Hello, Mukesh

ISRO hires engineers for various posts, Private colleges as you have mentioned are good for doing B.tech. As long as you fulfill the eligibility criteria provided by ISRO for applying for the job. ISRO hires mechanical, refrigeration, civil architecture engineers.

For detailed info about the recruitment process and requiremnet, please visit; 

https://engineering.careers360.com/articles/isro-recruitment

All the best!