Admission in Shibpur University, Kolkata is considered on the basis of JEE Mains. And minimum 12th percentage required to get in is 75% for General candidates and 65% for SC/ST candidates. IF the candidate would not satisfy this condition then he will not be considered for admission into any course, so yes it is necessary to score minimum qualifying percentage in 10+2.

For particular branch it will depend on your marks in JEE Mains, better the marks better would be the choice for B.Tech branches.