A connector comprising: an insulated housing having a slot; and a transmission assembly located inside the insulated housing, wherein the transmission assembly comprises a main circuit board, an expanded circuit board, a plurality of first terminals and at least one second terminal, the expanded circuit board has a top surface, a first lateral side and a second lateral side, wherein the expanded circuit board is disposed on the main circuit board, and the first lateral side and the second lateral side of the expanded circuit board which are opposite to each other have a plurality of first electrical contacts and at least one second electrical contact, respectively, and the first terminals and the at least one second terminal are plugged in the main circuit board, wherein the first terminals bend and form a first limit section and a first contact section, the at least one second terminal bends and forms a second limit section and a second contact section, one end of each first limit section and one end of the second limit section are plugged in the main circuit board, while the expanded circuit board is disposed between the other ends of the first limit section and the other end of the second limit section which are in electrical contact with the first electrical contacts and the second electrical contact, respectively, and wherein at least a part of the second contact section extends towards the first lateral side of the expanded circuit board and is pressed against the top surface of the expanded circuit board, thereby fixing the expanded circuit board to the main circuit board and making the expanded circuit board and the main circuit board be electrically connected to each other, wherein the sum of the numbers of the first electrical contacts and the number of the at least one second electrical contact is eight, the sum of the number of the first terminals and the number of the at least one second terminal is eight, the first lateral side of the expanded circuit board has at least one first recess portion, the second lateral side has at least one second recess portion, each first electrical contact is formed on one at least one first recess portion, and each second electrical contact is formed on one at least one second recess portion. an insulated housing having a slot; and a transmission assembly located inside the insulated housing, wherein the transmission assembly comprises a main circuit board, an expanded circuit board, a plurality of first terminals and at least one second terminal, the expanded circuit board has a top surface, a first lateral side and a second lateral side, wherein the expanded circuit board is disposed on the main circuit board, and the first lateral side and the second lateral side of the expanded circuit board which are opposite to each other have a plurality of first electrical contacts and at least one second electrical contact, respectively, and the first terminals and the at least one second terminal are plugged in the main circuit board, wherein the first terminals bend and form a first limit section and a first contact section, the at least one second terminal bends and forms a second limit section and a second contact section, one end of each first limit section and one end of the second limit section are plugged in the main circuit board, while the expanded circuit board is disposed between the other ends of the first limit section and the other end of the second limit section which are in electrical contact with the first electrical contacts and the second electrical contact, respectively, and wherein at least a part of the second contact section extends towards the first lateral side of the expanded circuit board and is pressed against the top surface of the expanded circuit board, thereby fixing the expanded circuit board to the main circuit board and making the expanded circuit board and the main circuit board be electrically connected to each other, wherein the sum of the numbers of the first electrical contacts and the number of the at least one second electrical contact is eight, the sum of the number of the first terminals and the number of the at least one second terminal is eight, the first lateral side of the expanded circuit board has at least one first recess portion, the second lateral side has at least one second recess portion, each first electrical contact is formed on one at least one first recess portion, and each second electrical contact is formed on one at least one second recess portion.