Can a motherboard be 'repaired'

I took my son's Iphone 5S to a local repair shop as it was not charging. I was charged £40 for a new charging port and a new battery. 3 weeks later the phone again stopped charging and eventually the battery ran down to zero. When I took it back to the same shop I was told that there is no problem with the items recently replaced and that the issue is with the motherboard. The phone worked fine with an alternative battery and registered connection to a PC and charger via the charging port, but after 5 minutes the charge on the battery had not increased. The 'repairer' told me that he would need to send it to someone who can solder repair the motherboard for £50. He also disclaimed any responsibility for the problem despite it (the motherboard) working fine for 18 months before he opened it up!

Can a motherboard really be solder repaired or is it as easy to replace it (knowing that any phone data would be lost!)

Also, how likely is it that this problem has actually been caused by the initial repair?

btw When the charge port and battery were replaced the touch ID sensor stopped working. I was not told about this happening before he took on the work because "everybody knows this". - Grrrr!