Wiring substrate and electronic device

Abstract

The present disclosure relates to a wiring substrate and an electronic device. A wiring substrate comprises: a base member having a first surface; a first differential signal line disposed on the first surface of the base member; and a second differential signal line disposed on the first surface of the base member adjacent to the first differential signal line. A ground layer facing the first and second differential signal lines has a plurality of openings arranged continuously along a predetermined direction. In a plan view of the wiring substrate, the length of each of the plurality of openings in a direction along the signal line is a length L1, the length of the opening in a direction orthogonal to L1 is a length L2, and the distance between the first and second differential signal lines is a length L3, L1 is equal to or greater than 4 times L2, and L2 is equal to or less than L3.

Description

Technical Field

[0001] The present disclosure relates generally to a wiring substrate for an electronic device, and particularly to a technique for reducing noise generated from the wiring substrate. Background Art

[0002] Two semiconductor devices in an electronic device use digital signals to communicate data with each other. Digital signals in data communication are usually transmitted via differential signal lines. Radiated noise generated by the differential signal lines and crosstalk noise generated between the differential signal lines may cause degradation of digital signal quality and failure of the semiconductor device. Japanese Patent Laid-Open No. 2000-077802 discusses a wiring substrate including a shield having a predetermined opening pattern for reducing radiated noise generated by the differential signal lines. Summary of the invention

[0003] A first aspect of the present disclosure provides a wiring substrate, which includes: a base member having a first surface; a first differential signal line arranged on the first surface of the base member, including a first pair of signal lines; a second differential signal line arranged on the first surface of the base member adjacent to the first differential signal line, including a second pair of signal lines; and a ground layer, facing the first differential signal line and the second differential signal line and having an opening portion, the opening portion including a plurality of openings arranged continuously along a predetermined direction, wherein, in a plan view of the wiring substrate, a length of each of the plurality of openings in a direction along the signal line is a length L1, a length of the opening in a direction orthogonal to the length direction of the length L1 is a length L2, and a distance between the first differential signal line and the second differential signal line is a length L3, the length L1 is equal to or greater than 4 times the length L2, and the length L2 is equal to or less than the length L3.

[0004] A second aspect of the present disclosure provides an electronic device including: a wiring substrate as defined in the first aspect; and a housing accommodating the wiring substrate therein.

[0005] Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a schematic diagram of an image pickup apparatus as an example of an electronic device according to the first exemplary embodiment.

[0007] Figure 2A is an explanatory diagram illustrating an image capturing unit according to the first exemplary embodiment. Figure 2B is a cross-sectional view of a flexible wiring board according to the first exemplary embodiment. Figure 2C: is an explanatory diagram showing the positional relationship of a ground layer and differential signal lines according to the first exemplary embodiment.

[0008] Figure 3A , Figure 3B and Figure 3C It is an explanatory diagram showing the shape of the opening portion in the ground layer.

[0009] Figure 4 is a cross-sectional view of a flexible wiring board according to a modified example.

[0010] Figure 5 is a diagram illustrating a system for measuring radiated noise according to an example.

[0011] Figure 6 is a diagram illustrating a system for evaluating transmission characteristics according to an example.

[0012] Figure 7 : is an explanatory diagram showing the routes of a signal current and a return current on a wiring substrate according to a first comparative example.

[0013] Figure 8 1 is an explanatory diagram showing the positional relationship between a ground layer and differential signal lines according to a first comparative example. DETAILED DESCRIPTION

[0014] Various exemplary embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0015] Figure 1 1 is an explanatory diagram showing a digital camera 600 as an image capturing device as an example of an electronic device according to the first exemplary embodiment. The digital camera 600 as the image capturing device is a lens interchangeable digital camera and includes a camera body 601. A lens unit (lens barrel) 602 including a lens can be detached from the camera body 601. The camera body 601 includes a housing 611 and an image capturing unit 100 and a wireless communication unit 150 accommodated in the housing 611.

[0016] The image capture unit 100 includes a first printed circuit board 101, a second printed circuit board 102, and a flexible wiring board 11 as a wiring substrate (wiring board) that electrically connects the first printed circuit board 101 and the second printed circuit board 102. The flexible wiring board 11 contributes to reducing the weight of the wiring structure compared to a coaxial cable.

[0017] The first printed circuit board 101 includes a first printed wiring board 110 and a first semiconductor device 111 provided on the first printed wiring board 110 . The second printed circuit board 102 includes a second printed wiring board 120 and a second semiconductor device 121 provided on the second printed wiring board 120 .

[0018] The first semiconductor device 111 is an image sensor as an image capturing element. The image sensor is, for example, a complementary metal oxide semiconductor (CMOS) image sensor or a charge coupled device (CCD) image sensor. The image sensor has a function of converting incident light via the lens unit 602 into an electrical signal. The second semiconductor device 121 is a digital signal processor as a processing circuit. The digital signal processor has a function of obtaining an electrical signal indicating image data from the image sensor, correcting the obtained electrical signal, and generating corrected image data.

