ORCID and its QR-code on business card back cover as a researcher?
It is not necessary.

It is not too much.

Note that the back of your business card might be occupied, though:


Multilingual business cards sometimes feature another language on either side. (Although this approach is obviously limited as soon as you want to include more than two languages.)
Business cards sometimes feature a QR code with all the business card information in vCard format on their back side. (IMHO, all business cards should have this. There is no real excuse not to.) If that is the case, it depends on your stylistic preferences whether or not to add one or more smaller QR codes next to the vCard one.