TWI804000B - Co-axial via structure - Google Patents

Abstract

A co-axial structure includes a substrate, a first conductive structure, a second conductive structure, and an insulating layer. The substrate includes a first surface. The first conductive structure includes a first circuit disposed on the first surface and a first via penetrating the substrate. The second conductive structure includes a second circuit disposed on the first surface and a second via penetrating the substrate. The first via and the second via extend along a first direction. The first circuit and the second circuit extend along a second direction, and the second direction is perpendicular to the first direction. The insulating layer is located between the first via and the second via. The insulating layer includes fillers. The first conductive structure and the second conductive structure are electrically insulated. The first circuit and the second circuit are co-planar.

Description

coaxial via structure

The present disclosure relates to a coaxial via structure, in particular to a coaxial via structure with coplanar signal lines and ground lines.

Most of the current coaxial via structures require a build-up process to place a dielectric layer between the ground line and the signal line of different layers, which requires a lot of cost. Since the inner and outer traces in the via are not at the same height, an impedance mismatch problem arises. The dielectric layer disposed between the ground wire and the signal wire will also produce shielding gaps, resulting in poor electromagnetic shielding effect. In addition, because most of the hole-filling materials of the insulating layer have a high dielectric constant, the power loss caused by impedance mismatch is a serious problem.

In view of this, how to provide a coaxial via structure that can improve impedance matching and electromagnetic shielding effects is still one of the goals that the industry needs to study urgently.

One technical aspect of the present disclosure is a coaxial through-hole structure.

In an embodiment of the present disclosure, the coaxial via structure includes a substrate, a first conductive structure, a second conductive structure, and an insulating layer. The substrate has the a surface. The first conductive structure includes a first circuit on the first surface and a first through hole penetrating through the substrate. The second conductive structure includes a second line on the first surface of the substrate and a second through hole penetrating through the substrate. The first through hole and the second through hole extend in a first direction, the first circuit and the second circuit extend in a second direction, and the second direction is perpendicular to the first direction. The insulating layer is located between the first through hole and the second through hole, and the insulating layer has filling material, wherein the first conductive structure is electrically insulated from the second conductive structure, and the first circuit and the second circuit are coplanar.

In an embodiment of the present disclosure, the filling material includes air.

In an embodiment of the present disclosure, the first through hole of the first conductive structure surrounds the second through hole of the second conductive structure and the insulating layer.

In an embodiment of the disclosure, the insulating layer, the first through hole and the second through hole are coaxial.

In an embodiment of the present disclosure, the insulating layer has a protruding portion located at an end of the insulating layer close to the first surface.

One technical aspect of the present disclosure is a coaxial through-hole structure.

In an embodiment of the present disclosure, the coaxial via structure includes a substrate, a first conductive structure, a second conductive structure, an insulating layer, and an air hole. The substrate has a first surface. The first conductive structure includes a first circuit on the first surface and a first through hole penetrating through the substrate. The second conductive structure includes a second line on the first surface of the substrate and a second through hole penetrating through the substrate. The first through hole and the second through hole extend in a first direction, the first circuit and the second circuit extend in a second direction, and the second direction is perpendicular to the first direction. The insulating layer is located between the first through hole and the second through hole, and the insulating layer has filling material, Wherein the first conductive structure is electrically insulated from the second conductive structure, and the first circuit and the second circuit are coplanar. The air hole is located between the first through hole and the second through hole, and the air hole penetrates the insulating layer along the first direction.

In an embodiment of the present disclosure, the top view shape of the air hole in the first direction is an arc, and the air hole surrounds the second through hole.

In an embodiment of the present disclosure, the first through hole of the first conductive structure surrounds the second through hole of the second conductive structure and the insulating layer.

In an embodiment of the disclosure, the insulating layer, the first through hole and the second through hole are coaxial.

In an embodiment of the present disclosure, the insulating layer has a protruding portion located at an end of the insulating layer close to the first surface.

In the above-mentioned embodiments, since the coaxial via structure of the present disclosure has the coplanar first line and the second line, and the first conductive structure and the second conductive structure can be electrically insulated through the insulating layer, the coaxial via structure of the present disclosure The shaft through-hole structure can have better electromagnetic noise shielding and impedance matching effects to improve high-frequency signal integrity. The disclosed coaxial via structure can reduce the number of dielectric layers, reduce the thickness of the coaxial via structure, and lower the cost. In addition, the overall dielectric constant of the insulating layer of the coaxial via structure can be reduced by fillers or air holes. In this way, the problem of power loss caused by the impedance mismatch of the vias can be reduced.

