IPC-TM-650 EN 2022 试验方法-- - 第556页
frequencies where the conductor losses dom inate. Addition- ally, in the high freq uency range, the smo othing may preserve unrealistic features of the de-embe dded insertion loss. 5. 4.2 C umu lati ve D ie lectr ic and …
Probe performance may degrade over time. It is necessary to
periodically check the probe quality to assure the electrical
requirement in Figure 4-3 is met.
5 Procedure
The procedure section is to be used to detail
all of the specific steps necessary to perform the actual test.
It
include any specific conditioning requirements, or
other specimen preparation not previously detailed. It
then describe in detail the successive steps of the procedure,
grouping related operations into logical divisions in a concise
manner. It
include times, temperatures, voltages, pres-
sures, concentrations, linear measurements and quantitative
criteria when necessary in applicable units (both Metric and
English).
It
then state any detailed information required in report-
ing the test results. When two or more procedures are
described in the same test method, the report
indicate
which of the procedures was used. When a test method
allows variations in operating or other conditions, the report
state the particular conditions utilized for the test.
This specification currently outlines measuring Frequency
Domain characteristics using a VNA.
5.1 VNA Settings
Follow the VNA manual for proper
operation of equipment. Recommended settings for the VNA
include an IF bandwidth of 1 kHz (can be decreased based on
instrument and applications), and a step size of 10 MHz.
Smoothing is not allowed.
The cables and connectors used in the measurement should
be sufficiently rated for the maximum intended measurement
frequency.
5.2 Conditioning of Test Sample
Refer to 3.8 for proper
conditioning of test sample before test.
5.3 VNA Calibration and De-embedding
Calibration
and/or de-embedding techniques outlined in 1.2.1 must be
performed to remove the effects of cable, connector, and test
fixtures.
5.4 Smoothing and Fitting of Insertion Loss Measure-
ment Curve
5.4.1 Insertion Loss Smoothing Basics
Printed board
testing facilities often report insertion loss per inch at a hand-
ful of frequencies (e.g., 4 GHz, 8 GHz, 12.89 GHz, etc.). An
ideal insertion loss curve for a printed board conductor is
expected to follow transmission line behavior and be smooth.
However, in some testing houses, the de-embedded insertion
loss curves may have oscillations and deviations due to vari-
ous sources of measurement and de-embedding error, as
shown in blue curve in Figure 5-1. Without proper post-
processing of the data, the measurement house can easily fail
to report the true loss performance of the test coupon at des-
ignated frequencies. One common methodology for obtaining
a smooth de-embedded insertion loss curve is to use an iter-
ated moving average. The result is a very smooth red curve
shown in Figure 5-1.
While smoothing with an iterative moving average addresses
most of the challenges posed by the measurement errors,
there remain some disadvantages. The resulting smooth curve
is non-physical and unlikely to be representative of the true
loss of printed board conductor. For example, the smoothed
curve usually deviates from the correct answer at low
IPC-25514-4-3
IPC-25514-5-1
Red denotes the smoothed curve
Number
2.5.5.14
Subject
Measuring High Frequency Signal Loss and Propagation on
Printed Boards with Frequency Domain Methods
Date
02/2021
Revision
0
0
5
10
15
20
Frequency
(GHz)
Frequency(GHz)
Figure
4-3
Insertion
Loss
Requirement
for
the
Probe
Quality
Test
Setup
in
Figure
4-2
shall
shall
shall
shall
shall
shall
Figure
5-1
An
Iterative
Moving
Average
Applied
to
a
Typical
Insertion
Loss
Curve
Note
1.
IPC-TM-650
—
3
5
2
5
1
5
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1
.
6
m
p)
q
o
u-
sso.
(8P)
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frequencies where the conductor losses dominate. Addition-
ally, in the high frequency range, the smoothing may preserve
unrealistic features of the de-embedded insertion loss.
5.4.2 Cumulative Dielectric and Conductor Loss Fit-
ting
As it has been discussed in [14], the cumulative dielec-
tric and conductor losses can be generally approximated by
IL
dB
(,) = a
√
, + b, + c,
2
(Eq. 6)
where , is the frequency in GHz and a, b and c are constants.
For most of the cases coefficient c << 1 and can be
neglected. Therefore, as a first approximation the total loss
curve can be fitted to
IL
dB
(,) = a
√
, + b, (Eq. 7)
There are number of algorithms that can be used to perform
the printed board loss fit to Eq. 7. One of the most well-known
and widely available algorithms is the least squares fit,
example of which is shown in the Figure 5-2 below.
Even though least squares generally provide a good curve
approximation with the specified behavioral function, there are
many other fitting algorithms that can be applied.
5.4.3 An Alternative Cumulative Dielectric and Conduc-
tor Loss Fitting
Alternatively, when losses cannot be fitted
to the conventional physical based behavioral functions in (Eq.
