isolator

Abstract

To provide an isolator capable of improving power efficiency of a transformer.SOLUTION: An isolator comprises a first pad Pd1, a second pad Pd2, a first coil CL1, an insulating layer, a third pad Pd3, a fourth pad Pd4, and a second coil CL2. The first coil includes first wiring 41 and second wiring 42. The first coil is connected to the first pad and the second pad. The second coil includes third wiring 51 and fourth wiring 52. The second coil is disposed so as to face the first coil via the insulating layer. The second coil is connected to the third pad and the fourth pad. The first wiring and the second wiring are connected in parallel to each other between the first pad and the second pad. The third wiring and the fourth wiring are connected in parallel to each other between the third pad and the fourth pad.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] Embodiments of the present invention relate to isolators.

Background Art

[0002] An isolator is known that transmits a signal from a transmission-side circuit to a reception-side circuit in a state where the transmission-side circuit and the reception-side circuit are insulated from each other.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0004] To provide an isolator capable of improving the power efficiency of a transformer.

Means for Solving the Problems

[0005] The isolator according to the embodiment includes a first pad, a second pad, a first coil, an insulating layer, a third pad, a fourth pad, and a second coil. The first coil includes a first wiring and a second wiring. The first coil is connected to the first pad and the second pad. The second coil includes a third wiring and a fourth wiring. The second coil is arranged to face the first coil with the insulating layer interposed therebetween. The second coil is connected to the third pad and the fourth pad. The first wiring and the second wiring are connected in parallel to each other between the first pad and the second pad. The third wiring and the fourth wiring are connected in parallel to each other between the third pad and the fourth pad.

Brief Description of Drawings

[0006]

Figure 1

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MODE FOR CARRYING OUT THE INVENTION

[0007] Hereinafter, embodiments will be described with reference to the drawings. The dimensions and ratios in the drawings are not necessarily the same as those in reality. In the following description, components having substantially the same functions and configurations are denoted by the same reference numerals, and repeated descriptions may be omitted. When particularly distinguishing between elements having similar configurations, different characters or numbers may be added to the end of the same reference numeral. Also, all descriptions of one embodiment apply to the descriptions of another embodiment as well, unless explicitly or implicitly excluded.

[0008] 1. First Embodiment The isolator according to the first embodiment will be described. Hereinafter, a digital isolator that can transmit a signal from a transmission-side circuit to a reception-side circuit by magnetically coupling a coil connected to the transmission-side circuit and a coil connected to the reception-side circuit in a state where the transmission-side circuit and the reception-side circuit are insulated from each other will be described as an example.

[0009] 1.1 Structure of the Isolator The structure of the isolator will be described with reference to FIGS. 1 and 2. FIG. 1 is a plan view showing an example of the planar layout of the isolator. FIG. 2 is a cross-sectional view taken along line S1-S1 of FIG. 1, showing an example of the cross-sectional structure of the isolator.

[0010] The isolator 1 is, for example, a semiconductor package. As shown in FIGS. 1 and 2, the isolator 1 includes die pads 10 and 20, semiconductor chips 11 and 21, leads 15 and 25, frames 30a and 30b, transformer TR, and insulating member 100. Note that the illustration of the insulating member 100 is omitted in FIG. 1.

[0011] The die pads 10 and 20 are members that support semiconductor chips. The die pad 10 supports the semiconductor chip 11. The die pad 20 supports the semiconductor chip 21.

[0012] The leads 15 and 25 are members that connect the semiconductor chips and external wiring. The isolator 1 includes a plurality of leads 15 and a plurality of leads 25. The lead 15 connects the semiconductor chip 11 and the external wiring via a bonding wire 16. The number of bonding wires 16 is the same as the number of leads 15. The lead 25 connects the semiconductor chip 21 and the external wiring via a bonding wire 26. The number of bonding wires 26 is the same as the number of leads 25.

[0013] Frames 30a and 30b are members that support the transformer TR and connect the semiconductor chip 21 and the transformer TR. Frame 30a connects the semiconductor chip 21 and the transformer TR via bonding wires 24a and vias 32a. Frame 30b connects the semiconductor chip 21 and the transformer TR via bonding wires 24b and vias 32b.

[0014] The die pads 10 and 20, the leads 15 and 25, and the frames 30a and 30b constitute a lead frame. Hereinafter, the die pads 10 and 20, the leads 15 and 25, and the frames 30a and 30b are collectively referred to as the "lead frame LF". The lead frame LF has, for example, a plate-like shape. The lead frame LF is composed of a conductive material. The lead frame LF includes, for example, a metal material.

[0015] Hereinafter, a plane parallel to the plane of the lead frame LF is defined as the XY plane. Directions perpendicular to each other in the XY plane are defined as the X direction and the Y direction. A direction intersecting the XY plane is defined as the Z direction. Among the Z directions, the direction from the lead frame LF toward the semiconductor chips 11 and 21 is also referred to as the upward direction.

[0016] As shown in FIG. 1, the die pads 10 and 20 are arranged spaced apart from each other in the X direction. The frames 30a and 30b are arranged spaced apart from each other in the Y direction. The frames 30a and 30b are arranged between the die pad 10 and the die pad 20 in the X direction and are away from the die pads 10 and 20. The plurality of leads 15 are arranged spaced apart from each other in the Y direction. The plurality of leads 15 are arranged on the side opposite to the side where the frames 30a and 30b of the die pad 10 are arranged in the X direction and are away from the die pad 10. The plurality of leads 25 are arranged spaced apart from each other in the Y direction. The plurality of leads 25 are arranged on the side opposite to the side where the frames 30a and 30b of the die pad 20 are arranged in the X direction and are away from the die pad 20.

[0017] The semiconductor chips 11 and 21 are, for example, IC (Integrated Circuit) chips. The semiconductor chips 11 and 21 are arranged to be spaced apart from each other in the X direction.

[0018] The semiconductor chip 11 includes a circuit 12. The circuit 12 includes a signal transmission / reception circuit and a modulation / demodulation circuit. The circuit 12 is connected to a bonding wire 14a via wiring (not shown) within the semiconductor chip 11. The circuit 12 is connected to a bonding wire 14b via wiring (not shown) within the semiconductor chip 11. The circuit 12 is connected to a bonding wire 16 via wiring (not shown) within the semiconductor chip 11.

[0019] The semiconductor chip 21 includes a circuit 22. The circuit 22 includes a signal transmission / reception circuit and a modulation / demodulation circuit. The circuit 22 is connected to a bonding wire 24a via wiring (not shown) within the semiconductor chip 21. The circuit 22 is connected to a bonding wire 24b via wiring (not shown) within the semiconductor chip 21. The circuit 22 is connected to a bonding wire 26 via wiring (not shown) within the semiconductor chip 21.

[0020] The transformer TR is, for example, an isolation transformer. The transformer TR is arranged between the semiconductor chip 11 and the semiconductor chip 21 in the X direction and is separated from the semiconductor chips 11 and 21.

[0021] The transformer TR includes, for example, a wiring board 31. The wiring board 31 is, for example, a flexible printed circuit board (FPC: Flexible Printed Circuits) having flexibility. The wiring board 31 has, for example, a plate-like shape.

[0022] The wiring board 31 includes, for example, a primary circuit FC, an insulating layer, and a secondary circuit SC, which will be described later. The primary circuit FC includes a coil CL1, which will be described later. The secondary circuit SC includes a coil CL2, which will be described later. The wiring board 31 is configured to transmit signals from the circuit 12 to the circuit 22 or from the circuit 22 to the circuit 12 in an insulated state between the circuit 12 in the semiconductor chip 11 and the circuit 22 in the semiconductor chip 21 using the coils CL1 and CL2. Details of the wiring board 31 will be described later.

[0023] When a signal is transmitted from the circuit 12 to the circuit 22, the circuit 12 functions as a transmitting circuit, and the circuit 22 functions as a receiving circuit. On the other hand, when a signal is transmitted from the circuit 22 to the circuit 12, the circuit 22 functions as a transmitting circuit, and the circuit 12 functions as a receiving circuit.

[0024] The insulating member 100 includes, for example, an insulating resin. The die pads 10 and 20, the semiconductor chips 11 and 21, the bonding wires 14a, 14b, 16, 24a, 24b, and 26, the frames 30a and 30b, the wiring board 31, and the vias 32a and 32b are sealed by the insulating member 100.

