Chosen Solution
Yes the board has two layers. It is connected by what we call an iterposer board.
When you separate them the interposer board stays on the bottom section of the logic board as the solder compound used on the top of the layer is of low melt. Depending on how successful you are at removing the top layer will determine if you need to re-ball it or not. If the phone is water damaged more than likely some of the solder balls will have oxidised so you would need to wick the interposer board and re-ball. There are also spacers on the interposer board which if removed makes it difficult to solder the top board back on. It is not an easy job to re-ball the interposer board. You need the right type of solder and plenty of practice. If you are getting into board repair with the iPhones it is essential that you learn how to take apart these boards and put them back together. A good way to practice is on iCloud locked boards. Once you are competent you can move on to customer boards.
You have to purchase a jig to split the board. You heat it up and lift the top half off. You have to heat it to put back together. They sell tools to do this on union repair and there are videos on YouTube from jessa at ipad rehab ipadrehab.com and Jason from sts telecom ststelecom.com. there is a Facebook page called microsoldering for beginners that would be a good idea to join.
A super easy rule to judge its difficulty: If you need to ask, you can’t do it. Board level repairs are all beyond DIY scope, iPhone board level repairs are considered to be one of the most difficult among all smartphones, and ones like the iPhone X with dual-layer boards are considered the most difficult among iPhones. This kind of repair needs specialized equipment, model-specific fixtures and masks to properly disassemble and reassemble. You might trash a few boards just practicing the basics, then trash a few more to properly master the skills. This may be thousands of dollars of upfront investment and several weeks of training to get started at least, if you are still at “asking” level. I’m not discouraging newcomers into the trade, but if you want to get in, consider doing it professionally instead of just looking to fix something by yourself for cheap, that would cost you several times over buying a brand new device.
