Printed circuit board and method for manufacturing the same

Abstract

To provide a printed circuit board and a method for manufacturing the same, which can realize a wiring layer having a fine pitch, a wiring layer in which some parts are buried and other parts protrude, and improve the reliability.SOLUTION: The present disclosure relates to a printed circuit board including a first insulating layer including a groove portion on an upper side thereof, a buried portion buried in the groove portion, and a first wiring layer having a protruding portion protruding onto the first insulating layer, and the protruding portion of the first wiring layer has a width at its lower end that is narrower than that at its upper end, and also relates to a method for manufacturing the same.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to printed circuit boards and methods for manufacturing printed circuit boards. [Background technology]

[0002] Recently, with the development of artificial intelligence (AI) technology, multi-chip packages containing memory chips such as HBM (High Bandwidth Memory) and processor chips such as CPU (Central Processing Unit), GPU (Graphics Processing Unit), ASIC (Application Specific Integrated Circuit), and FPGA (Field Programmable Gate Array) are being used to process data that has increased exponentially. In particular, the number of CPU and GPU cores in server products has increased dramatically, making it necessary to accommodate finer chip metal post pitches. Therefore, research is ongoing to develop structures that can reduce the pitch of circuit patterns on printed circuit boards in response to demands for higher density, as well as to increase yields. Summary of the Invention [Problem to be solved by the invention]

[0003] One of several objectives of the present disclosure is to provide a printed circuit board and a method for manufacturing the printed circuit board that can realize wiring layers having fine pitches.

[0004] Another of several objects of the present disclosure is to provide a printed circuit board and a method for manufacturing the printed circuit board that can realize a wiring layer in which some parts are embedded and other parts are protruding.

[0005] Another of several objects of the present disclosure is to provide a printed circuit board and a method for manufacturing a printed circuit board that can improve reliability. [Means for solving the problem]

[0006] One of several solutions proposed through this disclosure is to provide a printed circuit board including a first insulating layer including a groove portion on an upper side, a buried portion buried in the groove, and a first wiring layer having a protruding portion protruding onto the first insulating layer, wherein the protruding portion of the first wiring layer has a width at its lower end that is narrower than the width at its upper end.

[0007] Another of several solutions proposed through the present disclosure is to provide a printed circuit board including a first insulating layer including a groove portion on an upper side, a first wiring layer having a buried portion buried in the groove and a protruding portion protruding onto the first insulating layer, and a second wiring layer buried under the first insulating layer and separated from the first wiring layer, wherein the wiring density of the first wiring layer is greater than the wiring density of the second wiring layer. Effect of the Invention

[0008] One of the various effects of the present disclosure is that it is possible to provide a printed circuit board and a method for manufacturing the printed circuit board that can realize a wiring layer having a fine pitch.

[0009] Another of the various effects of the present disclosure is that it is possible to provide a printed circuit board and a method for manufacturing the printed circuit board that can realize a wiring layer in which some parts are embedded and other parts protrude.

[0010] Another of the various effects of the present disclosure is that it is possible to provide a printed circuit board and a method for manufacturing a printed circuit board that can improve reliability. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram illustrating a schematic example of an electronic device system. [Diagram 2] FIG. 1 is a perspective view illustrating an example of an electronic device. [Diagram 3] FIG. 1 is a cross-sectional view illustrating a schematic diagram of a printed circuit board according to an example. [Figure 4] FIG. 11 is a cross-sectional view illustrating a printed circuit board according to another example. [Diagram 5] FIG. 11 is a cross-sectional view showing a schematic configuration of a printed circuit board according to yet another embodiment. [Figure 6] FIG. 11 is a cross-sectional view showing a schematic configuration of a printed circuit board according to yet another embodiment. [Figure 7] 1A to 1C are cross-sectional views illustrating a method for manufacturing a printed circuit board according to an embodiment of the present invention. [Figure 8] 1A to 1C are cross-sectional views illustrating a method for manufacturing a printed circuit board according to an embodiment of the present invention. [Figure 9] 11A to 11C are cross-sectional views each showing a schematic diagram of a part of a method for manufacturing a printed circuit board according to another example. [Figure 10] 10A to 10C are cross-sectional views illustrating a method for manufacturing a printed circuit board according to still another embodiment of the present invention. [Figure 11] 10A to 10C are cross-sectional views illustrating a method for manufacturing a printed circuit board according to still another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the present disclosure will be described with reference to the accompanying drawings. The shapes and sizes of elements in the drawings may be scaled (or highlighted or simplified) for a clearer description.

[0013] electronic equipment FIG. 1 is a block diagram illustrating an example of an electronic device system.

[0014] Referring to the drawing, an electronic device 1000 houses a main board 1010. Chip-related components 1020, network-related components 1030, and other components 1040 are physically and / or electrically connected to the main board 1010. These are also coupled to other electronic components described below to form various signal lines 1090.

[0015] The chip-related components 1020 include, but are not limited to, memory chips such as volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), and flash memory; application processor chips such as central processors (e.g., CPU), graphic processors (e.g., GPU), digital signal processors, encryption processors, microprocessors, and microcontrollers; and logic chips such as analog-to-digital converters and ASICs (application-specific ICs). In addition, these chip-related components 1020 may be combined with each other. The chip-related components 1020 may be in the form of a package including the above-mentioned chips and electronic components.

[0016] The network-related components 1030 may include, but are not limited to, any other wireless and wired protocols designated as Wi-Fi (e.g., IEEE 802.11 family), WiMAX (e.g., IEEE 802.16 family), IEEE 802.20, LTE (long term evolution), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPS, GPRS, CDMA, TDMA, DECT, Bluetooth, 3G, 4G, 5G, and beyond, as well as any of numerous other wireless or wired standards and protocols. The network-related components 1030 may also be combined with the chip-related components 1020.

[0017] The other components 1040 include high-frequency inductors, ferrite inductors, power inductors, ferrite beads, LTCC (low temperature co-firing ceramics), EMI (electromagnetic interference) filters, MLCC (multi-layer ceramic capacitors), etc. However, the other components 1040 are not limited to these, and may include passive elements in the form of chip components used for various other applications. In addition, the other components 1040 may be combined with the chip-related components 1020 and / or the network-related components 1030.

