Patent ID: 8305150

Claim:
A surface mount crystal oscillator comprising a crystal piece held by first and second crystal holding terminals on a rectangular ceramic substrate, wherein a metal cover is disposed to close and seal the crystal piece on the substrate, on wall faces of through holes formed in corner portions of the substrate, through terminals are formed, on the front surface of the substrate, a first leading terminal led from the first crystal holding terminal is connected to the through terminal of the shortest corner portion, and a second leading terminal led from the second crystal holding terminal is connected to the through terminal of the corner portion in a direction reverse to a direction in which the first leading terminal is led, on the back surface of the substrate, mount terminals connected to the through terminals are formed, on the outer peripheral front surface of the substrate, an insulating film is formed at such a position as to face the opening end face of the metal cover, a curvature radius of the insulating film is set to be smaller than the opening end face of the metal cover in the corner portions of the substrate, and a corner region of the insulating film is projected from a circular outer peripheral end of the opening end face of the metal cover in the corner portions of the substrate.