Insertion loss test structure

Abstract

The application relates to an insertion loss test structure, comprising: a shielding layer; a solidification layer located on the shielding layer; a signal layer located on the side of the solidification layer away from the shielding layer, comprising first transmission lines and second transmission lines arranged at intervals, the length of the second transmission lines being greater than that of the first transmission lines; the characteristic impedance of the first transmission lines and the second transmission lines being within a preset impedance range; and a connecting structure connected with the two ends of the first transmission lines and the second transmission lines along the extension direction, respectively, the connecting structure being used as a test connecting point. The insertion loss test structure is simple in structure and low in cost, and the first transmission lines and the second transmission lines are both single-end transmission structures, so that the impedance matching control difficulty is low.

Description

Technical Field

[0001] This application relates to the field of PCB testing technology, and in particular to an insertion loss testing structure. Background Technology

[0002] Insertion loss performance is a key evaluation indicator for PCB signal transmission performance. The roughness and material of the signal carrier on the PCB affect the magnitude of insertion loss. Therefore, it is necessary to test the insertion loss of different types of carriers in order to screen out low-loss carriers.

[0003] Current insertion loss testing mostly uses differential line structures. However, the line width and spacing of differential lines are difficult to control, and dimensional deviations are prone to occur during the production process, resulting in large fluctuations in test impedance and increasing the difficulty of testing. Summary of the Invention

[0004] Therefore, it is necessary to provide an insertion loss test structure that is easy to test.

[0005] In one embodiment, this application provides an insertion loss test structure, comprising:

[0006] Shielding layer;

[0007] A curing layer is located on the shielding layer;

[0008] The signal layer, located on the side of the solidified layer away from the shielding layer, includes a first transmission line and a second transmission line spaced apart, the length of the second transmission line being greater than the length of the first transmission line; the characteristic impedances of the first transmission line and the second transmission line are within a preset impedance range;

[0009] A connection structure is provided, which is connected to both ends of the first transmission line and the transmission line along the extension direction, respectively. The connection structure is used as a test connection point.

[0010] In one embodiment, the first transmission line is arranged in parallel with the second transmission line.

[0011] In one embodiment, the length of the first transmission line is greater than or equal to twice the length of the second transmission line.

[0012] In one embodiment, the insertion loss test structure further includes a ground layer, which is located on the side of the curing layer away from the shielding layer and is spaced apart from both the first transmission line and the second transmission line;

[0013] Wherein, the distance between the first transmission line and the grounding layer is equal on both sides in the width direction;

[0014] The second transmission line is spaced equidistant from the grounding layer on both sides in the width direction.

[0015] In one embodiment, the grounding layer is provided with a plurality of first vias, the plurality of first vias being located on the periphery of the connection structure and spaced apart from the connection structure;

[0016] The cured layer is provided with a plurality of second vias, and the second vias are connected to the corresponding first vias.

[0017] In one embodiment, the grounding layer is further provided with a plurality of third vias, the plurality of third vias being located on the periphery of the first transmission line and the second transmission line, and being spaced apart from the first transmission line and the second transmission line;

[0018] The cured layer also includes a plurality of fourth vias, which are connected to the corresponding third vias.

[0019] In one embodiment, both the first transmission line and the second transmission line include a first sub-transmission section, a second sub-transmission section and a third sub-transmission section connected in sequence.

[0020] The first sub-transmission section and the third sub-transmission section are connected to different connection structures respectively; the width of the first sub-transmission section is different from that of the second sub-transmission section, and the width of the third sub-transmission section is different from that of the second sub-transmission section.

[0021] In one embodiment, the distance between the first sub-transmission unit and the ground layer, and the distance between the third sub-transmission unit and the ground layer, are both smaller than the distance between the second sub-transmission unit and the ground layer.

