A base includes: a mount surface; a lateral wall located around the mount surface, the lateral wall including: a pair of first protrusions having first upper surfaces and located opposite to each other in a first direction that is parallel to a side of the mount surface, wherein each first protrusion has a same height from the mount surface, a pair of second protrusions having second upper surfaces and located opposite to each other in a second direction which is perpendicular to the first direction, wherein each second protrusion has a height from the mount surface less than the height of the first protrusion; and at least one conduction region disposed on at least one of the first upper surfaces and/or at least one of the second upper surfaces.