IPC-TM-650 EN 2022 试验方法--.pdf - 第521页
1 Scope This document d escribes five m ethods for deter- mi ning t he a moun t of si gnal pr opag at ion l oss c ause d by mat eri al ch ar acte ri stic s of co ndu cto rs an d acc om pan yin g structures on printed boa…
6.4.2 Waveform Averaging and Number of Samples in
the Measurement Zone
Waveform averaging reduces the
effective noise level of the measurement by M
-1/2
, where M is
the number of acquired waveforms (typically, 8 ≤ M ≤ 256).
Consequently, averaging can reduce measurement noise.
This reduction is limited by the number of bits of the analog-
to-digital converter of the TDR system and the linearity of the
timebase. However, if the TDR system exhibits drift in the
timebase, averaging too many waveforms may result in a
reduction of t
sys
and a commensurate reduction in the
temporal/spatial resolution of the TDR.
The number of samples (data points) in the waveform epoch
will affect the accuracy and uncertainty of the computed value
of t
d
because this value is typically computed by interpolating
between adjacent datum values. Therefore, the more samples
in the waveform epoch, the smaller will be the error and stan-
dard deviation of the computed t
d
value.
6.4.3 Selection of Waveform Period
Inconsistency in
defining the waveform epoch may cause a significant but
unknown error than can exceed two sample intervals. Speci-
fying the waveform period to be consistent for both long and
short line measurements improves t
d
repeatability, and this
can improve assessment of design and fabrication quality and
vendor capability. This waveform epoch should be long
enough to accurately determine if the waveform has settled on
both sides of the waveform transition but should be short
enough, given the number of samples in the waveform, to
accurately compute the transition instant. The waveform
epoch is defined in 5.1.3.
Number
2.5.5.11
Subject
Propagation Delay of Lines on Printed Boards by TDR
Date
04/2009
Revision
IPC-TM-650
Page
16
of
16
1 Scope
This document describes five methods for deter-
mining the amount of signal propagation loss caused by
material characteristics of conductors and accompanying
structures on printed boards. These losses result in frequency
dependent attenuation, α, as described in IPC-2141. Four of
these methods to assess this loss are time domain based,
and one is frequency domain (FD) based. These methods are:
• Method A: Effective Bandwidth (EBW) method
• Method B: Root Impulse Energy (RIE) method
• Method C: Short Pulse Propagation (SPP) method
• Method D: Single-Ended TDR to Differential Insertion Loss
(SET2DIL) method
• Method E: Frequency Domain (FD) method
Method A and B and one aspect of E reduce the attenuation
to a single number. Method C and D, and another aspect of
E, report the frequency attenuation versus frequency.
Table 1-1 provides an overview of the five methods described
in this document for determining the amount of signal propa-
gation loss on printed board conductors.
1.1 EBW (Method A Description)
In this method a TDR
step with a specified rise time is injected into an unterminated
conductor, and the conductor’s loss is determined from the
degradation of the maximum slew rate of the step rise time at
the open end of the interconnect. The maximum slope
method described here does not use a 10 - 90% rise time
measurements method. Instead, it uses the maximum slew
rate to extrapolate an effective bandwidth parameter. The via
loss, skin effect loss, and dielectric loss all influence the rise
time of the TDR step as it appears at the end of the intercon-
nect. This method is not intended to measure absolute loss or
each component of loss. Rather, it determines a relative total
loss factor called EBW that can be used to discern loss varia-
tions in transmission lines from panel to panel or lot to lot.
1.1.1 EBW Measurement System Caveats
This method
is not intended for rigorous analysis of the signal attenuation
of printed board interconnects but for a simple production
test. Therefore, there are several recognized limitations in the
measurement methodology:
a) This procedure does not deliver absolute values of loss in
dB but instead delivers a parameter called EBW which is a
qualitative measure of transmission line loss α.
b) There is no attempt to separate the various loss compo-
nents (i.e., skin effect, dielectric, via loss, etc.).
Instrument TDR TDR/VNA TDT TDR/TDT VNA/TDT
Stimulus
Selected for
appropriate
spectral content
250 ps or specified 11-35 ps 11-35 ps
300 KHz to 10 GHz
or as specified
Coupon >5 cm
1.25 cm and 20.32
cm or as specified
3.0 cm and
10.0 cm
4″
(8″ effective length)
20.32 cm
or as specified
SW Scope Algorithm
Algorithm and IPC
web site pointer
Algorithm and IPC
web site for software
Algorithm Algorithm
Probe
Matched impedance
probe
Matched impedance
probe
Matched impedance
probe, RF connector
High Frequency
hand-held probe
Matched impedance
probe, RF connector
Test Quantity
Maximum slope
in MV/sec
Averaged loss (dB)
Tanδ, ε
r
, α, β, and Z
0
vs. frequency
SDD21 vs. frequency Loss fit and slope
Applicability
Printed board
fabrication testing
Printed board
fabrication testing
Printed board
material qualification,
printed board
model generation
Printed board
fabrication
qualification
and testing
Printed board
fabrication testing,
printed board design
guide specification
3000 Lakeside Drive, Suite 309S
Bannockburn, IL 60015-1249
IPC-TM-650
TEST METHODS MANUAL
Number
2.5.5.12
Subject
Test Methods to Determine the Amount of Signal
Loss on Printed Boards
Date
07/12
Revision
A
Originating Task Group
Propagation Loss Test Methods Task Group (D-24b)
Association
Connecting
Electronics
Industries
Table
1-1
Methods
Overview
EBW
RIE
SPP
SET2DIL
FD
Material
/n
this
Test
Methods
Manual
was
voluntarily
established
by
Technical
Committees
of
I
PC.