[0025] As shown in FIG. 2, a semiconductor chip 11 is provided on the die pad 10 via an adhesive member 13. One end of a bonding wire 14a and one end of a bonding wire 16 are provided on the semiconductor chip 11.

[0026] The other end of the bonding wire 16 is provided on the lead 15.

[0027] A semiconductor chip 21 is provided on the die pad 20 via an adhesive member 23. One end of a bonding wire 24a and one end of a bonding wire 26 are provided on the semiconductor chip 21.

[0028] The other end of the bonding wire 26 is provided on the lead 25.

[0029] On the frame 30a, the other end of the bonding wire 24a is provided. Also, on the frame 30a, a via 32a is provided. On the via 32a, a wiring board 31 is provided. On the wiring board 31, the other end of the bonding wire 14a is provided.

[0030] The die pads 10 and 20, semiconductor chips 11 and 21, adhesive members 13 and 23, bonding wires 14a, 16, 24a, and 26, a part of the lead 15, a part of the lead 25, the frame 30a, the wiring board 31, and the via 32a are covered by an insulating member 100. The leads 15 and 25 are fixed by the insulating member 100 and have portions exposed outside the insulating member 100.

[0031] Note that the cross-sectional structure of the surface including the bonding wires 14b and 24b and the via 32b is the same as the cross-sectional structure of the surface including the bonding wires 14a and 24a and the via 32a shown in FIG. 2. Specifically, one end of the bonding wire 14b is provided on the semiconductor chip 11. One end of the bonding wire 24b is provided on the semiconductor chip 21. On the frame 30b, the other end of the bonding wire 24b is provided. Also, on the frame 30b, a via 32b is provided. On the via 32b, a wiring board 31 is provided. On the wiring board 31, the other end of the bonding wire 14b is provided.

[0032] 1.2 Structure of the Wiring Board The structure of the wiring board 31 will be described with reference to FIGS. 3, 5 to 8.

[0033] FIG. 3 is a plan view showing an example of the planar layout of the primary circuit FC in the wiring board 31. As shown in FIG. 3, the wiring board 31 includes pads Pd1 and Pd2 and a coil CL1. Note that in FIG. 3, the illustration of the secondary circuit SC and the insulating layer in the wiring board 31 is omitted.

[0034] Pad Pd1 is a member that connects coil CL1 and bonding wire 14a. Pad Pd2 is a member that connects coil CL1 and bonding wire 14b. Pad Pd1 includes a base BP1 and a protruding portion PP1 that protrudes from base BP1. The protruding portion PP1 protrudes in the X direction from the base BP1. More specifically, the protruding portion PP1 protrudes from the base BP1 on the side opposite to pad Pd2. Pad Pd2 includes a base BP2 and a protruding portion PP2 that protrudes from base BP2. The protruding portion PP2 protrudes in the Y direction from the base BP2. More specifically, the protruding portion PP2 protrudes from the base BP2 toward pad Pd1. Thus, pads Pd1 and Pd2 have, for example, a substantially L-shaped configuration in top view (when viewed from above the paper surface). Pads Pd1 and Pd2 are made of a conductive material.

[0035] Coil CL1 includes wiring 41 and wiring 42.

[0036] Wiring 41 has a first end E1 and a second end E2. The first end E1 is connected to the base BP1 of pad Pd1. The second end E2 is connected to the base BP2 of pad Pd2. Wiring 41 has, for example, a spiral shape that rotates clockwise and outward from the first end E1 in top view.

[0037] Wiring 42 has a third end E3 and a fourth end E4. The third end E3 is connected to the protruding portion PP1 of pad Pd1. The fourth end E4 is connected to the protruding portion PP2 of pad Pd2. Wiring 42 is, for example, spaced apart from wiring 41 and has a spiral shape that rotates clockwise and outward from the third end E3 in top view.

[0038] Wirings 41 and 42 are made of a conductive material. Wirings 41 and 42 include, for example, copper.

[0039] With the above structure, coil CL1 is connected to pads Pd1 and Pd2. More specifically, in the present embodiment, wirings 41 and 42 are connected in parallel to each other between pad Pd1 and pad Pd2.

[0040] Also, in the present embodiment, the wirings 41 and 42 are designed with the same size and the same design rules (line and space) as the case where the coil CL1 is formed by single wiring.

[0041] When designed in this way, for example, the spiral shapes of the wirings 41 and 42 are formed in an elliptical shape. That is, the outer diameter of the coil CL1 in the Y direction is formed to be longer than the outer diameter of the coil CL1 in the X direction. Note that the spiral shapes of the wirings 41 and 42 may be rectangular or polygonal.

[0042] Also, in the Y direction, the total number of turns of the wirings 41 and 42 on the pad Pd2 side of the pad Pd1 (2 in the example of FIG. 3) is formed to be less than the total number of turns of the wirings 41 and 42 on the side opposite to the pad Pd2 of the pad Pd1 (3 in the example of FIG. 3). For this reason, the sum of the length of the wiring 41 and the length of the wiring 42 is shorter than the length of the wiring when the coil CL1 is formed by single wiring. Note that the sum of the length of the wiring 41 and the length of the wiring 42 may be equal to the length of the wiring when the coil CL1 is formed by single wiring.

[0043] Furthermore, in the present embodiment, the electrical length of the wiring 42 is designed to be equal to the electrical length of the wiring 41. That is, the relationship between the electrical length of the wiring 42 and the electrical length of the wiring 41 is expressed as in the following formula (1). Electrical length of wiring 42 = Electrical length of wiring 41 (1) The electrical length is the length calculated based on the velocity of the current propagating in the wiring. The velocity of the current propagating in the wiring is calculated based on the relative permittivity and relative permeability of the wiring. The velocity of the current propagating in the wiring is slower than the velocity in a vacuum. The wavelength of the current propagating in the wiring is shorter than the wavelength in a vacuum. For example, when the wavelength of the current propagating in the wiring is 50 [cm], the 1 / 4 wavelength is 12.5 [cm], and the 1 / 4 electrical length is about 6 [cm].

[0044] Here, the power efficiency of the transformer TR will be described. The power efficiency of the transformer TR depends on the product of the coupling coefficient k and the Q value. Also, the power efficiency of the transformer TR affects the power efficiency of the isolator 1.

[0045] The coupling coefficient k is a value indicating the degree of coupling between two coils constituting the transformer TR. The coupling coefficient k is expressed as in the following formula (2). k = M / √(L1×L2) (2) In the above formula (2), M is the mutual inductance. L1 is the self - inductance of one coil. L2 is the self - inductance of the other coil.

[0046] The Q value is a value indicating the quality of the coil. The higher the Q value, the lower the loss for high - frequency signals. The Q value is expressed as in the following formula (3). Q = ωL / R (3) In the above formula (3), ω is the frequency of the current. L is the self - inductance of the coil. R is the resistance of the coil.

[0047] From the above formula (3), the smaller the resistance R of the coil, the larger the Q value. As described above, since the power efficiency of the transformer TR depends on the product of the coupling coefficient k and the Q value, the larger the Q value, the larger the power efficiency of the transformer TR.

[0048] Figure 4 is a diagram for explaining the cancellation of magnetic fluxes generated by the phase shift of currents flowing through two wirings. In Figure 4, the waveforms of the currents flowing through one wiring and the other wiring are shown by the solid line and the broken line respectively. Hereinafter, one wiring will also be referred to as "wiring A". The other wiring will also be referred to as "wiring B". The vertical axis indicates the current value. The horizontal axis indicates the frequency of the current. In the example of Figure 4, a state where the phases of the currents flowing through wiring A and wiring B are shifted is shown. Also, a case where the frequencies of the currents flowing through wiring A and B are 600 [MHz] is shown.

[0049] As shown in FIG. 4, when the phases of the current flowing through wiring A and the current flowing through wiring B are shifted, cancellation occurs between the magnetic flux Φ1 generated by the current flowing through wiring A and the magnetic flux Φ2 generated by the current flowing through wiring B. In the example of FIG. 4, the region where magnetic flux cancellation occurs is indicated by hatching as the magnetic flux cancellation region. When magnetic flux cancellation occurs, the sum of magnetic flux Φ1 and magnetic flux Φ2 becomes smaller compared to the case where magnetic flux cancellation does not occur.