[0022] In one embodiment, the connection structure includes:

[0023] The first pad is located on the side of the shielding layer away from the curing layer;

[0024] Signal vias penetrate the cured layer and are respectively connected to the first pad and the first transmission line or the second transmission line;

[0025] The second pad is located on the side of the shielding layer away from the curing layer, surrounds the first pad, and is connected to the shielding layer.

[0026] In one embodiment, the spacing between the first transmission line and the second transmission line is greater than or equal to 5 mm.

[0027] The aforementioned insertion loss test structure includes a shielding layer, a curing layer, a signal layer, and a connection structure. The signal layer includes a first transmission line and a second transmission line spaced apart. The length of the second transmission line is greater than the length of the first transmission line, and the characteristic impedances of both the first and second transmission lines are within a preset impedance range. The connection structure connects to both ends of the first and second transmission lines along their extension direction, serving as test connection points. It is understood that both the first and second transmission lines in this application are single-ended transmission structures. When adjusting the first and second transmission lines for impedance matching, only the linewidths of the first and second transmission lines need to be adjusted. Compared to differential line structures, the adjustment difficulty of this application is significantly reduced. Thus, the consistency of multiple insertion loss test structures is better, and the test results obtained from testing multiple insertion loss test structures will more accurately reflect the true loss characteristics of the carrier. Furthermore, traditional differential line structures often have four or more layers, while this application only requires a three-layer structure: a shielding layer, a curing layer, and a signal layer. The structure is simpler and the cost is lower. When performing insertion loss testing on the insertion loss test structure of this application, the net insertion loss of the target length of the transmission line (i.e., signal carrier) can be accurately obtained by comparing and analyzing the test results of the first transmission line and the second transmission line. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 A schematic cross-sectional view of an insertion loss test structure provided in one embodiment;

[0030] Figure 2 A schematic diagram of the signal layer in an insertion loss test structure provided in one embodiment;

[0031] Figure 3 A schematic diagram of the shielding layer in an insertion loss test structure provided in one embodiment;

[0032] Figure 4 A schematic diagram of the ground layer in an insertion loss test structure provided in one embodiment;

[0033] Figure 5 for Figure 4 A magnified view of the selected area;

[0034] Figure 6 for Figure 3 A magnified view of the selected area;

[0035] Figure 7 Impedance tests were performed on five insertion loss test structures, all made of copper foil C, in one embodiment, and the resulting impedance diagrams were obtained.

[0036] Figure 8 The insertion loss test was performed on five insertion loss test structures, all made of copper foil C, in one embodiment, and the resulting S21 parameter diagram was obtained.

[0037] Figure 9 This represents the net insertion loss of 5 inches after de-embedding of three types of copper foil in one embodiment.

[0038] Explanation of reference numerals in the attached figures:

[0039] 100 - Shielding layer, 200 - Curing layer, 300 - Signal layer, 301 - First sub-transmission section, 302 - Second sub-transmission section, 310 - First transmission line, 320 - Second transmission line, 400 - Connection structure, 410 - First pad, 420 - Signal via, 430 - Second pad, 500 - Ground layer, 510 - Ground via, 520 - First via, 530 - Third via. Detailed Implementation

[0040] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0042] It is understood that the terms "first," "second," etc., used in this application may be used herein to describe various structures, but these structures are not limited by these terms. These terms are only used to distinguish one structure from another. For example, without departing from the scope of this application, a first transmission line may be referred to as a second transmission line, and similarly, a second transmission line may be referred to as a first transmission line. Both the first transmission line and the second transmission line are transmission lines, but they are not the same transmission line.

[0043] It is understandable that "at least one" refers to one or more, and "multiple" refers to two or more. "At least a part of an element" refers to part or all of an element.

[0044] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0045] In one embodiment, such as Figures 1-3 As shown, this application provides an insertion loss test structure, including a shielding layer 100, a curing layer 200, a signal layer 300, and a connection structure 400.

