IPC-TM-650 EN 2022 试验方法-- - 第646页
1 Scope The fungus resistance test is used to determine the resis tance of materials t o fungi and to determine if such material is adversely affected by fungi under conditions favor- able for their devel opment, namely …
level approaches 0.160 W. With increasing power above
0.160 W the resistance value gradually starts to deviate from
its stable value. The resistor fails ‘‘open’’ at P
failure
of 0.360 W.
The resistance plot in Figure 2b suggests that P
max
≈0.160 W.
Thus in the above illustration, the power density rating for that
resistor, for which S ≈ 0.44 mm
2
, calculated from equation (4),
PDR = 0.16 W / 0.44 mm
2
≈ 0.36 W / mm
2
.
7.1 PDR Safety Factor
In the example above, the surface
temperature at the tested resistors measured (optionally) at P
n
= 0.160 W was about 42 °C. Depending on the material’s
physical characteristics, this heating effect might lead to an
accelerating aging and shortening the device operational life.
Therefore it is recommended that P
max
is reduced accordingly
by a certain safety factor that can be deduced, for example,
from the aging study.
8 Accuracy Considerations
Several uncertainty factors
such as instrumentation, dimensional uncertainty of the test
specimen geometry, resistance of contacts and interconnects
among others contribute to the combined uncertainty of the
measurements. The complexity of modeling these factors may
be considerably higher when the measurements are per-
formed at elevated temperatures for resistors embedded in
complex multilayer assemblies. Adequate analysis can be per-
formed, however, using the partial derivative technique for
equation (4) It is recommended that the combined instrumen-
tation uncertainties should be 10 times smaller than the nomi-
nal tolerance value of the resistor. Likewise, it is recom-
mended that uncertainty in the surface area, S, is considered
very carefully since S is the primary parameter used in scaling
the PDR ratings for different form-factor resistors.
Additional limitations may arise from the systematic uncer-
tainty of the particular instrumentation, calibration standards,
and the dimensional imperfections of the actually imple-
mented test specimen. The test may require specialized
instrumentation when P
n
approaches the instrument maxi-
mum power compliance conditions before P
failure
is reached.
9 Notes
9.1 Resistor De-Rating
In engineering practice and in typi-
cal manufacturer specifications, resistor power ratings is nor-
mally specified at +25 °C. The power rating is reduced as the
resistor operational temperature increases. A de-rating chart
is often employed, with de-rating typically starting at 70 °C.
Power de-rating charts are often included in manufacturers’
specifications to be considered as a general guideline when
projecting the power rating for application specific conditions.
The safest design rules recommend using the largest geo-
metrical size and assuming conservative (higher than actual)
operating temperatures.
In the case of embedded resistive devices operating at tem-
perature conditions above 25 °C, the heat dissipation is highly
nonlinear with additional complexity resulting from a particular
package design. In the presented example the tested resistor
failed ‘‘open’’ at the temperature t
failure
≈ 52 °C, while the
stable P
max
corresponded to temperature t
max
≈ 38 °C. The
operational temperature of embedded resistors may vary con-
siderably, depending on construction, materials and manufac-
turing technology of the embedded package. Consequently, a
reliable universal de-rating chart cannot be constructed, and
therefore, it is recommended that the power rating be deter-
mined at the specific operating conditions of the device
according to procedure described in this document, rather
than estimated from a power de-rating chart.
9.2 Hazards
During testing, a high voltage and current may
be present. The experimental set-up must be properly insu-
lated with wiring properly grounded to minimize the possibility
of electrical shock. This test may cause burning of the resis-
tive material, which in turn may produce hazardous sub-
stances resulting from material decomposition and possible
subsequent chemical reactions. In all cases, the exposure lim-
its and guidance that are set by government agencies should
be observed.
The Notes section is to be used to discuss any special con-
siderations, or detail other reference documents necessary or
recommended for the test. This section should include any
safety precautions, hazard information, or warning statements
necessary for the safe completion of the test method. This
section should also be used to show sources of obtaining
specialized test apparatus or materials for the test.
10 References and Contact Information
Jan Obrzut, National Institute of Standards and Technology
(NIST), jan.obrzut@nist.gov;
Jason Ferguson, Naval Surface Warfare Center (NSWC
Crane), jason.ferguson@navi.mil;
Michael Azarian, Center for Advanced Life Cycle Engineering
(CALCE), University of Maryland, mazarian@umd.edu.
Number
2.5.34
Subject
Power Density Rating for Embedded Resistors
Date
07/12
Revision
IPC-TM-650
Page
4
of
4
1 Scope
The fungus resistance test is used to determine
the resistance of materials to fungi and to determine if such
material is adversely affected by fungi under conditions favor-
able for their development, namely high humidity, warm atmo-
sphere, and presence of inorganic salts.
