Microstrip line design method based on high-frequency pure glue and circuit board

Abstract

The invention discloses a microstrip line design method based on high-frequency pure glue and a circuit board. The method comprises the following steps: acquiring the thickness of the high-frequency pure glue of a microstrip line and the initial line width of the microstrip line; and based on the thickness of the high-frequency pure glue of the microstrip line, the initial line width of the microstrip line and the non-fringing field capacitance of the microstrip line, calculating the line width of the fringing field at the tail end of the microstrip line. The circuit board comprises a top reference ground layer and a base material layer, and the top reference ground layer is provided with the microstrip designed and manufactured by adopting the design method. Capacitance is increased and impedance is adjusted by adjusting the line width of the tail end of the microstrip line, meanwhile, unit area stress of high-frequency pure glue of the microstrip line is dispersed, and collapse is reduced; impedance abrupt change in the microstrip line testing process is reduced, return loss is increased, and the influence of a horizontal probe on a transition position is remarkably reduced; through the circuit board structure and the microstrip line designed by adopting the design method, the dielectric constant and dielectric loss of the high-frequency pure glue can be directly obtained, the test of the single pure glue is realized, and the test result is not influenced by the electrical property of the substrate.

Description

Technical Field

[0001] The invention belongs to the technical field of circuit boards, and in particular relates to a microstrip line design method based on high-frequency pure glue and a circuit board. Background Art

[0002] With the rapid development of microwave communication technology, microstrip lines are used in more and more places. When testing circuit boards, fixtures containing horizontal probes are often used to test the impedance, insertion loss and other electrical properties of microstrip lines. To ensure the uniformity of instantaneous impedance, the microstrip lines are evenly distributed, but signal anomalies are prone to occur in high frequency bands (approximately above 30GHz), such as low return loss and other problems. When using a fixture containing a horizontal probe for testing, there will be a problem of impedance discontinuity at the transition position between the horizontal probe and the test microstrip line: Figure 1 , due to the fringe field effect, the internal capacitance of the microstrip line is C in =C1+C2+C3, and the end microstrip line is suspended. At this time, the capacitor C edge =C1+C2 <C in , instantaneous impedance = , at this time the capacitance C decreases, making the instantaneous impedance The impedance discontinuity will cause the instantaneous impedance at the end of the microstrip line to be greater than the instantaneous impedance inside the microstrip line. The reflection caused by the impedance discontinuity will lead to poor signal transmission effect. When the impedance at the end of the microstrip line changes, the existing technology often uses de-embedding to remove the influence of the fixture and the transition section of the microstrip line, but this method is too dependent on the accuracy of the algorithm and the consistency of the impedance of the de-embedded short and long lines.

[0003] For high-frequency pure glue of flexible circuit boards, due to its soft nature and the fact that it is often used in combination with a substrate, the performance test of high-frequency pure glue is often a comprehensive test of high-frequency pure glue and substrate, and only indirect analysis of high-frequency pure glue can be performed. Moreover, the analysis results of high-frequency pure glue are affected by the electrical properties of the substrate, and it is difficult to obtain the dielectric constant DK and dielectric loss DF of high-frequency pure glue more conveniently. In addition, due to the soft nature of high-frequency pure glue, when only high-frequency pure glue is tested, whether using an ordinary probe or a fixture, the test point is prone to collapse, causing the dielectric to become thinner, thereby increasing the capacitance, reducing the impedance, and increasing the reflection coefficient; and if a test board is made whose dielectric only contains high-frequency pure glue, the test board is prone to wrinkles and various quality problems such as poor etching, uneven dielectric thickness, and poor holes, which affect the test, also because the high-frequency pure glue is too soft. Summary of the invention

[0004] In order to overcome one or more of the above-mentioned technical defects, the present invention provides a microstrip line design method and circuit board based on high-frequency pure glue, which increases capacitance and adjusts impedance by adjusting the end line width, reduces impedance mutations and increases return loss during microstrip line testing, and significantly reduces the influence of horizontal probes on transition positions; and realizes testing of a single pure glue and the test results are not affected by the electrical properties of the substrate.