[0046] The shielding layer 100 can be used as a reference ground. The material of the shielding layer 100 can be copper foil, and the thickness of the shielding layer 100 can be reasonably set according to the application scenario, for example, it can be 12. 18 35 The curing layer 200 is located on the shielding layer 100, and the curing layer 200 can act as an adhesive to bond the signal layer 300 to the shielding layer 100. The curing layer 200 can be made of common adhesive materials, such as prepreg (PP).

[0047] The signal layer 300 is located on the side of the curing layer 200 away from the shielding layer 100. The signal layer 300 includes a first transmission line 310 and a second transmission line 320 spaced apart, which serve as carriers for transmitting signals. The length of the second transmission line 320 is greater than the length of the first transmission line 310, where length refers to the length of the first transmission line 310 and the second transmission line 320 in their respective extending directions. The first transmission line 310 and the second transmission line 320 have the same linewidth and material. The materials of the first transmission line 310 and the second transmission line 320 can be any suitable signal carrier material in the art, such as copper foil.

[0048] The characteristic impedances of the first transmission line 310 and the second transmission line 320 are within a preset impedance range. The preset impedance range is the impedance matching constraint condition for the first transmission line 310 and the second transmission line 320. In this embodiment, both the first transmission line 310 and the second transmission line 320 are single-ended transmission lines, and the preset impedance range can be 45Ω to 55Ω, for example, 45Ω, 49Ω, 50Ω, 51Ω, 55Ω, etc. The characteristic impedance of the first transmission line 310 is related to its linewidth and the thickness of the curing layer 200, and the characteristic impedance of the second transmission line 320 is related to its linewidth and the thickness of the curing layer 200. During the design phase, the linewidths of the first transmission line 310 and the second transmission line 320, as well as the thickness of the curing layer 200, can be adjusted through simulation to ensure that the characteristic impedances of both the first transmission line 310 and the second transmission line 320 are within the preset impedance range.

[0049] The connection structure 400 is connected to the first transmission line 310 and both ends of the transmission line along its extension direction. For example, there can be four connection structures 400, connecting to both ends of the first transmission line 310 and both ends of the second transmission line 320, respectively. The connection structure 400 serves as a test connection point and can also be connected to an external measuring instrument, such as a vector network analyzer.

[0050] In this embodiment, the insertion loss test structure includes a shielding layer 100, a curing layer 200, a signal layer 300, and a connection structure 400. The signal layer 300 includes a first transmission line 310 and a second transmission line 320 spaced apart. The length of the second transmission line 320 is greater than the length of the first transmission line 310, and the characteristic impedances of the first and second transmission lines 310 and 320 are within a preset impedance range. The connection structure 400 is connected to the first transmission line 310 and both ends of the transmission line along its extension direction, serving as test connection points. It is understood that the first and second transmission lines 310 and 320 in this application are both single-ended transmission structures. When adjusting the first and second transmission lines 310 and 320 for impedance matching, only the linewidth of the first and second transmission lines 310 and 320 needs to be adjusted. Compared to a differential line structure, the adjustment difficulty of this application is significantly reduced. Thus, the consistency of multiple insertion loss test structures is better, and the test results obtained from testing multiple insertion loss test structures will more accurately reflect the true loss characteristics of the carrier. Furthermore, traditional differential line structures typically have four or more layers, while this application only requires a three-layer structure consisting of a shielding layer 100, a curing layer 200, and a signal layer 300. This structure is simpler and less expensive.

[0051] In one embodiment, the first transmission line 310 and the second transmission line 320 are arranged in parallel to ensure that the first transmission line 310 and the second transmission line 320 are in a completely consistent electromagnetic environment, thus ensuring the accuracy of subsequent de-embedding operations.

[0052] In one embodiment, the length of the first transmission line 310 is greater than or equal to twice the length of the second transmission line 320. In this embodiment, the first transmission line 310 serves as a de-embedding fixture for performing a de-embedding operation during insertion loss testing, and the second transmission line 320 serves as the object to be de-embedding, with the insertion loss of the second transmission line 320 being the target of the insertion loss test. To eliminate or weaken the influence of reflected signals within the second transmission line 320 on the insertion loss test results, the length of the second transmission line 320 after de-embedding cannot be too short. Therefore, in this embodiment, the length of the first transmission line 310 is set to be greater than or equal to twice the length of the second transmission line 320.

