A motherboard as the name suggest is the main board of a computer and iPhone 6s is similar to the computer. The motherboard comprises of several main units like CPU and memory. It is also involved in providing connections to various components. The motherboard of iPhone 6s also has several components and provides support to many units inside the system of the phone including processor and memory.
The iPhone 6s does millions of calculations each second just like a normal laptop or a desktop computer which is all done through the motherboard. Hence, the worst harm that can happen to your iPhone 6s is to the motherboard. However, it is not an irreparable problem and MyCelCare has a team of experts who are always available to help you out with this.