[0019] The wireless communication unit 150 that performs wireless communication in the GHz band is a modular wireless communication module. The wireless communication unit 150 includes a third printed wiring board 151 and a wireless communication integrated circuit (IC) 152 disposed on the third printed wiring board 151, and the third printed wiring board 151 is provided with an antenna (not shown). The antenna is disposed on the same plane as the wireless communication IC 152, and is arranged at a position close to the housing 611 to facilitate easy communication with the outside world. The wireless communication IC 152 transmits and receives image data via the antenna through wireless communication with an external device (such as a personal computer (PC), a wireless router, etc.). In other words, the wireless communication IC 152 modulates a digital signal indicating image data and transmits the modulated signal from the antenna as a radio wave having a communication frequency of a wireless communication standard. In addition, the wireless communication IC 152 demodulates the radio wave received by the antenna into a digital signal indicating image data. The wireless communication IC 152 communicates with the external device in accordance with a standard such as and Wireless communication using standards such as

[0020] Figure 2A 2 is an explanatory diagram showing the image capturing unit 100 . Figure 2B It is along Figure 2A 2 is a cross-sectional view of the flexible wiring board 11 taken along the line AA in FIG. Figure 2C 1 is an explanatory diagram showing a positional relationship between a ground layer and differential signal lines in a plan view of the flexible wiring board 11 viewed from the first surface 12A of the base member 12 .

[0021] like Figure 2A As shown in FIG. 1 , a connector 112 is provided on a first printed wiring board 110. The connector 112 is electrically connected to a first semiconductor device 111 through a conductor provided on the first printed wiring board 110. A connector 122 is provided on a second printed wiring board 120. The connector 122 is electrically connected to a second semiconductor device 121 through a conductor provided on the second printed wiring board 120. In other words, the first semiconductor device 111 and the second semiconductor device 121 are electrically connected to each other through the first printed wiring board 110, the flexible wiring board 11, and the second printed wiring board 120, and can communicate with each other.

[0022] like Figure 2B As shown in , in the flexible wiring board 11 , the base member 12 has a first surface 12A on one side of the base member 12 and has a second surface 12B on the other side opposite to the first surface 12A.

[0023] The wiring layer 13 is disposed on the first surface 12A. The wiring layer 13 includes a first differential signal line 13A having a pair of signal lines including a first signal line 131 and a second signal line 132, and a second differential signal line 13B having a pair of signal lines including a third signal line 133 and a fourth signal line 134. The distance between the second signal line 132 of the first differential signal line 13A and the third signal line 133 of the second differential signal line 13B is a length L3.

[0024] On the second surface 12B, the ground layer 16 having the opening portion 21 including a plurality of openings is provided. The ground layer 16 has the opening portion 21 and a non-opening portion 16A where no opening is formed.

[0025] In the case where the wiring substrate is a flexible wiring board, the material of the base member 12 is a resin. Examples of resins include polyimide-based resins (such as polyimide, polyamide and polyamide-imide resins), thermosetting resins (such as epoxy resins) and thermoplastic resins (such as liquid crystal polymer resins). Among these materials, polyimide or liquid crystal polymer is desirable. Polyimide has excellent heat resistance and mechanical properties and is easily commercially available. Liquid crystal polymer has a low relative dielectric constant, so it is suitable for applications that transmit high-speed signals, and has low hygroscopicity and excellent dimensional stability. The thickness of the base member 12 is not particularly limited, but it is desirable to be within the range of 10 μm or more and 100 μm or less. If the thickness is less than 10 μm, the distance between the first differential signal line 13A and the ground layer 16 is short, so the characteristic impedance value may increase. At the same time, if the thickness exceeds 100 μm, the rigidity of the resin increases, so its flexibility may be insufficient. The thickness of the base member 12 is more desirable to be within the range of 12 μm or more and 75 μm or less.

[0026] In the case where the wiring substrate is a rigid substrate, the material of the base member 12 is a fiber base member. Examples of the fiber base member include glass fiber base members (such as glass fabric and glass non-woven fabric) and inorganic fiber base members (such as fabric or non-woven fabric including an inorganic compound other than glass as a component). Examples thereof further include organic fiber base members containing organic fibers (such as aromatic polyamide, polyamide, aromatic polyester, polyester, polyimide, and fluororesin). Among these materials, the glass fiber base member is desirable from the viewpoint of excellent strength and low water absorption.

[0027] The wiring layer 13 includes a first differential signal line 13A and a second differential signal line 13B, which are transmission paths of differential signals. A data signal, which is a digital signal indicating image data, is transmitted via the first differential signal line 13A and the second differential signal line 13B. The wiring layer 13 may include, in addition to the differential signal line, a line for transmitting a single-ended signal such as a control signal and a response signal, and a line for grounding.