[0053] In one embodiment, such as Figure 4 As shown, the insertion loss test structure also includes a ground layer 500. The ground layer 500 is located on the side of the cured layer 200 away from the shielding layer 100, and is spaced apart from both the first transmission line 310 and the second transmission line 320. The ground layer 500 is connected to the shielding layer 100. For example, a ground via 510 can be provided on the ground layer 500, penetrating the cured layer 200 to connect the ground layer 500 and the shielding layer 100. The ground vias 510 can be distributed in the edge region of the ground layer 500. The material of the ground layer 500 can be any suitable substrate material, such as copper foil.

[0054] Both the first transmission line 310 and the second transmission line 320 are spaced apart from the ground layer 500 to prevent short circuits. The spacing between the first transmission line 310, the second transmission line 320 and the ground layer 500 can be reasonably set according to the actual scenario requirements, as long as it ensures that the first transmission line 310 and the second transmission line 320 are not short-circuited.

[0055] The first transmission line 310 has equal spacing from the ground layer 500 on both sides in the width direction to ensure uniform impedance. The second transmission line 320 has equal spacing from the ground layer 500 on both sides in the width direction to ensure uniform impedance.

[0056] In one embodiment, such as Figure 5As shown, the grounding layer 500 has multiple first vias 520, which are located on the periphery of the connecting structure 400 and spaced apart from it. The curing layer 200 has multiple second vias, which communicate with their corresponding first vias 520. It can be understood that the through-holes formed by the first vias 520 and their corresponding second vias can connect the grounding layer 500 and the shielding layer 100, achieving grounding. Simultaneously, the through-holes formed by the first vias 520 and the second vias on the periphery of the connecting structure 400 can form an equipotential metal barrier, reducing radiation loss of transmitted signals.

[0057] The number of first vias 520 and second vias is the same, and the first vias 520 can be evenly distributed along the periphery of the connecting structure 400. For example, 5-9 first vias 520 can be evenly distributed along the periphery of each connecting structure 400.

[0058] In one embodiment, such as Figure 5 As shown, the grounding layer 500 also includes multiple third vias 530, which are located around the first transmission line 310 and the second transmission line 320 and are spaced apart from each other. The curing layer 200 also includes multiple fourth vias, which are connected to their corresponding third vias 530. It can be understood that the multiple vias formed by the connection between the third and fourth vias are respectively located around the first transmission line 310 and the second transmission line 320, constituting a grounding shield. This constrains the electromagnetic field distribution of the first and second transmission lines 310 and 320, reduces the radiation loss of transmitted signals on the first and second transmission lines 310 and 320, shortens the return path, and maintains the continuity of the transmission line impedance.

[0059] The number of third vias 530 is the same as that of the fourth vias, and multiple third vias 530 can be evenly distributed around the first transmission line 310 and the second transmission line 320.

[0060] In one embodiment, such as Figure 5 As shown, both the first transmission line 310 and the second transmission line 320 include a first sub-transmission section 301, a second sub-transmission section 302, and a third sub-transmission section connected in sequence. The first sub-transmission section 301 and the third sub-transmission section are connected to different connection structures 400, and the widths of the first sub-transmission section 301 and the second sub-transmission section 302 are different, as is the width of the third sub-transmission section.

[0061] It is understandable that, since the first sub-transmission unit 301 and the third sub-transmission unit need to be connected to the connection structure 400, and the connection structure 400 is used as a test connection point to connect to an external measuring instrument, the specifications of the connection structure 400 are usually fixed. In order to make the first sub-transmission unit 301 and the third sub-transmission unit compatible with the specifications of the connection structure 400, and at the same time, the first transmission line 310 and the second transmission line 320 need to meet impedance matching, the widths of the first sub-transmission unit 301 and the second sub-transmission unit 302 are set to be different, and the widths of the third sub-transmission unit and the second sub-transmission unit 302 are also different.

