A package comprises a substrate (101, 401) with a longitudinal direction and a lateral direction perpendicular thereto. The substrate (101, 401) has a recess (103, 403) formed in a first surface (102, 402) and the recess (103, 403) extends in the longitudinal direction of the substrate (101, 401), said recess (103, 403) having an inner surface. The inner surface of the recess (103, 403) comprises at least a first set of conductive areas. The first set comprises at least a first area (106, 406) and a second area (107, 407) being provided with a conductive layer, said first area (106, 406) and said second area (107, 407) being mutually spaced in the lateral direction. The package additionally comprises a cap (151, 251, 351, 451.) with a first surface (152, 252, 352, 452) for mounting on top of said first surface (102, 402) of said substrate (101, 401), the cap (151, 251, 351, 451) and the recess (103, 403) of the substrate (101, 401) defining an elongated channel in the longitudinal direction. The cap (151, 251, 351) comprises at least a first set of conductive areas, said first set comprising at least a first area (156, 256, 356) and a second area (157, 257, 357) provided with a conductive layer, said first area (156, 256, 356) and said second area (157, 257, 357) being mutually spaced in the lateral direction.