Circuit board impedance detection method and test circuit board

Abstract

The present application discloses a circuit board impedance detection method and a circuit board for testing, the circuit board impedance detection method comprising: providing a circuit board, the circuit board comprising an internal signal layer, the internal signal layer being provided with an impedance test line; processing a test hole to expose at least part of the impedance test line; extending a test probe of an impedance test device into the test hole and electrically connecting it to the exposed impedance test line, and then performing an impedance test. The circuit board impedance detection method provided by the present application can reduce the time for the first impedance confirmation of the circuit board and improve competitiveness.

Description

Technical Field

[0001] The present application relates to the technical field of circuit boards, and in particular to a method for detecting circuit board impedance and a testing circuit board. Background Art

[0002] Circuit boards not only conduct current in electronic products, but also transmit signals. The high frequency and high speed of electronic products require that the circuit performance provided by the circuit board must ensure that the signal does not reflect during transmission, and keep the signal intact and undistorted. As circuit design becomes increasingly complex and high-speed, how to ensure the integrity of various signals (especially high-speed signals), that is, to ensure signal quality, has become a difficult problem. At this time, controlling the characteristic impedance matching of the signal line becomes the key. Inaccurate impedance control will cause considerable signal reflection and signal distortion, leading to design failure.

[0003] With the development of communications, the requirements for the inner layer impedance control of circuit boards have become increasingly stringent. Since the inner layer impedance control of circuit boards is affected by major factors such as line width, copper thickness, dielectric thickness and material dielectric constant, it is generally difficult to accurately control the required impedance value when processing the circuit board for the first time. Therefore, it is necessary to confirm whether the inner layer impedance of the circuit board meets the requirements based on the inner layer impedance data of the first processed circuit board. If it meets the requirements, normal mass production can be carried out. Otherwise, the line width compensation needs to be adjusted for optimization before processing.

[0004] The inventors of this application have discovered that, currently, when confirming the impedance during the first processing of a circuit board, the processing time is relatively long, generally requiring 7 to 13 days. For customers who urgently need high-precision inner layer impedance circuit boards, confirming the impedance during the first processing of the circuit board has a significant impact on the delivery time. If the time for the first inner layer impedance confirmation can be reduced, this is very important for improving product competitiveness. Summary of the invention

[0005] The main technical problem solved by the present application is to provide a circuit board impedance detection method and a test circuit board, which can reduce the time for the first impedance confirmation of the circuit board and improve product competitiveness.

[0006] In order to solve the above technical problems, a technical solution adopted in the present application is: to provide a method for detecting the impedance of a circuit board, the detection method comprising: providing a circuit board, the circuit board comprising an internal signal layer, the internal signal layer being provided with an impedance test line; processing a test hole to expose at least a portion of the impedance test line; extending a test probe of an impedance testing device into the test hole and electrically connecting it to the exposed impedance test line, and then performing an impedance test.

[0007] In order to solve the above-mentioned technical problems, another technical solution adopted in the present application is: to provide a test circuit board, the test circuit board includes an internal signal layer, the internal signal layer is provided with an impedance test line, and the test circuit board is provided with a test hole that exposes at least part of the impedance test line, so that a test probe of an impedance testing device can be inserted into the test hole and electrically connected to the exposed impedance test line, thereby performing an impedance test.

[0008] The beneficial effects of the present application are as follows: the method for detecting the impedance of the circuit board of the present application processes the test hole to expose at least a portion of the impedance test line, so that when performing the impedance test, the test probe is directly inserted into the test hole and electrically connected to the impedance test line. Compared with the prior art, the method for detecting the impedance of the circuit board of the present application has fewer steps and a simpler method, which can reduce the time for the first impedance confirmation of the circuit board and improve competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0010] Figure 1 It is a flow chart of an implementation method of a circuit board impedance detection method of the present application;

[0011] Figure 2 It is an application scenario corresponding to Figure 1 Schematic diagram of the structure;

[0012] Figure 3 It is another application scenario corresponding to Figure 1 Schematic diagram of the structure;

[0013] Figure 4 This is another application scenario corresponding to Figure 1 Schematic diagram of the structure;