[0018] Depending on the type of electronic device 1000, the electronic device 1000 may include other electronic components that may or may not be physically and / or electrically connected to the main board 1010. Examples of other electronic components include, but are not limited to, a camera module 1050, an antenna module 1060, a display 1070, and a battery 1080. Other electronic components may include, but are not limited to, an audio codec, a video codec, a power amplifier, a compass, an accelerometer, a gyroscope, a speaker, a mass storage device (e.g., a hard disk drive), a compact disk (CD), a digital versatile disk (DVD), and the like. In addition, other electronic components used for various purposes may be included depending on the type of electronic device 1000.

[0019] The electronic device 1000 may be a smart phone, a personal digital assistant, a digital video camera, a digital still camera, a network system, a computer, a monitor, a tablet, a laptop, a netbook, a television, a video game, a smart watch, an automotive, etc. However, the electronic device 1000 is not limited to these, and may be any other electronic device that processes data.

[0020] FIG. 2 is a perspective view that illustrates an example of an electronic device.

[0021] Referring to the drawings, the electronic device may be, for example, a smartphone 1100. A motherboard 1110 is housed inside the smartphone 1100, and various components 1120 are physically and / or electrically connected to the motherboard 1110. In addition, other components, such as a camera module 1130 and / or a speaker 1140, which may or may not be physically and / or electrically connected to the motherboard 1110, are housed inside the smartphone 1100. Some of the components 1120 may be the above-mentioned chip-related components, for example, a component package 1121, but are not limited thereto. The component package 1121 may be in the form of a printed circuit board on which electronic components including active components and / or passive components are mounted on a surface. Alternatively, the component package 1121 may be in the form of a printed circuit board in which active components and / or passive components are built in. Meanwhile, the electronic device is not necessarily limited to the smartphone 1100, but may be other electronic devices as described above.

[0022] Printed Circuit Board FIG. 3 is a schematic cross-sectional view of a printed circuit board according to an example.

[0023] 3, a printed circuit board according to an example includes a first insulating layer 110 including a groove, and a first wiring layer 120 having a buried portion buried in the groove and a protruding portion protruding onto the first insulating layer 110. The first wiring layer 120 includes a first metal layer 121 disposed on an inner wall of the groove and extending along a portion of an upper surface of the first insulating layer 110, and a second metal layer 122 disposed on the first metal layer 121, and the protruding portion of the first wiring layer 120 may have a width at a lower end narrower than a width at an upper end.

[0024] The first insulating layer 110 may include an insulating material. The insulating material may include a thermosetting resin such as an epoxy resin, a thermoplastic resin such as a polyimide, or a material including such a resin together with an inorganic filler, an organic filler, and / or glass fiber (glass fiber, glass cloth, and / or glass fabric). The insulating material may be a photosensitive material and / or a non-photosensitive material. For example, the insulating material of the first insulating layer 110 may be an insulating material such as ABF (Ajinomoto Build-up Film), but is not limited thereto, and may include PPG (Prepreg), RCC (Resin Coated Copper), PID (Photo Imageable Dielectric), FR-4, BT (Bismaleimide Triazine), etc. However, it is not limited thereto, and other materials having excellent rigidity may be used as necessary.

[0025] The first insulating layer 110 may have a groove on the upper side. The groove is a portion in which at least a portion of the upper side of the first insulating layer 110 is removed, and may penetrate a portion of the first insulating layer 110. The groove may penetrate only a portion of the first insulating layer 110, and may not penetrate the entire first insulating layer 110 so that the upper and lower surfaces of the first insulating layer 110 are connected. The groove may be formed by etching a portion of the first insulating layer 110 on the upper side of the first insulating layer 110, but is not limited thereto, and may be formed using any method that can remove a portion of the first insulating layer 110 and form a groove that penetrates a portion of one side of the first insulating layer 110.

[0026] The first wiring layer 120 may include a first metal layer 121 and a second metal layer 122 disposed on the first metal layer 121. The first wiring layer 120 may include a metal material. The metal material may be copper (Cu), aluminum (Al), silver (Ag), tin (Sn), gold (Au), lead (Pb), titanium (Ti), or an alloy thereof. The first wiring layer 120 may preferably include copper (Cu), but is not limited thereto. The first wiring layer 120 may include the first metal layer 121 and the second metal layer 122, so that each metal layer may include a different metal material.

[0027] The first wiring layer 120 may perform various functions according to the design, including, but not limited to, a signal pattern, a power pattern, a ground pattern, and the like, and may also function as a pad for mounting electronic components and chips. Each of these patterns may have various forms, such as a line, a plane, and a pad.

[0028] A part of the first wiring layer 120 may be embedded in the first insulating layer 110, and another part of the first wiring layer 120 may protrude onto the first insulating layer 110. At this time, the embedded part of the first wiring layer 120 may not completely penetrate the first insulating layer 110, and may be formed to penetrate only a part of the first insulating layer 110. Specifically, the first wiring layer 120 may be formed by filling a groove part penetrating a part of the first insulating layer 110, but is not necessarily limited thereto. The other part of the first wiring layer 120 may be disposed on the first insulating layer 110 to form a protruding part protruding from the first insulating layer 110. The width of the embedded part of the first wiring layer 120 may be narrower than the width of the protruding part of the first wiring layer 120. This may be a result of forming a groove part having a finer width than the wiring width of the protruding part of the first wiring layer 120.

[0029] The first metal layer 121 may include one metal material from the group of metal materials of the first wiring layer 120 described above. The first metal layer 121 may preferably include copper (Cu), but is not limited thereto, and the first metal layer 121 may be composed of a plurality of metal layers in some cases. In this case, when the first metal layer 121 is composed of a plurality of metal layers, each of the plurality of metal layers may include a different metal material. The first metal layer 121 may function as a seed for forming the second metal layer 122. The first metal layer 121 may include an electroless plating layer (or chemical copper) or a sputtering layer, or may include both as necessary.

[0030] The first metal layer 121 may be disposed on the inner wall of the groove and extend to a part of the upper side of the first insulating layer 110. The first metal layer 121 may form a buried portion of the first wiring layer 120, or may form a protruding portion of the first wiring layer 120. The first metal layer 121 may be conformally disposed along the groove formed in the first insulating layer 110. That is, the first metal layer 121 may be formed along the inner wall of the groove formed in the first insulating layer 110 and disposed to extend to the upper surface of the first insulating layer 110.

