A test method for loss tangent tanδ of microwave materials

Abstract

The present invention discloses a method for testing the loss tangent tanδ of microwave materials. The method uses a high and low temperature dielectric performance test system to test the loss tangent tanδ of a test sample; first, the first metal ground plate, the test sample, the resonant guide strip, and the second metal ground plate are placed in the sample fixture in sequence; second, the assembled sample fixture is then placed as a whole in the stripline resonant cavity; third, the dielectric constant and the loss factor are measured; fourth, the dielectric constant is calculated; and fifth, the loss factor is calculated. The present invention is used to test the loss tangent tanδ. When the loss tangent tanδ is ≤0.0020, the uncertainty is ≤0.0003; when the loss tangent tanδ is greater than 0.0020, the uncertainty is ≤10%tanδ+0.0003. The practicability of the method is improved, the guidance is stronger, and the accurate test of the loss tangent tanδ of a thinner test sample is achieved.

Description

Technical Field

[0001] The invention relates to the field of microwave material testing, and in particular to a microwave material loss tangent tanδ testing method. Background Art

[0002] GBT12636-1990 microwave dielectric substrate complex dielectric constant stripline test method is an improved stripline test method based on IPC TM-6502.5.5.5c, and is also the current national standard method. The main advantage of this method is that the sample used in the test can be tested with a completely corroded sample, without the need for photolithography to obtain the test pattern. However, it is precisely because its test pattern is not of fixed size that the loss tangent value test can easily cause a large test error. The nominal uncertainty of the GBT12636-1990 standard is: ≤15% tanδ+0.0003. At the same time, the GBT 12636-1990 standard is for samples with a thin thickness such as 0.25mm. When directly tested, for samples with a low material loss tangent, the standard calculation will result in meaningless negative values, so it can only be tested by stacking multiple layers, and the stacking of multiple layers will introduce more air layers, making the loss tangent test error larger. Although the standard proposes that it can be improved by the method of empirical coefficient correction, it cannot be fundamentally improved. Summary of the invention

[0003] In view of the problems existing in the existing testing methods, the present invention provides a method for testing the loss tangent tanδ of microwave materials. L and the quality factor Q that characterizes the copper loss of the stripline c There is a relationship between the dielectric constant value and the loss tangent value, but there is no direct relationship between the dielectric constant value and the loss tangent value. From the quality factor Q that characterizes the copper loss of the stripline c The calculation formula shows that the quality factor Q of the stripline copper loss c Mainly affected by the stripline attenuation constant α c , Stripline characteristic impedance Z c The stripline characteristic impedance Z c It is mainly affected by the resonant conduction band width, the resonant conduction band thickness, the total thickness of the dielectric substrate, the resonant conduction band surface resistance and other factors. Therefore, the present invention adjusts the quality factor Q of the stripline copper loss. c The coefficient of dielectric constant is obtained, and the relationship between dielectric constant and loss tangent is established to form a new test and calculation method, which is the design idea of ​​the present invention.

[0004] The technical solution adopted by the present invention is: a microwave material loss tangent tanδ testing method, using a high and low temperature dielectric performance testing system composed of a vector network analyzer, a stripline resonant cavity, a temperature control device, a pressure test device, a digital display vernier caliper, a micrometer and an automated testing program to test the loss tangent tanδ of the test sample, the method steps are as follows:

[0005] Step 1: Use a digital vernier caliper to test the length, width, thickness of the sample and the width of the resonant conduction strip. After using a micrometer to test the thickness of the resonant conduction strip, place the first metal ground plate, the test sample, the resonant conduction strip, and the second metal ground plate into the sample fixture in sequence, wherein the resonant conduction strip is parallel to the length direction of the test sample and is placed in the middle of the test sample, and the first metal ground plate and the second metal ground plate are placed on the outside of the test sample, respectively.

[0006] Step 2: quickly cut off the redundant resonant conductive strips on both sides along the edge of the test sample, and then place the assembled sample fixture as a whole into the stripline resonant cavity.

