IPC-TM-650 High Frequency Resonator Test Method Task …

1 Number ASSOCIATION CONNECTING Subject ELECTRONICS INDUSTRIES Relative Permittivity and Loss Tangent Using a 3000 Lakeside Drive Split-Cylinder Resonator Bannockburn, IL 60015-1249. Date Revision 01/07. Originating Task Group IPC-TM-650 High Frequency Resonator Test Method Task Group TEST methods MANUAL (D-24c). 1 Scope This Method describes the nondestructive mea- surement of the relative permittivity and loss tangent of unclad z dielectric substrates at microwave frequencies using a split- cylinder Resonator (see Figure 1). Coupling Loop Upper L Cylindrical Cavity Region d Sample Region p Lower Cylindrical L Cavity Region Coupling Loop IPC-25513-1. Figure 1 Split-Cylinder Resonator 2a This test Method is directly applicable for measuring the 2b in-plane (the plane parallel to the surface of the specimen). IPC-25513-2. permittivity of the specimen because the electric field is in-plane. The permittivity of isotropic dielectrics can also be Figure 2 Split-Cylinder Resonator Diagram measured with this Method .

2 Although the dielectric substrate thickness can vary from Note: This measurement Method does not measure the out- mm to mm [ in to in], thin substrates may of-plane (direction normal to the surface of the specimen) per- lead to larger measurement uncertainties, while the dielectric mittivity of the specimen. However, for most printed boards losses in thicker substrates may prevent the split-cylinder fix- the measurement uncertainties associated with this Method ture from resonating properly. A substrate thickness on the are typically less than the difference between in-plane and order of mm [ in] is typical. out-of-plane permittivity values. Furthermore, comparison with methods measuring the out-of-plane permittivity is difficult The measurement theory assumes the dielectric substrate has because those methods typically do not provide measure- a uniform thickness. Therefore, to reduce the measurement ment confidence intervals. uncertainty, variation and uncertainty in substrate thickness should be minimized.

3 A typical uncertainty in thickness should 2 Applicable Documents See be no more than mm [ in]. In general, warped samples should also be avoided as these can lead to biases 3 Test Specimen The test specimen is an unclad dielectric in the calculated values of the relative permittivity and loss substrate. The substrate geometry can be either square or tangent. circular as long as the substrate extends beyond the diameter 2a of the two cylindrical cavity sections as shown in Figure 2. For the split-cylinder Resonator described here, the measure- In particular, for the 10 GHz split-cylinder Resonator discussed ment Frequency of the split-cylinder Resonator is a function of in this Method , the dimensions of the substrate should be at the relative permittivity and thickness of the substrate. Thicker least mm [ in] in diameter for circular samples or substrates and higher values of relative permittivity drive the mm [ in] on a side for square samples. resonant Frequency lower, as shown in Figure 6.

4 Material in this Test methods Manual was voluntarily established by Technical Committees of IPC. This material is advisory only and its use or adaptation is entirely voluntary. IPC disclaims all liability of any kind as to the use, application, or adaptation of this Page 1 of 4. material. Users are also wholly responsible for protecting themselves against all claims or liabilities for patent infringement. Equipment referenced is for the convenience of the user and does not imply endorsement by IPC. IPC-TM-650 . Number Subject Date Relative Permittivity and Loss Tangent Using a Split-Cylinder 01/07. Resonator Revision 4 Measurement Apparatus 7x10. -4 10 GHz Split-Cylinder Resonator Split-Cylinder Resonator The Method employs a 35 GHz Split-Cylinder Resonator split-cylinder Resonator , which is a cylindrical cavity separated 6 Linear Least Squares Fit into two halves of equal length, with a dielectric substrate Loss Tangent 5. placed in the gap between the two cavity sections.

5 The split- TE013. 4. cylinder Resonator must be constructed to allow an adjustable, TE017. 3. variable gap between the two cavity sections for introduction TE015. 2 TE011. of the dielectric substrate. Additional details about the con- TE. TE021 TE023 025. struction of a split-post Resonator are given in the references 1 TE013. TE011. described in Over the years there have been commercial 0. manufacturers of this fixture. 10 20 30 40 50. In order to excite and detect the desired fundamental TE011 Frequency (GHz) IPC-25513-4. resonant mode in the split-cylinder Resonator , a coupling loop Figure 4 Typical Measurements of the Loss-tangent is introduced, through a small hole in the cavity wall, in each using 10 GHz and 35 GHz Split-cylinder Resonators of the two cavity regions. The plane of the coupling loop including Measurements with Higher Modes should be parallel to the plane of the sample, in order to allow maximum interaction with the vertical component of the mag- Network Analyzer A scalar or vector network analyzer netic field.

