IPC-TM-650 EN 2022 试验方法-- - 第546页
4 Measurement Apparatus 4. 1 Sp l it -C yl in de r Re so na to r T he m e th od e m pl oy s a split-cylinder resonator, which i s a cylindrical cavity separated into two halves of equal length, with a dielectric substrat…
1 Scope
This method describes the nondestructive mea-
surement of the relative permittivity and loss tangent of unclad
dielectric substrates at microwave frequencies using a split-
cylinder resonator (see Figure 1).
This test method is directly applicable for measuring the
in-plane (the plane parallel to the surface of the specimen)
permittivity of the specimen because the electric field is
in-plane. The permittivity of isotropic dielectrics can also be
measured with this method.
This measurement method does not measure the out-
of-plane (direction normal to the surface of the specimen) per-
mittivity of the specimen. However, for most printed boards
the measurement uncertainties associated with this method
are typically less than the difference between in-plane and
out-of-plane permittivity values. Furthermore, comparison with
methods measuring the out-of-plane permittivity is difficult
because those methods typically do not provide measure-
ment confidence intervals.
2 Applicable Documents
See 6.2.
3 Test Specimen
The test specimen is an unclad dielectric
substrate. The substrate geometry can be either square or
circular as long as the substrate extends beyond the diameter
2a of the two cylindrical cavity sections as shown in Figure 2.
In particular, for the 10 GHz split-cylinder resonator discussed
in this method, the dimensions of the substrate should be at
least 50.0 mm [1.97 in] in diameter for circular samples or
50.0 mm [1.97 in] on a side for square samples.
Although the dielectric substrate thickness can vary from
0.05 mm to 5.0 mm [0.0020 in to 0.20 in], thin substrates may
lead to larger measurement uncertainties, while the dielectric
losses in thicker substrates may prevent the split-cylinder fix-
ture from resonating properly. A substrate thickness on the
order of 1.0 mm [0.040 in] is typical.
The measurement theory assumes the dielectric substrate has
a uniform thickness. Therefore, to reduce the measurement
uncertainty, variation and uncertainty in substrate thickness
should be minimized. A typical uncertainty in thickness should
be no more than 0.02 mm [0.00079 in]. In general, warped
samples should also be avoided as these can lead to biases
in the calculated values of the relative permittivity and loss
tangent.
For the split-cylinder resonator described here, the measure-
ment frequency of the split-cylinder resonator is a function of
the relative permittivity and thickness of the substrate. Thicker
substrates and higher values of relative permittivity drive the
resonant frequency lower, as shown in Figure 6.
IPC-25513-1
IPC-25513-2
3000 Lakeside Drive
Bannockburn, IL 60015-1249
IPC-TM-650
TEST METHODS MANUAL
Number
2.5.5.13
Subject
Relative Permittivity and Loss Tangent Using a
Split-Cylinder Resonator
Date
01/07
Revision
Originating Task Group
High Frequency Resonator Test Method Task Group
(D-24c)
ASSOCIATION CONNECTING
ELECTRONICS INDUSTRIES
®
Figure
1
Split-Cylinder
Resonator
z
/
卜
Coupling
L
Loop
—
Q
Upper
Cylindrical
Cavity
Region
d
Sample
Region
A
P
i
卜
L
、
r
Lower
Cylindrical
Cavity
Region
o
_
Coupling
Loop
y
a
2a
2b
Figure
2
Split-Cylinder
Resonator
Diagram
Note:
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/n
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IPC.
Page
1
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4
4 Measurement Apparatus
4.1 Split-Cylinder Resonator
The method employs a
split-cylinder resonator, which is a cylindrical cavity separated
into two halves of equal length, with a dielectric substrate
placed in the gap between the two cavity sections. The split-
cylinder resonator must be constructed to allow an adjustable,
variable gap between the two cavity sections for introduction
of the dielectric substrate. Additional details about the con-
struction of a split-post resonator are given in the references
described in 6.2. Over the years there have been commercial
manufacturers of this fixture.
In order to excite and detect the desired fundamental TE
011
resonant mode in the split-cylinder resonator, a coupling loop
is introduced, through a small hole in the cavity wall, in each
of the two cavity regions. The plane of the coupling loop
should be parallel to the plane of the sample, in order to allow
maximum interaction with the vertical component of the mag-
netic field. Each of the coupling loops is connected to a
coaxial transmission line that is connected to the input port of
a network analyzer. To minimize the effect of coupling losses,
the distance to which the loops extend radially into each of the
cavity sections must also be adjustable. In addition to the fun-
damental TE
011
mode, higher modes can be used to extend
the measurement frequency. Typical measurements on fused
silica with higher mode measurements are shown in Figures 3
and 4.
4.2 Network Analyzer
A scalar or vector network analyzer
is necessary to perform the measurement with the split-
cylinder resonator. Commercially available network analyzers
operate over various frequency ranges, so care is needed to
ensure that the network analyzer covers the necessary fre-
quency range for the particular split-cylinder resonator used.
4.3 Digital Micrometer
The dielectric substrate thickness
can be measured with a digital micrometer with a minimal
resolution of 0.001 mm [0.000039 in].
5 Procedure
5.1
Turn on the network analyzer and allow the unit to
warm-up and stabilize according to the manufacturer’s
instructions.