[0062] In one embodiment, the distance between the first sub-transmission unit 301 and the ground layer 500, and the distance between the third sub-transmission unit and the ground layer 500, are both smaller than the distance between the second sub-transmission unit 302 and the ground layer 500. For example, the distance between the first sub-transmission unit 301 and the ground layer 500 is 12 mil, the distance between the third sub-transmission unit and the ground layer 500 is 12 mil, and the distance between the second sub-transmission unit 302 and the ground layer 500 is 50 mil.

[0063] In one embodiment, such as Figure 6 As shown, the connection structure 400 includes a first pad 410, a signal via 420, and a second pad 430. The first pad 410 is located on the side of the shielding layer 100 away from the curing layer 200. The signal via 420 penetrates the curing layer 200 and connects the first pad 410 to either the first transmission line 310 or the second transmission line 320. The second pad 430 is located on the side of the shielding layer 100 away from the curing layer 200, surrounds the first pad 410, and is connected to the shielding layer 100. It can be understood that this connection structure 400 can be an SMA connector, wherein the first pad 410 can be used to receive high-frequency signals and transmit the high-frequency signals to the corresponding first transmission line 310 or second transmission line 320 through the signal via 420, and the second pad 430 can be used for grounding.

[0064] In one embodiment, the spacing between the first transmission line 310 and the second transmission line 320 is greater than or equal to 5 mm, thereby avoiding crosstalk between the signals on the first transmission line 310 and the second transmission line 320.

[0065] In one embodiment, the procedure for testing the insertion loss of the insertion loss test structure is described. The connection structure 400 of the insertion loss test structure can be connected to a measuring instrument, such as the fixture of a vector network analyzer, to measure the S21 parameters of the first transmission line 310 and the second transmission line 320. Based on the S21 parameters of the first transmission line 310 and the second transmission line 320, a de-embedding operation is performed on the second transmission line 320 to eliminate the length of the fixture portion and port parasitic effects, thus obtaining the net insertion loss at the target length.

[0066] The de-embedding operation is as follows: the S21 parameter of the first transmission line 310 is gated; the mismatch, loss and delay introduced by the fixture are identified and extracted by analyzing the time domain reflection and transmission response; a mathematical model of port parasitism + fixture line length is established based on the extracted characteristic parameters; the S21 parameter of the second transmission line 320 is stripped in reverse according to the mathematical model, and finally the net insertion loss of the target length is obtained.

[0067] In this embodiment, by comparing the first transmission line 310 and the second transmission line 320, the net insertion loss of the target length can be accurately extracted, thereby improving the test accuracy.

[0068] Taking three types of insertion loss test structures as examples, the effectiveness of the insertion loss test structure provided in this application is introduced. These three types of insertion loss test structures use different types of copper foil, while other parameters are the same. The thickness of the shielding layer 100 is 35 mm. The curing layer 200 is of model S7136H, with a thickness of 0.762mm and a dielectric constant of 3.61. The first transmission line 310 has a line width of 44mil and a line length of 5inch. The second transmission line 320 has a line width of 44mil and a line length of 10inch, and the distance between it and the first transmission line 310 is greater than or equal to 5mm. The distance between the second sub-transmission section 302 and the ground layer 500 is 50mil, and the distance between the first sub-transmission section 301 and the ground layer 500 is 12mil. In the connection structure 400, the diameter of the first pad 410 is 20mil, the distance between it and the center of the first via 520 is 40mil, the diameter of the signal via is 10mil, and the diameter of the copper-free area (i.e., the exposed curing layer 200) inside the second pad 430 is 40mil. The diameters of the first via 520 and the second via are both 10mil.