6 Each of the coupling loops is connected to a is necessary to perform the measurement with the split- coaxial transmission line that is connected to the input port of cylinder Resonator . Commercially available network analyzers a network analyzer. To minimize the effect of coupling losses, operate over various Frequency ranges, so care is needed to the distance to which the loops extend radially into each of the ensure that the network analyzer covers the necessary fre- cavity sections must also be adjustable. In addition to the fun- quency range for the particular split-cylinder Resonator used. damental TE011 mode, higher modes can be used to extend the measurement Frequency . Typical measurements on fused Digital Micrometer The dielectric substrate thickness silica with higher mode measurements are shown in Figures 3 can be measured with a digital micrometer with a minimal and 4. resolution of mm [ in]. 5 Procedure Turn on the network analyzer and allow the unit to 10 GHz Split-Cylinder Resonator 35 GHz Split-Cylinder Resonator warm-up and stabilize according to the manufacturer's Relative Permittivity instructions.

7 TE015. TE021 TE017. TE011TE013 Connect the network analyzer's two input ports to the TE split-cylinder Resonator 's coupling loops using coaxial trans- TE023 025 TE011 TE013 mission lines. Measure the thickness of the substrate over several locations using a digital micrometer, and compute the mean substrate thickness. 10 20 30 40 50. Frequency (GHz) Determine split-cylinder Resonator properties. The IPC-25513-3 length, radius and conductivity of the split-cylinder Resonator Figure 3 Typical Measurements of the Real Part of must be known before the substrate relative permittivity and the Permittivity using 10 GHz and 35 GHz Split-cylinder loss tangent can be calculated. If these variables have not Resonators including Measurements with Higher Modes been already determined, the following procedure can be used: Page 2 of 4. IPC-TM-650 . Number Subject Date Relative Permittivity and Loss Tangent Using a Split-Cylinder 01/07. Resonator Revision Measure the length L of each of the two split-cylinder ing on the thickness and relative permittivity of the dielectric Resonator sections over several locations and compute the substrate being measured, the resonant Frequency for the mean length of both sections.

8 Split-cylinder plus substrate can be significantly lower than the resonant Frequency of the empty split-cylinder Resonator as With the split-cylinder empty (no substrate) and closed shown in Figure 6. (d=0), find the TE011 resonance with the network analyzer. To reduce the coupling losses to a negligible level, adjust the radial position of the coupling loops so that the peak of TE011 Resonant Frequency (GHz). 10. the resonance curve is less than -40 dB. For the particular 10 GHz split-cylinder Resonator described in this Method , the 8. resonant Frequency should be approximately GHz. If another split-cylinder geometry is being used, use the follow- 6. ing approximation to estimate the TE011 resonant Frequency of an empty split-cylinder Resonator : 4. ( ) ( ). 2 2 2. c j1 . 011 = +. 2 a 2L. 0. where c is the speed of light in a vacuum, j1 is the first zero of 0 1 2 3 4 5. the Bessel function of the first kind J1, a is the split-cylinder Substrate Thickness (mm).

9 Radius in meters and L is the length, in meters, of each of the split-cylinder sections as shown in Figure 2. Sample Relative Permittivity 2. Once the TE011 resonance has been identified and 4. displayed on the network analyzer display, measure the reso- 6. nant Frequency f011 and quality factor Q of the resonance and 8. use the following expressions to compute the radius a and the 10. 20. conductivity of the empty split-cylinder's Resonator sections: 50. 100 IPC-25513-5. [( ) ( ) ]. 1. 2 2 2. Figure 5 Frequency of the TE011 Resonant Mode as a 2 011 . a = j1 Function of Permittivity and Substrate Thickness for c 2L the 10 GHz Split-Cylinder Resonator 2 011 0 In order to identify the correct mode, one can use Figure 6 to = 2. 2Rs predict the resonant Frequency of the TE011 resonant mode. For a more accurate estimate of this resonant Frequency and where 0 is the permeability of free space and the frequencies of the higher-order resonant modes, software is available from the National Institute of Standards and Tech- [( ) ( ) ].

10 3. 2 2 2 nology (NIST) which calculates the split-cylinder Resonator 0 j1 dimensions, substrate thickness, and provides an estimate of +. 0 a 2L the relative permittivity of the substrate. As of the publication [ ( ) ( )]. Rs = 2 2 of this Method , additional commercial vendors are developing 1 1 j1 similar software and will be listed through the IPC-TM-650 . 2Q +. 2L 2L a a Test methods web page. Estimate the TE 0 1 1 Resonant Frequency of Measure the Relative Permittivity and Loss Tangent Substrate-Loaded Split-Cylinder Resonator In addition to the desired TE011 resonant mode, other modes are excited Place the substrate in the gap separating the two cav- in the split-cylinder Resonator as shown in Figure 5. Depend- ity sections of the split-cylinder Resonator in such a way that Page 3 of 4. IPC-TM-650 . Number Subject Date Relative Permittivity and Loss Tangent Using a Split-Cylinder 01/07. Resonator Revision of the higher-order TE0np resonant modes. The user must ensure that these modes are symmetric and not distorted by adjacent resonant modes.