[0050] In a transformer in which two coils each including wiring A and wiring B are arranged opposite to each other, when the above-described magnetic flux cancellation occurs, the coupling coefficient k decreases compared to the case where the above-described magnetic flux cancellation does not occur. As described above, since the power efficiency of transformer TR depends on the product of the coupling coefficient k and the Q value, the higher the coupling coefficient k, the higher the power efficiency of transformer TR.

[0051] FIG. 5 is a plan view showing an example of the planar layout of the secondary circuit SC in the wiring board 31. As shown in FIG. 5, the wiring board 31 includes pads Pd3 and Pd4, and coil CL2. In FIG. 5, the illustration of the primary circuit FC and the insulating layer in the wiring board 31 is omitted.

[0052] The structure of the secondary circuit SC is the same as that of the primary circuit FC. Specifically, it is as follows.

[0053] Pad Pd3 is a member that connects coil CL2 and via 32a. Pad Pd4 is a member that connects coil CL2 and via 32b. Pad Pd3 includes a base BP3 and a protruding portion PP3 protruding from the base BP3. The protruding portion PP3 protrudes in the X direction from the base BP3. More specifically, the protruding portion PP3 protrudes from the base BP3 on the side opposite to pad Pd4. Pad Pd4 includes a base BP4 and a protruding portion PP4 protruding from the base BP4. The protruding portion PP4 protrudes in the Y direction from the base BP4. More specifically, the protruding portion PP4 protrudes from the base BP4 toward pad Pd3. Thus, pads Pd3 and Pd4 have, for example, a substantially L-shaped configuration in top view. Pads Pd3 and Pd4 are made of a conductive material.

[0054] Coil CL2 includes wiring 51 and wiring 52.

[0055] Wiring 51 has a fifth end E5 and a sixth end E6. The fifth end E5 is connected to the base BP3 of pad Pd3. The sixth end E6 is connected to the base BP4 of pad Pd4. Wiring 51 has, for example, a spiral shape that rotates clockwise and outward from the fifth end E5 in a top view.

[0056] Wiring 52 has a seventh end E7 and an eighth end E8. The seventh end E7 is connected to the protrusion PP3 of pad Pd3. The eighth end E8 is connected to the protrusion PP4 of pad Pd4. Wiring 52 is, for example, spaced apart from wiring 51 and has a spiral shape that rotates clockwise and outward from the seventh end E7 in a top view.

[0057] Wiring 51 and 52 are made of a conductive material. Wiring 51 and 52 contain, for example, copper.

[0058] With the above structure, coil CL2 is connected to pads Pd3 and Pd4. More specifically, in this embodiment, wiring 51 and 52 are connected in parallel to each other between pad Pd3 and pad Pd4.

[0059] Also, in this embodiment, wiring 51 and 52 are designed with the same size and the same design rules (line and space) as when coil CL2 is formed by single-layer wiring.

[0060] When designed in this way, for example, the spiral shapes of wiring 51 and 52 are formed in an elliptical shape. That is, the outer diameter of coil CL2 in the Y direction is formed to be longer than the outer diameter of coil CL2 in the X direction. Note that the spiral shapes of wiring 51 and 52 may be rectangular or polygonal.

[0061] Also, in the Y direction, the total number of turns of wirings 51 and 52 on the pad Pd4 side of the pad Pd3 (2 in the example of FIG. 5) is formed to be less than the total number of turns of wirings 51 and 52 on the side of the pad Pd3 opposite to the pad Pd4 (3 in the example of FIG. 5). For this reason, the sum of the length of the wiring 51 and the length of the wiring 52 is shorter than the length of the wiring when the coil CL2 is formed of single-layer wiring. Note that the sum of the length of the wiring 51 and the length of the wiring 52 may be equal to the length of the wiring when the coil CL2 is formed of single-layer wiring.

[0062] Furthermore, in the present embodiment, the electrical length of the wiring 52 is designed to be equal to the electrical length of the wiring 51.

[0063] FIG. 6 is a perspective view showing an example of the structure of the wiring board 31. FIG. 7 is a cross-sectional view taken along the line S2 - S2 of FIG. 6 showing an example of the cross-sectional structure of the wiring board 31. FIG. 8 is a cross-sectional view taken along the line S3 - S3 of FIG. 6 showing an example of the cross-sectional structure of the wiring board 31.

[0064] As shown in FIGS. 6 to 8, the wiring board 31 includes pads Pd1 and Pd2, a coil CL1, pads Pd3 and Pd4, a coil CL2, and insulating layers 61 to 65. FIGS. 6 to 8 also show bonding wires 14a, 14b, 24a, and 24b, frames 30a and 30b, and vias 32a and 32b. Note that in FIG. 6, the illustration of the vias 32a and 32b and the insulating layers 61 to 65 is omitted.

[0065] As shown in FIG. 6, coil CL1 is provided above coil CL2 in the Z direction. That is, coil CL1 is provided at a position overlapping coil CL2 in the Z direction. In other words, coil CL2 is arranged to face coil CL1 via insulating layer 63. In the example of FIG. 6, pad Pd1 and Pd2, and coil CL1, and pad Pd3 and Pd4, and coil CL2 are arranged with their directions aligned, but they may be arranged after being rotated. In other words, coil CL1 and coil CL2 only need to be arranged such that the magnetic flux passing through coil CL1 also passes through coil CL2, and the magnetic flux passing through coil CL2 also passes through coil CL1.

[0066] Pad Pd1 is connected to bonding wire 14a. Pad Pd2 is connected to bonding wire 14b. Semiconductor chip 11 is connected to coil CL1 via bonding wires 14a and 14b, and pads Pd1 and Pd2.

[0067] Pad Pd3 is connected to bonding wire 24a via via 32a and frame 30a. Pad Pd4 is connected to bonding wire 24b via via 32b and frame 30b. Semiconductor chip 21 is connected to coil CL2 via bonding wires 24a and 24b, frames 30a and 30b, vias 32a and 32b, and pads Pd3 and Pd4.

[0068] As shown in FIGS. 7 and 8, wiring board 31 has a structure in which insulating layers 61, 62, 63, 64, and 65 are laminated in this order.

[0069] As shown in FIG. 7, insulating layer 61 has an opening for connecting pad Pd3 and via 32a. Via 32a is provided inside the opening of insulating layer 61 and around the opening on the lower surface of insulating layer 61. Also, via 32a is in contact with the upper surface of frame 30a. Via 32a is composed of a conductive material. Bonding wire 24a is provided on frame 30a.

[0070] An insulating layer 62 is provided over the insulating layer 61 and the via 32a. In the insulating layer 62, a pad Pd3, and wirings 51 and 52 (coil CL2) are provided. In other words, the pad Pd3, and the wirings 51 and 52 are provided in the same layer. The pad Pd3 is provided over the via 32a. In other words, the pad Pd3 is in contact with the via 32a.

[0071] An insulating layer 63 is provided over the insulating layer 62, the pad Pd3, and the wirings 51 and 52.

[0072] An insulating layer 64 is provided over the insulating layer 63. In the insulating layer 64, a pad Pd1, and wirings 41 and 42 (coil CL1) are provided. In other words, the pad Pd1, and the wirings 41 and 42 are provided in the same layer.

[0073] An insulating layer 65 is provided over the insulating layer 64, and the wirings 41 and 42. The insulating layer 65 has an opening for connecting the pad Pd1 and the bonding wire 14a. The pad Pd1 is provided under the opening of the insulating layer 65. The bonding wire 14a is provided over the pad Pd1.

[0074] As shown in FIG. 8, the insulating layer 61 has an opening for connecting the pad Pd4 and the via 32b. The via 32b is provided in the opening of the insulating layer 61 and around the opening on the lower surface of the insulating layer 61. Also, the via 32b is in contact with the upper surface of the frame 30b. The via 32b is made of a conductive material. The bonding wire 24b is provided over the frame 30b.

[0075] An insulating layer 62 is provided over the insulating layer 61 and the via 32b. In the insulating layer 62, the pad Pd4 is provided. In other words, the pad Pd4 is provided in the same layer as the pad Pd3. The pad Pd4 is provided over the via 32b. In other words, the pad Pd4 is in contact with the via 32b.

[0076] A pad Pd2 is provided in the insulating layer 64. In other words, the pad Pd2 is provided in the same layer as the pad Pd1.