[0031] The second metal layer 122 may include one metal material from the group of metal materials of the first wiring layer 120 described above. The second metal layer 122 may include substantially the same metal material as the first metal layer 121. For example, the second metal layer 122 may preferably include copper (Cu), but is not limited thereto. The second metal layer 122 may include an electrolytic plating layer (or electrolytic copper), and may further include other components required for electrolytic plating as necessary. The second metal layer 122 may be formed by performing electrolytic plating using the first metal layer 121 as a seed, but is not necessarily limited thereto.

[0032] The second metal layer 122 may be disposed on the first metal layer 121, and the second metal layer 122 may also constitute the buried portion of the first wiring layer 120, and may also constitute the protruding portion of the first wiring layer 120. That is, a part of the second metal layer 122 may be buried in the first insulating layer 110, and another part of the second metal layer 122 may protrude onto the first insulating layer 110. Since the width of the protruding portion of the first wiring layer 120 may be wider than the width of the buried portion of the first wiring layer 120, the width of the second metal layer 122 constituting the protruding portion may be wider than the width of the second metal layer 122 constituting the buried portion. This is related to the width of the protruding portion and the width of the buried portion of the first wiring layer 120, and since the first metal layer 121 may have a certain thickness as a seed for the second metal layer 122, the width of the second metal layer 122 may have the above-mentioned difference.

[0033] The protruding portion of the first wiring layer 120 may have at least a part of a side surface having an inclined surface. This may mean that the side surface of the first metal layer 121 constituting the protruding portion of the first wiring layer 120 may have an inclined surface, or may mean that at least a part of the side surface of the second metal layer 122 constituting the protruding portion of the first wiring layer 120 may have an inclined surface, but is not limited thereto, and may mean that at least a part of the side surface of the first metal layer 121 and the side surface of the second metal layer 122 may have an inclined surface. Also, without being limited thereto, it may mean that the inclined surface formed on the side surface of the first metal layer 121 extends from the inclined surface formed on at least a part of the side surface of the second metal layer 122, and the inclined surface of the first metal layer 121 and the inclined surface of the second metal layer 122 may be integrated. The fact that the inclined surface of the first metal layer 121 and the inclined surface of the second metal layer 122 can be integrated may mean that the inclination angle formed by the inclined surface of the first metal layer 121 and the first insulating layer 110 is substantially the same as the inclination angle formed by the virtual extension plane of the inclined surface of the second metal layer 122 and the first insulating layer 110.

[0034] The side of the first metal layer 121 constituting the protruding portion of the first wiring layer 120 may have an inclined surface. Since the first metal layer 121 functions as a seed for the second metal layer 122, a part of the first metal layer 121 may be removed in a step of removing a part of the seed during the manufacturing process, and at this time, an inclined surface may be formed on the side of the first metal layer 121. That is, the inclined surface formed on the side of the first metal layer 121 may be generated in a step of removing a part of the seed, and may be generated when the step of removing the seed is performed by an etching method, but is not necessarily limited thereto. Meanwhile, the side of the first metal layer 121 may have a tapered shape in which the width becomes narrower toward the first insulating layer 110. That is, the side of the first metal layer 121 may have a tapered shape on the lower side. This occurs when the step of removing a part of the seed is performed isotropically, and may occur because the lower part of the first metal layer 121 is removed more than the upper part of the first metal layer 121. In this case, the width of the first metal layer 121 may refer to the distance between one side surface of the first metal layer 121 and the other side surface facing the first metal layer 121, with respect to the first metal layer 121 constituting the protruding portion of the first wiring layer 120. In other words, it may refer to the horizontal distance between the side surfaces of the first metal layer 121 constituting the protruding portion of the first wiring layer 120.

[0035] Since the first metal layer 121 and the second metal layer 122 may include substantially the same metal material, not only a portion of the first metal layer 121 but also a portion of the second metal layer 122 may be removed together in the step of removing a portion of the seed during the manufacturing process. Since a portion of the second metal layer 122 may be removed together, an inclined surface may be formed on the side of the second metal layer 122. Furthermore, since a portion of the first metal layer 121 and a portion of the second metal layer 122 may be removed simultaneously, the inclined surface formed on the side of the first metal layer 121 may extend from the inclined surface formed on the side of the second metal layer 122. That is, the inclined surface of the first metal layer 121 and the inclined surface of the second metal layer 122 may be formed to be integral with each other. Meanwhile, since a portion of the second metal layer 122 may be removed in the step of removing a portion of the seed, an inclined surface may be formed only on a portion of the second metal layer 122 adjacent to the first metal layer 121. However, this is not necessarily limited thereto, and an inclined surface may be formed from the upper side of the second metal layer 122, or the second metal layer 122 may not have an inclined surface, and only the first metal layer 121 may have an inclined surface. Since the side surface of the first metal layer 121 and / or the side surface of the second metal layer 122 may have an inclined surface, the protrusion of the first wiring layer 120 may be formed such that the width of the lower end is narrower than the width of the upper end.

[0036] 3, and may include any shape of the first wiring layer 120 that may be generated in the step of removing the plating seed. For example, a structure in which the first metal layer 121 constituting the protruding portion of the first wiring layer 120 is entirely removed is also possible, and the first wiring layer 120 may have an hourglass shape in which the width of the protruding portion is narrower than the width of the buried portion of the first wiring layer 120.

[0037] In the printed circuit board according to an example, the first wiring layer 120 includes a buried portion in which a part of the first wiring layer 120 is buried in the first insulating layer 110, so that the first wiring layer 120 may not peel off from the first insulating layer 110 even if the side surfaces of the first metal layer 121 and / or the second metal layer 122 each have an inclined surface. If the printed circuit board includes fine wiring, an undercut may occur in the step of removing the seed, and a defect may occur in which the wiring peels off from the insulating layer and falls off. However, in the printed circuit board according to an example, the first wiring layer 120 is buried in a part of the first insulating layer 110, so that the contact area between the first insulating layer 110 and the first wiring layer 120 can be further increased, so that the adhesion can be ensured even if an undercut occurs in the step of removing the seed. That is, as the first wiring layer 120 is formed to fill the groove formed in the first insulating layer 110, the contact area between the first wiring layer 120 and the first insulating layer 110 increases by the area corresponding to the sidewall of the groove. In addition, the region where the undercut of the first wiring layer 120 occurs during seed removal is not only in close contact with the first insulating layer 110, but is also connected to the buried region of the first wiring layer 120, so that the first wiring layer 120 can be prevented from being detached from the first insulating layer 110. Since the region where the undercut occurs in the first wiring layer 120 and the buried portion of the first wiring layer 120 are integrally formed, even if the undercut occurs, there is a possibility that a defect will not occur due to the bonding force between the buried portion and the protruding portion of the first wiring layer 120 including the metal material having the same composition. In other words, if a part of the first wiring layer 120 is not buried, the bond must be maintained only by the adhesion force between the first wiring layer 120 and the first insulating layer 110, so it may be more advantageous for a part of the first wiring layer 120 to be buried in the first insulating layer 110.

