and it didn't function. I am assuming that the phone needs a new fpc connector for the back camera. To answer your question about any other signs of power : No . When I connect it to iTunes, iTunes doesn't automatically recognize it. I have to put it in recovery mode in order for it to recognize the iPhone. Also I tested the motherboard with my multimeter and it gave me a reading of ~3.0-3.5 around there. I've restored the phone in hopes that it would turn on but I get nothing

@nrodriguez914 The fact you didn't even touch the battery explains why the phone got damaged. Some connector pins and some other components carry power even when the phone is turned off..when you reseat screen and/or other parts it might unfortunately happen something gets shorted by mistake. You'll likely need thorough testing at component level to understand where the failure may come from.

Ya, not disconnecting the battery is most likely your issue. That needs to be the first thing disconnected with any type of repair, because current still runs through the phone even when it is off.