[0077] The insulating layer 65 has an opening for connecting the pad Pd2 and the bonding wire 14b. The pad Pd2 is provided under the opening of the insulating layer 65. The bonding wire 14b is provided on the pad Pd2.

[0078] According to the isolator 1 of the present embodiment, the power efficiency of the transformer TR can be improved.

[0079] In a transformer including two coils formed by single wiring wound in a spiral shape, as the number of turns of the coil increases, the single wiring becomes longer, so the resistance (winding resistance) of the single wiring increases with a quadratic curve change tendency. For this reason, the Q value of the coil decreases. Due to the decrease in the Q value, the power efficiency of the transformer also decreases.

[0080] On the other hand, in the present embodiment, the isolator 1 includes pads Pd1 and Pd2, coil CL1, an insulating layer, pads Pd3 and Pd4, and coil CL2. Coil CL1 includes wirings 41 and 42. Coil CL1 is connected to pads Pd1 and Pd2. Coil CL2 includes wirings 51 and 52. Coil CL2 is arranged to face coil CL1 via the insulating layer. Coil CL2 is connected to pads Pd3 and Pd4.

[0081] Wirings 41 and 42 are connected in parallel to each other between pad Pd1 and pad Pd2. In other words, coil CL1 has a double wiring structure of wirings 41 and 42. Wirings 51 and 52 are connected in parallel to each other between pad Pd3 and pad Pd4. In other words, coil CL2 has a double wiring structure of wirings 51 and 52.

[0082] As a result, the combined resistance of wirings 41 and 42 between pad Pd1 and pad Pd2 becomes smaller compared to the case where wirings 41 and 42 are connected in series between pad Pd1 and pad Pd2. The combined resistance of wirings 51 and 52 between pad Pd3 and pad Pd4 becomes smaller compared to the case where wirings 51 and 52 are connected in series between pad Pd3 and pad Pd4.

[0083] Therefore, the Q value of coil CL1 becomes larger compared to the case where coil CL1 is formed by single-layer wiring. The Q value of coil CL2 becomes larger compared to the case where coil CL2 is formed by single-layer wiring. Thus, according to the present embodiment, the power efficiency of transformer TR can be improved.

[0084] Also, in the present embodiment, the sum of the length of wiring 41 and the length of wiring 42 is shorter than the length of the wiring when coil CL1 is formed by single-layer wiring. In other words, the total number of turns of wirings 41 and 42 included in coil CL1 is smaller than the number of turns of the wiring when coil CL1 is formed by single-layer wiring. The sum of the length of wiring 51 and the length of wiring 52 is shorter than the length of the wiring when coil CL2 is formed by single-layer wiring. In other words, the total number of turns of wirings 51 and 52 included in coil CL2 is smaller than the number of turns of the wiring when coil CL2 is formed by single-layer wiring. As a result, the self-inductance of coil CL1 decreases compared to the case where coil CL1 is formed by single-layer wiring. The self-inductance of coil CL2 decreases compared to the case where coil CL2 is formed by single-layer wiring.

[0085] From the above formula (2), the smaller the self-inductances L1 and L2, the smaller the coupling coefficient k. However, the increase amount of the Q value due to the double-wiring structure of wirings 41 and 42 and the double-wiring structure of wirings 51 and 52 is larger than the decrease amount of the coupling coefficient k. For this reason, according to the present embodiment, the power efficiency of transformer TR can be improved.

[0086] Also, the smaller the self-inductance of coil CL1, the higher the resonance frequency of coil CL1. The smaller the self-inductance of coil CL2, the higher the resonance frequency of coil CL2. Therefore, according to this embodiment, compared with the case where coil CL1 is formed by single-layer wiring, the resonance frequency of coil CL1 is increased. Compared with the case where coil CL2 is formed by single-layer wiring, the resonance frequency of coil CL2 is increased. That is, according to this embodiment, the frequency band of transformer TR can be expanded. For example, when the operating frequency of transformer TR is 600 [MHz], the resonance frequencies of coils CL1 and CL2 are preferably 1800 [MHz] or higher, which is three times that of 600 [MHz].

[0087] Furthermore, in this embodiment, the electrical length of wiring 42 is equal to the electrical length of wiring 41. The electrical length of wiring 52 is equal to the electrical length of wiring 51. Thereby, the occurrence of a phase shift between the current flowing through wiring 41 and the current flowing through wiring 42 can be suppressed. The occurrence of a phase shift between the current flowing through wiring 51 and the current flowing through wiring 52 can be suppressed.

[0088] Therefore, compared with the case where the electrical length of wiring 42 is different from the electrical length of wiring 41, the occurrence of magnetic flux cancellation can be suppressed. Compared with the case where the electrical length of wiring 52 is different from the electrical length of wiring 51, the occurrence of magnetic flux cancellation can be suppressed. Thereby, a decrease in the coupling coefficient k can be suppressed. For this reason, according to this embodiment, the power efficiency of transformer TR can be improved. The longer the lengths of wirings 41 and 42, and wirings 51 and 52, the larger the magnetic flux cancellation region. Therefore, the lower the operating frequency of transformer TR, the more remarkable the effect of improving the power efficiency of transformer TR appears.

[0089] Also, in this embodiment, pads Pd1 and Pd2 have a substantially L-shaped configuration. Pads Pd3 and Pd4 have a substantially L-shaped configuration. Thereby, it is possible to adjust so that the electrical length of wiring 42 becomes equal to the electrical length of wiring 41. It is possible to adjust so that the electrical length of wiring 52 becomes equal to the electrical length of wiring 51.

[0090] 2. Second Embodiment The isolator according to the second embodiment will be described. In the isolator 1A according to the second embodiment, the structure of the wiring board 31A is different from that of the first embodiment. In the following description, the parts different from the first embodiment will be mainly described.

[0091] 2.1 Structure of Wiring Board The structure of the wiring board 31A will be described with reference to FIGS. 9 to 14.

[0092] FIG. 9 is a plan view showing an example of the planar layout of the primary circuit FCA in the wiring board 31A. As shown in FIG. 9, the wiring board 31A includes pads Pd1A, Pd2A, and Pd5, coil CL1A, vias 43 and 44, and wiring 45. In FIG. 9, the illustration of the secondary circuit SCA and the insulating layer in the wiring board 31A is omitted.

[0093] The pad Pd5 is a member that connects the wiring 41A and the pad Pd2A via the vias 43 and 44 and the wiring 45. The pads Pd1A, Pd2A, and Pd5 have, for example, a substantially rectangular shape in top view. The pad Pd5 is made of a conductive material.

[0094] The first end E1 of the wiring 41A is connected to the pad Pd1A. The second end E2 of the wiring 41A is connected to the pad Pd5. Also, the second end E2 is connected to the pad Pd2A via the pad Pd5, via 44, wiring 45, and via 43. The wiring 41A has, for example, a spiral shape that rotates clockwise and outward from the first end E1 in top view.

[0095] The third end E3 of the wiring 42A is connected to the pad Pd1A. The fourth end E4 of the wiring 42A is connected to the pad Pd2A. The wiring 42A is, for example, spaced apart from the wiring 41A and has a spiral shape that rotates clockwise and outward from the third end E3 in top view.

[0096] Via 43 is provided under pad Pd2A. In other words, via 43 is in contact with pad Pd2A. Via 44 is provided under pad Pd5. In other words, via 44 is in contact with pad Pd5. Vias 43 and 44 are composed of a conductive material.

[0097] Wiring 45 is a member that connects via 43 and via 44. Wiring 45 is provided under vias 43 and 44. In other words, wiring 45 is in contact with vias 43 and 44. Wiring 45 is composed of a conductive material.

[0098] With the above structure, coil CL1A is connected to pads Pd1A and Pd2A. More specifically, in this embodiment, wirings 41A and 42A are connected in parallel to each other between pad Pd1A and pad Pd2A.

[0099] Also, in this embodiment, the thickness of wiring 41A is designed to be thinner than the thickness of wiring 42A, and the resistance of wiring 41A is designed to be greater than the resistance of wiring 42A.