[0069] Impedance and insertion loss tests were performed on five insertion loss test structures, all made of copper foil C. The resulting impedance diagrams and S21 parameters are shown below. Figure 7 and Figure 8 As shown, the impedance fluctuation and insertion loss fluctuation of the five insertion loss test structures, all made of copper foil C, are very small, which means that the insertion loss test structures of this application have high consistency.

[0070] Insertion loss test structures prepared using copper foils A, B, and C were connected to a vector network analyzer. The test frequency range was set to 0.01 GHz–25 GHz, with 2500 scan points. The S21 parameters of the first transmission line 310 and the second transmission line 320 in each test structure were measured. The second transmission line 320 was de-embedded. The net insertion loss over 5 inches after de-embedding of the three copper foils was measured. Figure 9As shown, at 25 GHz, the loss of copper foil A is -0.623 dB, copper foil B is -0.573 dB, and copper foil C is -0.58 dB. Copper foil B has the lowest net insertion loss.

[0071] In the description of this specification, references to terms such as "some embodiments," "other embodiments," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0072] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0073] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. An insertion loss test structure, characterized in that, include: Shielding layer; A curing layer is located on the shielding layer; The signal layer, located on the side of the solidified layer away from the shielding layer, includes a first transmission line and a second transmission line spaced apart, the length of the second transmission line being greater than the length of the first transmission line; the characteristic impedances of the first transmission line and the second transmission line are within a preset impedance range; A connection structure is provided, which is connected to both ends of the first transmission line and the transmission line along the extension direction, respectively. The connection structure is used as a test connection point.

2. The insertion loss test structure according to claim 1, characterized in that, The first transmission line is arranged in parallel with the second transmission line.

3. The insertion loss test structure according to claim 1, characterized in that, The length of the first transmission line is greater than or equal to twice the length of the second transmission line.

4. The insertion loss test structure according to claim 1, characterized in that, The insertion loss test structure also includes a grounding layer, which is located on the side of the curing layer away from the shielding layer and is spaced apart from both the first transmission line and the second transmission line. Wherein, the distance between the first transmission line and the grounding layer is equal on both sides in the width direction; The second transmission line is spaced equidistant from the grounding layer on both sides in the width direction.

5. The insertion loss test structure according to claim 4, characterized in that, The grounding layer is provided with a plurality of first vias, which are located on the periphery of the connection structure and are spaced apart from the connection structure. The cured layer is provided with a plurality of second vias, and the second vias are connected to the corresponding first vias.

6. The insertion loss test structure according to claim 4, characterized in that, The grounding layer is also provided with a plurality of third vias, which are located on the periphery of the first transmission line and the second transmission line and are spaced apart from the first transmission line and the second transmission line. The cured layer also includes a plurality of fourth vias, which are connected to the corresponding third vias.

7. The insertion loss test structure according to claim 4, characterized in that, Both the first transmission line and the second transmission line include a first sub-transmission section, a second sub-transmission section, and a third sub-transmission section connected in sequence; The first sub-transmission section and the third sub-transmission section are connected to different connection structures respectively; the width of the first sub-transmission section is different from that of the second sub-transmission section, and the width of the third sub-transmission section is different from that of the second sub-transmission section.

8. The insertion loss test structure according to claim 7, characterized in that, The distance between the first sub-transmission unit and the ground layer, and the distance between the third sub-transmission unit and the ground layer are both smaller than the distance between the second sub-transmission unit and the ground layer.

9. The insertion loss test structure according to claim 1, characterized in that, The connection structure includes: The first pad is located on the side of the shielding layer away from the curing layer; Signal vias penetrate the cured layer and are respectively connected to the first pad and the first transmission line or the second transmission line; The second pad is located on the side of the shielding layer away from the curing layer, surrounds the first pad, and is connected to the shielding layer.

10. The insertion loss test structure according to claim 1, characterized in that, The distance between the first transmission line and the second transmission line is greater than or equal to 5 mm.

Images