IPC-TM-650 EN 2022 试验方法--.pdf - 第681页
During the remainder of the preparation, handle boards by the edges o nly an d use non contaminating g loves. 3.1.3 Dry the cleaned boards for two hours at 50 °C . 3.1.4 If boards are to be store d before treatment, p la…
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During the remainder of the preparation, handle boards by the
edges only and use noncontaminating gloves.
3.1.3
Dry the cleaned boards for two hours at 50 °C.
3.1.4
If boards are to be stored before treatment, place the
boards in Kapak™ bags or other contamination-free contain-
ers (do not heat seal) in a desiccator. (Kapak™ bags are avail-
able from Fischer, VWR and other distributors.)
3.1.5
When measured as described in Sections 4 and 5, if
the control board readings are less than 1000 MΩ at any point
after the initial 24 hours of SIR exposure, a new set of test
coupons shall be obtained and the entire test repeated.
3.2 Blank Process Controls
If performing process valida-
tion testing, two samples from an unprocessed blank should
be run with the samples taken from the processed boards.
Values obtained from unprocessed board samples are useful
when failure is observed within the processed board sample.
Failure of the unprocessed samples may indicate a problem
with the incoming bare board rather than an assembly pro-
cess.
4 Equipment/Apparatus
It is the responsibility of the user
of this method to verify equipment suitability. This method
intends for all tolerances to be interpreted as uncertainties
with a confidence interval of 95% as referenced in ANSI/NCSL
Z540-1 and ANSI/NCSL Z540-2. Quantitative, qualitative and
default information follow in the paragraphs below.
4.1 Electrometer
Electrometer, High Resistance Meter,
Picoammeter or equivalent as described by ASTM D 257.
a) System must be capable of taking measurements and
controlling the switching automatically (unattended).
b) Minimum resistance measurement accuracy (not only
meter, but as implemented)
5% of full scale up to 10
10
Ω @ 5V
10% of full scale up to 10
11
Ω @ 5V
20% of full scale above 10
11
Ω @ 5V
c) Accuracy with respect to the ‘‘true’’ value requires assess-
ment of stability of the measurement system (after switch-
ing from bias voltage to the measurement voltage). There-
fore, if the system does not automatically assess stability
before logging, use an arbitrary time of one minute.
d) The system described in this section must be able to make
all measurements required within a 20 minute period and
meet the requirements of 5.3.
It is preferred that the resistance reading be stable before
acquiring the readings or data. If after one minute the signal
remains unstable, a measurement should still be recorded.
4.2 Switching System
a) Must have a channel-to-channel isolation resistance ten
times greater than the resistance of typical SIR require-
ments, or a default channel-to-channel isolation resistance
of 10
12
Ω.
b) <20-minute cycle while obtaining measurements as
described above.
c) Unique 10
6
Ω current limiting capability per channel.
4.3 Wire Attachments
a) Single solid copper wire with PTFE insulation.
b) Preferred solid wire solders (no flux), or nominally 1% by
weight rosin nonactivated. See wire attach section of this
document for more information.
c) Electrical (EMI) shielding to guard cabling from stray cur-
rents.
4.3.2 Alternative
Wire attachments such as stranded wire,
non-PTFE insulation, edge connectors rather than hard wiring,
and guarding techniques may be used provided the system
accuracy is not compromised.
4.4 Controlled Temperature and Humidity Chamber
a) Produce 40 ± 1 °C at 90 ± 3% R.H.
b) Continuous or semicontinuous recording of this environ-
ment. ± 2 °C and ± 3% R.H.
c) Samples should not significantly impede airflow.
d) Adequate mixing of water vapor and air is imperative to
ensure condensation does not occur anywhere in the
chamber except on/around cooling or dehumidification
coils. If any part of interior of the chamber is below the dew
point (possibly due to insulation or control issues), conden-
sation will occur. This is not necessarily a problem as long
as the samples are kept above the dew point and are
shielded from dripping or flying condensate.
4.5 Camera
Camera capable of recording color image.