[0100] Furthermore, in this embodiment, the electrical length of wiring 42A is designed to be equal to the sum of the length that is N times the wavelength of the current flowing through wirings 41A and 42A (N is an integer of 1 or more) and the electrical length of wiring 41A. That is, the relationship between the electrical length of wiring 42A and the electrical length of wiring 41A is expressed as in the following formula (4). Hereinafter, the length that is N times the wavelength of the current flowing through wirings 41A and 42A is also referred to as the "N-fold wavelength". Electrical length of wiring 42A = N-fold wavelength + Electrical length of wiring 41A (N = 1, 2, 3, …) (4)

[0101] Also, in this embodiment, wiring 42A and wiring 45 are arranged so as to be separated from each other and intersect perpendicularly.

[0102] FIG. 10 is a plan view showing an example of the planar layout of the secondary circuit SCA in the wiring board 31A. As shown in FIG. 10, the wiring board 31A includes pads Pd3A, Pd4A, and Pd6, coil CL2A, vias 53 and 54, and wiring 55. In FIG. 10, illustration of the primary circuit FCA and the insulating layer in the wiring board 31A is omitted.

[0103] The structure of the secondary circuit SCA is the same as that of the primary circuit FCA. Specifically, it is as follows.

[0104] Pad Pd6 is a member that connects pad Pd4A and wiring 51A via vias 53 and 54 and wiring 55. Pads Pd3A, Pd4A, and Pd6 have, for example, a substantially rectangular shape in top view. Pad Pd6 is made of a conductive material.

[0105] The fifth end E5 of wiring 51A is connected to pad Pd3A. The sixth end E6 of wiring 51A is connected to pad Pd6. Also, the sixth end E6 is connected to pad Pd4A via pad Pd6, via 54, wiring 55, and via 53. Wiring 51A has, for example, a spiral shape that rotates clockwise and outward from the fifth end E5 in top view.

[0106] The seventh end E7 of wiring 52A is connected to pad Pd3A. The eighth end E8 of wiring 52A is connected to pad Pd4A. Wiring 52A is, for example, spaced apart from wiring 51A and has a spiral shape that rotates clockwise and outward from the seventh end E7 in top view.

[0107] Via 53 is provided on pad Pd4A. In other words, via 53 is in contact with pad Pd4A. Via 54 is provided on pad Pd6. In other words, via 54 is in contact with pad Pd6. Vias 53 and 54 are made of a conductive material.

[0108] The wiring 55 is a member that connects the via 53 and the via 54. The wiring 55 is provided on the vias 53 and 54. In other words, the wiring 55 is in contact with the vias 53 and 54. The wiring 55 is composed of a conductive material.

[0109] With the above structure, the coil CL2A is connected to the pads Pd3A and Pd4A. More specifically, in the present embodiment, the wirings 51A and 52A are connected in parallel to each other between the pad Pd3A and the pad Pd4A.

[0110] Also, in the present embodiment, the thickness of the wiring 51A is made thinner than the thickness of the wiring 52A, and the resistance of the wiring 51A is designed to be larger than the resistance of the wiring 52A.

[0111] Furthermore, in the present embodiment, the electrical length of the wiring 52A is designed to be equal to the sum of the length that is N times the wavelength of the current flowing through the wirings 51A and 52A (N is an integer of 1 or more) and the electrical length of the wiring 51A. Hereinafter, the length that is N times the wavelength of the current flowing through the wirings 51A and 52A is also referred to as the "N-fold wavelength".

[0112] Also, in the present embodiment, the wiring 52A and the wiring 55 are arranged so as to be separated from each other and intersect perpendicularly.

[0113] FIG. 11 is a perspective view showing an example of the structure of the wiring board 31A. FIG. 12 is a cross-sectional view taken along the line S4-S4 of FIG. 11 showing an example of the cross-sectional structure of the wiring board 31A. FIG. 13 is a cross-sectional view taken along the line S5-S5 of FIG. 11 showing an example of the cross-sectional structure of the wiring board 31A. FIG. 14 is a cross-sectional view taken along the line S6-S6 of FIG. 11 showing an example of the cross-sectional structure of the wiring board 31A.

[0114] As shown in FIGS. 11 to 14, the wiring board 31A includes pads Pd1A, Pd2A, and Pd5, coil CL1A, vias 43 and 44, wiring 45, pads Pd3A, Pd4A, and Pd6, coil CL2A, vias 53 and 54, wiring 55, and insulating layers 71 to 79. FIGS. 11 to 13 also show bonding wires 14a, 14b, 24a, and 24b, frames 30a and 30b, and vias 32a and 32b. Note that in FIG. 11, the illustration of vias 43 and 44, wiring 45, vias 53 and 54, wiring 55, vias 32a and 32b, and insulating layers 71 to 79 is omitted.

[0115] As shown in FIG. 11, coil CL1A is provided above coil CL2A in the Z direction. That is, coil CL1A is provided at a position overlapping coil CL2A in the Z direction. In other words, coil CL2A is arranged to face coil CL1A via insulating layers 73 to 77. In the example of FIG. 11, pads Pd1A, Pd2A, and Pd5, and coil CL1A, and pads Pd3A, Pd4A, and Pd6, and coil CL2A are arranged with the same orientation, but they may be arranged after being rotated. In other words, coil CL1A and coil CL2A may be arranged such that the magnetic flux passing through coil CL1A also passes through coil CL2A, and the magnetic flux passing through coil CL2A also passes through coil CL1A.

[0116] Pad Pd1A is connected to bonding wire 14a. Pad Pd2A is connected to bonding wire 14b. The semiconductor chip 11 is connected to coil CL1A via bonding wires 14a and 14b, pads Pd1A and Pd2A, via 43, wiring 45, via 44, and pad Pd5.

[0117] Pad Pd3A is connected to bonding wire 24a via via 32a and frame 30a. Pad Pd4A is connected to bonding wire 24b via via 32b and frame 30b. Semiconductor chip 21 is connected to coil CL2A via bonding wires 24a and 24b, frames 30a and 30b, vias 32a and 32b, pads Pd3A and Pd4A, via 53, wiring 55, via 54, and pad Pd6.

[0118] As shown in FIGS. 12 to 14, wiring board 31A has a structure in which insulating layers 71, 72, 73, 74, 75, 76, 77, 78, and 79 are laminated in this order.

[0119] As shown in FIG. 12, insulating layer 71 has an opening for connecting pad Pd3A and via 32a. Via 32a is provided within the opening of insulating layer 71 and around the opening on the lower surface of insulating layer 71.

[0120] Insulating layer 72 is provided over insulating layer 71 and via 32a. Pad Pd3A, and wirings 51A and 52A (coil CL2A) are provided within insulating layer 72. In other words, pad Pd3A, and wirings 51A and 52A are provided in the same layer. Pad Pd3A is provided over via 32a. In other words, pad Pd3A is in contact with via 32a.

[0121] Insulating layer 73 is provided over insulating layer 72, pad Pd3A, and wirings 51A and 52A. Insulating layer 74 is provided over insulating layer 73. Insulating layer 75 is provided over insulating layer 74. Insulating layer 76 is provided over insulating layer 75. Insulating layer 77 is provided over insulating layer 76.

[0122] Insulating layer 78 is provided over insulating layer 77. Pad Pd1A, and wirings 41A and 42A (coil CL1A) are provided within insulating layer 78. In other words, pad Pd1A, and wirings 41A and 42A are provided in the same layer.

[0123] An insulating layer 78 and an insulating layer 79 are provided over the wirings 41A and 42A. The insulating layer 79 has an opening for connecting the pad Pd1A and the bonding wire 14a. The pad Pd1A is provided under the opening of the insulating layer 79.

[0124] As shown in FIG. 13, the insulating layer 71 has an opening for connecting the pad Pd4A and the via 32b. The via 32b is provided in the opening of the insulating layer 71 and around the opening on the lower surface of the insulating layer 71.

[0125] An insulating layer 72 is provided over the insulating layer 71 and the via 32b. The pad Pd4A is provided in the insulating layer 72. In other words, the pad Pd4A is provided in the same layer as the pad Pd3A. The pad Pd4A is provided over the via 32b. In other words, the pad Pd4A is in contact with the via 32b.

[0126] The pad Pd2A is provided in the insulating layer 78. In other words, the pad Pd2A is provided in the same layer as the pad Pd1A.

[0127] The insulating layer 79 has an opening for connecting the pad Pd2A and the bonding wire 14b. The pad Pd2A is provided under the opening of the insulating layer 79.