[0007] Step 3: Relative dielectric constant and loss factor measurement

[0008] 1. Apply pressure to the upper and lower surfaces of the metal grounding plate outside the test sample respectively, and apply pressure using the pressure test device according to the hardness and flatness of the metal grounding plate.

[0009] 2. Use a vector network analyzer to make the test resonance peak frequency close to 10GHz, and then adjust the knob for the parallel movement of the test probe to make the test probe as close to the test sample as possible without affecting the up, down, left, and right movement of the probe;

[0010] 3. Adjust the distance between the test probe and the test sample up, down, left, and right to maximize the coupling of the resonance peak frequency;

[0011] 4. Adjust the horizontal knob of the test probe to make the test probe close to the test sample, and then adjust the test probe to make it away from the test sample, and the distance between the test probe and both ends of the sample is equal;

[0012] 5. After the adjustment is completed, run the automatic test program, and the program automatically collects the frequency value f and Q corresponding to the resonance peak of the vector network analyzer in the S21 mode. L1 Value and Q corresponding to the resonance peak in S12 mode L2 After the test is completed, release the pressure of the test sample and take out the test sample;

[0013] Step 4: Dielectric constant calculation

[0014] The dielectric constant ε′ is calculated as follows:

[0015]

[0016] In formula (1):

[0017] c is the speed of light: 2.998×10 11 mm / s;

[0018] n is the number of half-wavelengths of standing waves distributed along the resonant conduction band during resonance;

[0019] f n is the test resonant frequency value of the nth mode, Hz;

[0020] L is the resonant conduction band length, mm;

[0021] ΔL is the effective growth of the resonant conduction band at the edge of the two ports of the resonant conduction band, mm;

[0022] 5. Loss factor calculation

[0023] In sub-step 5 of step 3, the vector network analyzer test values ​​Q obtained in the test S21 and S12 modes are respectively L1 and the test value Q L2 The minimum value of is used to calculate the loss tangent tanδ to reduce the test error;

[0024] The vector network analyzer test value Q L1 and the test value Q L2 The minimum value Q′ L The expression is as follows:

[0025] Q' L =MIN(Q L1 , Q L2 ) (2)

[0026] In formula (2):

[0027] MIN means taking the minimum value;

[0028] Q L1 , Q L2 These are the test values ​​of the vector network analyzer in S21 and S12 modes respectively.

[0029] The loss tangent tanδ is calculated as follows:

[0030]

[0031] In formula (3):

[0032] Q c Figure of merit that characterizes the copper loss of striplines;

[0033] A, B, C, D, and E are constants;

[0034] ROUND(ε′ / 3,0) means that the value of ε′ / 3 is calculated and the decimal point is zero.

[0035] The quality factor Q of the stripline copper loss c The calculation of is as follows:

[0036]

[0037] In formula (4):

[0038] α c is the attenuation constant of the stripline;

[0039] f is the resonant frequency value tested by the vector network analyzer, Hz;

[0040] ε′ is the dielectric constant.

[0041] The stripline attenuation constant α c The expression of is as follows:

[0042]

[0043] In formula (5):

[0044] W is the resonant conduction band width, mm;

[0045] t is the thickness of the resonant conduction band, mm;

[0046] b is the total thickness of the dielectric substrate, mm;

[0047] R s is the resonant conduction band surface resistance, Ω / mm 2 ;

[0048] Z c is the stripline characteristic impedance, Ω.

[0049] The stripline characteristic impedance Z c The expression of is as follows:

[0050]

[0051] In formula (6):

[0052] C f is the lateral edge capacitance per unit length of the resonant conduction strip, pF / mm.