100, 100a, 100b: coaxial through-hole structure

110: Substrate

112: first surface

114: second surface

116: Internal wiring

120: the first conductive structure

120M: the first conductive material

122: The first line

124: the first through hole

126: The third line

130: second conductive structure

130M: second conductive material

132: second line

134: Second through hole

136: The fourth line

140, 140a, 140b: insulating layer

140M: insulating layer material

142: The first protrusion

144: second protrusion

146: filler

148a, 148b: air hole

150: dielectric layer

160: mask

170: insulating protective layer

D1: the first direction

D2: Second direction

OP1: the first through hole

OP2: Second through hole

TR1: first groove

TR2: second groove

A: axis

3B-3B, 4B-4B, 5B-5B, 6B-6B, 7B-7B, 8B-8B, 9B-9B, 10B-10B, 11B-11B, 12B-12B: line segment

W1, W2: width

I: Spacing

FIG. 1 is a cross-sectional view of a coaxial via structure according to an embodiment of the present disclosure.

Fig. 2 is a perspective view of the first through hole, the second circuit, the second through hole and the insulating layer in Fig. 1 .

FIG. 3A to FIG. 11A are top views of intermediate steps of a method for manufacturing a coaxial via structure according to an embodiment of the present disclosure.

Figures 3B to 11B are cross-sectional views along line 3B-3B to line 11B-11B in Figures 3A to 11A, respectively.

FIG. 12A is a top view of a coaxial via structure according to another embodiment of the present disclosure.

Figure 12B is a cross-sectional view along line 12B-12B in Figure 12A.

FIG. 13 is a top view of a coaxial via structure according to another embodiment of the disclosure.

Several embodiments of the present invention will be disclosed in the following figures. For the sake of clarity, many practical details will be described together in the following description. It should be understood, however, that these practical details should not be used to limit the invention. That is, in some embodiments of the present invention, these practical details are unnecessary. In addition, for the sake of simplifying the drawings, some well-known structures and components will be shown in a simple and schematic manner in the drawings. Also, the thicknesses of layers and regions in the drawings may be exaggerated for clarity, and the same reference numerals denote the same elements in the description of the drawings.

FIG. 1 is a cross-sectional view of a coaxial via structure 100 according to an embodiment of the present disclosure. The coaxial via structure 100 includes a substrate 110, a second A conductive structure 120 , a second conductive structure 130 and an insulating layer 140 .

The substrate 110 has a first surface 112 and a second surface 114 opposite to each other. The first conductive structure 120 includes a first circuit 122 and a first through hole 124 , and the second conductive structure 130 includes a second circuit 132 and a second through hole 134 . The first wiring 122 and the second wiring 132 are located on the first surface 112 . The first through hole 124 and the second through hole 134 pass through the substrate 110 . The first through hole 124 and the second through hole 134 extend in the first direction D1. The first line 122 and the second line 132 extend in a second direction D2 perpendicular to the first direction D1. The first trace 122 of the first conductive structure 120 is coplanar with the second trace 132 of the second conductive structure 130 . In other words, the first line 122 and the second line 132 are on the same level.

In this embodiment, the first direction D1 is a vertical direction in the figure, that is, the first direction D1 is a direction from the first surface 112 to the second surface 114 . The second direction D2 can be any horizontal direction perpendicular to the first direction D1, which will be described first. In this embodiment, the first line 122 and the third line 126 can be ground lines, and the second line 132 and the fourth line 136 can be signal lines, but the disclosure is not limited thereto.

As shown in FIG. 1 , the first conductive structure 120 further includes a third circuit 126 on the second surface 114 , and the second conductive structure 130 further includes a fourth circuit 136 on the second surface 114 . Two ends of the first through hole 124 are respectively connected to the first circuit 122 and the third circuit 126 . Two ends of the second through hole 134 are respectively connected to the second circuit 132 and the fourth circuit 136 . The third line 126 and the fourth line 136 extend in the second direction D2, and the third line 126 and the fourth line 136 are coplanar. In other words That is, the third line 126 and the fourth line 136 are on the same level.