[0128] As shown in FIG. 14, the insulating layer 71 has an opening for exposing the pad Pd6. The pad Pd6 is provided in the insulating layer 72. In other words, the pad Pd6 is provided in the same layer as the pads Pd3A and Pd4A. The pad Pd6 is provided over the opening of the insulating layer 71.

[0129] The vias 53 and 54 are provided in the insulating layer 73. The via 53 is provided over the pad Pd4A. The via 54 is provided over the pad Pd6.

[0130] The wiring 55 is provided in the insulating layer 74. The wiring 55 is provided over the vias 53 and 54.

[0131] The insulating layer 79 has an opening for exposing the pad Pd5. The pad Pd5 is provided within the insulating layer 78. In other words, the pad Pd5 is provided in the same layer as the pads Pd1A and Pd2A. The pad Pd5 is provided under the opening of the insulating layer 79.

[0132] The vias 43 and 44 are provided within the insulating layer 77. The via 43 is provided under the pad Pd2A. The via 44 is provided under the pad Pd5.

[0133] The wiring 45 is provided within the insulating layer 76. The wiring 45 is provided under the vias 43 and 44.

[0134] According to the isolator 1A of this embodiment, the power efficiency of the transformer TRA can be improved.

[0135] In this embodiment, the wirings 41A and 42A are connected in parallel to each other between the pad Pd1A and the pad Pd2A. In other words, the coil CL1A has a double-wiring structure of the wirings 41A and 42A. The wirings 51A and 52A are connected in parallel to each other between the pad Pd3A and the pad Pd4A. In other words, the coil CL2A has a double-wiring structure of the wirings 51A and 52A.

[0136] Thereby, compared with the case where the wirings 41A and 42A are connected in series between the pad Pd1A and the pad Pd2A, the combined resistance of the wirings 41A and 42A between the pad Pd1A and the pad Pd2A becomes smaller. Compared with the case where the wirings 51A and 52A are connected in series between the pad Pd3A and the pad Pd4A, the combined resistance of the wirings 51A and 52A between the pad Pd3A and the pad Pd4A becomes smaller.

[0137] Therefore, compared with the case where the coil CL1A is formed by single wiring, the Q value of the coil CL1A becomes larger. Compared with the case where the coil CL2A is formed by single wiring, the Q value of the coil CL2A becomes larger. Thereby, according to this embodiment, the power efficiency of the transformer TRA can be improved.

[0138] Also, in this embodiment, the thickness of wiring 41A is thinner than that of wiring 42A, and the resistance of wiring 41A is greater than that of wiring 42A. The thickness of wiring 51A is thinner than that of wiring 52A, and the resistance of wiring 51A is greater than that of wiring 52A. As a result, compared with the case where the resistance of wiring 41A is the same as that of wiring 42A, the combined resistance of wirings 41A and 42A between pad Pd1A and pad Pd2A becomes smaller. Compared with the case where the resistance of wiring 51A is the same as that of wiring 52A, the combined resistance of wirings 51A and 52A between pad Pd3A and pad Pd4A becomes smaller.

[0139] Therefore, compared with the case where the resistance of wiring 41A is the same as that of wiring 42A, the Q value of coil CL1A becomes larger. Compared with the case where the resistance of wiring 51A is the same as that of wiring 52A, the Q value of coil CL2A becomes larger. Thus, according to this embodiment, the power efficiency of transformer TRA can be improved.

[0140] Furthermore, in this embodiment, the electrical length of wiring 42A is equal to the sum of an N-fold wavelength (N is an integer of 1 or more) and the electrical length of wiring 41A. The electrical length of wiring 52A is equal to the sum of an N-fold wavelength (N is an integer of 1 or more) and the electrical length of wiring 51A. Thereby, generation of a phase shift between the current flowing through wiring 41A and the current flowing through wiring 42A can be suppressed. Generation of a phase shift between the current flowing through wiring 51A and the current flowing through wiring 52A can be suppressed.

[0141] Therefore, compared with the case where the electrical length of wiring 42A is different from the sum of an N-fold wavelength (N is an integer of 1 or more) and the electrical length of wiring 41A, generation of magnetic flux cancellation can be suppressed. Compared with the case where the electrical length of wiring 52A is different from the sum of an N-fold wavelength (N is an integer of 1 or more) and the electrical length of wiring 51A, generation of magnetic flux cancellation can be suppressed. Thereby, a decrease in the coupling coefficient k can be suppressed. For this reason, according to this embodiment, the power efficiency of transformer TRA can be improved.

[0142] Also, in this embodiment, wiring 42A and wiring 45 are spaced apart from each other and intersect perpendicularly. Wiring 52A and wiring 55 are spaced apart from each other and intersect perpendicularly. As a result, the direction of the current flowing through wiring 42A is shifted by 90 degrees from the direction of the current flowing through wirings 45 and 41A. The direction of the current flowing through wiring 52A is shifted by 90 degrees from the direction of the current flowing through wirings 55 and 51A. Therefore, the direction of the magnetic flux generated by the current flowing through wiring 42A is shifted by 90 degrees from the direction of the magnetic flux generated by the current flowing through wirings 45 and 41A. The direction of the magnetic flux generated by the current flowing through wiring 52A is shifted by 90 degrees from the direction of the magnetic flux generated by the current flowing through wirings 55 and 51A.

[0143] Accordingly, cancellation between the magnetic flux generated by the current flowing through wiring 42A and the magnetic flux generated by the current flowing through wirings 45 and 41A can be suppressed. Cancellation between the magnetic flux generated by the current flowing through wiring 52A and the magnetic flux generated by the current flowing through wirings 55 and 51A can be suppressed. Thereby, a decrease in the coupling coefficient k can be suppressed. For this reason, according to this embodiment, the power efficiency of transformer TRA can be improved.

[0144] 3. Modifications and the like As described above, the isolator (1 / 1A) according to the embodiment includes a first pad (Pd1 / Pd1A), a second pad (Pd2 / Pd2A), a first coil (CL1 / CL1A), an insulating layer (63 / 73-77), a third pad (Pd3 / Pd3A), a fourth pad (Pd4 / Pd4A), and a second coil (CL2 / CL2A). The first coil (CL1 / CL1A) includes a first wiring (41 / 41A) and a second wiring (42 / 42A). The first coil (CL1 / CL1A) is connected to the first pad (Pd1 / Pd1A) and the second pad (Pd2 / Pd2A). The second coil (CL2 / CL2A) includes a third wiring (51 / 51A) and a fourth wiring (52 / 52A). The second coil (CL2 / CL2A) is arranged to face the first coil (CL1 / CL1A) via the insulating layer (63 / 73-77). The second coil (CL2 / CL2A) is connected to the third pad (Pd3 / Pd3A) and the fourth pad (Pd4 / Pd4A). The first wiring (41 / 41A) and the second wiring (42 / 42A) are connected in parallel to each other between the first pad (Pd1 / Pd1A) and the second pad (Pd2 / Pd2A). The third wiring (51 / 51A) and the fourth wiring (52 / 52A) are connected in parallel to each other between the third pad (Pd3 / Pd3A) and the fourth pad (Pd4 / Pd4A).

[0145] Note that the embodiment is not limited to the form described above, and various modifications are possible.

[0146] 3.1 Variation of the Second Embodiment An isolator according to a variation of the second embodiment will be described. The isolator 1B according to the variation of the second embodiment is different from the second embodiment in that the structure of the wiring board 31B is different from that of the second embodiment, and the vias 32a and 32b, and the frames 30a and 30b are eliminated. In the following description, the configuration different from that of the second embodiment will be mainly described.

[0147] 3.1.1 Structure of the Isolator The structure of isolator 1B will be described with reference to FIGS. 15 to 17. FIG. 15 is a plan view showing an example of the planar layout of isolator 1B. FIG. 16 is a cross-sectional view taken along line S7-S7 of FIG. 15, showing an example of the cross-sectional structure of isolator 1B. FIG. 17 is a cross-sectional view taken along line S8-S8 of FIG. 15, showing an example of the cross-sectional structure of isolator 1B.

[0148] As shown in FIGS. 15 to 17, isolator 1B includes die pads 10 and 20, semiconductor chips 11 and 21, leads 15 and 25, transformer TRB, and insulating member 100. Note that in FIG. 15, the illustration of insulating member 100 is omitted.

