Circuit board

Abstract

To obtain a circuit board that can suppress the occurrence of partial discharge without adjusting the thickness of the circuit board. [Solution] The conductive layer has an insulating layer, a first conductive layer provided on a first surface which is the surface in the thickness direction of the insulating layer, and a second conductive layer provided on a second surface which is the surface opposite to the first surface in the thickness direction of the insulating layer, and a protective part which has a first protective part and a second protective part and protects the conductive layer, the second conductive layer has a first conductive pattern and a second conductive pattern provided at a distance from the first conductive pattern and on the lower voltage side than the first conductive pattern, the protective part is an insulator, the first protective part covers the second surface and the portion where the second conductive layer is not provided, and the second protective part is provided on the outer circumference of the first conductive pattern and has a higher dielectric constant or a higher dielectric strength than the first protective part.

Description

【Technical Field】 【0001】 This disclosure relates to a circuit board. 【Background Art】 【0002】 Conventionally, there is a circuit board in which conductive layers and insulating layers made of copper foil are alternately provided. In Patent Document 1, there is provided an insulating board, a conductor layer joined by a bonding material on the surface of the insulating board, and a dielectric layer provided in a region not joined by the bonding material between the insulating board and the conductor layer, and between the relative permittivity εg of the dielectric layer, the relative permittivity εb of the insulating board, the distance Lg between the insulating board and the conductor layer, and the thickness Lb of the insulating board, there is a relationship of εg≧εb×(Lg / Lb). A circuit board characterized by having such a configuration is disclosed. With such a configuration, the circuit board described in Patent Document 1 can suppress the occurrence of partial discharge. 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 8-186190 <了 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 However, the circuit board described in Patent Document 1 has a problem that it is necessary to adjust the thickness of the insulating board of the circuit board in order to suppress the occurrence of partial discharge. 【0005】 This disclosure has been made to solve the above problems, and an object thereof is to suppress the occurrence of partial discharge without adjusting the thickness of the circuit board. 【Means for Solving the Problems】 【0006】 The circuit board according to this disclosure has an insulating layer, a conductive layer having a first conductive layer provided on a first surface which is a surface in the thickness direction of the insulating layer, and a second conductive layer provided on a second surface which is a surface opposite to the first surface in the thickness direction of the insulating layer, and a protective part having a first protective part and a second protective part to protect the conductive layer, wherein the second conductive layer has a first conductive pattern and a second conductive pattern provided at a distance from the first conductive pattern and on the lower voltage side than the first conductive pattern, the protective part is an insulator, the first protective part covers the second surface and the portion where the second conductive layer is not provided, and the second protective part is provided on the outer circumference of the first conductive pattern and has a higher dielectric constant or a higher dielectric strength than the first protective part. 【0007】 Furthermore, the circuit board according to this disclosure has an insulating layer, a conductive layer having a first conductive layer provided on a first surface which is a surface in the thickness direction of the insulating layer, and a second conductive layer provided on a second surface which is a surface opposite to the first surface in the thickness direction of the insulating layer, the second conductive layer having a first conductive pattern and a second conductive pattern provided at a distance from the first conductive pattern and on the lower voltage side than the first conductive pattern, and the insulating layer has grooves formed along the outer circumference of the first conductive pattern. [Effects of the Invention] 【0008】 The circuit board according to this disclosure has the effect of suppressing the occurrence of partial discharge without adjusting the thickness of the circuit board. [Brief explanation of the drawing] 【0009】 [Figure 1] This is a top view of a circuit board according to Embodiment 1 of the present disclosure. [Figure 2] This is a cross-sectional view taken along line A-A in