[0028] The manufacturing method of the wiring layer 13 is not particularly limited, and the wiring layer 13 can be formed by a known method such as lamination of metal foils, metal plating, and an inkjet process. In the case of using copper foil as the metal foil, a transmission line pattern can be formed by a photolithography and etching process using a film stacked together by an adhesive or the like. In the case of using an inkjet process, a necessary pattern is drawn using a polymer ink including conductive metal particles, and the pattern can be formed by firing at a temperature below the glass transition point (Tg) of the base member 12. The thickness of the wiring layer (the thickness of the differential signal line) is not particularly limited, but is, for example, in the range of 0.1 μm or more and 20 μm or less.

[0029] If the average lengths of the positive phase signal and the negative phase signal transmitted via the differential signal line are different, a part of the differential signal is converted into a common mode signal, also called mode conversion, and common mode noise is caused. If the common mode noise resonates on the wiring substrate, a large radiation noise is generated at the frequency of the common mode noise. Moreover, in recent years, with the increase in the amount of communication data, differential signals with high transmission speeds in the order of gigabits per second (Gbps) (such as 5Gbps or higher) are transmitted via differential signal lines. The relationship R=2f is satisfied between the signal transmission speed R [bps] and the signal frequency f [Hz]. Generally, as the frequency of the transmitted differential signal increases, the time variation of the current flowing through the transmission line increases, thereby generating more radiation noise. The frequency of the generated radiation noise is close to the communication band of the wireless communication device, and therefore, during wireless communication between the wireless communication IC and an external device (PC, wireless router, etc.) via an antenna, the radiation noise may be superimposed on the communication data.

[0030] As is well known, in a wiring substrate in which a conductor layer is stacked on a base member, a conductor layer on one surface of the base member is used as a wiring layer to set a transmission line, and another conductor layer set on the other surface is used as a ground layer (shielding layer) for suppressing radiation noise. It is also known to use a ground layer with openings in a mesh pattern as discussed in Japanese Patent Application Laid-Open No. 2000-077802. However, as a result of an inspection conducted by the inventor of the present application, it has been found that the technology discussed in Japanese Patent Application Laid-Open No. 2000-077802 cannot fully suppress the radiation noise in the case of transmitting a high-speed differential signal. In addition, it has been found that the technology discussed in Japanese Patent Application Laid-Open No. 2000-077802 cannot fully suppress the crosstalk noise generated between differential signal lines adjacent to each other.

[0031] Therefore, according to the present exemplary embodiment, the ground layer 16 in the flexible wiring board 11 has an opening portion 21, which includes a plurality of openings arranged continuously along a predetermined direction. In other words, the plurality of openings are arranged at predetermined intervals. The size of the opening of the opening portion 21 can be expressed using the lengths L1, L2, and L3 described below, and is characterized in that the length L1 is more than 4 times the length L2, and the length L2 is equal to or less than the length L3. In the plan view of the flexible wiring board 11, the length L1 is the maximum length of the opening in the direction along the longitudinal direction of the signal lines 131, 132, 133, and 134. L2 is the maximum length of the opening in the direction orthogonal to the length direction of the length L1. The length L3 is the distance between the first differential signal line 13A and the second differential signal line 13B. Figure 2C The relationship between the lengths L1, L2 and L3 according to the first exemplary embodiment is shown. Figure 2C As can be seen in FIG. 1 , the ground layer 16 includes an opening portion 21 including a plurality of openings, and the shape of the openings is continuously patterned two-dimensionally. The predetermined direction is, for example, a direction in which the signal line is installed.

[0032] The length L1 having a length of more than 4 times the length L2 means that the length of the opening in the signal transmission direction is sufficiently long relative to the length of the opening in the orthogonal direction. In addition, L1 having such a length also means that the aspect ratio of the opening is large and the opening has a highly anisotropic shape. Since the ground layer 16 has the above-mentioned configuration, the return route of the first differential signal line 13A and the second differential signal line 13B can be shortened. As the return route is reduced, the inductance of the return route is reduced, and therefore, compared with the configuration in which the length L1 is less than 4 times the length L2, the radiation noise generated from the first differential signal line 13A and the second differential signal line 13B can be reduced. In addition, the non-opening portion 16A of the ground layer 16 can also be arranged closer to the first differential signal line 13A and the second differential signal line 13B. The non-opening portion 16A arranged closer to the first differential signal line 13A and the second differential signal line 13B increases the mutual inductance of both the first differential signal line 13A and the second differential signal line 13B, thereby reducing the radiation noise even when transmitting high-speed signals.

[0033] The length L1 is preferably 1.5 mm or less. If the length L1 is longer than 1.5 mm, the ratio of the opening portion in the ground layer (aperture ratio) becomes too large, the shielding effect against the radiation noise is reduced, and there is a possibility of affecting the wireless communication device in the electronic device. The length L1 is more preferably 1.2 mm or less.

[0034] In addition, the length L2 having a length less than the length L3 means that at most only one differential signal line is arranged for one opening. The ground layer 16 has the above configuration, so that the non-opening portion 16A is inserted between the first differential signal line 13A and the second differential signal line 13B, so that the crosstalk noise can be reduced compared to the case where the length L2 is less than the length L3.