The insulating layer 140 is located between the first through hole 124 and the second through hole 134 , and the insulating layer 140 extends in the first direction D1. The first through hole 124 surrounds the second through hole 134 and the insulating layer 140 , and the insulating layer 140 surrounds the second through hole 134 . As shown in FIG. 1 , the insulating layer 140 , the first through hole 124 and the second through hole 134 are coaxial with respect to the axis A. As shown in FIG.

The insulating layer 140 is a pore filler with a filler 146 , and the filler 146 includes air. Since the dielectric constant value (Dk) of air is 1, the dielectric constant of the insulating layer 140 as a whole can be reduced by adding air. In this way, the power loss problem (Impedance Mismatch Loss) caused by impedance mismatch can be reduced.

FIG. 2 is a perspective view of the first through hole 124 , the second circuit 132 , the second through hole 134 and the insulating layer 140 in FIG. 1 . Refer to Figure 1 and Figure 2 at the same time. The insulating layer 140 has a first protruding portion 142 , and the first protruding portion 142 is located at an end of the insulating layer 140 close to the first surface 112 . The first protrusion 142 protrudes away from the second through hole 134 along the second direction D2. As shown in FIG. 1 , the substrate 110 further includes a dielectric layer 150 between the first surface 112 and the second surface 114 . In this embodiment, the substrate 110 further includes multilayer internal circuits 116 separated by the dielectric layer 150 , but the disclosure is not limited thereto. The first protrusion 142 of the insulating layer 140 contacts the dielectric layer 150 close to the first surface 112 . In other words, the first protruding portion 142 extends to the dielectric layer 150 through the first through hole 124 .

As shown in Figure 1, the first through hole of the first conductive structure 120 124 , the first protruding portion 142 of the insulating layer 140 , and the second line 132 of the second conductive structure 130 overlap in the first direction D1. The second line 132 of the second conductive structure 130 extends from the second through hole 134 and crosses the first protrusion 142 . In other words, the first through hole 124 and the second circuit 132 are electrically insulated by the first protrusion 142 , and the coplanar first circuit 122 and the second circuit 132 are separated from each other, so that the first conductive structure 120 and the second circuit 132 are separated from each other. The second conductive structure 130 is electrically insulated.

According to the above, since the first line 122 and the second line 132 of the coaxial via structure 100 are coplanar, and the first conductive structure 120 and the second conductive structure 130 are electrically insulated, the addition of an additional dielectric layer in the past can be omitted. A step of electrically isolating the first wiring on different layers from the second wiring. In this way, the first through hole 124 and the second through hole 134 in this application may have approximately the same height, so that the overall structure of the coaxial through hole structure 100 is more symmetrical, thereby improving the effect of impedance matching. In addition, since the present invention can omit the dielectric layer between the first circuit and the second circuit in different layers, the situation that the second through hole 134 protrudes out of the insulating layer is avoided. In this way, the coaxial through-hole structure in this case can avoid the problem of poor electromagnetic shielding effect caused by the gap in the shielding structure.

As shown in FIG. 1 , the insulating layer 140 also has a second protruding portion 144 , and the second protruding portion 144 is located at an end of the insulating layer 140 close to the second surface 114 . The second protrusion 144 protrudes away from the second through hole 134 along the second direction D2. The second protrusion 144 of the insulating layer 140 contacts the dielectric layer 150 near the second surface 114 . In other words, the second protrusion 144 extends to the dielectric layer 150 through the first through hole 124 .

As shown in FIG. 1 , the first through hole 124 of the first conductive structure 120 , the second protrusion 144 of the insulating layer 140 , and the fourth line 136 of the second conductive structure 130 overlap in the first direction D1 . The fourth line 136 of the second conductive structure 130 extends from the second through hole 134 and crosses the second protrusion 144 . In other words, the first through hole 124 and the fourth circuit 136 are electrically insulated by the second protrusion 144, and the third circuit 126 and the fourth circuit 136 are separated from each other, thereby making the first conductive structure 120 and the second conductive structure 120 electrically insulated. Structure 130 is electrically insulated. As mentioned above, the extending direction of the fourth line 136 can be any horizontal direction perpendicular to the first direction D1, and FIG. 1 is only an example, and the present disclosure is not limited thereto.