[0014] Figure 5 This is a top view of the impedance test line before the test hole is processed;

[0015] Figure 6 It is a schematic cross-sectional structure diagram of an embodiment of a test circuit board of the present application;

[0016] Figure 7 It is a schematic diagram of the cross-sectional structure of the test circuit board of the present application in an application scenario;

[0017] Figure 8 is a schematic diagram of the cross-sectional structure of the test circuit board of the present application in another application scenario;

[0018] Fig. 9 yes Figure 6 A top view of the medium impedance test lead. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0020] See also Figure 1 , Figure 1 The present invention is a flow chart of an embodiment of the circuit board impedance detection method of the present invention. The circuit board impedance detection method of the present invention is mainly used to detect the inner layer impedance of the processed circuit board when the circuit board is processed for the first time to confirm whether the inner layer impedance of the circuit board meets the requirements. If it meets the requirements, the subsequent normal mass production work can be carried out. If it does not meet the requirements, the circuit board is further optimized.

[0021] Combination Figure 2 , the detection method comprises:

[0022] S110 : providing a circuit board 1000 , the circuit board 1000 comprising an internal signal layer 1100 , and the internal signal layer 1100 is provided with an impedance test line 1110 .

[0023] First, a circuit board 1000 is prepared as a multi-layer board, wherein an internal signal layer 1100 is located inside the circuit board 1000, and the material of the internal signal layer 1100 is a conductive material, such as copper that is easily available and inexpensive. The internal signal layer 1100 is patterned to form an impedance test line 1110. The impedance test line 1110 is different from the signal line for transmitting signals. It is specifically used to detect the internal impedance of the circuit board 1000, and does not transmit signals. The impedance test line 1110 can be a single-ended impedance test line or a differential impedance test line, which is not limited here.

[0024] In an application scenario, such as Figure 1 As shown, the number of internal signal layers 1100 can be multiple layers, for example, three layers. Among the multiple layers of internal signal layers 1100, some internal signal layers 1100 are provided with impedance test lines 1110, and some internal signal layers 1100 are provided with ground lines 1120. Of course, the internal signal layer 1100 can also be a single layer.

[0025] In another application scenario, Figure 1As shown, the circuit board 1000 further includes a surface signal layer 1200, which is disposed on the surface of the circuit board 1000 and is also made of a conductive material, such as copper. The surface signal layer 1200 may be a single layer, distributed only on one side of the circuit board 1000, or may be two layers, distributed on both sides of the circuit board 1000.

[0026] S120 : Processing the test hole 1300 to expose at least a portion of the impedance test line 1110 .

[0027] The test hole 1300 is processed by laser processing or mechanical processing so that the test hole 1300 penetrates from the surface layer of the circuit board 1000 into the internal signal layer 1100 to expose at least a portion of the impedance test line 1110 .

[0028] S130: Extend the test probe 1400 of the impedance test equipment into the test hole 1300 and electrically connect it to the exposed impedance test line 1110 to perform impedance testing.

[0029] After the test hole 1300 is processed, a test probe 1400 of an impedance test device (not shown) is directly inserted into the test hole 1300 to directly contact the impedance test line 1110 exposed in the test hole 1300, thereby performing an impedance test.

[0030] From the above content, it can be seen that when performing the first impedance test, it is only necessary to open a hole in the circuit board to expose at least part of the impedance test line 1110, and then directly insert the test probe 1400 into the test hole 1300. There are few steps and the method is simple, which can effectively reduce the time of the first impedance test and facilitate improving the company's competitiveness.

[0031] In one application scenario, combined with Figure 2 , step S120 specifically includes:

[0032] S121 : machining a test hole 1300 that penetrates the circuit board 1000 and is a cylindrical through hole, so as to expose at least a portion of the impedance test line 1110 from a side wall 1301 of the test hole 1300 .

[0033] That is to say, in this application scenario, the test hole 1300 is a cylindrical through hole that passes through the circuit board 1000 .