[0035] The lengths L1, L2, and L3 satisfy the above relationship. Therefore, even when transmitting high-speed differential signals at the Gbps level, the wiring substrate according to this exemplary embodiment can suppress both the radiation noise generated by the differential signal lines and the crosstalk noise generated between two adjacent differential signal lines.

[0036] It is desirable that the thickness of the ground layer 16 (non-opening portion 16A) is within a range of 1 μm or more and 20 μm or less. If the thickness is less than 1 μm, the resistance value of the ground layer 16 (non-opening portion 16A) becomes large. Therefore, in the case where common mode noise is generated, it is difficult for the return current to flow, so the amount of radiation noise may increase. Meanwhile, if the thickness of the ground layer 16 is greater than 20 μm, it becomes difficult to smooth the surface shape of the second insulating layer 17. It is more desirable that the thickness of the ground layer 16 is within a range of 2 μm or more and 15 μm or less.

[0037] The aperture ratio, which is the ratio of the area of ​​the opening portion 21 to the ground layer 16, is desirably in the range of 40% or more and 90% or less. In other words, the aperture ratio is the ratio of the area of ​​the opening portion 21 to the total area of ​​the non-opening portion 16A and the opening portion 21. More desirably, the aperture ratio is in the range of 50% or more and 85% or less.

[0038] If the aperture ratio is less than 40%, the characteristic impedance value decreases, and the transmission characteristics may deteriorate depending on the speed of the transmission signal. In addition, the rigidity of the ground layer 16 increases, and if the wiring substrate is a flexible wiring board 11, the flexibility may be insufficient. Meanwhile, if the aperture ratio is greater than 90%, the radiation noise may be sufficiently suppressed, and the communication of the wireless communication device may be affected.

[0039] The aperture ratio can be measured by, for example, the following method. An image of the ground layer 16 is taken from a direction perpendicular to the second surface 12B of the base member 12 by a laser microscope or a scanning electron microscope (SEM). The image to be taken should include more than 10 openings. The portion corresponding to the opening portion 21 and the non-opening portion 16A is binarized using the captured rectangular image, and the corresponding area of ​​the opening portion 21 and the non-opening portion 16A is calculated by using the number of pixels. The corresponding area of ​​the opening portion 21 and the non-opening portion 16A can be calculated using the following formula.

[0040]

[0041] The size of the image to be captured in this operation is preferably 500 pixels × 500 pixels or more. The above-mentioned lengths L1 and L2 can also be calculated using the above-mentioned image. The lengths L1 and L2 are calculated by binarizing and separating the opening portion and the non-opening portion, measuring the pixel length, and averaging the values ​​of the lengths L1 and L2 of 10 openings.

[0042] The shape of the opening portion 21 is not particularly limited as long as the relationship between the lengths L1, L2 and L3 is satisfied. Figure 2C As shown in FIG. , the shape of the opening portion 21 may be a rhombus, or FIG. 3A to FIG. 3C As shown in , it may also be an ellipse, a rectangle and a hexagon. In addition, the shape of the opening portion 21 may include a plurality of shapes selected from the above shapes. Among these shapes, polygons such as quadrilaterals and hexagons are desirable. If the shape of the opening portion 21 is a polygon, the deviation of the width of the non-opening portion can be prevented or reduced, and therefore, since the return route of the radiated noise becomes uniform, the noise can be suppressed more effectively.

[0043] The method for forming the grounding layer 16 is not particularly limited. For example, the method for forming the grounding layer 16 on the base member 12 can be a subtractive method, a chemical plating method, an electrolytic plating method, and a physical vapor deposition method such as vapor deposition and a sputtering method. In addition, a method for joining conductive fibers and a screen printing method can be adopted. The process of forming the grounding layer 16 by plating is described below. First, a metal layer is deposited on the base member by metal vapor deposition. The metals used to form the metal layer include copper, aluminum, nickel, iron, gold, silver, platinum, tungsten, chromium, titanium, tin, lead and palladium, and one or more of them can be combined. Among these metals, silver, copper or nickel is desirable from the perspective of conductivity and low cost. Next, a mesh-like resist layer is set on the metal layer. In this case, a resist layer is formed by gravure printing using a printing method, and then the metal layer is etched and removed using the resist layer as a mask, and then the resist layer is removed. Therefore, a mesh structure made of a metal layer is formed as a grounding layer including an opening portion.

[0044] It is desirable that, in the housing 611 of the electronic device, the distance between the wireless communication unit 150 and the ground layer 16 is shorter than the distance between the wireless communication unit 150 and the wiring layer 13. In other words, it is desirable to provide the ground layer 16 at a position closer to the wireless communication unit 150 than the wiring layer 13. Since the ground layer 16 is closer to the wireless communication unit 150 than the wiring layer 13, it is possible to prevent radiation noise generated by the wiring layer 13 from being superimposed on radio waves for external communication performed by the wireless communication unit 150.

