As you want to get the details of maximum salary for an IIT B.Tech Engineer so here is the information of the same for you:

According to me there are no limits for the maximum salary

If you are really an expert in your field in IIT, the companies which come for placements in the college can be very high ranging from 10 lakhs to 30 lakhs initial salary and plus many perks and bonuses.

But this is not true for every student and depends on the capabilities of an individual student.

It also depends on the performance of yours in the college period