Crystal used for closing the top of the case of a portable object and method of welding a crystal of this type

A case of a portable object whose top is closed by a crystal made of a transparent plastic material and secured to the case of the portable object by ultrasonic welding, wherein the crystal includes has a top surface and a bottom surface that carries one or more conductive paths made of a transparent conductive material, and a peripheral rim that extends along at least one portion of the perimeter of the crystal, wherein the peripheral rim provides at least one surface for ultrasonic welding of the crystal to the case of the portable object, wherein the peripheral rim includes a top ultrasonic welding surface and a bottom ultrasonic welding surface, the bottom surface of the peripheral rim being closer to the top surface of the crystal than to the bottom surface of the crystal, the top surface and the bottom surface of the peripheral rim being connected to each other by a third ultrasonic welding surface,

• wherein the case comprises:
• a bezel that abuts on the top surface of the crystal;
• an assembly formed by the crystal and the bezel being mounted on a middle part to form the case of a portable object;
• wherein the crystal is ultrasonic welded, via at least one of the welding surfaces provided by the peripheral rim, to the middle part or the bezel.

A method for ultrasonic assembly of a crystal used to close a top of a case of a portable object, wherein the crystal is made of a transparent plastic material and secured to the case of the portable object by ultrasonic welding, wherein the crystal includes a top surface and a bottom surface that carries one or more conductive paths made of a transparent conductive material, and a peripheral rim that extends along at least one portion of the perimeter of the crystal, wherein the peripheral rim provides at least one surface for ultrasonic welding of the crystal to the case of the portable object, wherein the peripheral rim includes a top ultrasonic welding surface and a bottom ultrasonic welding surface, the bottom surface of the peripheral rim being closer to the top surface of the crystal than to the bottom surface of the crystal, the top surface and the bottom surface of the peripheral rim being connected to each other by a third ultrasonic welding surface, wherein the case of the portable object includes a bezel that abuts on the top surface of the crystal, an assembly formed by the crystal and the bezel being mounted on a middle part to form the case of the portable object, wherein the method includes:

• taking the crystal and ultrasonic welding the crystal to the middle part of the case by the bottom welding surface thereof and to the bezel by at least one of the top welding surface and the third welding surface thereof.