[0038] The printed circuit board according to an example may further include a second wiring layer 130 disposed under the first insulating layer 110. The second wiring layer 130 being disposed under the first insulating layer 110 may mean that the second wiring layer 130 is embedded under the first insulating layer 110 as shown in FIG. 3, but is not limited thereto, and may include a structure in which the second wiring layer 130 is disposed on the lower surface of the first insulating layer 110 and protrudes. The second wiring layer 130 being embedded under the first insulating layer 110 may include a structure in which the remaining surfaces of the second wiring layer 130 except for the lower surface thereof are covered by the first insulating layer 110, and the lower surface of the second wiring layer 130 is not covered by the first insulating layer 110 and is exposed by the lower surface of the first insulating layer 110.

[0039] Meanwhile, the second wiring layer 130 may be separated from the first wiring layer 120. The fact that the second wiring layer 130 is separated from the first wiring layer may mean that the buried region of the first wiring layer 120 is not in direct contact with the second wiring layer 130. That is, this may mean that the buried portion of the first wiring layer 120 has a different configuration from a via that provides interlayer connection, and can be distinguished from a via. This is because the buried portion of the first wiring layer 120 does not penetrate substantially the entire first insulating layer 110, but only a portion of the first insulating layer 110.

[0040] The second wiring layer 130 may include a metal material. The metal material may be copper (Cu), aluminum (Al), silver (Ag), tin (Sn), gold (Au), lead (Pb), titanium (Ti), or an alloy thereof. The second wiring layer 130 may preferably include, but is not limited to, copper (Cu). The second wiring layer 130 may be formed by any one of a semi-additive process (SAP), a modified semi-additive process (MSAP), a tenting (TT), or a subtractive process, but is not limited to these. The second wiring layer 130 may include, but is not limited to, an electroless plating layer (or chemical copper) as a seed layer and an electrolytic plating layer (or electrolytic copper) as a plating layer. A sputtering layer may be formed instead of chemical copper as the electroless plating layer. If necessary, a copper foil may be further included. The second wiring layer 130 may perform various functions according to the design. For example, they may include, but are not limited to, signal patterns, power patterns, ground patterns, etc., and may function as pads for mounting electronic components and chips, or pads for connecting to other substrates. Each of these patterns may have various forms, such as lines, planes, and pads.

[0041] The first wiring layer 120 may have a higher wiring density than the second wiring layer 130. That is, the first wiring layer 120 may include finer wiring than the wiring of the second wiring layer 130. Higher wiring density is a relative concept, and may mean, for example, that the average pitch of the wiring included in the first wiring layer 120 may be smaller than the average pitch of the wiring included in the second wiring layer 130. The pitch may be measured by photographing a cut cross section of the printed circuit board with a scanning microscope, and the average pitch may be an average value of pitches between wirings measured at any five points. That is, the wiring included in the first wiring layer 120 may be a high-density fine wiring having a smaller L / S (Line / Space) than the wiring included in the second wiring layer 130. As a non-limiting example, the wiring included in the first wiring layer 120 may have a line / space of about 2 / 2 μm, but is not limited thereto. By embedding a part of the first wiring layer 120 in the first insulating layer 110, it is possible to realize finer wiring in the first wiring layer 120 than in the second wiring layer 130, and the wiring density of the first wiring layer 120 can be greater than the wiring density of the second wiring layer 130. Meanwhile, in FIG. 3, the thickness of the first wiring layer 120 and the thickness of the second wiring layer 130 are shown to be almost similar, but this is not limited thereto, and the first wiring layer 120 can be formed finer than the second wiring layer 130, and the thickness of the first wiring layer 120 can be formed thinner than the thickness of the second wiring layer 130.

[0042] The printed circuit board according to the embodiment is not limited to the configuration shown in Fig. 3, which shows only a part of the printed circuit board, and may further include other configurations. For example, other configurations such as an insulating layer, a circuit, and an interlayer via may further be included below the first insulating layer 110, and an insulating layer, a circuit, and an interlayer via may further be included above the first insulating layer 110. That is, the printed circuit board may further include configurations that can be used by a person having ordinary skill in the art.

[0043] FIG. 4 is a cross-sectional view that illustrates a schematic configuration of a printed circuit board according to another embodiment.

[0044] 4, the first wiring layer 120 of the printed circuit board according to another example may further include a third metal layer 123 disposed under the first metal layer 121. A portion of the third metal layer 123 may be embedded in the first insulating layer 110 like the first metal layer 121, and another portion may be disposed on the first insulating layer 110. The third metal layer 123 may be conformally disposed along a groove formed in the first insulating layer 110. That is, the third metal layer 123 may be formed along an inner wall of the groove formed in the first insulating layer 110 and disposed to extend to an upper surface of the first insulating layer 110.

[0045] The third metal layer 123 may include one metal material from the group of metal materials of the first wiring layer 120 described above. The third metal layer 123 may include a metal material different from that of the first metal layer 121. The third metal layer 123 may also include a metal material different from that of the second metal layer 122. The third metal layer 123 may preferably include titanium (Ti), but is not limited thereto, and may be composed of a plurality of metal layers in some cases. In this case, when the third metal layer 123 is composed of a plurality of metal layers, each of the plurality of metal layers may include a different metal material. The third metal layer 123 may be formed before the first metal layer 121 is formed. The third metal layer 123 may be disposed between the first metal layer 121 and the first insulating layer 110 to ensure the adhesion of the first metal layer 121. The third metal layer 123 may include a sputtering layer, but is not necessarily limited thereto. The third metal layer 123 can include a sputtering layer, and thus the first metal layer 121 can also include a sputtering layer, but is not limited thereto.