[0005] In order to solve the above problems, the first aspect of the present invention provides a microstrip line design method based on high-frequency pure glue, comprising: Obtain the high-frequency pure glue thickness of the microstrip line and the initial line width of the microstrip line; Based on the high-frequency pure glue thickness of the microstrip line, the initial line width of the microstrip line and the non-fringe field capacitance of the microstrip line, the line width of the fringe field at the end of the microstrip line is calculated. :

[0006] in, is the fringe field capacitance at the end of the microstrip line, is the relative dielectric constant, is the high frequency pure glue thickness of the microstrip line, is the dielectric constant of vacuum, is the initial line width of the microstrip line.

[0007] Furthermore, it also includes: The capacitance per unit length of the microstrip line is calculated based on the high-frequency pure glue thickness of the microstrip line and the initial line width of the microstrip line.

[0008] Furthermore, the line width of the edge field at the end of the microstrip line is calculated based on the high-frequency pure glue thickness of the microstrip line, the initial line width of the microstrip line and the non-edge field capacitance of the microstrip line. ,include: Combine the microstrip line capacitance per unit length and the non-fringe field capacitance of the microstrip line to calculate the fringe field capacitance of the microstrip line; According to the corresponding relationship between the non-fringe field capacitance and the fringe field capacitance of the microstrip line, the line width of the fringe field at the end of the microstrip line is solved.

[0009] A second aspect of the present invention provides a circuit board, comprising a top reference ground layer and a substrate layer, wherein the top reference ground layer is bonded to the substrate layer by high-frequency pure glue; The substrate layer includes an intermediate reference ground, a high modulus substrate and a bottom reference ground which are laminated in sequence; The top reference stratum is provided with a microstrip line designed by the above method. The end of the microstrip line is quasi-square, and the side length is the line width obtained by the above method. The connection between the non-edge part of the microstrip line and the end of the microstrip line is set to be an arc or a curve. Furthermore, through holes are provided on both sides of the top reference ground layer along the microstrip line, and the through holes penetrate the top reference ground layer, the high-frequency pure glue, the middle reference ground layer, the high modulus substrate and the bottom reference ground layer.

[0010] Furthermore, the top reference layer is pure copper foil, and the high modulus substrate is copper clad laminate.

[0011] A third aspect of the present invention provides an electronic device, comprising a device body and the circuit board described in any one of claims 4-5.

[0012] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a microstrip line design method based on high-frequency pure glue and a circuit board. The method comprises the following steps: obtaining the thickness of the high-frequency pure glue of the microstrip line and the initial line width of the microstrip line; calculating the line width of the edge field at the end of the microstrip line based on the thickness of the high-frequency pure glue of the microstrip line, the initial line width of the microstrip line and the non-edge field capacitance of the microstrip line; since the impedance change caused by the edge field is not large, the capacitance changes more obviously relative to the inductance, the capacitance is increased by adjusting the end line width, the impedance is adjusted, and the stress per unit area of ​​the high-frequency pure glue of the microstrip line is dispersed to reduce collapse; reducing impedance mutation and increasing return loss during the microstrip line test, and significantly reducing the influence of the horizontal probe on the transition position.

[0013] The circuit board includes a top reference layer and a substrate layer. The top reference layer is provided with a microstrip line designed and manufactured using the design method. The microstrip line designed and manufactured using the method can directly obtain the dielectric constant and dielectric loss of high-frequency pure glue during testing, thereby realizing the test of a single pure glue and the test result is not affected by the electrical properties of the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings, wherein: Figure 1 A schematic diagram of the background technology; Figure 2 This is a flow chart of the microstrip line design method based on high-frequency pure glue described in Example 1; Figure 3 The structure of the microstrip line design method based on high-frequency pure glue described in Example 1 is shown in FIG. Figure 1 ; Figure 4 The structure of the microstrip line design method based on high-frequency pure glue described in Example 1 is shown in FIG. Figure 2 ; Figure 5 A comparison diagram of the return loss of the conventionally designed microstrip line described in Example 1 and the return loss of the microstrip line designed according to the design method described in this application; Figure 6An exploded view of the circuit board described in Example 2; Figure 7 A schematic diagram of the structure of the top reference ground layer of the circuit board described in Example 2; Figure 8 This is an enlarged view of the end of the microstrip line of the top reference layer of the circuit board described in Example 2.