Figure 1 of a circuit board according to Embodiment 1 of the present disclosure. [Figure 3] This is a partially enlarged view of the A-A cross-sectional view of a circuit board according to Embodiment 1 of the present disclosure. [Figure 4] Figure 3 is the equivalent circuit diagram. [Figure 5] This is a schematic diagram showing the conditions for Calculation 1 and Calculation 2. [Figure 6] This figure shows the result of Calculation 1. [Figure 7] This figure shows the result of calculation 2. [Figure 8] This is a top view of a circuit board used in an experiment to measure the voltage at which partial discharge begins when the external shape of the first conductive pattern viewed from above and the presence or absence of the second protective part are changed. [Figure 9] This is a cross-sectional view of the circuit board in the experiment, taken along line B-B in Figure 8. [Figure 10] This is a magnified section of a cross-sectional view showing the process of applying overresist to a circuit board. [Figure 11] This is a top view of a circuit board according to Embodiment 2 of the present disclosure. [Figure 12] This is a cross-sectional view taken along line C-C in Figure 11 of a circuit board according to Embodiment 2 of the present disclosure. [Modes for carrying out the invention] 【0010】 Embodiments of this disclosure will be described below with reference to the drawings. However, this disclosure is not limited to the embodiments described below, and modifications or omissions are permitted without departing from the spirit of this disclosure. Furthermore, common elements in each drawing are denoted by the same reference numerals, and redundant explanations are omitted. 【0011】 Embodiment 1. Figure 1 is a top view of circuit board 1 according to Embodiment 1 of the present disclosure. Figure 2 is a cross-sectional view of circuit board 1 according to Embodiment 1 of the present disclosure taken along line A-A in Figure 1. The configuration of circuit board 1 will be explained using Figures 1 and 2. Although the figures define the up and down and left and right directions of circuit board 1, these are defined for the purpose of explaining the embodiments and do not limit the orientation of the devices and components of the present disclosure. 【0012】 As shown in Figure 2, circuit board 1 is a four-layer circuit board. More specifically, the circuit board is a PCB (Printed Circuit Board). Circuit board 1 has an insulating layer 10, a conductive layer 20, and a protective layer 30. 【0013】 The insulating layer 10 electrically insulates the conductive layers 20 from each other. The insulating layer 10 includes a first prepreg 11, a core layer 12, and a second prepreg 13. 【0014】 The conductive layer 20 provides electrical connection between electronic components. Specifically, the conductive layer 20 is a copper foil. The conductive layer 20 is provided alternately with the insulating layer 10. Specifically, it includes a first conductive layer 21, a second conductive layer 22, a third conductive layer 23, and a fourth conductive layer 24. The first conductive layer 21 is provided on the first prepreg 11. Also, the second conductive layer 22 is provided between the first prepreg 11 and the core layer 12. Also, the third conductive layer 23 is provided between the core layer 12 and the second prepreg 13. Also, the fourth conductive layer 24 is provided under the second prepreg 13. 【0015】 As shown in FIG. 1, the first conductive layer 21 has two conductive patterns, a first conductive pattern 211 and a second conductive pattern 212. The second conductive pattern 212 is provided on the low-voltage side of the first conductive pattern 211 with a gap therebetween. 【0016】 As shown in FIG. 1, the first conductive pattern 211 and the second conductive pattern 212 are elliptical when viewed from above. 【0017】 The protection part 30 protects the conductive layer 20. More specifically, the protection part 30 protects the first conductive layer 21 and the fourth conductive layer 24. The protection part 30 is an insulator. Also, the protection part 30 includes a first protection part 311 and a second protection part 312. 【0018】 FIG. 3 is a partially enlarged view of the A - A cross-sectional view of the circuit board 1 according to Embodiment 1 of the present disclosure. Specifically, FIG. 3 is a partially enlarged view showing the first prepreg 11, the first conductive layer 21, the second conductive layer 22, and the protection part 30 of the circuit board 1. The detailed configuration of the protection part 30 will be described using FIG. 3. 【0019】 As shown in Figure 3, the protective portion 30 is provided on the second surface 352 of the first prepreg 11, which is the surface opposite to the first surface 351 on which the second conductive layer 22 is provided, and on which the first conductive layer 21 is provided. The first surface 351 and the second surface 352 are surfaces provided perpendicular to the vertical direction, that is, surfaces provided in the thickness direction. The first protective portion 311 is a solder resist and covers the second surface 352 and the portion where the first conductive layer 21 is not provided. The first protective portion 311 is made of an insulator such as epoxy. 