[0046] The side of the third metal layer 123 may have an inclined surface. The side of the third metal layer 123 constituting the protruding portion of the first wiring layer 120 may have an inclined surface. The side of the third metal layer 123 may have the same meaning as the side of the first metal layer 121. That is, the side of the third metal layer 123 may mean the side of the region disposed on the upper surface of the first insulating layer 110. Since the third metal layer 123 may be conformally disposed on the first insulating layer 110 before forming the first metal layer 121, the step of completing the first wiring layer 120 may include a step of removing a part of the third metal layer 123. When the step of removing a part of the third metal layer 123 is performed by an etching method, the side of the third metal layer 123 may have an inclined surface at the step of removing a part of the third metal layer 123. At this time, since the step of removing a portion of the third metal layer 123 may be performed after the step of removing a portion of the first metal layer 121, the inclined surface of the third metal layer 123 may be formed along the inclined surface formed in the first metal layer 121. This may be a result of an etchant permeating along the inclined surface of the first metal layer 121 when isotropic etching is performed.

[0047] 4, the inclined surface of the first metal layer 121 and the inclined surface of the third metal layer 123 are shown to be integral, but the present invention is not limited thereto, and the inclined surface of the first metal layer 121 and the inclined surface of the third metal layer 123 may have various shapes. The third metal layer 123 may contain a metal material different from that of the first metal layer 121 and the second metal layer 122, so that the third metal layer 123 may not react in the step of removing a part of the first metal layer 121, and the first metal layer 121 and the second metal layer 122 may not react in the step of removing a part of the third metal layer 123, and therefore the third metal layer 123 may have various shapes. For example, the inclined surface of the first metal layer 121 and the inclined surface of the third metal layer 123 may have different inclination angles, but the present invention is not limited thereto, and the side of the third metal layer 123 may protrude from the first metal layer 121 at the interface between the third metal layer 123 and the first metal layer 121.

[0048] In addition, among the configurations other than the content related to the third metal layer 123, the same configuration as that of the printed circuit board of one example can also be applied to the printed circuit board of another example, so duplicated explanations regarding this will be omitted.

[0049] FIG. 5 is a cross-sectional view that illustrates a schematic diagram of a printed circuit board according to still another embodiment.

[0050] 5, in a printed circuit board according to yet another example, the first wiring layer 120 may protrude above the first insulating layer 110 without contacting the upper surface of the first insulating layer 110. That is, a part of the first wiring layer 120 may form an embedded portion embedded in the first insulating layer 110, and another part of the first wiring layer 120 may form a protruding portion protruding above the first insulating layer 110. In this case, the upper surface of the first wiring layer 120 may be positioned higher than the upper surface of the first insulating layer 110.

[0051] In the printed circuit board according to another example, the third metal layer 123 is formed without removing the dry film formed on the first insulating layer 110, so that the third metal layer 123 can be formed along the wall surface of the opening formed in the dry film. Since the dry film is removed in a later stage, the third metal layer 123 can be disposed on the first insulating layer 110 along the shape of the opening formed in the dry film. That is, since the third metal layer 123 and the first metal layer 121 are immediately formed without removing the dry film for forming the groove, the first wiring layer 120 can not contact the upper surface of the first insulating layer 110. Therefore, the protruding portion of the first wiring layer 120 can have a substantially constant width.

[0052] With respect to the configuration other than the contents related to the arrangement and shape of the first wiring layer 120, the same configuration as that of the printed circuit board of one example and that of the printed circuit board of another example may also be applied to the printed circuit board of the other example, and therefore duplicate explanations related thereto will be omitted.

[0053] FIG. 6 is a cross-sectional view that illustrates a schematic configuration of a printed circuit board according to still another embodiment.

[0054] Referring to FIG. 6, in the printed circuit board according to another embodiment, the first wiring layer 120 may have a region in which at least a portion of the first metal layer 121 and the second metal layer 122 are recessed. Meanwhile, the first wiring layer 120 may have a step formed between the third metal layer 123 and the first metal layer 121 and / or the second metal layer 122. This may occur when the first metal layer 121 and the second metal layer 122 each contain substantially the same metal material as the seed layer, specifically, when the first metal layer 121, the second metal layer 122, and the seed layer 140 each contain copper (Cu). In the step of removing the seed layer, a portion of the first metal layer 121 and the second metal layer 122 each containing substantially the same metal material as the seed layer may be removed. The step of removing the seed layer will be described later in the method for manufacturing the printed circuit board.

[0055] 6, the recessed region is shown to have a flat surface, but is not limited thereto, and the surface of the recessed region may be uneven. Alternatively, the recessed region may have a concave shape with a center recessed like a dimple phenomenon, or conversely, may have a convex shape with a center protruding, and the recessed shape may be unlimited.

[0056] Other than the contents relating to the arrangement and shape of the first wiring layer 120, the same configuration as that of the printed circuit board according to one example, the printed circuit board according to another example, and the printed circuit board according to yet another example can also be applied to the printed circuit board according to yet another example, and therefore duplicate explanations regarding this will be omitted.

[0057] Printed circuit board manufacturing method 7 and 8 are cross-sectional views that briefly show a method for manufacturing a printed circuit board according to an example.

[0058] A method for manufacturing a printed circuit board according to an example may include forming a groove 300 penetrating a portion of the first insulating layer 110, and forming a first wiring layer 120 including a buried portion filling the groove 300 and a protruding portion protruding onto the first insulating layer 110. In this case, the step of forming the first wiring layer 120 may include forming a first metal layer 121 along the groove 300 and an upper surface of the first insulating layer 110, and forming a second metal layer 122 on the first metal layer 121, and may include removing a portion of the first metal layer 121. In the step of removing the portion of the first metal layer 121, the protruding portion of the first wiring layer 120 may have a narrower width at a lower end than at an upper end.

[0059] Referring to FIG. 7, a method for manufacturing a printed circuit board according to an example may include forming a dry film 201 on a first insulating layer 110. The step of forming the dry film 201 may include laminating a dry film 201′ and patterning the dry film 201 through exposure and development. An opening may be formed in the dry film 201, and a groove may be formed in the first insulating layer 110 to correspond to the opening. The dry film 201 may be a known dry film, and any material having a different reactivity from the first insulating layer 110 in the step of removing a portion of the first insulating layer 110 may be used without limitation. Meanwhile, FIG. 7 shows the steps of forming the dry film 201 including a photosensitive insulating material, exposing it to light, and developing it, but the present invention is not necessarily limited thereto. Any material that can function as a mask or resist in the step of forming the groove 300 in a portion of the first insulating layer 110 may be used without limitation, and any material and processing method that can be used by a person having ordinary skill in the art may be used.

