Up to till ISRO is working in the space mechanics and satellite launching and not in Astrobiology or Astro chemistries etc. So for a PCBian you have lesser scopes to pursue your expertise there. Now if you want to be a part of ISRO then some of the not so traditional ways are:

• Study managerial courses in order to work as a manager in ISRO
• To be a doctor and serve in ISRO as a physician.

Now if you want to be a part of technical team then I would say you have to be in Engineering/ Physical Sciences/Chemical Sciences. Now for Physical Sciences you need to have Mathematics. Also for Engineering you need to have mathematics but this bound is removed this year.

The most preferred way to enter ISRO is to go for BTech courses at IIST. Pursuing this course will offer you a placement just after your graduation if you have score >8GPA.

To know more about IIST you may visit the link below:

https://www.iist.ac.in/

I hope my answer helps. All the very best for your future endeavors!