A wafer assembly (30) includes a substrate (71), in turn including a wafer (70) or a stack of wafers. The wafer assembly (30) further includes an electrical connection (32) arranged through at least a part of the substrate (71). The electrical connection (32) is made by low-resistance silicon. The electrical connection (32) is positioned in a hole (84) penetrating at least a part of the substrate (71). A surface (78) of the substrate (71) confining the hole (84) is electrically insulating. The electrical connection (32) has at least one protrusion (75), which protrudes transversally to a main extension (83) of the hole (84) and the protrusion (75) protrudes outside a minimum hole diameter (85), as projected in the main extension (83) of the hole (84). Preferably, the protrusion (75) is supported by a support surface (81) of the substrate (71). A manufacturing method is also disclosed.