[0060] At this time, the second wiring layer 130 may be embedded under the first insulating layer 110. More specifically, after the first insulating layer 110 is formed on the second wiring layer 130, the method for manufacturing the printed circuit board according to the example may be performed. Other components of the printed circuit board may further be included under the first insulating layer 110, as described above in the printed circuit board according to the example.

[0061] After forming the dry film 201 on the first insulating layer 110, the method may include forming a groove portion penetrating a portion of the first insulating layer 110. As described above in the printed circuit board according to an example, the groove portion 300 may be a position where the embedded portion of the first wiring layer 120 is to be formed. The groove portion 300 may not completely penetrate the first insulating layer 110. Since the groove portion 300 does not completely penetrate the first insulating layer 110, the second wiring layer 130 may not be exposed by the groove portion, and even if the first wiring layer 120 is subsequently formed to fill the groove portion 300, the first wiring layer 120 and the second wiring layer 130 may maintain a state in which they are spaced apart from each other. That is, the groove portion 300 penetrating a portion of the first insulating layer 110 may correspond to a configuration different from a via hole for performing interlayer connection. The groove portion 300 may be formed by etching the first insulating layer 110, and at this time, the width and depth of the groove portion may be set through an opening formed in the dry film 201. That is, the dry film 201 may correspond to a mask or a resist for forming the groove 300 .

[0062] After forming the groove portion 300, the dry film 201 can be removed. The method for removing the dry film 201 can be any method available to a person having ordinary skill in the art.

[0063] Referring to FIG. 8, a first metal layer 121 may be formed on a first insulating layer 110. The first metal layer 121 may function as a seed for forming a second metal layer 122 described later, and the first metal layer 121 may be formed by electroless plating, or may be formed by sputtering or the like in some cases. The first metal layer 121 may be formed along the boundary of the groove portion 300 and may be formed to extend onto the upper surface of the first insulating layer 110. The method for forming the first metal layer 121 may be a method having excellent step coverage, and the thickness of the first metal layer 121 may be thin, so that the first metal layer 121 is not formed to fill the groove portion 300, but may be formed conformally along the outer shape of the groove portion 300.

[0064] Thereafter, a dry film 202' is disposed, exposed, and developed to form a dry film 202. The dry film 202 may include an opening, which may be an area for forming the second metal layer 122. The opening of the dry film 202 may be formed to correspond to the groove portion 300. The dry film 202 may include the same material as the above-mentioned dry film 201, but is not necessarily limited thereto, and may be used without limitation as long as it can function as a plating resist or mask for forming the second metal layer 122 thereafter. The method for forming the dry film 202 may be any method that can be used by a person having ordinary skill in the art.

[0065] Then, the second metal layer 122 may be formed. The second metal layer 122 may be formed through electrolytic plating using the first metal layer 121 as a seed, but is not limited thereto.

[0066] Thereafter, the dry film 202 may be removed. A method known to those skilled in the art may be used to remove the dry film 202. In the step of removing the dry film 202, the first metal layer 121 and the second metal layer 122 may not be deformed.

[0067] Then, the first metal layer 121 is partially removed to complete the first wiring layer 120. Since the first metal layer 121 functions as a seed, the unnecessary first metal layer 121 is removed after the second metal layer 122 is formed, so that the adjacent first wiring layers 120 can perform the required function without shorting each other. The step of removing the part of the first metal layer 121 can be performed by an etching method. More specifically, flash etching can be used, but is not necessarily limited thereto. The step of removing the part of the first metal layer 121 can be performed by a method that can be used by a person having ordinary skill in the art by removing the unnecessary part of the seed.

[0068] At this time, an undercut may occur in at least a portion of the first wiring layer 120. The occurrence of an undercut in at least a portion of the first wiring layer 120 may mean that a portion of the first metal layer 121 disposed under the second metal layer 122 may be removed, and may mean that a portion of the second metal layer 122 may also be removed together. In the printed circuit board according to an example, the first wiring layer 120 having a buried portion buried in the first insulating layer 110 is formed, so that even if an undercut occurs in the step of removing a portion of the first metal layer 121, a defect in which the first wiring layer 120 is peeled off from the first insulating layer 110 may not occur.

[0069] Meanwhile, as described above, the manufacturing method of the printed circuit board according to the example is not limited to the contents shown in Figures 7 and 8. As described above in the configuration of the printed circuit board according to the example, other components may be further included on the lower surface of the first insulating layer 110, and after completing the first wiring layer 120, the method may further include a step of forming other components on the first insulating layer 110 so that other components are further included.

[0070] FIG. 9 is a cross-sectional view that illustrates a part of a method for manufacturing a printed circuit board according to another embodiment.

[0071] The method for manufacturing a printed circuit board according to another example may include, like the method for manufacturing a printed circuit board according to the one example, a step of forming a groove 300 on an upper side of the first insulating layer 110. The method for manufacturing a printed circuit board according to another example will be described focusing on a step after the step of forming the groove 300.

[0072] 9, the method may include forming a third metal layer 123 and forming a first metal layer 121. The method may include forming the third metal layer 123 before forming the first metal layer 121. The method may include forming the third metal layer 123 by sputtering, but is not limited thereto. In this case, the method may also include forming the first metal layer 121 by sputtering. When the method of forming the third metal layer 123 and the method of forming the first metal layer 121 are performed by the same method, the method of forming the first metal layer 121 may be performed immediately after the method of forming the third metal layer 123. The third metal layer 123 may be a means for ensuring adhesion with the first metal layer 121, and the third metal layer 123 may include a metal material different from that of the first metal layer 121.

[0073] Thereafter, a dry film 202 may be formed as a plating resist, and the second metal layer 122 may be formed, and a step of removing the dry film 202 may be included.

[0074] Thereafter, the method may include removing a portion of the first metal layer 121 and removing the third metal layer 123. The step of removing a portion of the first metal layer 121 may be the same as the method for manufacturing a printed circuit board according to an example, and the step of removing a portion of the third metal layer 123 may be performed using the same method as the step of removing the first metal layer 121.

