An assembly includes: a first circuit board, having an electrical connector assembly and an optical fiber connector assembly side by side, the electrical connector assembly is protrudingly provided with a first guiding mechanism in a front-rear direction, which includes a first guiding section and a second guiding section, and the optical fiber connector assembly has an aligning portion; and a second circuit board, having a mating electrical connector assembly and a mating optical fiber connector assembly side by side, the mating electrical connector assembly has a first matching region, which includes a first matching section and a second matching section, and the mating optical fiber connector assembly has an adaptation portion. When the first guiding section penetrates through the first matching section and enters the second guiding section, the aligning portion starts entering the adaptation portion.