[0045] The first insulating layer 14 is provided over the wiring layer 13 of the flexible wiring board 11. The first insulating layer 14 includes a first adhesive portion 14A and a first covering portion 14B. The wiring layer 13, the first adhesive portion 14A, and the first covering portion 14B are stacked in this order.

[0046] The second insulating layer 17 is provided over the ground layer 16 of the flexible wiring board 11. The second insulating layer 17 includes a second adhesive portion 17A and a second covering portion 17B. The wiring layer 13, the second adhesive portion 17A and the second covering portion 17B are stacked in this order.

[0047] It is desirable that the first adhesive part 14A and the second adhesive part 17A have high electrical insulation. Cured products of known adhesives can be used as the first adhesive part 14A and the second adhesive part 17A. For example, adhesives based on acrylonitrile-butadiene rubber (NBR), adhesives based on polyamide, adhesives based on polyester, adhesives based on acrylic acid, adhesives based on polyester polyurethane, and adhesives based on silicone can be used.

[0048] Although the thickness of the first adhesive part 14A and the second adhesive part 17A is not particularly limited, it is desirable that the transmission line is sufficiently covered and the surface of each part is smooth. Specifically, the thickness of the first adhesive part 14A and the second adhesive part 17A is desired to be in the range of 2 μm or more and 50 μm or less, and particularly desired to be in the range of 5 μm or more and 30 μm or less. If the thickness of the first adhesive part 14A and the second adhesive part 17A is less than 2 μm, the filling between the lines is insufficient, which may cause peeling, etc. when the first covering part 14B and the second covering part 17B are joined. In addition, if the thickness of the first adhesive part 14A and the second adhesive part 17A exceeds 50 μm, the amount of adhesive that oozes out from these parts may increase.

[0049] The method for forming the first adhesive portion 14A and the second adhesive portion 17A is not particularly limited, and may be a method for stacking and curing sheet adhesives, a method for applying a liquid adhesive by a dispenser or a printing method and curing the applied adhesive by heating or ultraviolet irradiation, etc.

[0050] The first covering part 14B and the second covering part 17B act as a protective layer for suppressing the energization of other components in the electronic device. Therefore, the first covering part 14B and the second covering part 17B have insulation and are made of resin, and the resin includes a flexible covering film and a covering layer of insulating resin. As a covering film, engineering plastics can be used. For example, polypropylene, cross-linked polyethylene, polyester, polybenzimidazole, polyamide, polyimide, polyimide amide, polyetherimide, polyphenylene sulfide (PPS), polyethylene naphthalate (PEN) and polyether ketone (PEEK) can be used. From the viewpoint of low cost, polyester film is desired. From the aspect of excellent flame retardancy, it is desired to use polyphenylene sulfide film, and in the case of further needing heat resistance, it is desired to use aromatic polyamide film and polyimide film.

[0051] The insulating resin may be any resin having insulating properties, and may include, for example, a thermosetting resin or an ultraviolet curable resin. Thermosetting resins may include phenolic resins, acrylic resins, epoxy resins, melamine resins, silicone resins, and silicone resins modified with acrylic acid. Ultraviolet curable resins may include epoxy acrylic resins, polyester acrylic resins, and methacrylate modified materials thereof. The curing form may be any one of thermal curing, ultraviolet curing, electron beam, etc. In addition, other known additives such as color pigments, flame retardants, antioxidants, lubricants, dust suppressants, and curing accelerators may be mixed if necessary.

[0052] The method for forming the first covering part 14B and the second covering part 17B is not particularly limited, and known methods can be used to coat the insulating resin. The solution prepared by dissolving the insulating resin in a solvent can be applied by gravure coating, kiss coating, die coating, scraper coating, roller coating, knife coating, spray coating, rod coating, spin coating and dip coating. The solvent can be appropriately selected according to the type of resin to be used. For example, ketone-based solvents (such as acetone, methyl ethyl ketone and cyclohexanone) and alcohol-based solvents (such as methanol, ethanol, propanol, ethylene glycol, glycerol and propylene glycol monomethyl ether) can be used. In addition, acid (such as acetic acid), amide-based solvents (such as formamide, dimethylacetamide and N-methylpyrrolidone), nitrile-based solvents (such as acetonitrile and propionitrile) and ester-based solvents (such as methyl acetate and ethyl acetate) can be used. In addition, carbonate-based solvents such as dimethyl carbonate and diethyl carbonate can be used. In the coating process, if necessary, heating or drying processes can be included to volatilize the solvent. Known heating and drying devices such as a hot air dryer and an infrared heater may be used for heating and drying, and the temperature and time of heating and drying may be appropriately selected.