[0149] Die pads 10 and 20, and leads 15 and 25 constitute a lead frame. Hereinafter, die pads 10 and 20, and leads 15 and 25 together will be referred to as "lead frame LFB".

[0150] As shown in FIG. 15, wiring board 31B is disposed on semiconductor chips 11 and 21. Die pads 10 and 20, semiconductor chips 11 and 21, bonding wires 14a, 14b, 16, 24a, 24b, and 26, and wiring board 31B are encapsulated by insulating member 100.

[0151] As shown in FIG. 16, one end of the lower surface of wiring board 31B is provided on semiconductor chip 11. The other end of the lower surface of wiring board 31B is provided on semiconductor chip 21.

[0152] As shown in FIG. 17, one end of bonding wire 24a is provided on semiconductor chip 21. The other end of bonding wire 24a is provided on wiring board 31B.

[0153] 3.1.2 Structure of Wiring Board The structure of wiring board 31B will be described with reference to FIGS. 18 to 23.

[0154] FIG. 18 is a plan view showing an example of the planar layout of the primary circuit FCB in the wiring board 31B. As shown in FIG. 18, the wiring board 31B includes pads Pd1A, Pd2A, Pd5, Pd7, and Pd8, coil CL1A, vias 43, 44, 46, and 47, and wiring 45. Note that in FIG. 18, the illustration of the secondary circuit SCB and the insulating layer in the wiring board 31B is omitted.

[0155] Pad Pd7 is a member that connects coil CL2A and bonding wire 24a. Pad Pd8 is a member that connects coil CL2A and bonding wire 24b. Pads Pd7 and Pd8 have, for example, a substantially rectangular shape in top view. Pads Pd7 and Pd8 are made of a conductive material.

[0156] Via 46 is provided under pad Pd7. In other words, via 46 is in contact with pad Pd7. Via 47 is provided under pad Pd8. In other words, via 47 is in contact with pad Pd8. ViAs 46 and 47 are made of a conductive material.

[0157] FIG. 19 is a plan view showing an example of the planar layout of the secondary circuit SCB in the wiring board 31B. As shown in FIG. 19, the wiring board 31B includes pads Pd3A, Pd4A, Pd6, Pd9, and Pd10, coil CL2A, vias 46, 47, 53, 54, and 56, and wiring 55. Note that in FIG. 19, the illustration of the primary circuit FCB and the insulating layer in the wiring board 31B is omitted.

[0158] Pads Pd9 and Pd10 are members that connect pad Pd3A and pad Pd7. Pad Pd9 is provided above pad Pd3A. Pad Pd10 is provided above pad Pd4A. Pads Pd9 and Pd10 have, for example, a substantially rectangular shape in top view. Pads Pd9 and Pd10 are made of a conductive material.

[0159] Via 46 is provided on pad Pd10. In other words, via 46 is in contact with pad Pd10. Via 47 is provided on pad Pd4A. In other words, via 47 is in contact with pad Pd4A. Via 56 is provided on pad Pd3A. Via 56 is provided under pad Pd9. In other words, via 56 is in contact with pads Pd3A and Pd9. Via 56 is composed of a conductive material.

[0160] The structures of pad Pd3A and coil CL2A are the same as those shown in FIG. 10 of the second embodiment. The structure of pad Pd4A is the same as that of FIG. 10 except that it is larger in size than that of FIG. 10.

[0161] FIG. 20 is a perspective view showing an example of the structure of wiring board 31B. FIG. 21 is a cross-sectional view taken along line S9 - S9 of FIG. 20, showing an example of the cross-sectional structure of wiring board 31B. FIG. 22 is a cross-sectional view taken along line S10 - S10 of FIG. 20, showing an example of the cross-sectional structure of wiring board 31B. FIG. 23 is a cross-sectional view taken along line S11 - S11 of FIG. 20, showing an example of the cross-sectional structure of wiring board 31B.

[0162] As shown in FIGS. 20 to 23, wiring board 31B includes pads Pd1A, Pd2A, Pd5, Pd7, and Pd8, coil CL1A, vias 43, 44, 46, and 47, wiring 45, pads Pd3A, Pd4A, Pd6, Pd9, and Pd10, coil CL2A, vias 53, 54, and 56, wiring 55, and insulating layers 71 to 79. FIGS. 20 to 22 also show bonding wires 14a, 14b, 24a, and 24b. Note that in FIG. 20, the illustration of insulating layers 71 to 79 is omitted.

[0163] As shown in FIG. 20, pad Pd7 is connected to bonding wire 24a. Pad Pd8 is connected to bonding wire 24b.

[0164] As shown in FIG. 21, via 56 is provided in insulating layer 73. Via 56 is provided on pad Pd3A.

[0165] A pad Pd9 is provided in the insulating layer 74. The pad Pd9 is provided on the via 56.

[0166] As shown in FIG. 22, a via 53 is provided in the insulating layer 73. The via 53 is provided on the pad Pd4A.

[0167] A wiring 55 is provided in the insulating layer 74. The wiring 55 is provided on the via 53.

[0168] A via 43 is provided in the insulating layer 77. The via 43 is provided under the pad Pd2A.

[0169] A wiring 45 is provided in the insulating layer 76. The wiring 45 is provided under the via 43.

[0170] As shown in FIG. 23, a pad Pd10 is provided in the insulating layer 74. Note that the pad Pd10 is electrically connected to the pad Pd9. The via 46 penetrates the insulating layers 75 to 77. The via 46 is provided on the pad Pd10. The via 46 is provided under the pad Pd7. In other words, the via 46 is in contact with the pads Pd7 and Pd10. The via 47 penetrates the insulating layers 73 to 77. The via 47 is provided on the pad Pd4A. The via 47 is provided under the pad Pd8. In other words, the via 47 is in contact with the pads Pd4A and Pd8.

[0171] According to the isolator 1B of this modified example, similarly to the second embodiment, the power efficiency of the transformer TRB can be improved.

[0172] 3.2 Modified Example of the First Embodiment An isolator according to a modified example of the first embodiment will be described. The isolator 1C according to the modified example of the first embodiment is different from the first embodiment in that the structure of the wiring board 31C is different from that of the first embodiment, and the vias 32a and 32b, and the frames 30a and 30b are omitted. In the following description, the configurations different from those of the first embodiment will be mainly described.

[0173] 3.2.1 Structure of the Isolator The structure of the isolator 1C is the same as that shown in FIGS. 15 to 17 in the second embodiment.

[0174] 3.2.2 Structure of the Wiring Board The structure of the wiring board 31C will be described with reference to FIGS. 24 to 29.

[0175] FIG. 24 is a plan view showing an example of the planar layout of the primary circuit FCC in the wiring board 31C. As shown in FIG. 24, the wiring board 31C includes pads Pd1, Pd2, Pd7, and Pd8, a coil CL1, and vias 46 and 47. Note that in FIG. 24, the illustration of the secondary circuit SCC and the insulating layer in the wiring board 31C is omitted.

[0176] The pad Pd7 is a member that connects the coil CL2 and the bonding wire 24a. The pad Pd8 is a member that connects the coil CL2 and the bonding wire 24b. The pads Pd7 and Pd8 have, for example, a substantially rectangular shape in a top view. The pads Pd7 and Pd8 are made of a conductive material.

[0177] The via 46 is provided under the pad Pd7. In other words, the via 46 is in contact with the pad Pd7. The via 47 is provided under the pad Pd8. In other words, the via 47 is in contact with the pad Pd8. The vias 46 and 47 are made of a conductive material.

[0178] The structures of the pads Pd1, Pd2, and the coil CL1 are the same as those shown in FIG. 3 in the first embodiment.

[0179] FIG. 25 is a plan view showing an example of the planar layout of the secondary circuit SCC in the wiring board 31C. As shown in FIG. 25, the wiring board 31C includes pads Pd3, Pd4, Pd9, and Pd10, a coil CL2, and vias 46, 47, and 56. Note that in FIG. 25, the illustration of the primary circuit FCC and the insulating layer in the wiring board 31C is omitted.

[0180] Pads Pd9 and Pd10 are members that connect pad Pd3 and pad Pd7. Pad Pd9 is provided above pad Pd3. Pad Pd10 is provided above pad Pd4. Pads Pd9 and Pd10 have, for example, a substantially rectangular shape in top view. Pads Pd9 and Pd10 are made of a conductive material.