It should be understood that the connection relationship, materials and functions of the components that have been described will not be repeated, and will be described first. In the following description, the manufacturing method of the coaxial via structure will be described.

FIG. 3A to FIG. 10A are top views of intermediate steps of a method for manufacturing a coaxial via structure according to an embodiment of the present disclosure. Figures 3B to 10B are cross-sectional views along line 3B-3B to line 10B-10B in Figures 3A to 10B, respectively. As shown in FIG. 3A and FIG. 3B , the manufacturing method of the coaxial via structure begins with forming the first through hole OP1 in the substrate 110 . The first through hole OP1 penetrates through the internal circuit 116 and the dielectric layer 150 of the substrate 110 . For example, the method of forming the first through hole OP1 may be laser drilling.

As shown in FIG. 4A and FIG. 4B, in the manufacturing method of the coaxial through hole structure, the first conductive material 120M is then formed on the first surface 112, on the second surface 114 and in the first through hole OP1 wall superior. The method of forming the first conductive material 120M is, for example, electroplating, and the first conductive material 120M is, for example, copper, but the present disclosure is not limited thereto, and those skilled in the art can select appropriate methods and materials according to actual conditions.

As shown in FIG. 5A and FIG. 5B , in the manufacturing method of the coaxial through-hole structure, the first groove TR1 is formed next. The first groove TR1 is recessed from the first surface 112 , and the first groove TR1 communicates with the first through hole OP1 . The method of forming the first groove TR1 includes drilling from the first surface 112 along the first direction D1, and exposing the dielectric layer 150 close to the first surface 112 from the first conductive material 120M.

Referring to FIG. 5B, this step also includes forming a second groove TR2. The second groove TR2 is recessed from the second surface 114 , and the second groove TR2 communicates with the first through hole OP1 . The method of forming the second groove TR2 includes drilling from the second surface 114 along the direction opposite to the first direction D1, and exposing the dielectric layer 150 close to the second surface 114 from the first conductive material 120M. For example, the method of forming the first groove TR1 and the second groove TR2 may be laser drilling.

In the top view of FIG. 5A, the distance between the first groove TR1 and the first through hole OP1 can be calculated according to the width of the second line 132 and the required distance between the first line 122 and the second line 132 . Similarly, in a bottom view (not shown), the distance between the second groove TR2 and the first through hole OP1 can be determined according to the width of the fourth line 136 and the required distance between the third line 126 and the fourth line 136 calculated.

As shown in FIG. 6A and FIG. 6B, in the manufacturing method of the coaxial via structure, the insulating layer material 140M is then filled into the first via hole OP1, the first groove TR1 and the second groove TR2, and make the insulating layer material 140M contact the dielectric layer 150 exposed from the first conductive material 120M. In this embodiment, the insulating layer material 140M can be, for example, hole-filling ink, but the disclosure is not limited thereto. As mentioned above, the insulating layer material 140M has a filler 146 containing air. After filling the insulating layer material 140M, the exposed parts of the insulating layer material 140M from the first surface 112 and the second surface 114 are ground so that the upper surface and the lower surface of the insulating layer 140 are respectively flush with the first conductive material 120M.

As shown in FIG. 7A and FIG. 7B , in the manufacturing method of the coaxial via structure, the second through hole OP2 is then formed in the insulating layer material 140M. In this embodiment, the second through hole OP2 and the first through hole OP1 are concentric circles. For example, the method of forming the second through hole OP2 is laser drilling, thereby removing a part of the insulating layer material 140M. After the second through hole OP2 is formed, the remaining insulating layer material 140M includes the part (ie, the insulating layer 140 ) located in the first through hole OP1 and the first protruding portion 142 and the second protruding portion 142 respectively located on both sides of the substrate 110 . protrusion 144 .

As shown in FIG. 8A and FIG. 8B , in the manufacturing method of the coaxial via structure, the second conductive material 130M is then formed on the first surface 112 , on the second surface 114 and in the second through hole OP2 . The method of forming the first conductive material 120M can be, for example, electroplating, and the first conductive material 120M is, for example, copper, but the present disclosure is not limited thereto, and those skilled in the art can select appropriate methods and materials according to actual conditions.