[0053] The thickness of the first covering portion 14B and the second covering portion 17B is not particularly limited, but is desirably within a range of 5 μm or more and 50 μm or less, and is particularly desirably within a range of 10 μm or more and 30 μm or less. If the thickness of the first covering portion 14B and the second covering portion 17B is less than 5 μm, the strength thereof may be insufficient. Meanwhile, if the thickness of the first covering portion 14B and the second covering portion 17B exceeds 50 μm, the slidability and flexibility thereof may be reduced. In addition, the volume resistance value of the first covering portion 14B and the second covering portion 17B is desirably 10 9 Ω·cm or more, and more preferably 10 13 Ω·cm or more.

[0054] In the case where the first cover portion 14B and the second cover portion 17B have the function of bonding to the base member 12 and the wiring layer 13 , the first adhesive portion 14A and the second adhesive portion 17A are not necessary.

[0055] (Variation Example)

[0056] According to the present exemplary embodiment, the ground layer 16 is provided on the first surface 12A of the base member 12. However, the position of the ground layer 16 is not limited to the above configuration. Figure 4 As shown in , the ground layer 16 may be provided, for example, on the first insulating layer 14 provided on the wiring layer 13. In this modification, the second cover portion 17B formed on the ground layer 16 has an adhesive function.

[0057] (Example)

[0058] Next, the present disclosure will be described in more detail with reference to examples and comparative examples, but the present disclosure is not limited to the following examples. The measurement method according to the present disclosure is as follows.

[0059] Evaluation methods of wiring substrates according to Examples and Comparative Examples are described below.

[0060] (1) Radiated noise measurement

[0061] Use includes Figure 5 The system of the configuration shown in evaluates the radiation noise amount of the flexible wiring board 11 as the wiring substrate.

[0062] First, a differential wiring substrate for measuring the amount of radiation noise of a wiring substrate without a ground layer as a reference was prepared. On a base member of a polyimide film having a thickness of 25 μm (manufactured by DU PONT-TORAY CO., LTD. A copper foil with a thickness of 12 μm was stacked on one surface of the 100H) as a wiring layer. Then, a differential transmission line with a line width of 140 μm, a line interval of 55 μm, and a total length of 120 mm was formed on the wiring layer by etching.

[0063] Next, a polyimide film having a thickness of 12.5 μm and a cover layer having a thickness of 15 μm (CISV1215 manufactured by NIKKAN INDUSTRIES CO., LTD.) were stacked over the wiring layer, thereby obtaining a differential wiring substrate having no ground layer as a reference.

[0064] Next, the wiring substrate was connected to the connection substrate 35. The signal generator 31 (M8041A manufactured by Keysight Technologies) was used to transmit a signal having a data pattern of 5.3 Gbps bit rate as a pseudo random binary sequence (PRBS) 23. Then, the waveform of the common mode voltage was observed using an oscilloscope 32 (92504A manufactured by Agilent Technologies Japan, Ltd.), and the input amplitude was adjusted so that the common mode voltage became 150 mV.

[0065] Next, the flexible wiring board 11 (of the example and comparative example) as the measurement target is connected to the connection substrate 35, and the signal generator 31 transmits a signal with a data pattern of 5.3 Gbps bit rate as PRBS23. Here, the signal is transmitted with an input amplitude adjusted using a differential wiring substrate without a ground layer as a reference. The 5 GHz radiation noise 36 generated from the flexible wiring board 11 is detected by a pen-type electric near-field probe 34 with a length of 110 mm (manufactured by Electric-Metrics) and measured by a spectrum analyzer 33 (E4440A manufactured by Keysight Technologies). The amount of radiation noise is measured as follows. The electric near-field probe 34 is installed at a height of 5 mm from the wiring substrate, and each point is scanned 5 times. Then, the average value calculated from the value obtained by scanning all points in the area where the ground layer is formed at intervals of 1 mm by the electric near-field probe 34 is taken as the amount of radiation noise. A smaller amount of radiation noise means that the radiation noise can be successfully shielded and the wiring substrate has better shielding. The radiated noise was measured in a frequency range from 300 kHz to 20 GHz in an atmosphere with a temperature of 25°C and a relative humidity of 23% to 50%. The evaluation criteria were as follows, and Grade B or higher was accepted.

[0066] A: Less than 20dBμV

[0067] B: 20dBμV or more and less than 25dBμV

[0068] C: 25dBμV or more

[0069] (2) Transmission characteristics evaluation (eye diagram)

[0070] Use includes Figure 6 The system of the configuration shown in evaluates output waveform characteristics of a wiring substrate.

[0071] The system includes a signal generator 41 (M8041A manufactured by Agilent Technologies Japan, Ltd.), an oscilloscope 42 (92504A manufactured by Agilent Technologies Japan, Ltd.), and a pair of connection substrates 35. The connection substrate 35 includes an input terminal and an output terminal, and the flexible wiring board 11 as a measurement target is connected between the pair of connection substrates 35 in a state where the flexible wiring board 11 floats in the air. In addition, the signal generator 41 is connected to one of the connection substrates 35 to input a pseudo-random signal of PRBS23 with a bit rate of 5.3 Gbps. The amplitude of the input signal is 150 mV / side (differential 300 mV). In addition, the other connection substrate 35 is connected to the oscilloscope 42, and the opening amplitude of the signal eye diagram output from the connection substrate 35 is observed. The measurement is performed in an atmosphere with a temperature of 25°C and a relative humidity of 30% to 50%. The evaluation criteria are as follows, and B or above is accepted.