[0015] Marking instructions: 110, top layer reference ground layer; 111, microstrip line; 112, through hole; 120, high-frequency pure glue; 130, middle layer reference ground; 140, high modulus substrate; 150, bottom layer reference ground. DETAILED DESCRIPTION

[0016] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0017] Example 1 This embodiment discloses a microstrip line design method based on high-frequency pure glue, such as Figure 2-4 ,include: S1. Get the high frequency pure glue thickness of the microstrip line and the initial line width of the microstrip line .

[0018] S2, according to the high frequency pure glue thickness of the microstrip line and the initial line width of the microstrip line , calculate the capacitance per unit length of the microstrip line :

[0019] in, is the relative dielectric constant.

[0020] S3, combined with microstrip line unit length capacitance and the non-fringe field capacitance of the microstrip line , calculate the fringe field capacitance per unit length of the microstrip line :

[0021] in, is the dielectric constant of vacuum; It is the ideal capacitor in the microstrip line without considering the edge field effect (i.e. non-edge field capacitor); the relative dielectric constant of commonly used high-frequency pure glue is 2.2~3; Obtained by the plate capacitor determination formula.

[0022] S4. Based on the correspondence between the non-edge field capacitance and the edge field capacitance of the microstrip line, the line width of the edge field at the end of the microstrip line is solved. Specifically, the fringe field capacitance should be equal to the non-fringe field capacitance:

[0023]

[0024] Combining the above formula with the two-dimensional field solver, we can get:

[0025] Since the impedance and medium of the microstrip line are the same, and The ratio is a fixed value, and the two-dimensional field solver is used to solve the dielectric thickness (i.e. the high-frequency pure glue thickness ) and the initial line width The relationship between.

[0026] Since the impedance change caused by the edge field is not large, the capacitance changes more obviously than the inductance. The impedance is adjusted by adjusting the end line width to increase the capacitance. The unit length capacitance generated by the edge effect at the end of the microstrip line is obtained by subtracting the unit length capacitance of the microstrip line from the ideal capacitance of the microstrip line (i.e., the non-edge field capacitance). Since the capacitance at the end edge decreases, the instantaneous impedance increases. The end line width is adjusted to keep the edge field capacitance equal to the non-edge line capacitance. At the same time, the stress per unit area of ​​the high-frequency pure glue of the microstrip line is dispersed to reduce collapse; the impedance mutation and increase of return loss during the microstrip line test are reduced, the influence of the horizontal probe on the transition position is significantly reduced, and the requirements for the de-embedding algorithm, de-embedding sample preparation and test uniformity are reduced. More accurate test results can be obtained without de-embedding.

[0027] Figure 5 The figure is a comparison chart of the return loss of a conventionally designed microstrip line and the return loss of a microstrip line designed according to the design method described in the present application.

[0028] Example 2 This embodiment discloses a circuit board, such as Figure 6-8 , including a top reference ground layer 110 and a substrate layer, the top reference ground layer 110 is bonded to the substrate layer by a high-frequency pure glue 120; the substrate layer includes an intermediate reference ground 130, a high modulus substrate 140 and a bottom reference ground 150 bonded in sequence; the top reference ground layer 110 is provided with a microstrip line 111 designed by the method described in Example 1, the end of the microstrip line is quasi-square, the side length is the line width obtained by the method described in Example 1, and the connection between the non-edge part of the microstrip line and the end of the microstrip line is set to be an arc or a curve.

[0029] Specifically, the top reference ground layer 110 is provided with through holes 112 on both sides along the microstrip line, and the through holes 112 penetrate the top reference ground layer 110 , the high-frequency pure glue 120 , the middle reference ground 130 , the high modulus substrate 140 and the bottom reference ground 150 .

[0030] Specifically, the top reference layer is pure copper foil, and the high modulus substrate is copper clad laminate. The copper clad laminate supports the high-frequency pure adhesive, and the copper clad laminate has no electrical performance effect, so it will not affect the high-frequency pure adhesive during testing. The copper clad laminate is a double-sided copper clad laminate, which is not etched, reducing the warping and wrinkling of the copper clad laminate, making it convenient for testing. By setting a microstrip signal line on the pure copper foil, the only media that can affect the microstrip signal line are high-frequency pure adhesive and air.