This
material
/s
advisory
only
and
"s
use
or
adaptation
，
s
entirely
voluntary.
IPC
disclaims
all
liability
of
any
kind
as
to
the
use,
application,
or
adaptation
of
this
material.
Users
are
also
wholly
responsible
for
protecting
themselves
against
all
claims
or
liabilities
for
patent
infringement.
Equipment
referenced
/s
for
the
convenience
of
the
user
and
does
not
imply
endorsement
by
IPC.
Page
1
of
24
c) There must be sufficient spectral content within the TDR
step pulse for the frequency range of interest where range
of interest is determined by application.
d) The repeatability of the measurement is limited by the noise
and jitter response from the TDR instrument.
1.1.2 EBW Test Coupon and Conductor Caveats
This
method is designed to be used on any conductor. However
comparison between measurements is only valid for like inter-
connect structures.
The launch vias should be designed with minimum return loss.
It is recommended that the test coupon or conductor be of a
length greater than 5.0 cm [2.0 in].
EBW applicable documents include IPC-2141, IPC-TM-650,
Method 1.9 and Method 2.5.5.7.
1.2 RIE (Method B Description)
In this method a TDR
step with a specified rise time is injected into each of two
lengths of an unterminated conductor. The gated derivative of
the reflected edges is an impulse response for each respec-
tive line. The RIE value is the ratio of energy obtained by inte-
grating the impulse responses. One of the two lengths is
intended to be a relatively short piece; the other is substan-
tially longer and in close proximity to a considerably long con-
ductor on the same printed board layer. The RIE ratio is a
single value that is directly proportional to the aggregate trans-
mission line loss α, which is described in IPC-2141.
1.2.1 RIE Measurement System Limitations
RIE values
can vary depending on equipment used and how the tests
were performed. Following the specified method ensures con-
sistent results. Both single-ended and differential line mea-
surements have limitations in common which include the fol-
lowing:
a) RIE values are dependent on equipment bandwidth; this
document specifies only a minimum requirement for the
TDR signal source.
b) When attempting correlation between different systems, it
is critical that all systems have the same bandwidth.
c) The probe cabling, launch, test coupon vias affect mea-
surement accuracy.
d) All RIE loss values are derived and not directly measured.
e) The RIE process utilizes a filter algorithm to improve mea-
surement consistency.
1.2.2 RIE Test Coupon and Conductor Caveats
Various
limitations can be attributed to test samples and probing such
as:
a) The probe and launch structure reduces the signal energy
injected into the transmission line.
b) Crosstalk and associated effects, other than differential
coupling, are out of the scope of the RIE method.
c) The RIE method applies to reference structures and test
structures with specified transmission line lengths.
RIE applicable documents include IPC-2141, IPC-TM-650,
Methods 1.9 and 2.5.5.7.
1.3 SPP (Method C Description)
The SPP method allows
the extraction of broadband printed board electrical charac-
teristics that affect signal propagation using Time Domain
Reflectometry/Time Domain Transmission (TDR/TDT) equip-
ment. The SPP method produces frequency dependent mea-
surement results. Such frequency-dependent parameters
include the propagation constant (attenuation and phase con-
stant), dielectric constant, loss tangent, and characteristic
impedance. Conductor resistivity and line capacitance are
also assessed. The extracted parameters may be used to
generate predictive causal transmission line models for sys-
tem performance evaluations as well for monitoring produc-
tion line output.
The SPP technique employs a time-domain measurement that
is used to extract the broadband permittivity. The technique is
used on representative stripline structures built with small
interface discontinuities such as lands and vias.
A short pulse is injected into two lines of different lengths.
Signal processing of the digitized pulses consists of rectangu-
lar time windowing of the unwanted reflections from interface
discontinuities. This is followed by Fourier transformation.
From the ratio of the two Fourier transforms, the total attenu-
ation α(f) and phase constant β(f) are obtained. R(f), L(f), C(f),
and G(f), namely resistance, inductance, capacitance, and
conductance per unit length, are calculated using a causally-
enforced two-dimensional (2D) field solver that has a built-in
Debye function for the relation between C(f), and G(f), which
enforces the Kramer-Kronig causality requirement. The total
attenuation α(f) and β(f) are fitted to the measured values and
smooth interpolation and extrapolation is made over the
desired frequency range. The broadband Z
0
(f) can also be
obtained from Equation [1-1]:
Z
0
(,) =
Γ(,)
G(,) + j2πC(,)
[1-1]
Number
2.5.5.12
Subject
Test Methods to Determine the Amount of Signal Loss on
Printed Boards
Date
07/12
Revision
A
IPC-TM-650
Page
2
of
24