June 24 1990 / fromthearchive / Globe Staff photo by Jonathan Wiggs / Nelson Mandela waved goodbye to Boston from the 727 airplane doorway. Mandela's six-week, 13-nation tour was designed to raise awareness of the antiapartheid struggle of South African blacks and to raise money for the African National Congress. It was the black leader's first visit to the United States since he was freed in February after 27 years as a political prisoner in South Africa. Boston was Mandela's second stop after New York and more than $ 500,000 in contributions were raised here for the ANC.