[0053] The transverse edge capacitance per unit length of the resonant conductive strip is C f The expression of is as follows:

[0054]

[0055] The beneficial effect of the present invention is that when the loss tangent tanδ is tested by the present method, when the loss tangent tanδ≤0.0020, the uncertainty can be ≤0.0003, and when the loss tangent tanδ>0.0020, the uncertainty can be ≤10%tanδ+0.0003. The practicability of the method is improved, and the guidance is stronger. The present invention can realize the accurate test of the loss tangent of thin layer samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a schematic diagram of the main view of a test sample in an embodiment of the present invention;

[0057] Figure 2 It is a schematic side view of a test sample in an embodiment of the present invention. DETAILED DESCRIPTION

[0058] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0059] This method uses a high and low temperature dielectric performance test system composed of a vector network analyzer, a stripline resonant cavity, a temperature control device, a pressure test device, a digital display vernier caliper, a micrometer and an automated test program (the high and low temperature dielectric performance test system is a patented product developed by the 46th Institute of China Electronics Technology Group Corporation) to test the loss tangent tanδ of the test sample. The specific steps are as follows:

[0060] Step 1: Use a digital vernier caliper to test the length, width, thickness of the sample and the width of the resonant conduction band. After using a micrometer to test the thickness of the resonant conduction band, place the first metal ground plate 1, the test sample 2, the resonant conduction band 3, and the second metal ground plate 4 into the sample fixture in sequence, where the resonant conduction band is parallel to the length direction of the test sample and is placed in the middle of the test sample. The first metal ground plate and the second metal ground plate are placed on the outside of the test sample, respectively.

[0061] like Figure 1 , Figure 2 As shown, the test sample 2 given in this embodiment is a pair of dielectric substrates to be tested, and the size of the two dielectric substrates after being superimposed is L×L′×b, wherein L and L′ are the length and width of the dielectric substrate to be tested, respectively, and b is the thickness of the dielectric substrates to be tested after being superimposed; a resonant conductive strip 3 with a width w of 2.0mm±0.5mm and a thickness t not greater than 0.018mm is placed in the middle of the dielectric substrate to be tested, and the resonant conductive strip used in this embodiment is a red copper center conductive strip, and the first metal ground plate 1 and the second metal ground plate 4 are respectively made of red copper ground plates, and are respectively placed on the outside of the two dielectric substrates.

[0062] Step 2: Use a sharp blade to quickly cut off the excess copper center guide strips on both sides along the edge of the measured medium substrate, and then place the assembled sample fixture as a whole into the stripline resonant cavity.

[0063] Step 3: Relative dielectric constant and loss factor measurement

[0064] 1. In order to eliminate the gap between the measured medium substrate and the copper grounding plate, pressure is applied to the upper and lower surfaces of the copper grounding plate outside the measured medium substrate. According to the hardness and flatness of the copper grounding plate, a pressure test device is used to apply pressure at a pressure of 350kg±10kg.

[0065] 2. Use a vector network analyzer to make the test resonance peak frequency close to 10GHz, and then adjust the knob for the parallel movement of the test probe to make the test probe as close to the test sample as possible without affecting the up, down, left, and right movement of the probe.

[0066] 3. Adjust the up, down, left, and right distances between the test probe and the test sample to maximize the coupling amount of the resonance peak frequency.

[0067] 4. Adjust the horizontal knob of the test probe to make the test probe close to the test sample, and then adjust the test probe to make it away from the test sample, and the distance between the test probe and both ends of the sample is equal.

[0068] 5. After adjustment, run the automatic test program, which will automatically collect the frequency value f and Q corresponding to the resonance peak of the vector network analyzer in S21 mode. L1 Value and Q corresponding to the resonance peak in S12 mode L2 After the test is completed, release the pressure of the test sample and take out the test sample.

[0069] Step 4: Dielectric constant calculation

[0070] The dielectric constant ε′ is calculated as follows:

[0071]

[0072] In formula (1):

[0073] c is the speed of light: 2.998×10 11 mm / s;

[0074] n is the number of half-wavelengths of standing waves distributed along the resonant conduction band during resonance;

[0075] f n is the test resonant frequency value of the nth mode, Hz;

[0076] L is the resonant conduction band length, mm;

[0077] ΔL is the effective growth of the resonant conduction band at the edge of the two ports of the resonant conduction band, mm;

[0078] The effective growth amount ΔL needs to be set according to the specific design of the stripline resonant cavity. Generally, the effective growth amount ΔL is less than 0.1 mm. If the dielectric constant ε′ is greater than 10, ΔL can be taken as 0.1 mm.

