USB plug without a metallic shell

1. A universal serial bus (USB) plug, comprising:

a first housing piece having a base portion and a tongue portion extending forwards from the base portion;

a second housing piece;

a plurality of contacts, each contact comprising a contacting portion, a retaining portion fixed in the first housing piece and a tail portion, the contacting portions exposed on the tongue portion for mating with a USB receptacle connector; and

a cable soldering with tail portions of the contacts; wherein

the first housing piece defines a depression on a bottom surface thereof, the second housing piece is received in the depression; and

wherein the first housing piece has a top wall, a front wall and a pair of lateral walls opposite to each other, the top wall is connected with the front wall and the pair of lateral walls to form the depression, the depression includes a first depression and a second depression facing downwards.

2. The USB plug as claimed in claim 1 , wherein the second housing piece is of a horizontal plate structure, and is fixed to the first housing piece via ultrasonic welding.

3. The USB plug as claimed in claim 1 , wherein the first depression and the second depression are communicated with each other along a front-to-back direction, the second depression is formed on the base portion.

4. The USB plug as claimed in claim 1 , wherein the second housing piece comprises a rear segment received in the first depression and a front segment accommodated in the second depression.

5. The USB plug as claimed in claim 1 , wherein the top wall defines a plurality of slots spaced apart from each other along a transverse direction, the contacting portions are extending upwards to insert into the corresponding slot.

6. The USB plug as claimed in claim 1 , wherein the retaining portion comprises a horizontal portion and an inclined portion slantly extending downwards and forwards from the horizontal portion to the contacting portion, and the horizontal portion is connected with the tail portion, the horizontal portion and the tail portion are located on a same horizontal plane.

7. The USB plug as claimed in claim 1 , wherein the first housing piece has a bottom surface coplanar with a bottom surface of the second housing piece.

8. The USB plug as claimed in claim 7 , wherein each contacting portion defines an elongated convex portion protruding upwards and an elongated sunken portion formed by the extrusion of the convex portion.

9. The USB plug as claimed in claim 8 , wherein the base portion defines a projection extending upwards and higher than the tongue portion, and the projection has a concave arc shape front surface connected with the tongue portion.

10. The USB plug as claimed in claim 8 , wherein the contacts are insert-molded in the first housing piece.

11. The USB plug as claimed in claim 7 , further comprising a magnet assembled or insert-molded with the second housing piece.

12. The USB plug as claimed in claim 7 , further comprising an inner insulator and an exterior insulator, wherein the inner insulator is molded on a conjunction area between the contacts and the cable, the exterior insulator is over-molded on the inner insulator, and combined with the first and second housing piece seamlessly.

13. The USB plug as claimed in claim 12 , wherein the bottom surface of the first housing piece is coplanar with that of the second housing piece and the exterior insulator, the first and second housing piece, and the inner insulator are made of plastic material, the exterior insulator is made of silicone.