The second conductive material 130M is located in the second through hole OP2, and the first conductive material 120M in the first through hole OP1 (that is, the first through hole 124) surround the insulating layer 140 and the second conductive material 130M in the second through hole OP2 (that is, the second through hole 134), so that the insulating layer 140, the first conductive material 120M in the first through hole OP1 and the second through hole The second conductive material 130M in OP2 is coaxial with respect to the axis A.

As shown in FIG. 9A and FIG. 9B , in the manufacturing method of the coaxial via structure, a mask 160 is then formed on the first surface 112 and the second surface 114 . The photomask 160 includes patterns for forming the first lines 122 and the second lines 132 and patterns for forming the third lines 126 and the fourth lines 136 .

As shown in FIG. 10A and FIG. 10B , in the manufacturing method of the coaxial via structure, the first conductive material 120M and the second conductive material 130M are then patterned by a photomask 160 . The second conductive material 130M and the first conductive material 120M exposed from the photomask 160 are successively removed until the insulating layer 140 and the dielectric layer 150 are exposed from the photomask 160 .

Also refer to Figures 10A, 10B, 11A and 11B. In the manufacturing method of the coaxial via structure, the photomask 160 is finally removed, and the insulating protection layer 170 is formed. The insulating protection layer 170 has openings for connecting conductive elements, such as metal bumps, bumps or solder balls (not shown).

As shown in FIG. 11B , after the above steps, the first lines 122 and the second lines 132 separated from each other can be formed, and the first lines 122 and the second lines 132 are coplanar. The first through hole 124 and the second circuit 132 are electrically insulated by the first protrusion 142 in the first groove TR1. The first line 122 can contain any line pattern, as long as the first line It is sufficient that the circuit 122 is electrically insulated from the second circuit 132 .

Similarly, after the above steps, the third lines 126 and the fourth lines 136 separated from each other can be formed, and the third lines 126 and the fourth lines 136 are coplanar. The first through hole 124 is electrically insulated from the fourth line 136 by the second protrusion 144 in the second groove TR2. The third circuit 126 may include any circuit pattern (not shown), as long as the third circuit 126 is electrically insulated from the fourth circuit 136 .

See Figure 11A. In this example, the second line 132 has a width W1, and the connection between the insulating layer 140 and the first protrusion 142 has a width W2. The width W2 can be correspondingly adjusted by changing the distance between the first groove TR1 and the first through hole OP1, and the width W2 can also depend on the diameter of the first groove TR1. Therefore, according to the required width W1, an appropriate distance between the first groove TR1 and the first through hole OP1 can be calculated in the step of forming the first groove TR1. In this way, the width W2 can be ensured to be wide enough to reduce the risk of disconnection of the second circuit 132 . There is an interval I between the second line 132 and the adjacent first line 122 . Under the limitation of specific impedance requirements, the distance I can be determined according to the width W1 and thickness of the second line 132 and the parameters of the dielectric layer 150 , so as to improve the impedance matching effect.

FIG. 12A is a top view of a coaxial via structure 100a according to another embodiment of the present disclosure. Figure 12B is a cross-sectional view along line 12B-12B in Figure 12A. The coaxial via structure 100a is substantially the same as the coaxial via structure 100 in FIG. 1, the difference is that the insulating layer 140a of the coaxial via structure 100a does not have a filler 146 (see FIG. 1), And the coaxial through-hole structure 100a has an air hole 148a. The air hole 148 a is located between the first through hole 124 and the second through hole 134 . The air hole 148a penetrates the insulating layer 140a along the first direction D1. The first direction D1 corresponds to the direction perpendicular to the paper in FIG. 12A. The air holes 148a can be formed by mechanical drilling. In this embodiment, the coaxial through-hole structure 100 a has six air holes 148 a arranged in a manner surrounding the second through-hole 134 , but the disclosure is not limited thereto. The number and size of the air holes 148 a can be adjusted according to actual requirements, as long as the insulating layer 140 a has enough structural support to support the second through hole 134 and the second circuit 132 . Since the dielectric constant value (Dk) of air is 1, the dielectric constant of the insulating layer 140a as a whole can be reduced by the air holes 148a. In this way, the problem of power loss caused by impedance mismatch can be reduced.