[0034] Optionally, in this application scenario, in order to ensure that the test probe 1400 can be inserted into the test hole 1300 and contact the impedance test line 1110 exposed from the side wall 1301, step S120 further includes:

[0035] S122: Process the side wall 1301 of the test hole 1300 except the area of ​​the impedance test line 1110 to form a first sub-test hole 1310 and a second sub-test hole 1320 which are cylindrical through holes bounded by the impedance test line 1110, and make the impedance test line 1110 protrude from the side wall of the first sub-test hole 1310 and the side wall of the second sub-test hole 1320.

[0036] Specifically, after step S121, a desmear treatment is performed, and the side wall 1301 of the test hole 1300 is processed so that the impedance test line 1110 protrudes from the side walls of the first sub-test hole 1310 and the second sub-test hole 1320. Optionally, the first sub-test hole 1310 and the second sub-test hole 1320 are coaxially arranged and have equal diameters, and the impedance test line 1110 protrudes from the side walls of the first sub-test hole 1310 and the second sub-test hole 1320 by 3-5um, for example 3um, 4um or 5um.

[0037] Optionally, in this application scenario, in order to prevent the test probe 1400 from being short-circuited due to contact with the surface signal layer 1200 when extending into the test hole 1300, thereby affecting the test result, step 120 further includes:

[0038] S123: processing one end of the test hole 1300 to enlarge the diameter of the one end of the test hole 1300.

[0039] Specifically, a drill bit with a diameter larger than the diameter of the test hole 1300 is used to perform shallow depth control at one end of the test hole 1300, thereby expanding the diameter of one end of the test hole 1300, wherein the depth of control is based on drilling off the surface signal layer 1200 of the circuit board 1000, for example, the depth of control is 0.05mm from the surface of the circuit board 1000 to the inside of the circuit board 1000. In a specific application scenario, when the diameter of the test hole 1300 is 1.0mm, a drill bit with a diameter of 1.5mm is used to perform shallow depth control processing at one end of the test hole 1300.

[0040] The present application does not limit the order of step S122 and step S123. Step S122 can be before step S123 or after step S123. Alternatively, in some application scenarios, step S120 does not include step S122 and step S123 at the same time.

[0041] In another application scenario, Figure 3 As shown, step S120 specifically includes:

[0042] S124 : machining a test hole 1300 that penetrates the circuit board 1000 and is a truncated cone-shaped through hole, so as to expose at least a portion of the impedance test line 1110 from a side wall 1301 of the test hole 1300 .

[0043] Specifically, when performing an impedance test, the test probe 1400 extends from the end of the test hole 1300 with a larger diameter into the test hole 1300 and is electrically connected to the impedance test line 1110. At this time, since the test hole 1300 is a truncated cone-shaped through hole, compared with the above application scenario, the contact area between the impedance test line 1110 and the test probe 1400 can be increased, thereby ensuring the electrical connection between the impedance test line 1110 and the test probe 1400.

[0044] Optionally, in this application scenario, in order to avoid electrical connection between the test probe 1400 and the surface signal layer 1200, the end with a larger diameter of the test hole 1300 can also be processed to expand the diameter of the test hole 1300. The detailed process can be found in the above application scenario and will not be repeated here.

[0045] In another application scenario, Figure 4 As shown, step S120 specifically includes:

[0046] S125 : Processing a blind test hole 1300 extending to the internal signal layer 1100 to expose at least a portion of the impedance test line 1110 from the bottom of the test hole 1300 .

[0047] Different from the above two application scenarios, in this application scenario, the test hole 1300 is a blind hole, so that the time for processing the test hole 1300 can be reduced.

[0048] Specifically, the test hole 1300 in this application scenario includes a third sub-test hole 1330 and a fourth sub-test hole 1340 that are connected and coaxially arranged, the third sub-test hole 1330 is connected to the surface layer of the circuit board 1000, and the fourth sub-test hole 1340 extends from the surface layer of the impedance test line 1110 to the impedance test line 1110, wherein the third sub-test hole 1310 is a cylindrical through hole, and the second sub-test hole 1340 is a conical buried hole. It is worth noting that by setting the second sub-test hole 1340 as a conical buried hole, the contact area between the test probe 1400 and the impedance test line 1110 can be increased. Of course, in other application scenarios, the test hole 1300 can also be other shapes, such as a cylindrical buried hole, which is not limited here.

