a long chat cannot be avoided unless your boss really hates you...if he calls you in for a chat, likely it means he/she appreciate you and want to know why you want to leave and are you not happy working there. If the boss ignores you, means, in his/her heart.."thanks god, you are leaving"

its always good to send the resignation letter to HR and cc to your immediate boss, not necessary the HOD. or even verbally tell your immediate boss first then follow up with a letter