[0079] 5. Loss factor calculation

[0080] This method needs to test Q in S21 and S12 modes respectively. L The vector network analyzer test value Q obtained in the test S21 and S12 modes in sub-step 5 of step 3 is used. L1 and the test value Q L2 The minimum value of is used to calculate the loss tangent tanδ to reduce the test error.

[0081] Vector network analyzer test value Q L1 and the test value Q L2 The minimum value Q′ L The expression is as follows:

[0082] Q' L =MIN(Q L1 , Q L2 ) (2)

[0083] In formula (2):

[0084] MIN means taking the minimum value;

[0085] Q L1 , Q L2 They are the test values ​​of the vector network analyzer in S21 and S12 modes, which means the loaded quality factor of the stripline resonator.

[0086] This method proposes a new loss tangent calculation formula. The loss tangent tanδ is calculated as shown in formula (3):

[0087]

[0088] In formula (3):

[0089] Q c Figure of merit that characterizes the copper loss of striplines;

[0090] A, B, C, D, and E are constants;

[0091] ROUND(ε′ / 3,0) means that the value of ε′ / 3 is calculated and the decimal point is zero.

[0092] Quality factor Q of stripline copper loss cThe calculation of is as follows:

[0093]

[0094] In formula (4):

[0095] α c is the attenuation constant of the stripline;

[0096] f is the resonant frequency value tested by the vector network analyzer, Hz;

[0097] ε′ is the dielectric constant.

[0098] The attenuation constant of the stripline is α c The expression of is as follows:

[0099]

[0100] In formula (5):

[0101] W is the resonant conduction band width, mm;

[0102] t is the thickness of the resonant conduction band, mm;

[0103] b is the total thickness of the dielectric substrate, mm;

[0104] R s is the resonant conduction band surface resistance, Ω / mm 2 ;

[0105] Z c is the stripline characteristic impedance, Ω.

[0106] Stripline characteristic impedance Z c The expression of is as follows:

[0107]

[0108] In formula (6):

[0109] C f is the lateral edge capacitance per unit length of the resonant conduction strip, pF / mm.

[0110] The transverse edge capacitance per unit length of the resonant conduction band is C f The expression of is as follows:

[0111]

[0112] The application of this method can solve the problem that the original GBT 12636-1990 loss tangent calculation formula will produce meaningless negative values ​​when calculating the loss tangent tanδ, so it can only be tested by superposition. After the superposition, the air between the samples is likely to cause the loss tangent tanδ test error. The use of this method can realize the testing of thin layer samples without superposition.

[0113] For the design of the stripline resonant test cavity, after obtaining the A, B, C, D, E constants, the length, width, thickness of the test sample, and the width and thickness of the resonant conduction strip, the stripline resonant test cavity is placed in a vector network analyzer to obtain the frequency value f and Q corresponding to the resonant peak in the S21 mode. L1 Value and Q corresponding to the resonance peak in S12 mode L2 After that, the loss tangent can be finally calculated according to formulas (1) to (7). The test data is shown in Table 1:

[0114] Table 1 Loss tangent test data table

[0115]

[0116]

[0117] The application effect of the present invention is exemplified as follows: the microwave material loss tangent tanδ test method of the present invention is verified: a high and low temperature dielectric performance test system (stripline method) and a vector network analyzer (Agilent N5230C) are used; and two test methods represented by the American German Technology dielectric performance test cavity 85072A (the cavity complies with the IPC TM-650 2.5.5.13 test standard) and a vector network analyzer (Agilent N5232A) are used to verify microwave dielectric substrate samples with different dielectric constants and different thicknesses. The verification data are shown in Table 2:

[0118] Table 2 Comparison of the test results of the method of the present invention and IPC TM-650 2.5.5.13

[0119]

[0120]

[0121] It can be seen from Table 2 that compared with the IPC TM-650 2.5.5.13 method, when the loss tangent tanδ≤0.0020, the uncertainty of this method is ≤0.00025, and when the loss tangent tanδ>0.0020, the uncertainty is ≤6%tanδ+0.0003, which achieves the design effect.

