hey,

see the mobile companies hires engineers to make UT and and physical design of a gadget. it can be a mobile or laptop or tablet. now coming to your points, if you are really interested to know about the electronics manufacturing and design you need to go for btech course after 10+2 course. electronics and communication engineering, electrical and electronics engineers work for mobile companies in different post like verification engineer, design engineer, ui and ux developers post etc.