IPC-TM-650 EN 2022 试验方法-- - 第506页
assumption invalid and introduces er rors in the reported delay b. Short test lines reducing the t D accuracy due to system temporal limits (see 4.1.2) c. Short test lines reducing ability to identify intentional dis- co…
1 Scope
This method specifies time domain reflectometry
(TDR) methods for measuring and calculating the propagation
delay of uniform, controlled impedance transmission lines fab-
ricated in printed board (PB) technology. The method defines
a propagation delay per unit length t
D
by specifying how to
measure the time it takes a signal to propagate a given length
of transmission line.
This method describes methods that utilize TDR measure-
ments of multiple, unterminated test lines that are designed to
differ only in length. A TDR signal, usually a step waveform
1
,
is injected into a transmission line or lines and the reflection
response is measured some time later. This method shows
how t
D
is determined as the difference between the time it
takes a TDR pulse to reflect from the unterminated ends of
two transmission lines divided by the length difference of the
two lines.
1.1 Applicability
Engineering development of high-speed
and high-frequency electronic circuits and systems requires
detailed information on the electrical performance of PBs to
assure that transmission line designs yield the expected per-
formance characteristics. Detailed analysis of the design and
fabrication variations expected throughout manufacturing
assures that a proposed design can be manufactured at a
useful quality level. Measuring and characterizing propagation
delay on transmission line test structures is a direct means of
assessing the success of the PB transmission line model.
Since transmission line measurements are affected by imped-
ance conditions at the transmission line boundaries, propaga-
tion measurements specified here may not return the actual
delay observed for a given application. The procedures test
whether uniform, impedance controlled PB transmission lines
exhibit the expected propagation delay based on an electrical
model or reference test structures.
This method is generally applicable to uniform transmission
lines fabricated with commercial PB processes (see IPC-
2141), and is also useful for various transmission lines and
material systems studied at the research and development
stages.
The method is applicable when:
• Electrical contacts (connectors or probes) are readily made
to the transmission lines test structures
• Transmission line characteristic impedance is neither
extremely high nor low compared to the instrument’s test
port impedance
• Transmission line propagation loss sets acceptable signal-
to-noise ratios for the measured signals
The current version of this method specifies singled-ended
TDR measurements of unbalanced transmission lines, though
the method is sufficiently general to be extended to differential
TDR measurements of balanced lines.
1.2 Measurement System Limitations
Applying a speci-
fied test method helps assure accurate and consistent propa-
gation delay results, however measurements of propagation
delay can vary depending on equipment used. Known mea-
surement system limitations include:
a. Electrical noise of the TDR receiver, limiting propagation
delay accuracy and repeatability when signal levels are low
b. Trigger, source, and receiver jitter in the TDR instrument,
limiting temporal resolution
c. Drift in the trigger point of the TDR sources limiting, tempo-
ral resolution
d. Slow TDR pulse rise times, limiting temporal resolution
e. Waveform distortion induced by the low-quality test set-up
cables, connectors, and the signal launch points, inducing
errors in the reported propagation delay
Further measurement system considerations and notes are
provided in Section 6.
1.3 Sample Limitations
The type of test sample used may
also impact propagation delay accuracy. The sample-based
limitations include:
a. Lines on a fabricated PB deviating significantly from
design. For example, microstrip lines longer than 15.0 cm
[5.91 in] on PBs with plated-through holes (PTH) often
have variations in line width due to nonuniform plating
and/or etching. This makes the uniform transmission line
1. The signals used in the TDR system are actually rectangular pulses; because the measured duration of the TDR waveform is much less than the actual pulse
duration, the TDR waveform appears to be a step function.
3000 Lakeside Drive, Suite 309S
Bannockburn, IL 60015-1249
IPC-TM-650
TEST METHODS MANUAL
Number
2.5.5.11
Subject
Propagation Delay of Lines on Printed Boards by
TDR
Date
04/2009
Revision
Originating Task Group
Propagation Delay Test Methods Task Group
(D-24a)
ASSOCIATION CONNECTING
ELECTRONICS INDUSTRIES
®
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
16
assumption invalid and introduces errors in the reported
delay
b. Short test lines reducing the t
D
accuracy due to system
temporal limits (see 4.1.2)
c. Short test lines reducing ability to identify intentional dis-
continuities from signal launch
d. Long test lines detrimentally reducing amplitude of reflec-
tion signal due to large skin effect and dielectric losses
2 Applicable Documents
Design Guide for High-Speed Controlled Imped-
ance Circuit Boards
Test Methods Manual
1.9 Measurement Precision Estimation for Variables Data
2.5.5.7 Characteristic Impedance of Lines on Printed Boards
by TDR
3 Test Specimens
The test specimen can take one of sev-
eral forms depending on the application, but it must contain at
least one transmission line (or interconnect) test structure and
be representative of the actual PB product. Four definite types
of specimens are described in 3.1.1 through 3.1.4. The trans-
mission lines to be measured may be of either stripline or
microstrip construction.
