A method of manufacturing a substrate of a display device is disclosed. The method comprises forming a pixel electrode having a side edge that is under a patterned thermosetting insulating material layer. The method also comprises forming, from the patterned thermosetting insulating material, an insulating layer that covers the side edge of the pixel electrode by heat-treatment of the patterned thermosetting insulating material. As a result of the heat treatment of the patterned thermosetting insulating material, the patterned thermosetting insulating layer melts over the side edge of the pixel electrode.