[0075] At this time, since the first metal layer 121 and the third metal layer 123 may contain different metal materials, the third metal layer 123 may not react when removing a portion of the first metal layer 121, and the first metal layer 121 may not react when removing the third metal layer 123. Meanwhile, the specific shapes of the first metal layer 121 and the third metal layer 123 are not limited to those in FIG. 9 and may be various, as described above in the printed circuit board.

[0076] Meanwhile, steps other than the step of forming the third metal layer 123 and the step of removing a portion of the third metal layer 123 that are similar to the steps in the method for manufacturing a printed circuit board according to one example can also be applied to a printed circuit board according to another example, and therefore duplicated explanations regarding these will be omitted.

[0077] 10 and 11 are cross-sectional views that roughly show a method for manufacturing a printed circuit board according to still another example.

[0078] Referring to FIG. 10, a method for manufacturing a printed circuit board according to another embodiment may include forming a seed layer 140 on a first insulating layer 110. The seed layer 140 may be formed by electroless plating, or may be formed by sputtering or the like in some cases. As a non-limiting example, the first insulating layer 110 may be used to which the seed layer 140 is attached in the form of copper foil. The seed layer 140 may be a temporary structure and may not remain in the completed result. The seed layer 140 may function as a seed to complement the third metal layer 123 and the first metal layer 121 in the step of forming the second metal layer 122 described below. Therefore, in some cases, the step of forming the seed layer 140 may be omitted. The seed layer 140 may include a metal material and may be selected from the same group of materials as the metal material of the first wiring layer 120, and may preferably include, but is not limited to, copper (Cu).

[0079] Thereafter, a dry film 201 may be formed on the seed layer 140. The step of forming the dry film 201 may include the steps of forming a dry film 201', exposing and developing it.

[0080] Thereafter, the method may include a step of forming a groove 300 penetrating a portion of the seed layer 140 and the first insulating layer 110. The step of forming the groove 300 may be performed by penetrating the seed layer 140 and a step of penetrating a portion of the first insulating layer 110, respectively, but is not limited thereto, and the seed layer 140 and the portion of the first insulating layer 110 may be penetrating simultaneously. When the groove 300 penetrating a portion of the first insulating layer 110 is formed in a separate process after the step of penetrating the seed layer 140, the groove 300 may be formed in the same manner as in the method of manufacturing a printed circuit board according to an example, and when the seed layer 140 and the first insulating layer 110 are processed simultaneously, a mechanical process may be performed. Since the seed layer 140 is disposed on the first insulating layer 110, it may be advantageous to adjust the degree of processing so as not to completely penetrate the first insulating layer 110 when forming the groove 300 in the first insulating layer 110.

[0081] 11, the method may include forming a third metal layer 123 and a first metal layer 121. In the printed circuit board according to another example, the third metal layer 123 and the first metal layer 121 are formed without removing the dry film 201, so that the third metal layer 123 may not contact the top surface of the first insulating layer 110, and the third metal layer 123 and the first metal layer 121 may be disposed to extend over the dry film 201.

[0082] Thereafter, the method may include a step of forming a second metal layer 122. The step of forming the second metal layer 122 may be performed by electrolytic plating using the first metal layer 121 as a seed. Meanwhile, the second metal layer 122 may be plated beyond the first metal layer 121 disposed on the dry film 201 after filling the entire groove 300. That is, the step of forming the second metal layer 122 may be performed by panel plating or over-plating, but is not limited thereto. Since the third metal layer 123 and the first metal layer 121 are disposed on the dry film 201, it may be difficult to cover the opening of the dry film 201 and the groove 300 of the first insulating layer 110. That is, it may not be easy to form the third metal layer 123 and the first metal layer 121 that are connected to the inner wall of the groove 300, the wall surface of the opening of the dry film 201, and the upper surface of the dry film 201. As a result, since the third metal layer 123 and the first metal layer 121 may not be sufficient as a seed for forming the second metal layer 122, the seed layer 140 formed on the first insulating layer 110 can supplement this. That is, the seed layer 140 is disposed in advance on the first insulating layer 110 and can function as an auxiliary for the third metal layer 123 and the first metal layer 121 in the step of forming the second metal layer 122.

[0083] Then, a step of removing a portion of the second metal layer 122 may be included. The step of removing a portion of the second metal layer 122 may be performed by removing the over-plated portion of the second metal layer 122, and may be performed using at least one of a chemical-mechanical polishing (CMP) process and an etching process, but is not limited thereto. In this case, when the chemical-mechanical polishing process is used, the first metal layer 121 and the third metal layer 123 may be partially removed together, and a flat surface may be obtained. On the other hand, when the etching process is used, the third metal layer 123 containing a metal material different from that of the second metal layer 122 may not react, the second metal layer 122 may be over-etched, and a portion of the first metal layer 121 containing substantially the same metal material as the second metal layer 122 may be removed together, and the first wiring layer 120 may include a recessed region.

[0084] Thereafter, a step of removing the seed layer 140 may be included. The seed layer 140 may include the same metal material as the first metal layer 121 and the second metal layer 122, and therefore the seed layer 140 may include a different metal material from the third metal layer 123. Therefore, even in the step of removing the seed layer 140, the third metal layer 123 may not react. That is, the third metal layer 123 may function as an etching barrier that separates the first metal layer 121 and the second metal layer 122 from the seed layer. By removing the seed layer 140, the first wiring layer 120 may be completed.

[0085] Among the configurations and steps other than those relating to the formation of the first wiring layer 120 and the seed layer 140, the configurations and steps similar to those of the method for manufacturing a printed circuit board according to one example and the method for manufacturing a printed circuit board according to another example may also be applied to the method for manufacturing a printed circuit board according to the other example, and therefore duplicated descriptions thereof will be omitted.

[0086] Meanwhile, in yet another example of a method for manufacturing a printed circuit board, as described above, in the step of removing the seed layer 140, portions of the first metal layer 121 and the second metal layer 122 may be further removed, and in the step of removing portions of the second metal layer 122, the first metal layer 121 and the second metal layer 122 may have recessed regions, as described above.

[0087] In the present disclosure, the cross-sectional meaning may refer to the cross-sectional shape of an object cut vertically or the cross-sectional shape of an object when viewed from the side, and the planar meaning may refer to the shape of an object cut horizontally or the planar shape of an object when viewed from the top or bottom.