Claims

1. A method for testing the loss tangent tanδ of microwave materials, characterized in that: The loss tangent tanδ of the test sample is tested using a high and low temperature dielectric performance test system consisting of a vector network analyzer, a stripline resonant cavity, a temperature control device, a pressure test device, a digital display vernier caliper, a micrometer, and an automated test program. The method steps are as follows: Step 1: Use a digital display vernier caliper to test the length, width, thickness of the sample and the width of the resonant conductive strip. After using a micrometer to test the thickness of the resonant conductive strip, place the first metal ground plate, the test sample, the resonant conductive strip, and the second metal ground plate into the sample fixture in sequence, wherein the resonant conductive strip is parallel to the length direction of the test sample and is placed in the middle of the test sample, and the first metal ground plate and the second metal ground plate are placed on the outside of the test sample respectively; Step 2: quickly cut off the redundant resonant conductive strips on both sides along the edge of the test sample, and then place the assembled sample fixture as a whole into the stripline resonant cavity; Step 3: Relative dielectric constant and loss factor measurement 1. Apply pressure to the upper and lower surfaces of the metal grounding plate outside the test sample respectively. According to the hardness and flatness of the metal grounding plate, the pressure test device is used to apply pressure, and the temperature of the test sample is set and read by the temperature control device; 2. Use a vector network analyzer to make the test resonance peak frequency close to 10GHz, and then adjust the knob for the parallel movement of the test probe to make the test probe as close to the test sample as possible without affecting the up, down, left, and right movement of the probe; 3. Adjust the distance between the test probe and the test sample up, down, left, and right to maximize the coupling of the resonance peak frequency; 4. Adjust the horizontal knob of the test probe to make the test probe close to the test sample, and then adjust the test probe to make it away from the test sample, and the distance between the test probe and both ends of the sample is equal; 5. After the adjustment is completed, run the automatic test program, and the program automatically collects the frequency value f and Q corresponding to the resonance peak of the vector network analyzer in the S21 mode. L1 Value and Q corresponding to the resonance peak in S12 mode L2 After the test is completed, release the pressure of the test sample and take out the test sample; Step 4: Dielectric constant calculation The dielectric constant ε′ is calculated as follows: In formula (1): c is the speed of light: 2.998×10 11 mm / s; n is the number of half-wavelengths of standing waves distributed along the resonant conduction band during resonance; f n is the test resonant frequency value of the nth mode, Hz; L is the resonant conduction band length, mm; ΔL is the effective growth of the resonant conduction band at the edge of the two ports of the resonant conduction band, mm; Step 5: Loss factor calculation In sub-step 5 of step 3, the vector network analyzer test values ​​Q obtained in the test S21 and S12 modes are respectively L1 and the test value Q L2 The minimum value of is used to calculate the loss tangent tanδ to reduce the test error; The vector network analyzer test value Q L1 and the test value Q L2 The minimum value Q′ L The expression is as follows: Q' L =MIN(Q L1 ,Q L2 ) (2) In formula (2): MIN means taking the minimum value; Q L1 , Q L2 They are the test values ​​of the vector network analyzer in S21 and S12 modes respectively. The loss tangent tanδ is calculated as follows: In formula (3): Q c Figure of merit that characterizes the copper loss of striplines; A, B, C, D, and E are constants; ROUND(ε′ / 3,0) means to calculate the value of ε′ / 3 and take the integer with zero decimal places; The quality factor Q of the stripline copper loss c The calculation of is as follows: In formula (4): α c is the attenuation constant of the stripline; f is the resonant frequency value tested by the vector network analyzer, Hz; ε′ is the dielectric constant; The stripline attenuation constant α c The expression of is as follows: In formula (5): W is the resonant conduction band width, mm; t is the thickness of the resonant conduction band, mm; b is the total thickness of the dielectric substrate, mm; R s is the resonant conduction band surface resistance, Ω / mm 2 ; Z c is the stripline characteristic impedance, Ω; The stripline characteristic impedance Z c The expression of is as follows: In formula (6): C f is the lateral edge capacitance per unit length of the resonant conduction strip, pF / mm; The transverse edge capacitance per unit length of the resonant conductive strip is C f The expression of is as follows:

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