3.1 Test Specimen Examples
3.1.1 Example 1
Test specimens are representative PBs
selected out of a lot of fabricated product. In some cases, this
sample set may contain all PBs in the lot. Agreed upon func-
tional and nonfunctional transmission lines on the PB are used
as the test set for this specimen. The selection of lines that
form the test set must be based on these criteria (nonexclu-
sive):
a. Inclusion of the PB’s critical features
b. Accessible line terminations for measurements
c. Absence of line branching
d. Absence of impedance changes within the transmission
line under test
e. Representation of controlled characteristic impedance Z
0
signal layers
3.1.2 Example 2
Test specimens are representative fabri-
cated PB samples or entire lots as in 3.1.1. The test lines used
in these specimens are nonfunctional lines designed into the
PB for easy termination and connection to TDR equipment.
Such test lines should be designed to include critical features
typical of functional lines and should lie in the controlled Z
0
signal layers of the application.
3.1.3 Example 3
Test specimens are test coupons cut
from representative fabricated PB samples or entire lots. The
test coupons are cut from the master PB at the time the indi-
vidual PBs are separated. Such test coupons will have one or
more nonfunctional transmission lines with termination suited
for TDR testing. Such test lines should include critical features
typical of functional lines and will be fabricated in the same
configuration and structure as the master PB on the same
controlled Z
0
signal layers as the application.
3.1.4 Example 4
Test specimens are a sample of the sub-
strate laminate to be characterized before PB manufacturing
and fabrication. The test line fabrication on these specimens
may involve laminating several PB layers together in the same
manner anticipated for PB manufacture.
3.2 Identification of Test Specimen
For specimens of
types called out in 3.1.1, 3.1.2, or 3.1.3, each specimen
be identified with no less than a PB part number, PB serial
number, and date code. Specimens of the type called for in
3.1.4 must include the lot or panel identification for the sub-
strate laminate being evaluated.
3.3 Conditioning
Environmental conditioning prior to test
may be called for as part of the test. When conditioning is
required, test specimens
be stored before testing at 23
+1/-5 °C and 50 ± 5% RH for no less than 16 hours. If a dif-
ferent conditioning procedure is required, it must be specified
and documented in test reports.
3.4 Test Interconnect Placement
The ability to correlate
propagation delay values derived from measurements of non-
functional test lines to propagation delay values of functional
lines is directly related to the proximity of the nonfunctional
test structure to the functional lines. The closer the test and
functional lines, the more likely the nominal material properties
will be the same. The placement of test structures on the PB
or panel should be analyzed for each PB design and be based
on the propagation delay tolerance and practicality of the lay-
out. When deciding on the best test interconnect placement,
consider the following placement priorities:
1) Inside the functional area of the PB;
2) At the edge of the PB but outside the functional circuit
area; or
Number
2.5.5.11
Subject
Propagation Delay of Lines on Printed Boards by TDR
Date
04/2009
Revision
IPC-TM-650
IPC-2141
IPC-TM-650
shall
Page
2
of
16
Figure 1 Distance from Clips
The Institute for Interconnecting and Packaging Electronic Circuits
2215 Sanders Road • Northbrook, IL 60062
Material in this Test Methods Manual was voluntarily established by Technical Committees of the 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
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 the IPC.
Page 1 of 1
回
IPC-TM-650
TEST
METHODS
MANUAL
1
Scope
This
test
method
determines
electrical
resistance
of
multilayer
PWBs.
2
Applicable
Documents
None
3
Test
Specimen
3.1
Test
coupon
"G”
4
Equipment/Apparatus
4.1
A
four-terminal
Kelvin
Bridge
or
equivalent
5
Procedure
5.1
Test
5.1.1
Measure
the
resistance
between
any
two
adjacent
holes
in
row
A
or
E
of
Specimen
G,
except
holes
A5
&
6,
E3,
4,
11
,
and
12
(see
Figure
1).
Diagram
A
(The
distance
between
dip
and
hole
should
be
as
short
as
possible.)
Number
2.5.12
Subject
Interconnection
Resistance,
Multilayer
Printed
Wiring
Date
Revision
4/73
Originating
Task
Group
N/A
5.1.2
Solder
leads
in
the
selected
holes
for
proper
connec¬
tion
to
the
four
terminals
of
the
test
instrument
according
to
diagram
A.
5.1.3
Repeat
this
test
for
each
of
the
five
pairs
of
holes.
5.2
Evaluation
Record
and
report
all
electrical
resistance
values.
I
PC-2-5-1
2-1