is it possible to do B.tech after B.Sc

yes you can but it is not possible due to age criteria eligibility criteria for b tech entrance is max 21 year. for clearing B sc you will be at least 12+5+3 =20 hardly eligible you need another 4 years to complete b tech if all is well you can go master in subjects and plan for phd within time y

After BTech you are supposed to be an engineer where as after BSc no. you are just a graduate btech is engineering degree..... whereas bsc is a basic degree......engineering has more scope....