5.2
Connect the network analyzer’s two input ports to the
split-cylinder resonator’s coupling loops using coaxial trans-
mission lines.
5.3
Measure the thickness of the substrate over several
locations using a digital micrometer, and compute the mean
substrate thickness.
5.4
Determine split-cylinder resonator properties. The
length, radius and conductivity of the split-cylinder resonator
must be known before the substrate relative permittivity and
loss tangent can be calculated. If these variables have not
been already determined, the following procedure can be
used:
IPC-25513-3
3.90
10 20
Frequency (GHz)
30 40 50
3.85
3.80
3.75
3.70
Relative Permittivity
10 GHz Split-Cylinder Resonator
35 GHz Split-Cylinder Resonator
TE
011
TE
013
TE
021
TE
023
TE
017
TE
025
TE
011
TE
013
TE
015
IPC-25513-4
7x10
-4
6
5
4
3
2
1
0
10 20
Frequency (GHz)
30 40 50
Loss Tangent
35 GHz Split-Cylinder Resonator
Linear Least Squares Fit
10 GHz Split-Cylinder Resonator
TE
011
TE
013
TE
021
TE
023
TE
017
TE
025
TE
011
TE
013
TE
015
Number
2.5.5.13
Subject
Relative Permittivity and Loss Tangent Using a Split-Cylinder
Resonator
Date
01/07
Revision
IPC-TM-650
Figure
4
Typical
Measurements
of
the
Loss-tangent
using
10
GHz
and
35
GHz
Split-cylinder
Resonators
including
Measurements
with
Higher
Modes
Figure
3
Typical
Measurements
of
the
Real
Part
of
the
Permittivity
using
10
GHz
and
35
GHz
Split-cylinder
Resonators
including
Measurements
with
Higher
Modes
Page
2
of
4
5.4.1
Measure the length L of each of the two split-cylinder
resonator sections over several locations and compute the
mean length of both sections.
5.4.2
With the split-cylinder empty (no substrate) and closed
(d=0), find the TE
011
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
the resonance curve is less than -40 dB. For the particular
10 GHz split-cylinder resonator described in this method, the
resonant frequency should be approximately 10.04 GHz. If
another split-cylinder geometry is being used, use the follow-
ing approximation to estimate the TE
011
resonant frequency of
an empty split-cylinder resonator:
ƒ
011
=
c
2π
√
(
j
1
a
)
2
+
(
π
2L
)
2
where c is the speed of light in a vacuum, j
1
is the first zero of
the Bessel function of the first kind J
1
, a is the split-cylinder
radius in meters and L is the length, in meters, of each of the
split-cylinder sections as shown in Figure 2.
5.4.3
Once the TE
011
resonance has been identified and
displayed on the network analyzer display, measure the reso-
nant frequency f
011
and quality factor Q of the resonance and
use the following expressions to compute the radius a and the
conductivity σ of the empty split-cylinder’s resonator sections:
a = j
1
[
(
2πƒ
011
c
)
2
−
(
π
2L
)
2
]
−
1
2
σ =
2πƒ
011
µ
0
2R
s
2
where µ
0
is the permeability of free space and
√
µ
0
ε
0
[
(
j
1
a
)
2
+
(
π
2L
)
2
]
3
2
R
s
=
2Q
[
1
2L
(
π
2L
)
2
+
1
a
(
j
1
a
)
2
]
5.5 Estima te the TE
01 1
Resonant Freq uen cy of
Substrate-Loaded Split-Cylinder Resonator
In addition
to the desired TE
011
resonant mode, other modes are excited
in the split-cylinder resonator as shown in Figure 5. Depend-
ing on the thickness and relative permittivity of the dielectric
substrate being measured, the resonant frequency for the
split-cylinder plus substrate can be significantly lower than the
resonant frequency of the empty split-cylinder resonator as
shown in Figure 6.
In order to identify the correct mode, one can use Figure 6 to
predict the resonant frequency of the TE
011
resonant mode.
For a more accurate estimate of this resonant frequency and
the frequencies of the higher-order resonant modes, software
is available from the National Institute of Standards and Tech-
nology (NIST) which calculates the split-cylinder resonator
dimensions, substrate thickness, and provides an estimate of
the relative permittivity of the substrate. As of the publication
of this method, additional commercial vendors are developing
similar software and will be listed through the IPC-TM-650
Test Methods web page.
5.6 Measure the Relative Permittivity and Loss Tangent
5.6.1
Place the substrate in the gap separating the two cav-
ity sections of the split-cylinder resonator in such a way that
IPC-25513-5
Substrate Thickness (mm)
Sample Relative Permittivity
2
4
6
8
10
20
50
100
10
8
6
4
2
0
0 1 2 3 4
5
TE
011
Resonant Frequency (GHz)
Number
2.5.5.13
Subject
Relative Permittivity and Loss Tangent Using a Split-Cylinder
Resonator
Date
01/07
Revision
IPC-TM-650
Figure
5
Frequency
of
the
TE011
Resonant
Mode
as
a
Function
of
Permittivity
and
Substrate
Thickness
for
the
10
GHz
Split-Cylinder
Resonator
Page
3
of
4