[0049] Similar to the above application scenario, in order to avoid a short circuit between the test probe 1400 and the surface signal layer 1200, step S120 specifically further includes:

[0050] S126 : processing one end of the third sub-test hole 1330 away from the second fourth sub-test hole 1340 to enlarge the diameter of one end of the third sub-test hole 1330 .

[0051] The processing process is similar to the above application scenario. For details, please refer to the above application scenario.

[0052] In general, the present application does not limit the shape of the test hole 1300 , as long as the test hole 1300 can expose at least a portion of the impedance test line 1110 .

[0053] When the test hole 1300 processed in different application scenarios has different shapes, the shape of the test probe 1400 is also different. Specifically, Figures 2 to 4 As shown, the test probe 1400 matches the shape of the test hole 1300 to ensure contact between the test probe 1400 and the impedance test line 1110 .

[0054] In addition, in this embodiment, Figure 2 and Figure 5 , Figure 5 The impedance test line 1110 includes an impedance test disc 1111 and an impedance test strip 1112 connected to each other. The diameter of the impedance test disc 1111 is greater than the width of the impedance test strip 1112 .

[0055] Step S120 specifically includes: processing the test hole 1300 to expose at least a portion of the impedance test plate 1111 .

[0056] Specifically, since the diameter of the impedance test disk 1111 is greater than the width of the impedance test strip 1112, when the test hole 1300 is processed from the surface of the circuit board 1000, the probability of aiming at the impedance test disk 1111 is greater than the probability of aiming at the impedance test strip 1112, thereby avoiding the test hole 1300 deviating from the predetermined position and failing to expose at least a portion of the impedance test line 1110 when processing the test hole 1300.

[0057] See also Figure 6 , Figure 6 The schematic diagram of the cross-sectional structure of an embodiment of the test circuit board of the present application is as follows. The test circuit board 2000 includes an internal signal layer 2100 .

[0058] The test circuit board 2000 of the present application is a multi-layer circuit board, and the internal signal layer 2100 is located inside the test circuit board 2000. The material thereof is a conductive material, such as copper which is easily available and inexpensive. The internal signal layer 2100 is provided with an impedance test line 2110, and the impedance test line 2110 is obtained by patterning the internal signal layer 2100, and is specifically used to detect the internal impedance of the test circuit board 2000. In an application scenario, the impedance test line 2110 does not transmit electrical signals. At the same time, the impedance test line 2110 can be a single-ended impedance test line or a differential impedance test line, which is not limited here.

[0059] In an application scenario, such as Figure 6As shown, the number of internal signal layers 2100 can be multiple layers, for example, three layers. Among the multiple layers of internal signal layers 2100, some internal signal layers 2100 are provided with impedance test lines 2110, and some internal signal layers 2100 are provided with ground lines 2120. Of course, the internal signal layer 2100 can also be a single layer.

[0060] In another application scenario, Figure 6 As shown, the test circuit board 2000 also includes a surface signal layer 2200, which is disposed on the surface of the test circuit board 2000 and is also made of a conductive material, such as copper. The surface signal layer 2200 can be a single layer, distributed only on one side of the circuit board 2000, or two layers, distributed on both sides of the circuit board 2000.

[0061] At the same time, the test circuit board 2000 is provided with a test hole 2300 that exposes at least part of the impedance test line 2110, so that the test probe of the impedance test equipment can be inserted into the test hole 2300 and electrically connected to the exposed impedance test line 2110, thereby performing an impedance test. Specifically, when performing an impedance test, the test probe of the impedance test equipment is inserted into the test hole 2300 and directly contacts the exposed impedance test line 2110, thereby electrically connecting the two, and finally performing an impedance test.

[0062] The test hole 2300 may be a through hole that penetrates the test circuit board 2000, or a blind hole that extends from the surface layer of the test circuit board 2000 to the internal signal layer 2100. When the test hole 2300 is a through hole, Figure 6 and Figure 7 As shown, at least part of the impedance test line 2110 is exposed from the side wall 2301 of the test hole 2300. When the test hole 2300 is a blind hole, as shown in FIG. Figure 8 As shown, at least a portion of the impedance test line 2110 is exposed from the bottom of the test hole 2300 .