[0031] Specifically, the high-frequency pure glue 112 can be replaced by other substrate materials that need to be tested for dielectric constant and dielectric loss.

[0032] The present application provides a circuit board, including a bottom reference ground, a copper-clad board with no electrical properties, an intermediate reference ground, a high-frequency pure glue, and a pure copper foil top reference ground layer, which are sequentially laminated from bottom to top. Since the copper-clad board has no electrical properties, the high-frequency pure glue will not be affected by the performance of the substrate during testing, and the copper-clad board provides support for the high-frequency pure glue, solving the problem of high-frequency pure glue easily collapsing and wrinkling during testing. In addition, by using the microstrip line design method described in Example 1 to design and manufacture a microstrip line, the problem of impedance change at the end edge during testing can be solved.

[0033] The circuit board described in this embodiment can be a single-sided board or a double-sided board, or a multi-layer board; it can be a soft board, a hard board, or a combination of soft and hard boards. The number of microstrip lines designed in the circuit board can be one or more. In short, this embodiment does not limit the number of layers and types of the circuit board and the number of microstrip lines designed in the circuit board. It can be understood that, depending on the actual circuit design, before and / or after making the microstrip line, other process steps can also be used to make other structures of the circuit board to complete the entire circuit production of the circuit board.

[0034] For other specific implementation details, please refer to Example 1 and will not be repeated here.

[0035] Example 3 This embodiment discloses an electronic device, including a device body and the circuit board described in Embodiment 2. For other specific implementation details, please refer to Embodiment 1 or Embodiment 2, which will not be repeated here.

[0036] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Therefore, any modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A microstrip line design method based on high-frequency pure glue, characterized in that: include: Obtain the high-frequency pure glue thickness of the microstrip line and the initial line width of the microstrip line; Based on the high-frequency pure glue thickness of the microstrip line, the initial line width of the microstrip line and the non-fringe field capacitance of the microstrip line, the line width of the fringe field at the end of the microstrip line is calculated. : ， in, is the fringe field capacitance at the end of the microstrip line, is the relative dielectric constant, is the high frequency pure glue thickness of the microstrip line, is the dielectric constant of vacuum, is the initial line width of the microstrip line.

2. The microstrip line design method based on high-frequency pure glue according to claim 1 is characterized in that: Also includes: The capacitance per unit length of the microstrip line is calculated based on the high-frequency pure glue thickness of the microstrip line and the initial line width of the microstrip line.

3. The microstrip line design method based on high-frequency pure glue according to claim 2 is characterized in that: The line width of the edge field at the end of the microstrip line is calculated based on the high-frequency pure glue thickness of the microstrip line, the initial line width of the microstrip line and the non-edge field capacitance of the microstrip line. ,include: Combine the microstrip line capacitance per unit length and the non-fringe field capacitance of the microstrip line to calculate the fringe field capacitance of the microstrip line; According to the corresponding relationship between the non-fringe field capacitance and the fringe field capacitance of the microstrip line, the line width of the fringe field at the end of the microstrip line is solved.

4. A circuit board, characterized in that: It includes a top reference layer and a base material layer, wherein the top reference layer is bonded to the base material layer by high-frequency pure glue; The substrate layer includes an intermediate reference ground, a high modulus substrate and a bottom reference ground which are laminated in sequence; The top reference stratum is provided with a microstrip line designed by the method described in any one of claims 1-3, the end of the microstrip line is square-like, the side length is the line width obtained by the method described in any one of claims 1-3, and the connection between the non-edge part of the microstrip line and the end of the microstrip line is set to be an arc or a curve.

5. The circuit board according to claim 4, characterized in that: The top reference ground layer is provided with through holes along both sides of the microstrip line, and the through holes penetrate the top reference ground layer, the high-frequency pure glue, the middle reference ground, the high modulus substrate and the bottom reference ground.

6. The circuit board according to claim 4, characterized in that: The top reference layer is pure copper foil, and the high modulus substrate is copper clad laminate.

7. An electronic device, characterized in that: It comprises a device body and the circuit board described in any one of claims 4-6.

Images