[General Questions and Answers] Nazo:
So I've had an Xperia Z3 Compact for some time now. Not long after I got it I managed to break the original back (sheer absolute carelessness.) I've since had a long line of third party backs. Unfortunately, my biggest problem is that even the ones claiming to be tempered extra strong glass still seem to break 100x more easily than the screen (still doesn't have even so much as a scratch.) Obviously no one here can do anything about that. (Though someday I'd like to figure out if I can come up with some sort of plastic solution. Then I could even use a more permanent and better sealing glue than official screen/back replacement glue because presumably it wouldn't break and have to be replaced every so often.) One problem I am having that maybe can be addressed here is that they keep coming loose.

I believe I'm doing it right. First I shut down the phone first (since there's so much heat involved I want to stress it as little as possible in the process.) Next I put the back with the glue up and use a heat gun on the low setting for quite a while on it to get the glue as malleable as possible. Then I line it up and put it in quickly and apply a fair bit of weight (I'm afraid to put too much and break something in the process, but I've tried to give it a fair bit of weight) and leave it for hours (actually, typically I just leave it overnight.) Half the time it works great for a fair little while and half the time it only lasts a short while, but always I find the back coming loose eventually. (I do not bend or pry at my phone a lot or anything like that.) I would add here that while I keep my phone in my pocket all the time, I keep it in a case I've modified to help protect it where I even put a metal plate on one side to help keep it pretty flat (the last thing in the world I want is any damage to my screen, so yeah, I go a bit above and beyond...) This should keep it from flexing very much in that pocket and it should remain fairly flat as far as I know more or less all of the time.

One thing I've been wondering: it's very difficult to keep the whole thing heated thoroughly. Also, it's easy to overheat one area (while underheating another for example) as I managed to warp the material over the camera lens (next time I'll pop that out first and put that back in only just before putting the back on.) So I had a bit of a thought: why not use an oven? This could warm it much more evenly potentially, getting the heat in deeper and more consistently than I can do with a heat gun. Well, presumably it must work because why wouldn't it? But it does beg a few questions. Most importantly, what temperature would I even use? For an oven it would obviously be something relatively low. For example, might it be something about like ~100C/~200F? More? Less? I honestly don't know and this is my main question here. Would a toaster oven be too focused (eg with the heating elements too close to the glass)? Because it would really be best if I could use it instead of a full sized one. Has anyone ever done this before? I only ever found people using heat guns in googling around. But something isn't going right and I have to assume it's the consistency because nothing else even makes sense.

PS. Has anyone ever 3D printed a back or anything? If I ever do try to go plastic I'll probably have to cut something the hardest possible way with very little precision which is no small part of why I keep putting off even trying it. This thing will never be back to the full waterproof rating it originally had, but I do at least want it to be safe if I have to make an emergency call in the rain or something. (Well, that and finding the right plastic since it needs to be flexible and not brittle but tough enough to resist bumps without smashing into the battery or something if anything pokes it.) Getting sick of glass...