In the account roles, under Entity Rights, you can select whether to provide access to the Board Member Portal - Login (this is needed for a board member to view the boards in the board portal - if they were made a member or committee member of multiple boards, they will be able to select the board to see the information in each), the Board Portal - View All Boards (if you provide this, they can view any board, even those they are not a member of), and Board Portal - View All Committees (if you provide this, they can view any board committee, even those they are not a committee member of).
If you want to restrict a board member to only be able to view the boards they are a member or committee member of, set them up as a member or committee member of the board you want them to have access to and then provide them with an account role of Board Member Portal - Login only.
