Abstract: In a process of forming through connections between metal circuit patterns formed in layers on opposite surfaces of a substrate characterized by forming an aperture through the pair of layers and the substrate, increasing the diameter of the aperture in the substrate, compressing the portions of each metal layer, which portions are overhanging the increased aperture, towards each other and subsequently forming a connection between the compressed portions of the opposite metal layers. Preferably, the apertures are formed by a mechanical operation such as drilling or punching and the substrate aperture is enlarged or widened by a selective etching process without substantially increasing the size of the aperture through the overlying metal layers.