【0020】 The second protective section 312 is provided so as to cover the first conductive pattern 211. Furthermore, the second protective section 312 has a higher dielectric constant than the first protective section 311. Specifically, the second protective section 312 is composed of an insulator such as polyimide, silicon, or fluorine. Alternatively, an insulator with a higher dielectric constant than the main component may be used as a filler, separate from the main component. In other words, the second protective section 312 has a configuration that includes a first insulator, which is the main component, and a second insulator with a higher dielectric constant than the first insulator. Examples of fillers (second insulators) include metal oxides such as titanium oxide and zinc oxide, or ceramic powder. 【0021】 Figure 4 is the equivalent circuit diagram of Figure 3. Using Figure 4, we will explain the configuration that suppresses the occurrence of partial discharge on the circuit board 1. 【0022】 As shown in Figure 4, the discharge path has a first discharge path 61, a second discharge path 62, a third discharge path 63, and a fourth discharge path 64. When the electric field strength flowing through each discharge path exceeds a certain value, the insulator breaks down, current begins to flow, and discharge occurs. The electric field strength is the value obtained by dividing the voltage by the distance. 【0023】 R1 in the first discharge path 61 is the insulation resistance of the first prepreg 11. R2 in the second discharge path 62 is the surface resistance from the first conductive pattern 211, which is a conductive pattern provided on the high-voltage side, to the second conductive pattern 212, which is a conductive pattern provided on the low-voltage side via the first protective section 311. In the third discharge path 63, C3, which is an air layer formed by voids or interfacial delamination within the substrate, and C4, which is the capacitance of the first prepreg 11, are connected in series. 【0024】 The fourth discharge path 64 has capacitances C1 and C2 connected in series. C1 is the capacitance formed between the first conductive pattern 211 and the second conductive pattern 212. C2 is the capacitance formed between the first conductive pattern 211 and the first prepreg 11. If the second protective section 312 is not provided, an air layer is formed between the first conductive pattern 211 and the first prepreg 212, so C2 is treated as an air capacitor. On the other hand, if the second protective section 312 is provided between the first conductive pattern 211 and the first prepreg 11, C2 is treated as a capacitor with a dielectric inserted between the electrodes. 【0025】 Next, we will explain the relationship between the relative permittivity of a capacitor and the electric field strength. Figure 5 is a schematic diagram showing the conditions for calculations 1 and 2. In Figure 5, the first dielectric is inserted to a length d1 between the electrodes. The relative permittivity of the first dielectric is assumed to be 4. Also, the distance between the electrodes, i.e., the sum of the lengths d1 and d2, is constant. That is, d2 is the value obtained by subtracting d1 from the distance between the electrodes, d. Note that the parallel plate capacitor in Figure 5 is assumed to have a uniform electric field distribution within the plate, that is, a uniform electric field is realized. 【0026】 Figure 6 shows the results of Calculation 1. In Calculation 1, the electric field strength E1 inside the air capacitor was determined when the length of the air capacitor was changed. In Calculation 1, the relative permittivity of the first dielectric inserted at d1 is constant at 4. Also, the length of d is assumed to be 0.5 mm. In Figure 6, since nothing is inserted at the length d2 between the electrodes, the length of d2 is treated as an air capacitor. As shown in Figure 6, E1, that is, the electric field strength inside the air capacitor, decreases as the length of d2 increases. As shown in Figure 6, the electric field strength can be reduced by increasing the distance between the electrodes of the capacitor. Therefore, in the fourth discharge path 64, discharge can be suppressed by increasing the distance between two points, but this presents the problem of increasing the size of the circuit. 