Rainbow color across main board
Hey guys I've seen this several times in iPhones and it usually ends up being something I cannot repair. So I am trying to understand what is causing this. Devices are non functioning when the come to me. Upon opening. The main board has a rainbow sheen to it. Looks like metal when you get it really hot. That rainbow look it gets. Has anyone else experienced this? Any answers on what caused this or if it is repairable or not?
UPDATE (added picture, by @refectio)
Is this a good question?