[0181] Via 46 is provided on pad Pd10. In other words, via 46 is in contact with pad Pd10. Via 47 is provided on pad Pd4. In other words, via 47 is in contact with pad Pd4. Via 56 is provided on pad Pd3. Via 56 is provided under pad Pd9. In other words, via 56 is in contact with pads Pd3 and Pd9. Via 56 is made of a conductive material.

[0182] The structure of pad Pd3 and coil CL2 is the same as that shown in FIG. 5 of the first embodiment. The structure of pad Pd4 is the same as that of FIG. 5 except that the size is larger than that of FIG. 5.

[0183] FIG. 26 is a perspective view showing an example of the structure of wiring board 31C. FIG. 27 is a cross-sectional view taken along line S12 - S12 of FIG. 26 showing an example of the cross-sectional structure of wiring board 31C. FIG. 28 is a cross-sectional view taken along line S13 - S13 of FIG. 26 showing an example of the cross-sectional structure of wiring board 31C. FIG. 29 is a cross-sectional view taken along line S14 - S14 of FIG. 26 showing an example of the cross-sectional structure of wiring board 31C.

[0184] As shown in FIGS. 26 to 29, wiring board 31C includes pads Pd1, Pd2, Pd7, and Pd8, coil CL1, vias 46 and 47, pads Pd3, Pd4, Pd9, and Pd10, coil CL2, via 56, and insulating layers 61 to 67. FIGS. 26 to 28 also show bonding wires 14a, 14b, 24a, and 24b. Note that in FIG. 26, the illustration of insulating layers 61 to 67 is omitted.

[0185] As shown in FIG. 26, pad Pd7 is connected to bonding wire 24a. Pad Pd8 is connected to bonding wire 24b.

[0186] As shown in FIGS. 27 to 29, wiring board 31C has a structure in which insulating layers 61, 62, 63, 66, 67, 64, and 65 are laminated in this order. In other words, wiring board 31C has a structure in which insulating layers 66 and 67 are provided between insulating layer 63 and insulating layer 64 shown in FIGS. 7 and 8 of the first embodiment.

[0187] As shown in FIG. 27, via 56 is provided in insulating layer 63. Via 56 is provided above pad Pd3.

[0188] Insulating layer 66 is provided above insulating layer 63. Insulating layer 67 is provided above insulating layer 66. Insulating layer 64 is provided above insulating layer 67.

[0189] Pad Pd9 is provided in insulating layer 66. Pad Pd9 is provided above via 56.

[0190] As shown in FIG. 28, pad Pd4 is larger in size than pad Pd2.

[0191] As shown in FIG. 29, pad Pd10 is provided in insulating layer 66. Note that pad Pd10 is electrically connected to pad Pd9. Via 46 is provided in insulating layer 67. Via 46 is provided above pad Pd10. Via 46 is provided below pad Pd7. In other words, via 46 is in contact with pads Pd7 and Pd10. Via 47 penetrates through insulating layers 63, 66, and 67. Via 47 is provided above pad Pd4. Via 47 is provided below pad Pd8. In other words, via 47 is in contact with pads Pd4 and Pd8.

[0192] According to isolator 1C of this modification, similar to the first embodiment, the power efficiency of transformer TRC can be improved.

[0193] In addition, the above-described embodiments and modifications are also applicable to isolators having two or more channels.

[0194] In this specification, "connection" means being electrically connected, and for example, it does not exclude having another element in between.

[0195] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0196] 1, 1A, 1B, 1C... isolators, 10, 20... die pads, 11, 21... semiconductor chips, 12, 22... circuits, 13, 23... adhesive members, 14a, 14b, 16, 24a, 24b, 26... bonding wires, 15, 25... leads, 30a, 30b... frames, 31, 31A, 31B, 31C... wiring boards, 32a, 32b, 43, 44, 46, 47, 53, 54, 56... vias, 41, 42, 45, 51, 52, 55... wirings, 61 - 67, 71 - 79... insulating layers, 100... insulating members, LF, LFB... lead frames, TR, TRA, TRB, TRC... transformers, CL1, CL1A, CL2, CL2A... coils, Pd1, Pd1A, Pd2, Pd2A, Pd3, Pd3A, Pd4, Pd4A, Pd5, Pd6, Pd7, Pd8, Pd9, Pd10... pads

Claims

1. a first pad, a second pad, a first coil including a first wiring and a second wiring, and connected to the first pad and the second pad, an insulating layer, a third pad, a fourth pad, a second coil including a third wiring and a fourth wiring, arranged to face the first coil via the insulating layer, and connected to the third pad and the fourth pad and comprising the first wiring and the second wiring are connected in parallel to each other between the first pad and the second pad, the third wiring and the fourth wiring are connected in parallel to each other between the third pad and the fourth pad, an isolator.

2. the electrical length of the second wiring is equal to the electrical length of the first wiring, the electrical length of the fourth wiring is equal to the electrical length of the third wiring, the isolator according to Claim 1.

3. the first pad includes a first base portion and a first protruding portion protruding from the first base portion in a first direction, the second pad includes a second base portion and a second protruding portion protruding from the second base portion in a second direction intersecting the first direction, the first wiring has a first end connected to the first base portion of the first pad and a second end connected to the second base portion of the second pad, the second wiring has a third end connected to the first protruding portion of the first pad and a fourth end connected to the second protruding portion of the second pad, the third pad includes a third base portion and a third protruding portion protruding from the third base portion in the first direction, the fourth pad includes a fourth base portion and a fourth protruding portion protruding from the fourth base portion in the second direction, The third wiring has a fifth end connected to the third base portion of the third pad and a sixth end connected to the fourth base portion of the fourth pad. The fourth wiring has a seventh end connected to the third protruding portion of the third pad and an eighth end connected to the fourth protruding portion of the fourth pad. The isolator according to claim 2.

4. The first wiring has a spiral shape that extends from the first end in the first rotation direction and outward in a top view. The second wiring is spaced apart from the first wiring and has a spiral shape that extends from the third end in the first rotation direction and outward in a top view. The third wiring has a spiral shape that extends from the fifth end in the first rotation direction and outward in a top view. The fourth wiring is spaced apart from the third wiring and has a spiral shape that extends from the seventh end in the first rotation direction and outward in a top view. The isolator according to claim 3.

5. The electrical length of the second wiring is equal to the sum of the electrical length of the first wiring and N times the wavelength of the current flowing through the first wiring and the second wiring (N is an integer of 1 or more). The electrical length of the fourth wiring is equal to the sum of the electrical length of the third wiring and N times the wavelength of the current flowing through the third wiring and the fourth wiring (N is an integer of 1 or more). The isolator according to claim 1.

6. A fifth pad, A fifth wiring, A sixth pad, A sixth wiring and further includes The first wiring has a first end connected to the first pad and a second end connected to the second pad. The second wiring has a third end connected to the first pad and a fourth end connected to the second pad. The second end of the first wiring is connected to the second pad via the fifth pad and the fifth wiring. The second wiring and the fifth wiring are spaced apart from each other and intersect perpendicularly. The third wiring has a fifth end connected to the third pad and a sixth end connected to the fourth pad. The fourth wiring has a seventh end connected to the third pad and an eighth end connected to the fourth pad. The sixth end of the third wiring is connected to the fourth pad via the sixth pad and the sixth wiring. The fourth wiring and the sixth wiring are spaced apart from each other and intersect perpendicularly. The isolator according to claim 5.

7. The first wiring has a spiral shape that extends from the first end in the first rotation direction and outward in a top view. The second wiring is spaced apart from the first wiring and has a spiral shape that extends from the third end in the first rotation direction and outward in a top view. The third wiring has a spiral shape that extends from the fifth end in the first rotation direction and outward in a top view. The fourth wiring is spaced apart from the third wiring and has a spiral shape that extends from the seventh end in the first rotation direction and outward in a top view. The isolator according to claim 6.

8. The thickness of the first wiring is thinner than the thickness of the second wiring. The thickness of the third wiring is thinner than the thickness of the fourth wiring. The isolator according to claim 5.

9. The second wiring is provided on the same layer as the first wiring. The fourth wiring is provided on the same layer as the third wiring. The isolator according to claim 1.

10. A first semiconductor chip connected to the first coil via the first pad and the second pad, A second semiconductor chip connected to the second coil via the third pad and the fourth pad further comprising the isolator according to claim 1.

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