Hi student ,

Yes the JEE mains exam is used to join the B-Tech in second year for Diploma students but it's mostly given by students who want admission in IITs , NiTs or GFTIs . If you are seeking for such colleges as you have mentioned you got good rank then you can apply in this type of colleges . But most of the Engineering college's in India whether it's B.E. or B.Tech provide direct second year admission for the students you have completed diploma. So it doesn't matter whether you give JEE mains or not .

Hope it may help you!!!!