[0072] A: The opening amplitude is 110mV or more

[0073] B: The opening amplitude is 100mV or more and less than 110mV

[0074] C: Opening amplitude is less than 100mV

[0075] (Examples 1 to 12)

[0076] Production has Figure 2B The flexible wiring board 11 has the shape shown in FIG.

[0077] A polyimide film having a thickness of 25 μm (manufactured by DU PONT-TORAY CO., LTD.) was prepared. 100H) as the base member 12. A copper foil with a thickness of 12 μm was stacked over the first surface 12A of the base member 12 as the wiring layer 13, and differential signal lines 13A and 13B with a total length of 120 mm were produced with the line width and line interval shown in Table 1 by etching.

[0078] Next, a copper foil having a thickness of 12 μm was stacked over the second surface 12B of the base member 12, and a ground layer 16 including an opening portion 21 having an opening and a non-opening portion 16A was formed by etching in a configuration having the numerical values ​​shown in Table 2. The inspection specification for circuit appearance and tolerance was based on the Japan Electronics Package and Circuit Association (JPCA) standard (JPCA-DG02).

[0079] Next, a first insulating layer 14 and a second insulating layer 17 were formed on the wiring layer 13 and the ground layer 16, respectively. Specifically, the wiring substrates of Examples 1 to 12 were obtained by bonding a coating (CISV1215 manufactured by NIKKAN INDUSTRIES CO., LTD.) with a polyimide film having a thickness of 12.5 μm as an insulating portion and an adhesive portion having a thickness of 15 μm. The differential signal line was designed to have a differential impedance of 100Ω±10Ω as a target value. Table 2 indicates the evaluation results of the above-mentioned (1) radiation noise measurement and (2) transmission characteristic evaluation of the wiring substrate.

[0080] Table 1

[0081]

[0082] Table 2

[0083]

[0084]

[0085] Note*1: The letters in the shape column indicate the following.

[0086] Rh: rhombus, Re: rectangle, E: ellipse, H: hexagon

[0087] As shown in Table 2, in all the wiring substrates of Examples 1 to 12, the amount of radiation noise at 5 GHz was small, and the opening widths of Class B and above were very good.

[0088] (First to Fifth Comparative Examples)

[0089] Production has Figure 2B A wiring substrate having the layer configuration shown in FIG.

[0090] A polyimide film having a thickness of 25 μm (manufactured by DU PONT-TORAY CO., LTD.) was prepared. A copper foil with a thickness of 12 μm was stacked on the first surface of the base member as a wiring layer, and the first differential signal line and the second differential signal line with a total length of 120 mm were produced by etching with the line width and line interval shown in Table 3.

[0091] Next, a copper foil having a thickness of 12 μm was stacked over the second surface of the base member, and a ground layer including an opening portion having an opening and a non-opening portion was formed by etching in a configuration having the numerical values ​​shown in Table 4. Inspection specifications for circuit appearance and tolerance were based on the JPCA standard (JPCA-DG02).

[0092] Next, a first insulating layer and a second insulating layer are formed on the wiring layer and the ground layer, respectively. Specifically, the wiring substrates of the first to fifth comparative examples are obtained by bonding a coating (CISV1215 manufactured by NIKKAN INDUSTRIES CO., LTD.) with a polyimide film having a thickness of 12.5 μm as an insulating portion and an adhesive portion having a thickness of 15 μm. The differential signal line is designed to have a differential impedance of 100Ω±10Ω as a target value. Table 4 indicates the evaluation results of the above-mentioned (1) radiation noise measurement and (2) transmission characteristic evaluation of the wiring substrate.

[0093] Table 3

[0094]

[0095] Table 4

[0096]

[0097]

[0098] In the first to third comparative examples in which the length L1 is less than 4 times the length L2, the radiation noise is large. Figure 7 FIG. 2 shows a wiring substrate of a first comparative example. Figure 7 As shown in , in the wiring substrate of the first comparative example, the route of the return current 54 flowing through the ground layer 51 is longer relative to the route of the signal current 53 flowing through the transmission line 52, compared with Examples 1 to 12 in which the length L1 is 4 times or more the length L2. Therefore, it can be considered that the wiring substrate of the first comparative example cannot sufficiently exert a suppressive effect on the increase in radiation noise due to the increase in the speed of the transmission signal.

