Upgrade logic board with better specs

Hi!

My MBPr is starting to feel a bit slow when working on some projects (I'm a software developer), why I'm starting to think about upgrading my computer. Since I'm not really into the new MBP series, I think about upgrading my current computer. Previously I upgraded the SSD from 128GB to 512GB, and I do have some skills when it comes to hardware assembly.

My question is; is it possible to upgrade the logic board to one with an i7 CPU and 16GB RAM?

Currently, my computer runs off of an i5 CPU and 4GB RAM, so the suggested upgrade would be a huge improvement.

I've found logic boards on Ebay, but they are quite expensive and if I'm about to do such an upgrade, I want to feel confident that it's going to work.