【0027】 Figure 7 shows the calculation results of Calculation 2. Calculation 2 shows the calculation results of the electric field strength E2 within the second dielectric when the relative permittivity of the second dielectric inserted between the electrodes is changed. In Calculation 2, the second dielectric is inserted over a length of d2. The length of d is assumed to be 0.3 mm. Specifically, Calculation 2 shows the calculation results for three conditions: when the dielectric constant of the dielectric inserted over a length of d2 is 1, 2.7, and 6. As shown in Figure 7, regardless of the length of d2, the electric field strength inside the air capacitor decreases as the relative permittivity of the dielectric inserted over a length of d2 increases. This is because increasing the relative permittivity of the dielectric inserted over a length of d2 increases the capacitance inside the second dielectric, and therefore the voltage applied inside the second dielectric can be reduced. 【0028】 The magnitude of capacitance is proportional to the dielectric constant. Furthermore, the voltage applied to C1 and C2 in the fourth discharge path 64 is determined by the inverse ratio of the capacitances of C1 and C2. In order to suppress discharge between the first conductive pattern 211 and the first prepreg 11 in the fourth discharge path 64, it is necessary to either decrease the capacitance of C1 or increase the capacitance of C2. 【0029】 In the circuit board 1, by providing a second protective portion 312 that covers the first conductive pattern 211, the capacitance of C2 can be increased compared to the case where the second protective portion 312 is not provided. Therefore, the circuit board 1 can suppress discharge without adjusting the thickness of the circuit board 1. 【0030】 Specifically, the relative permittivity of the second protective part 312 is higher than 3.8. This is because the relative permittivity of the first protective part 311 is generally between 2.7 and 3.8. For example, if the main component of the second protective part 312 is epoxy resin, the relative permittivity of the second protective part 312 is greater than 3.8 and 6 or less. Also, if the main component of the second protective part 312 is silicone resin, the relative permittivity of the second protective part 312 is greater than 3.8 and 5 or less. 【0031】 Furthermore, the second protection unit 312 may have a higher voltage rating than the first protection unit 311. By using a material with a higher voltage rating, discharge occurring on the circuit board 1 can be suppressed. 【0032】 Furthermore, as mentioned above, the first conductive pattern 211 is elliptical when viewed from above. By configuring the outline at these two points in this way, the circuit board 1 can more effectively suppress discharge. Calculations 1 and 2 were performed under the condition that a uniform electric field is achieved. However, a uniform electric field is not always achieved. When the electric field distribution is not uniform, the magnitude of the electric field is determined by the potential difference between two points where discharge may occur, the distance between the two points, and the outline at the two points. Therefore, in the circuit board 1 of Embodiment 1, by giving distinctive features to the potential difference and outline between the two points, discharge can be effectively suppressed without increasing the size. 【0033】 Figure 8 is a top view of circuit board 5 in an experiment to measure the voltage at which partial discharge begins when the external shape of the first conductive pattern 331 and the presence or absence of the second protective part 312 are changed. Figure 9 is a cross-sectional view of circuit board 5 in the experiment taken along line B-B in Figure 8. 【0034】 Table 1 shows the experimental results using circuit board 5. Table 1 shows the experimental results of the voltage at which partial discharge begins when the external shape of the first conductive pattern 331 viewed from above and the presence or absence of the second protective part 312 are changed. Specifically, experiments were conducted when the shape of the first conductive pattern 331 viewed from above was circular and when it was square. The partial discharge initiation voltage is shown as a relative voltage value with reference to the voltage value when the external shape of the first conductive pattern 331 viewed from above is circular and the second protective part 312 is absent. The partial discharge suppression effect of circuit board 1 will be explained using Table 1, Figure 8 and Figure 9. 【0035】 [Table 1] 【0036】 As shown in Figure 9, the circuit board 5 used in the experiment is a four-layer board. The circuit board 5 also has a slit 15 to confirm that partial discharge does not occur at the substrate surface. In the experiment, the partial discharge initiation voltage was measured by applying a voltage between the first and second layers of the circuit board. In the experiment, partial discharge was determined to have started when the charge amount reached 10 pC. In the experiment, the conditions of the first conductive pattern 331, which is located on the high-voltage side of the second conductive pattern 332, were changed. 