Well om you are having 640 category rank in NIMCET. Which is quite a good rank. I guess the category is OBC category.

So now if I consider previous year closing rank of different nit's then I find that in OBC category with the rank you have you will get nit but not the top ones like Trichy Warangal Surathkal. But you will get a seat in rest nit's.

All the best. 

Thank you.