[0099] In the fourth and fifth comparative examples in which the length L2 is longer than the length L3, the radiation noise is also large. Figure 8 FIG. 5 shows a wiring substrate of a fifth comparative example. Figure 8 As shown in , in the wiring substrate of the fifth comparative example, the region 63 where the ground layer does not exist between the differential transmission line 62A and the differential transmission line 62B is larger than in Examples 1 to 12 in which the length L2 is equal to or less than the length L3. Therefore, it can be considered that the crosstalk between the signal lines 622 and 623 becomes larger, and the radiation noise increases. Therefore, it can be considered that the wiring substrate of the fifth comparative example cannot sufficiently exert a suppressive effect on the increase in radiation noise caused by the increase in the speed of the transmission signal.

[0100] As described above, the present disclosure can provide a wiring substrate that generates less radiation noise and less crosstalk noise in the transmission of high-speed data signals. In addition, the present disclosure can provide an electronic device including the wiring substrate.

[0101] Although the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the present disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. A wiring substrate comprising a plurality of differential signal lines, characterized in that: The wiring substrate comprises: a base member having a first surface; a first differential signal line disposed on a first surface of the base member, the first differential signal line comprising a first pair of signal lines, the first pair of signal lines comprising a first signal line and a second signal line; a second differential signal line disposed on the first surface of the base member, the second differential signal line comprising a second pair of signal lines, the second pair of signal lines comprising a third signal line and a fourth signal line; and a ground layer facing the first differential signal line and the second differential signal line and having an opening portion including a plurality of openings arranged continuously along a predetermined direction, wherein the first differential signal line and the second differential signal line are adjacent differential signal lines among the plurality of differential signal lines, and the second signal line and the third signal line are arranged between the first signal line and the fourth signal line, wherein a first opening among the plurality of openings is not arranged on a differential signal line other than the first differential signal line but is arranged on the second signal line of the first differential signal line, and a second opening among the plurality of openings is not arranged on a differential signal line other than the second differential signal line but is arranged on the third signal line of the second differential signal line, and a third opening among the plurality of openings arranged between the first opening and the second opening is not arranged on at least one of the second signal line and the third signal line, In which, in a plan view of the wiring substrate, a length of each of the first opening and the second opening in a first direction along a longitudinal direction of the first pair of signal lines and the second pair of signal lines is a length L1 greater than 400 μm, a length of the first opening and the second opening in a second direction orthogonal to the first direction is a length L2, and a distance between the first differential signal line and the second differential signal line is a length L3, the length L1 is greater than the length L2, and the length L3 is less than the length L1.

2. The wiring substrate according to claim 1, wherein: In a plan view of the wiring substrate, an area ratio of the opening portion in the ground layer is within a range of greater than 40% and less than 90%, wherein the first opening is arranged on the first signal line and the second signal line, and the second opening is arranged on the third signal line and the fourth signal line.

3. The wiring substrate according to claim 1, wherein The length L1 is greater than or equal to 800 μm and less than or equal to 20 times the length L2.

4. The wiring substrate according to claim 1, wherein: Each shape of the first opening and the second opening is any one of a rhombus, a rectangle, a hexagon, and an ellipse.

5. The wiring substrate according to claim 1, wherein The thickness of the ground layer is in the range of greater than 1 μm and less than 20 μm, the line width of each of the first signal line and the second signal line is greater than the line spacing of the first pair of signal lines, and the line width of each of the third signal line and the fourth signal line is greater than the line spacing of the second pair of signal lines.

6. The wiring substrate according to claim 1, wherein The base member is made of resin, the wiring substrate is flexible, and the length L3 is greater than the line interval of the first pair of signal wires and the line interval of the second pair of signal wires.

7. The wiring substrate according to any one of claims 1 to 6, in, The base member has a second surface opposite to the first surface, and The ground layer is disposed on the second surface, wherein a third opening of the plurality of openings is disposed between the first opening and the second opening, and the third opening is not disposed on the first signal line and the fourth signal line.

8. The wiring substrate according to any one of claims 1 to 6, in, The wiring substrate includes an insulating layer provided between the ground layer and the first differential signal line and the second differential signal line, and The third opening of the plurality of openings is arranged between the first opening and the second opening, and the third opening is not arranged on the second signal line and the third signal line.

9. An electronic device, characterized in that: The electronic device comprises: The wiring substrate according to any one of claims 1 to 8; and A housing in which the wiring substrate is accommodated.

10. The electronic device according to claim 9, further comprising a first semiconductor device and a second semiconductor device, wherein: Each of the first differential signal line and the second differential signal line serves as a connection between the first semiconductor device and the second semiconductor device.

11. The electronic device according to claim 10, wherein: The signals transmitted via the first differential signal line and the second differential signal line are digital signals having a transmission speed of 5 gigabits per second (Gbps) or more.

12. The electronic device according to claim 10, in, The first semiconductor device is an image capturing element, and Here, the second semiconductor device is a processing circuit configured to process a signal transmitted from the image capturing element.

13. The electronic device according to claim 9, in, The housing further accommodates a wireless communication unit configured to wirelessly communicate with an external device, and The ground layer of the wiring substrate is arranged in the housing at a position closer to the wireless communication unit than the first differential signal line and the second differential signal line of the wiring substrate.

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