5 Test Procedure
5.1 Interconnect Samples
Number
2.6.3.7
Subject
Surface Insulation Resistance
Date
03/07
Revision
IPC-TM-650
Page
2
of
4
5.1.1
Hardwired samples need to be soldered without
adverse effect to test vehicles. Common good soldering
practice should be followed. Sample should be covered. See
IPC-9201 for reference. Heat should not be allowed to dam-
age sample. Flux is of great concern. Often samples can be
soldered without the use of flux, so users of this method
should have solid wire solder on hand. If flux is deemed nec-
essary by qualitative observation, use rosin nonactivated flux.
Wire all samples and retain relationship of interconnection
between test vehicle and testing system (nets, channels, etc.).
5.1.2
Connector interfacing inside the chamber has been
shown to be a capable implementation for SIR; however, as
the connectors are exposed to high heat and humidity they
obviously require a good deal of maintenance and verification.
5.2
Fixture samples in the chamber uniformly, vertically, and
parallel to airflow. The minimum spacing between samples
shall be 12.5 mm [0.5 in]. If hardwiring is used, dress wires
down from samples. Make appropriate connections to switch-
ing system.
5.3
Measurement and stress bias voltage are the same.
5.3.1
Apply direct current electrical bias to produce a field
strength of 25 ± 1 V/mm between adjacent parallel traces.
Assuming that SIR is much greater than current limiting resis-
tance this field corresponds to an applied voltage of 5 ± 0.2 V
for 200 µm [0.0079 in] spacing (example is technically equiva-
lent to IEC 61189-5). This bias shall be in place during an
aggregate 90% (minimum) of temperature/humidity condition-
ing (remaining percentage is related to measurement) in order
to facilitate electrochemical reactions.
5.3.2
Seal the chamber and ramp from laboratory ambient
conditions to 25 °C and 50% R.H. Dwell for one hour. Verify
the electrical system setup by taking a series of all measure-
ments at these specified ambient conditions. Because classi-
fication or ranking of sample performance by SIR at ambient
is not appropriate for these test vehicles, clarity suggests that
measurements need not be reported unless ‘‘shorts’’ are
observed and therefore the corresponding samples are
deemed inappropriate for test.
5.4
Increase the temperature to 40 °C while maintaining the
humidity at 50% R.H. ± 3% R.H. and dwell at this tempera-
ture for 15 minutes. After this period, gradually increase, within
0.5 hour, the relative humidity to 90 ± 3 % R.H. Do not allow
the temperature of the samples to drop below the dew point.
5.5
Allow chamber to stabilize at set point for one hour.
5.6
Duration of test shall be not less than 72 hours.
5.7
Take and record all SIR measurements (every unique net
or channel) at least once every 20 minutes.
5.8
After conditioning, remove samples from chamber and
examine at 30 to 40X in light field and dark field (back light).
Record the following:
a) Presence of dendrites: Yes/No
b) Maximum percent reduction of spacing: 0% for no den-
drites 1% to 100% for worst-case dendrite. Capture and
record image of worst case dendrite.
c) Presence of discoloration between conductors: Yes/No; if
yes, capture and record image.
d) Presence of water spots. Yes/No; if yes, capture and
record image.
e) Presence of subsurface metal migration. Yes/No; if yes,
capture and record image.
6 Reporting
6.1
Deviations from test method or specification shall be
recorded. All standard reporting shall be incorporated, includ-
ing enough information to exactly reproduce the test (equip-
ment, personnel, deviations or options within the method
etc.).
6.2
All items listed in 5.8.
6.3
All SIR measurements are to be reported in the form of
Log
10
(R
i
), where R
i
is the measured SIR of the i
th
measure-
ment.
7 Notes
7.1 Sampling
When using this test method for materials
characterization the sample selection, preparation and
requirements should follow IPC-J-STD-004.
When using this test method for process characterization the
sample selection, preparation and requirements should follow
IPC-J-STD-001.
This methodology may also be used with other specifications.
7.1.1
A test vehicle should be considered a sample count of
one. For example, an IPC-B-24 test vehicle is a sample count
Number
2.6.3.7
Subject
Surface Insulation Resistance
Date
03/07
Revision
IPC-TM-650
Page
3
of
4