6) and (Eq. 7), especially when measurement raw data has
high ringing resonances, other empirical approximations can
be used. Fox example, in [15], the following function is set as
the target function for the fitting algorithm:
IL
dB
(,) = a(, – ,
0
)
b
+ c(, – ,
0
)
2
+ d(, – ,
0
) + IL
0
(Eq. 8)
The first term represents the AC conductor loss (i.e., the skin-
effect losses), where ‘b’ is an additional fitting parameter
(instead of a constant 0.5 where ideal conductor loss is a
function of ,
0.5
) added to take into account the surface rough-
ness impact of the conductor. The second and the third terms
represent dielectric losses, and the constant represents the
conductor’s DC loss. Furthermore, a certain offset point (,
0
,
IL
0
) is introduced, where ,
0
is the first frequency point of the
measurement. The offset is added to accommodate the fact
that VNA measurements made at the printed board fabricator
usually do not provide results lower than 10 MHz.
The abovementioned methods fit the data to a smooth curve
over the entire bandwidth of the measurement where each
data point is allocated equal weight. As measurement errors
usually increase significantly at high frequencies, a weighting
scheme can be introduced to force the algorithm to prioritize
the curve fitting at the low frequencies and minimize (or ignore)
the impact of high frequency:
W(,) =
(
1–
(
,
,
max
))
3
(Eq.9)
where ,
max
is the maximum measurement frequency. Figure
5-3 shows the suggested weighted function where ,
max
= 20
GHz.
IPC-25514-5-2
Red represents the fitted curve.
IPC-25514-5-3
Number
2.5.5.14
Subject
Measuring High Frequency Signal Loss and Propagation on
Printed Boards with Frequency Domain Methods
Date
02/2021
Revision
IPC-TM-650
Figure
5-2
Least
Squares
Fit
Based
on
(eq.
7)
Applied
to
a
Representative
Insertion
Loss
Curve
Note
1.
Figure
5-3
The
Suggested
Weight
Function
for
Insertion
Loss
Curve
Fitting
.5
2
.5
1
.5
O
2
L
S
s
p)
uow
j
d
SSO1
Page
8
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1 Scope
This test method is used to determine the mois-
ture and insulation resistances of applied polymer solder mask
under two separate prescribed conditions of temperature and
humidity. One condition is described as Class T and the other
Class H. Raw material qualification testing is performed on
designated comb patterns. Production quality conformance
testing is performed on a standard ‘‘Y’’ pattern.
2 Applicable Documents
Multipurpose One-Sided Test Pattern -
Gerber Format
Qualification and Performance of Permanent
Solder Mask
Requirements for Soldering Fluxes
Acceptability for Printed Boards
3 Test Specimens
The IPC-A-25A-G-KIT artwork package
provides the Gerber files necessary for the fabrication of the
standard IPC-B-25A test board used with this test method.
3.1 Qualification Testing
3.1.1 Class H
Three IPC-B-25A boards using the D comb
patterns with 0.32 mm [0.0126 in] lines/spaces (see Figure 1).
Of which, two are to be coated and one uncoated with solder
mask according to the solder mask supplier’s recommenda-
tions.
3.1.2 Class T
Three IPC-B-25A boards using the E and F
comb patterns with 0.41 mm [0.016 in] lines and 0.51 mm
[0.020 in] spaces (see Figure 1). Of which, two are to be
coated and one uncoated with solder mask according to the
solder mask supplier’s recommendations.
3.2 Conformance Testing
IPC-B-25A board C (‘‘Y’’
shape) pattern with 0.64 mm lines/0.64 mm spacing [0.025 in
lines/0.025 in spacing] or pattern with minimum spacing on
the production board (see Figure 1), whichever has the small-
est line spacing, coated with solder mask according to the
solder mask suppliers recommendations.
4 Apparatus
4.1 Chamber
A clean chamber capable of programming
and recording an environment of 25 ± 2 °C [77 ± 3.6 °F] to at
least 65 ± 2 °C [149 ± 3.6 °F] and 90-98% relative humidity.
This test requires a clean chamber and clean water
for repeatable test results. The following recommendations
are made:
• Incoming water purity should be between 0.5 and 0.1
micro-siemens/cm.
• Fresh deionized water should be used for each test, rather
than using a recirculating water sump.
• Chamber workspaces should be cleaned at least every six
months.
1. www.ipc.org/onlinestore
IPC-2631-1
3000 Lakeside Drive, Suite 309S
Bannockburn, IL 60015-1249
IPC-TM-650
TEST METHODS MANUAL
Number
2.6.3.1
Subject
Solder Mask - Moisture and Insulation Resistance
Date
03/07
Revision
E
Originating Task Group
Solder Mask Performance Task Group (5-33b)
ASSOCIATION CONNECTING
ELECTRONICS INDUSTRIES
®
IPC-A-25A-G-KIT1
IPC-SM-840
J-STD-004
IPC-A-600
Figure
1
IPC-B-25A
Test
Board
NOTE:
Material
in
this
Test
Methods
Manual
was
voluntarily
established
by
Technical
Committees
of
IPC.
material
advisory
only
and
its
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
paten!
infringement.
Equipment
referenced
/s
the
convenience
of
the
user
and
does
not
imply
endorsement
by
IPC.
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