A method of manufacturing a mounting substrate accommodating therein an electronic component for use in a surface mount crystal oscillator and adapted to be joined to a bottom surface of a crystal unit has the steps of defining a recess with a bottom wall and a frame wall having an opening, placing the electronic component in the recess, filling the recess with a resin for protecting the electronic component, and, after the resin is cured, removing at least a portion of the frame wall. The electronic component typically comprises an IC (Integrated Circuit) chip incorporating an integrated oscillating circuit that employs a crystal unit.