【0037】 As shown in Table 1, the discharge initiation voltage is higher when the second protection unit is present than when it is absent, indicating that partial discharge is suppressed in the circuit board 1. Furthermore, the discharge initiation voltage is higher when the outer shape of the first conductive pattern 331, when viewed from above, is elliptical than when the outer shape of the first conductive pattern 331, when viewed from above, is not obtuse. Therefore, by making the outer shape of the first conductive pattern 211, when viewed from above, elliptical, partial discharge can be suppressed in the circuit board 1. 【0038】 An electrical triple junction is generated at the point where the three interfaces—the first conductive pattern 211, the first prepreg 11, and the air layer—intersect. When the outer shape of the first conductive pattern 211, as viewed from above, is elliptical, the contact angle of the electrical triple junction is not acute, thus suppressing partial discharge more effectively than when the outer shape of the first conductive pattern 211, as viewed from above, does not have an obtuse angle. 【0039】 Figure 10 is a partially enlarged cross-sectional view showing the application of overresist to a circuit board. Note that Figure 10 is a partially enlarged cross-sectional view taken at the same cutting point as the A-A cross-sectional view. Conventional technology includes overresist, which involves applying solder resist over conductive patterns. Using Figure 10, the differences and effects of the second protective section 312 of the circuit board 1 and overresist will be explained. 【0040】 Solder resist is an insulating material, but its main purpose is to prevent the adhesion of excess solder, short circuits caused by dirt or dust, or corrosion due to moisture. Therefore, since solder resist does not have a specified dielectric strength and sometimes uses materials with low dielectric constant, over-resist was an insufficient method for preventing partial discharge. By covering the first conductive pattern 211 with a material that has a higher dielectric constant than the solder resist, the circuit board 1 can achieve a greater partial discharge effect than by using over-resist. 【0041】 In the circuit board according to Embodiment 1, the second protective portion is provided so as to cover the first conductive pattern, but the configuration is not limited to this. The second protective portion may be provided on the outer periphery of the first conductive pattern. By providing the second protective portion only on the outer periphery of the first conductive pattern, the amount of insulating material used can be reduced. On the other hand, when the second protective portion is provided so as to cover the first conductive pattern, it has the advantage of being easy to provide. 【0042】 Embodiment 2. The circuit board 2 according to Embodiment 2 will now be described. Figure 11 is a top view of the circuit board 2 according to Embodiment 2 of this disclosure. Figure 12 is a cross-sectional view of the circuit board 2 according to Embodiment 2 of this disclosure taken along line C-C in Figure 11. The configuration of the circuit board 2 will be described using Figures 11 and 12. 【0043】 As shown in Figures 11 and 12, the circuit board 2 according to Embodiment 2 has grooves 80 compared to the circuit board 1 according to Embodiment 1. The configuration of the circuit board 2, excluding the grooves 80, is the same as that of the circuit board 1, so a description is omitted. 【0044】 The groove 80 of the circuit board 2 is formed along the outer circumference of the first conductive pattern 211. By providing the groove 80 on the circuit board 2, the circuit board 2 can suppress the occurrence of partial discharge in the fourth discharge path 64, similar to Embodiment 1. By providing the groove 80 along the outer circumference of the first conductive pattern 211, it is possible to prevent the occurrence of an electrical triple point that occurs at the point where the three interfaces of the first conductive pattern 211, the first prepreg 11, and the air layer intersect, thereby effectively suppressing the occurrence of partial discharge without adjusting the thickness of the circuit board 1. 【0045】 The depth of the grooves 80 may vary depending on their location. Specifically, the grooves 80 are made deeper where the electric field strength is high and shallower where the electric field strength is low. Furthermore, the grooves 80 do not need to be provided along the entire outer circumference of the first conductive pattern 211, as long as they are provided along at least a portion of it. In that case, the grooves 80 are provided only in the areas where the electric field strength is high. With this configuration, the circuit board 2 can effectively suppress partial discharge without increasing the thickness of the first prepreg 11. 