Thermally caulked combined structure, method of thermal caulking, and image sensor unit and image reading apparatus using the same

A method of manufacturing a molded product of an image sensor unit comprising a molded product having a substantially rectangular parallelepiped outer shape and incorporating a substrate on which photoelectric conversion elements are arranged in line, wherein the photoelectric conversion elements convert an image focused of a reflected light from an original by a lens array into an electric signal, the method comprising the steps of:

• forming a frame on the molded product to surround a periphery of the substrate;
• forming a plurality of caulking projections substantially linearly arranged on an upper surface of the frame in a longitudinal direction, with each caulking projection having a proximal portion extending from the frame;
• forming an antiwarping groove proximate to and apart from each proximal portion of the caulking projections;
• fitting the substrate to be fixed in the frame of the molded product;
• and
• bending the caulking projections by heat and pressure to fix the substrate in the frame.