Substrate for electronic component and method of producing the same

An electronic component substrate 1-1 includes an insulating base 10 and a flexible circuit board 20 mounted on the insulating base 10. The flexible circuit board 20 is a synthetic resin film provided thereon with terminal patterns 29 and a conductor pattern 25 whose surface is slidingly contacted with a slider. The insulating base 10 is a synthetic resin molded piece. The flexible circuit board 20 is insert-molded to the insulating base 10. The electronic component substrate 1-1 is produced by preparing the flexible circuit board 20 and first and second mold members 41 and 45 having a cavity C1 with a shape that corresponds to the external shape of the electronic component substrate 1-1. Then, the flexible circuit board 20 is accommodated in the cavity C1 between the first and second mold members 41 and 45, and a molten molding resin is filled into the cavity C1. After the filled molding resin has been solidified, the first and second mold members 41 and 45 are removed.