FIG. 13 is a top view of a coaxial via structure 100b according to another embodiment of the present disclosure. The coaxial through-hole structure 100b is substantially the same as the coaxial through-hole structure 100a in FIG. 12A, the difference is that the top view shape of the air hole 148b in the coaxial through-hole structure 100b in the first direction D1 (see FIG. 12B ) is an arc shape. The first direction D1 corresponds to the direction perpendicular to the paper surface in FIG. 13 . In other words, the arc-shaped air hole 148b can be regarded as a slot formed by a plurality of air holes 148a in FIG. 12 , and the air hole 148b can be formed by milling. In this embodiment, the coaxial through-hole structure 100a has three air holes 148b, but the disclosure is not limited thereto. The number and size of the air holes 148b can be adjusted according to actual needs, as long as the insulating layer 140b has enough structural support to support the second through hole 134 and the second circuit 132 . Due to the dielectric constant value of air (Dk) is 1, the overall dielectric constant of the insulating layer 140b can be reduced by the air holes 148b. In this way, the problem of power loss caused by the impedance mismatch of the vias can be reduced.

In summary, since the coaxial via structure of the present disclosure has coplanar ground lines and signal lines (the first line and the second line), and the first conductive structure and the second conductive structure can be electrically insulated through the insulating layer , so the coaxial via structure of the present disclosure can have better electromagnetic noise shielding and impedance matching effects, so as to improve the integrity of high-frequency signals. The disclosed coaxial via structure can also reduce the number of dielectric layers, reduce the thickness of the coaxial via structure, and lower the cost. In addition, the overall dielectric constant of the insulating layer of the coaxial via structure can be reduced by fillers or air holes. In this way, the problem of power loss caused by the impedance mismatch of the vias can be reduced.

Although the present invention has been disclosed above in terms of implementation, it is not intended to limit the present invention. Anyone skilled in this art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection of the present invention The scope shall be defined by the appended patent application scope.

110: Substrate

112: first surface

114: second surface

116: Internal wiring

120: the first conductive structure

122: The first line

124: the first through hole

126: The third line

130: second conductive structure

132: second line

134: Second through hole

136: The fourth line

140: insulating layer

142: The first protrusion

144: second protrusion

146: filler

150: dielectric layer

A: axis

D1: the first direction

D2: Second direction

Claims (10)

A coaxial via structure comprising: A substrate having a first surface; A first conductive structure, comprising a first circuit on the first surface and a first through hole penetrating the substrate; a second conductive structure comprising a second circuit on the first surface of the substrate and a second through hole penetrating through the substrate, the first through hole and the second through hole extending in a first direction, the first line and the second line extend in a second direction, and the second direction is perpendicular to the first direction; and An insulating layer is located between the first through hole and the second through hole, wherein the insulating layer has a filling material, the first conductive structure is electrically insulated from the second conductive structure, and the first circuit and the second conductive structure are electrically insulated. The second line is coplanar. The coaxial via structure as claimed in claim 1, wherein the filler contains air. The coaxial via structure as claimed in claim 1, wherein the first via of the first conductive structure surrounds the second via of the second conductive structure and the insulating layer. The coaxial via structure as claimed in claim 1, wherein the insulating layer, the first via hole and the second via hole are coaxial. The coaxial via structure as claimed in claim 1, wherein the insulating layer has a protruding portion located at an end of the insulating layer close to the first surface. A coaxial via structure comprising: A substrate having a first surface; A first conductive structure, comprising a first circuit on the first surface and a first through hole penetrating the substrate; a second conductive structure comprising a second circuit on the first surface of the substrate and a second through hole penetrating through the substrate, the first through hole and the second through hole extending in a first direction, the first line and the second line extend in a second direction, and the second direction is perpendicular to the first direction; an insulating layer located between the first via hole and the second via hole, wherein the first conductive structure is electrically insulated from the second conductive structure, and the first line is coplanar with the second line; and An air hole is located between the first through hole and the second through hole, and the air hole penetrates the insulating layer along the first direction. The coaxial through-hole structure according to claim 6, wherein the top view shape of the air hole in the first direction is arc-shaped, and the air hole surrounds the second through-hole. The coaxial via structure as claimed in claim 6, wherein the first via of the first conductive structure surrounds the second via of the second conductive structure and the insulating layer. The coaxial via structure according to claim 6, wherein the insulating layer, the first via hole and the second via hole are coaxial. The coaxial via structure as claimed in claim 6, wherein the insulating layer has a protruding portion located at an end of the insulating layer close to the first surface.

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