Hey ayush,
Talking about your academic that play the major role in campus placement as many of the companies release their own percentage criteria which may should vary accordingly companies .
What you need to take care is try to  maintain your percentage in between 70 and 75 and not less tha. 75. So you will not face any problem during your placement.
12th percentage also matters but not as the major factor ,you can still get the job in reputed company if you have not scored well in your 12th standard.
What i would suggest you to do sincerely your btech this is the only chance who can let you to grab the good job in good company.
So kindly pay attention to academic as well as your training session held in your college but practical knowledge is must wherever you go.
Good luck!