Chosen Solution
My sister upgraded from her shattered and falling apart iPhone 6s. Having changed screens on a few iPhone 6’s I decided to swap the screen out for a spare phone. I proceeded to attempt the repair and it went semi successful. The phone boots to the apple logo and turns off, then back to the apple logo in a never ended boot cycle (on and off every 2-3 seconds). Someone mentioned to me screw hole damage. When taking off the flex connector plate 2 screws would not come out, they would twist around like they were loose so I thought they were and the entire thing came out (see picture). Would that be why this is happening or is something else wrong.
Eeek! The standoffs are completely sheared off. That is what we call Long Screw Damage. As the greatest scientific mind of the 20th century (@albert8181) has stated, this kind of damage will damage copper traces that are below the surface, disabling key aspects of the phone. An iPhone logic board has 10 layers of traces, only two of which are visible. This is an advanced repair however an iPhone 6S still caries a lot of value and IMHO, certainly worth trying to repair. If there is critical data, then it is even more worthwhile. When searching for and selecting a micro-soldering tech, make you you pick one that likes and is successful at doing LSD (sorry, couldn’t resist :>). Depending on the level of damage, these can be horrible repairs and you want to insure you have someone who is skillful enough and is willing to apply themselves. You can’t do these haphazardly.
I think I see what the problem is. It appears as if you have pulled out a layer of the logic board with the screws. This means that some vital lines cannot make connections, as they have been severed in the middle. The iphone recognises there is a problem, and re starts the boot. There are some microsoldering technicians who can solve this, but they have to fix it with 0.1 mm jumper wire to reconnect the traces, making it really fiddly and time consuming. It would be expensive and might not work. It might be cheaper to replace the whole logic board EDIT @refectio has brought to my attention that it is actually 0.02 mm jumper wire
I don’t think this is long screw damage (LSD). Yes, you tore off a layer of the logic board, but this is the top ground plane and I don’t see any deeper impression of the screws, plus LSD is really forgiving on the 6s, not to mention that you’d be hard pressed to come up with a mechanism for how any of the (potentially) torn traces under those screw holes could cause what you are describing—-Apple logo boot loop. You would far more likely have a completely dead phone, or no display at all. (We fix a TON of long screw damage, but I don’t think that’s what is going on here.)
More likely is: Damage to the battery or battery flex. If the battery is not connected well, then this is the way it would present. Rule that out before worrying about deeper issues.
