A plastic frame includes a first frame having a first frame surface and a first end portion and a second end portion opposite to each other, and a second frame having a second frame surface, an end portion of the second frame being connected to the first end portion of the first frame. The first frame surface and the second frame surface are located on the same side of the plastic frame. A first height difference between the first frame surface at a first end portion of the first frame and the second frame surface is smaller than a height difference between the first frame surface at a middle portion of the first frame and the second frame surface. The first height difference may be, for example, 0.1-0.3 mm.