[0063] In an application scenario, such as Figure 6As shown, the test hole 2300 includes a first sub-test hole 2310 and a second sub-test hole 2320 bounded by an impedance test line 2110, wherein the impedance test line 2110 protrudes from the side walls of the first sub-test hole 2310 and the second sub-test hole 2320. Optionally, the impedance test line 2110 protrudes from the side walls of the first sub-test hole 2310 and the second sub-test hole 2320 by 3-5um, for example 3um, 4um or 5um. Since the impedance test line 2110 protrudes from the side walls of the first sub-test hole 2310 and the second sub-test hole 2320, it can be ensured that the test probe is in direct contact with the impedance test line 2110 when entering the test hole 2300, avoiding the direct contact between the test probe and the impedance test line 2110 being affected by the uneven side walls of the first sub-test hole 2310 and the second sub-test hole 2320 when the impedance test line 2110 is flush with the side walls of the first sub-test hole 2310 and the second sub-test hole 2320.

[0064] Optionally, in this application scenario, in order to prevent the test probe from contacting the surface signal layer 2200 and causing a short circuit when it is inserted into the test hole 2300, thereby affecting the test result, the diameter of the first sub-test hole 2310 decreases in the direction close to the second sub-test hole 2320, that is, the diameter of the first sub-test hole 2310 at one end away from the second sub-test hole 2320 is larger than the diameter of the end where the first sub-test hole 2310 and the second sub-test hole 2320 are connected, thereby ensuring that when the test probe is inserted into the test hole 2300, there is a predetermined distance between the test probe and the surface signal layer 2200. The diameter of the second sub-test hole 2320 can also decrease in the direction close to the first sub-test hole 2310, thereby ensuring that when the test probe passes through the test hole 2300 from one side of the circuit board 2000 to the other side, it can be ensured that both ends of the test probe are not electrically connected to the surface signal layers 2200 on both sides of the test circuit board 2000. Of course, if the test probe is not long enough to pass through the test hole 2300 , the second sub-test hole 2320 may also be configured as a cylindrical through hole.

[0065] In another application scenario, Figure 7 As shown, the test hole 2300 is a truncated cone-shaped through hole. Compared with a cylindrical through hole, the truncated cone-shaped through hole can increase the contact area between the test probe and the impedance test line 2110, thereby ensuring the test result.

[0066] In another application scenario, Figure 8As shown, the test hole 2300 includes a third sub-test hole 2330 and a fourth sub-test hole 2340 that are connected and coaxially arranged, wherein the third sub-test hole 2330 is connected to the surface layer of the test circuit board 2000, and the fourth sub-test hole 2340 extends from the surface layer of the impedance test line 2110 to the impedance test line 2110, wherein the fourth sub-test hole 2340 is a conical buried hole. The fourth sub-test hole 2340 is set as a conical buried hole to increase the contact area between the test probe and the impedance test line 2110.

[0067] Similarly, in order to avoid a short circuit between the test probe and the surface signal layer 2200, the diameter of the third sub-test hole 2330 decreases in the direction approaching the fourth sub-test hole 2340, that is, the diameter of the third sub-test hole 2330 at one end away from the fourth sub-test hole 2340 is larger than the diameter at the end close to the fourth sub-test hole 2340.

[0068] In summary, the present application does not limit the shape of the test hole 2300 , as long as the test hole 2300 can expose at least a portion of the impedance test line 2110 .

[0069] Combination Figure 6 and Fig. 9 In this embodiment, the impedance test line 2110 includes a connected impedance test disk 2111 and an impedance test strip 2112, wherein the diameter of the impedance test disk 2111 is greater than the width of the impedance test strip 2112, wherein the test hole 2300 exposes at least a portion of the impedance test disk 2111.

[0070] Specifically, since the diameter of the impedance test disk 2111 is greater than the width of the impedance test strip 2112, when the test hole 2300 is processed from the surface of the test circuit board 2000, the probability of aiming at the impedance test disk 2111 is greater than the probability of aiming at the impedance test strip 2112, thereby avoiding the test hole 2300 deviating from the predetermined position and failing to expose at least a portion of the impedance test line 2110 when processing the test hole 2300.

