Battery pack and manufacturing method thereof

A manufacturing method of manufacturing a battery pack, the manufacturing method comprising:

• disposing a plurality of battery cells directly in a pack case in a vertical coordinate system defined by a first direction, a second direction, and a third directions that are perpendicular to one another;
• and
• electrically connecting cell leads protruding in the second direction from at least two adjacent battery cells among the plurality of battery cells using a bus bar,
• wherein the electrically connecting of the cell leads using the bus bar comprises connecting each of the cell leads to the bus bar by welding in the third direction,
• wherein the pack case comprises:
• a pair of first outer walls extending in the first direction;
• a pair of second outer walls extending in the second direction, the pair of first outer walls and the pair of second outer walls defining an inner space of the pack case;
• a longitudinal beam provided between the pair of first outer walls and extending parallel to the pair of first outer walls;
• and
• a bottom part provided below the pair of first outer walls, the pair of second outer walls, and the longitudinal beam,
• wherein a wiring structure is provided on the longitudinal beam to be electrically connected to the plurality of battery cells, and
• wherein a heat sink is provided in the longitudinal beam.