【0046】 Although the circuit boards in Embodiments 1 and 2 are four-layer circuit boards, the configuration of the circuit board is not limited to this. The circuit board does not need to be four-layer; it can be two or more layers, with insulating layers provided between the conductive layers. The circuit board may be, for example, a double-sided printed circuit board. 【0047】 Furthermore, while the circuit boards according to Embodiment 1 and Embodiment 2 have an elliptical shape when viewed from above, the configuration is not limited to this. The configuration may be such that only the first conductive pattern, which is highly likely to generate discharge, is elliptical when viewed from above. Also, the first conductive pattern does not have to be elliptical when viewed from above; it may be a polygon with obtuse angles when viewed from above. The first conductive pattern may also include both an elliptical shape and a polygon with obtuse angles when viewed from above. Furthermore, the first conductive pattern may be configured in a substantially spherical shape. 【0048】 Furthermore, while Embodiment 1 described a configuration in which a second protective portion is provided on the circuit board, and Embodiment 2 described a configuration in which a groove portion is provided on the circuit board, the circuit board may also be configured to have both a second protective portion and a groove portion. 【0049】 The configurations shown in the embodiments described above are merely examples of the content of this disclosure and can be combined with other known technologies. Furthermore, it is possible to omit or modify parts of the configuration without departing from the gist of this disclosure. [Explanation of symbols] 【0050】 1 Circuit board, 2 Circuit board, 5 Circuit board, 10 Insulating layer, 11 First prepreg, 12 Core layer, 13 Second prepreg, 15 Slit, 20 Conductive layer, 21 First conductive layer, 22 Second conductive layer, 23 Third conductive layer, 24 Fourth conductive layer, 30 Protective section, 61 First discharge path, 62 Second discharge path, 63 Third discharge path, 64 Fourth discharge path, 80 Groove section, 211 First conductive pattern, 212 Second conductive pattern, 311 First protective section, 312 Second protective section, 331 First conductive pattern, 332 Second conductive pattern, 351 First surface, 352 Second surface.

Claims

[Claim 1] Insulating layer and, A conductive layer having a first conductive layer provided on a first surface which is a surface in the thickness direction of the insulating layer, and a second conductive layer provided on a second surface which is a surface opposite to the first surface in the thickness direction of the insulating layer, The protective part has a first protective part and a second protective part, and the protective part protects the conductive layer, It has, The second conductive layer has a first conductive pattern and a second conductive pattern that is spaced apart from the first conductive pattern and located on a lower pressure side than the first conductive pattern. The protective part is an insulator, The first protective portion covers the portion of the second surface and the portion where the second conductive layer is not provided. The second protective portion is provided on the outer periphery of the first conductive pattern and has a higher dielectric constant or a higher dielectric strength than the first protective portion. Circuit board. [Claim 2] Insulating layer and, A conductive layer having a first conductive layer provided on a first surface which is a surface in the thickness direction of the insulating layer, and a second conductive layer provided on a second surface which is a surface opposite to the first surface in the thickness direction of the insulating layer, It has, The second conductive layer has a first conductive pattern and a second conductive pattern that is spaced apart from the first conductive pattern and located on a lower pressure side than the first conductive pattern. The insulating layer is a circuit board having grooves formed along the outer circumference of the first conductive pattern. [Claim 3] The second protective portion includes a first insulator which is the main component, and a second insulator which has a higher dielectric constant than the first insulator. The circuit board according to claim 1. [Claim 4] The second protective part has silicon or fluorine as its main component. The circuit board according to claim 1. [Claim 5] The second protective part has a relative permittivity higher than 3.8 The circuit board according to claim 1. [Claim 6] The groove portion has a different depth in the thickness direction depending on its position. The circuit board according to claim 2. [Claim 7] The first conductive pattern includes an elliptical shape or a polygon with an obtuse angle when viewed from a direction perpendicular to the second surface. The circuit board according to claim 1 or 2.

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