[0071] In summary, different from the prior art, the circuit board impedance detection method of the present application processes the test hole to expose at least a portion of the impedance test line, so that when performing the impedance test, the test probe is directly inserted into the test hole and electrically connected to the impedance test line. Compared with the prior art, the circuit board impedance detection method of the present application has fewer steps and a simpler method, which can reduce the time for the first impedance confirmation of the circuit board and improve competitiveness.

[0072] The above description is only an implementation method of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for detecting circuit board impedance, It is characterized in that The detection method comprises: A circuit board is provided, the circuit board comprising an internal signal layer, the internal signal layer being provided with an impedance test line; Processing a test hole to expose at least a portion of the impedance test line; Inserting a test probe of an impedance test device into the test hole and electrically connecting it to the exposed impedance test line, thereby performing an impedance test; Wherein, the circuit board further comprises a surface signal layer, and the surface signal layer is arranged on the surface layer of the circuit board; the step of inserting the test probe of the impedance test equipment into the test hole and electrically connecting it with the exposed impedance test line, and then performing the impedance test, comprises: when the test probe is inserted into the test hole, there is a predetermined distance between the test probe and the surface signal layer; The impedance test line includes a connected impedance test disk and an impedance test strip, wherein the diameter of the impedance test disk is greater than the width of the impedance test strip; the step of processing the test hole to expose at least a portion of the impedance test line includes: processing the test hole to expose at least a portion of the impedance test disk.

2. The detection method according to claim 1, It is characterized in that The step of machining the test hole to expose at least a portion of the impedance test line comprises: The test hole which penetrates the circuit board and is a cylindrical through hole is processed to expose at least a portion of the impedance test line from the side wall of the test hole.

3. The detection method according to claim 2, It is characterized in that The step of machining the test hole to expose at least a portion of the impedance test line further includes: The side wall of the test hole is processed except for the area of ​​the impedance test line to form a first sub-test hole and a second sub-test hole which are cylindrical through holes bounded by the impedance test line, and the impedance test line is made to protrude from the side wall of the first sub-test hole and the side wall of the second sub-test hole.

4. The detection method according to claim 2, It is characterized in that The step of machining the test hole to expose at least a portion of the impedance test line further includes: One end of the test hole is processed to enlarge the diameter of the one end of the test hole.

5. The detection method according to claim 1, It is characterized in that The step of machining the test hole to expose at least a portion of the impedance test line comprises: The test hole which penetrates the circuit board and is a truncated cone-shaped through hole is processed to expose at least a portion of the impedance test line from the side wall of the test hole.

6. The detection method according to claim 1, It is characterized in that The step of machining the test hole to expose at least a portion of the impedance test line comprises: The test hole, which is a blind hole and extends to the inner signal layer, is processed to expose at least a portion of the impedance test line from the bottom of the test hole.

7. The detection method according to claim 6, It is characterized in that The test hole includes a first sub-test hole and a second sub-test hole that are connected and coaxially arranged, the first sub-test hole is connected to the surface layer of the circuit board, and the second sub-test hole extends from the surface layer of the impedance test line to the impedance test line, wherein the first sub-test hole is a cylindrical through hole, and the second sub-test hole is a conical buried hole.

8. The detection method according to claim 7, It is characterized in that The processing of the test hole to expose at least a portion of the impedance test line also includes: An end of the first sub-test hole away from the second sub-test hole is processed to enlarge a diameter of the end of the first sub-test hole.

9. A test circuit board, It is characterized in that The test circuit board includes an internal signal layer, the internal signal layer is provided with an impedance test line, and the test circuit board is provided with a test hole exposing at least a portion of the impedance test line, so that a test probe of an impedance test device can be inserted into the test hole and electrically connected to the exposed impedance test line, thereby performing an impedance test; Wherein, the circuit board further comprises a surface signal layer, the surface signal layer is arranged on the surface layer of the circuit board, and when the test probe is inserted into the test hole, there is a predetermined distance between the test probe and the surface signal layer; The impedance test line includes a connected impedance test disc and an impedance test strip, wherein the diameter of the impedance test disc is greater than the width of the impedance test strip; and the test hole is processed to expose at least a portion of the impedance test disc.

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