A stack structure of a circuit board includes a first substrate, a second substrate and a fixing element. The first substrate has a first component area, a plurality of supporting solder elements, and a plurality of signal solder elements, wherein the plurality of signal elements is disposed in the first component area. The first substrate stacks on the second substrate. The plurality of supporting solder elements is disposed between the first and the second substrates for providing a supporting force. The fixing element secures the first substrate and the second substrate, and the supporting solder elements are disposed around the fixing element.