[0088] In this disclosure, for convenience, the terms upper side, top, top surface, etc. are used to mean a direction toward a surface on which electronic components can be mounted based on a cross section of a drawing, and the terms lower side, bottom, bottom surface, etc. are used to mean the opposite direction. However, this is a definition of directions for convenience of explanation, and the scope of the claims is not particularly limited by the description of such directions.

[0089] In the present disclosure, the term "connected" refers not only to a direct connection but also to an indirect connection via an adhesive layer or the like. The term "electrically connected" refers to both a physical connection and a non-connection. Furthermore, the terms "first" and "second" are used to distinguish one component from another, and do not limit the order and / or importance of the components. In some cases, the first component may be named the second component, and similarly the second component may be named the first component, without departing from the scope of the right.

[0090] In the present disclosure, "substantially" can be determined by including process errors, positional deviations, and measurement errors that occur during the manufacturing process. For example, "substantially constant" can include not only cases where the values ​​are completely the same, but also cases where the values ​​are roughly the same. As another example, "substantially perpendicular" can include not only cases where the values ​​are completely perpendicular, but also cases where the values ​​are roughly perpendicular. As another example, "substantially coplanar" can include not only cases where the values ​​are completely in the same plane, but also cases where the values ​​are roughly in the same plane.

[0091] In the present disclosure, the width of a certain feature can be measured by photographing a cross section in the lamination direction using a scanning microscope or the like. The width of a certain feature can be interpreted as the distance across the certain feature, but can include measurement errors or errors in the manufacturing process. For example, the width of a certain feature can be the average value of the horizontal distances measured at any five points.

[0092] In the present disclosure, the thickness of a certain component can be measured by photographing a cross section in the lamination direction using a scanning microscope or the like. The thickness of a certain component can be interpreted as the distance across the component vertically, but can include measurement errors or errors in the manufacturing process. For example, the thickness of a certain component can be the average of the vertical distances measured at any five points.

[0093] In this disclosure, the term "same material or substance" refers not only to the exact same material, but also to the same type of material, and thus the compositions of the materials are substantially the same, although the specific composition ratios thereof may vary slightly.

[0094] The expression "one example" used in the present disclosure does not mean the same embodiment as the other, but is provided to emphasize and describe the unique features that are different from each other. However, the above-mentioned one example does not exclude being realized in combination with the features of another example. For example, even if the matter described in a particular example is not described in another example, it can be understood as being related to the other example, unless there is a description in the other example that is opposite or contradictory to the matter.

[0095] The terms used in the present disclosure are merely used to describe an example and are not intended to limit the present disclosure. In this case, the singular expression includes the plural expression unless the context clearly indicates otherwise. [Explanation of symbols]

[0096] 110 First insulating layer 120 1st wiring layer 121 First metal layer 122 Second metal layer 123 Third metal layer 130 2nd wiring layer 140 Seed Layer 201, 201', 202, 202' Dry Film 300 Groove 1000 Electronics 1010 Mainboard 1020 Chip-related parts 1030 Network-related parts 1040 Other parts 1050 Camera module 1060 Antenna module 1070 Display 1080 Battery 1090 Signal line 1100 Smartphone 1110 Smartphone internal main board 1120 Smartphone internal electronic components 1121 Smartphone Internal Antenna Module 1130 Smartphone internal camera module 1140 Smartphone internal speaker

Claims

1. a first insulating layer including a groove on an upper side thereof; a first wiring layer having a buried portion buried in the groove and a protruding portion protruding onto the first insulating layer, A printed circuit board, wherein the protruding portion of the first wiring layer has a width at a lower end that is narrower than a width at an upper end.

2. the first wiring layer includes a first metal layer disposed on an inner wall of the groove and extending along a portion of an upper surface of the first insulating layer, and a second metal layer disposed on the first metal layer; The printed circuit board according to claim 1 , wherein a width of the first metal layer at a portion adjacent to the upper surface of the first insulating layer is narrower than a width of the upper surface of the first metal layer.

3. The printed circuit board according to claim 2 , wherein a width of the second metal layer at a portion adjacent to the upper surface of the first insulating layer is narrower than a width of the upper surface of the second metal layer.

4. The printed circuit board according to claim 2 , wherein at least a portion of a side surface of the second metal layer that forms the protrusion has an inclined surface.

5. a side surface of the first metal layer forming the protrusion has an inclined surface; 5. The printed circuit board of claim 4, wherein an inclination angle between the inclined surface of the first metal layer and the first insulating layer is the same as an inclination angle between an extension of an inclined surface included in at least a portion of a side surface of the second metal layer and the first insulating layer.

6. The printed circuit board of claim 2 , wherein the first metal layer and the second metal layer each comprise the same metal.

7. the first wiring layer includes a third metal layer disposed below the first metal layer; The printed circuit board of claim 2 , wherein the third metal layer comprises a different metal than the first metal layer.

8. The printed circuit board according to claim 1 , wherein the width of the embedded portion is narrower than the width of the protruding portion.

9. The printed circuit board according to claim 1 , further comprising: a second wiring layer disposed below the first insulating layer and spaced apart from the first wiring layer.

10. a first insulating layer including a groove on an upper side thereof; a first wiring layer having a buried portion buried in the groove and a protruding portion protruding onto the first insulating layer; a second wiring layer embedded under the first insulating layer and spaced apart from the first wiring layer; A printed circuit board, wherein the wiring density of the first wiring layer is greater than the wiring density of the second wiring layer.

11. The printed circuit board according to claim 10 , wherein the protruding portion of the first wiring layer has a constant width.

12. The printed circuit board of claim 11 , wherein a width of an upper portion of the recessed portion is the same as a width of a lower portion of the protruding portion.

13. 11. The printed circuit board of claim 10, wherein the first wiring layer includes a first metal layer disposed on an inner wall of the groove portion and extending so as to protrude onto the first insulating layer, a second metal layer disposed on the first metal layer, and a third metal layer disposed on the second metal layer.

14. 14. The printed circuit board of claim 13, wherein the second metal layer comprises a different metal than the first metal layer.

15. 15. The printed circuit board of claim 14, wherein the second metal layer and the third metal layer comprise the same metal as each other.

16. The printed circuit board according to claim 13 , wherein the first wiring layer has an area in which at least a portion of the second metal layer and the third metal layer are recessed.

Images