A signal transmission device, comprising:
- a die pad;
- a transformer chip arranged on the die pad;
- and
- an encapsulation resin encapsulating the die pad and the transformer chip,
- wherein the transformer chip includes:
- an insulating layer including a front surface and a back surface facing away from each other in a thickness-wise direction;
- a first isolation transformer including a first front coil, a second front coil, a first back coil and a second back coil, the first front coil and the second front coil being located relatively close to the front surface in the insulating layer and spaced apart from each other in a first direction orthogonal to the thickness-wise direction, the first back coil and the second back coil being located relatively close to the back surface in the insulating layer and spaced apart from each other in the first direction, the first back coil and the second back coil facing the first front coil and the second front coil;
- a second isolation transformer including a third front coil, a fourth front coil, a third back coil, and a fourth back coil, the third front coil and the fourth front coil being located relatively close to the front surface in the insulating layer and spaced apart from each other in the first direction, the third back coil and the fourth back coil being located relatively close to the back surface in the insulating layer and spaced apart from each other in the first direction, the third back coil and the fourth back coil facing the third front coil and the fourth front coil, the second isolation transformer being spaced apart from the first isolation transformer in the first direction;
- a first outer pad disposed between the first front coil and the second front coil in the first direction as viewed in the thickness-wise direction, the first outer pad being electrically connected to both the first front coil and the second front coil;
- a second outer pad disposed between the third front coil and the fourth front coil in the first direction as viewed in the thickness-wise direction, the second outer pad being electrically connected to both the third front coil and the fourth front coil;
- first dummy wiring arranged at opposite sides of the first isolation transformer in a second direction orthogonal to the first direction as viewed in the thickness-wise direction, the first dummy wiring being electrically connected to the first outer pad;
- and
- second dummy wiring arranged at opposite sides of the second isolation transformer in the second direction, the second dummy wiring being electrically connected to the second outer pad and electrically insulated from the first dummy wiring, and
- the first dummy wiring and the second dummy wiring are aligned in the first direction.