CPU board vs circuit card

CPU board and circuit card both are nouns.

Word	Noun	Adjective	Verb	Adverb
CPU board	Yes	No	No	No
circuit card	Yes	No	No	No

As nouns, circuit card is a hypernym of CPU board; that is, circuit card is a word with a broader meaning than CPU board:

CPU board: the main circuit board for a computer
circuit card: a printed circuit that can be inserted into expansion slots in a computer to increase the computer's capabilities

Other hypernyms of CPU board include add-in, board, card, circuit board, plug-in.

CPU board (noun)	circuit card (noun)
the main circuit board for a computer	a printed circuit that can be inserted into expansion slots in a computer to increase the computer's capabilities