2 Applicable Documents
None
3 Test Specimen
Specimens must be a minimum size of
50 mm x 50 mm [1.97 in x 1.97 in] with copper foil (if appli-
cable) removed by etching using standard commercial prac-
tices.
4 Apparatus and Reagents
4.1 Test Chamber
The incubator shall be capable of main-
taining 30 ± 1 °C [86 ± 2 °F] and 95 ± 2% relative humidity
and have an ultraviolet (360 nm) source for subsequent
decontamination. Provisions shall be made to prevent con-
densation from dripping on the test item. There shall be free
circulation of air around the test item and the contact area of
fixtures supporting the test item shall be kept to a minimum.
4.2 Sterilizer
4.3 Centrifuge
4.4 pH Meter
4.5 Colony Counter
4.6 Incubator
4.7 Dishwasher
4.8 Petri Dishes
4.9 Filter Paper
4.10 Media Solutions
4.11 Microorganisms
4.12 Atomizer, 15,000 ± 3000 spores
5 Procedures
5.1 Preparation of Test Media
5.1.1 Mineral-Salts Solution
Prepare the solution to contain the following:
Potassium dihydrogen orthophosphate (KH
2
PO
4
) .......... 0.7g
Potassium monohydrogen orthophosphate (K
2
HPO
4
) ... 0.7g
Magnesium sulfate heptahydrate (MgSO
4
c7H
2
O) ........... 0.7g
Ammonium Nitrate (NH
4
NO
3
) ......................................... 1.0g
Sodium chloride (NaCl) .............................................. 0.005g
Ferrous sulfate heptahydrate (FeSO
4
c7H
2
O) ............... 0.002g
Zinc sulfate heptahydrate (ZnSO
4
c7H
2
O) .................... 0.002g
Manganous sulfate monohydrate (MnSO
4
cH
2
O) ......... 0.001g
Distilled water ........................................................... 1000 ml
Sterilize the mineral salt solution by incubating at 121 °C [250
°F] for a minimum of 20 minutes. Adjust the pH of the solution
by the addition of 0.01 normal solution of NaOH so that after
sterilization the pH is between 6.0 and 6.5. Prepare sufficient
salt solutions for the required tests.
5.1.2 Purity of Reagents
Reagent grade chemicals shall
be used in all tests. Unless otherwise specified, it is intended
that all reagents shall conform to the specification of the Com-
mittee on Analytical Reagents of the American Chemical Soci-
ety, where such specifications are available.
5.1.3 Purity of Water
Unless otherwise specified, refer-
ences to water shall be understood to mean distilled water or
water of equal purity.
5.1.4 Preparation of Mixed Spore Suspension
The following test fungi shall be used:
Description .................................................................. ATCC
Aspergillus niger ............................................................ 9642
Chaetomium globosum ................................................. 6205
Gliocladium virens ......................................................... 9645
Aureobasidium pullulans ............................................... 9348
Penicillium funiculosum ................................................. 9644
5.1.5
Maintain cultures of these fungi separately on an
appropriate medium such as potato dextrose agar. However,
the culture of Chaetomium globosum shall be cultured on
3000 Lakeside Drive, Suite 309S
Bannockburn, IL 60015-1249
IPC-TM-650
TEST METHODS MANUAL
Number
2.6.1
Subject
Fungus Resistance of Printed Board Materials
Date
03/07
Revision
G
Originating Task Group
Solder Mask Performance Task Group (5-33b)
ASSOCIATION CONNECTING
ELECTRONICS INDUSTRIES
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strips of filter paper on the surface of mineral salts agar. (Min-
eral salt agar is identical to mineral salt solution, but contains
an additional 15.0 g of agar per liter.)
5.1.6
The stock cultures may not be kept longer than four
months at 6 ± 4 °C [43 ± 7 °F] at which time subcultures shall
be made and new stocks shall be selected from the subcul-
tures.
5.1.7
If genetic or physiological changes occur in the cul-
ture, obtain new cultures in accordance with 5.1.4. Sub-
cultures used for preparing new stock cultures or the spore
suspension shall be incubated at 30 °C ± 1 °C [86 °F ± 2 °F]
for at least nine days.
5.1.8 Prepartion of Spore Suspension
5.1.8.1
Pour 10 ml of a sterile solution containing about
0.05 g/L of a nontoxic wetting agent such as sodium dioctyl
sulfosuccinate or sodium lauryl sulphate into one culture of
each fungus.
5.1.8.2
Use a sterile platinum or nichrome inoculating wire
to free the fungus from the culture medium by gently scraping
the surface growth of the agar from the culture of the medium.
5.1.8.3
Pour the spore suspension into a sterile 125-ml
glass-stoppered Erlenmeyer flask containing 45 ml of sterile
water and 50 to 75 solid glass beads, 5.0 mm [0.197 in] in
diameter.
5.1.8.4
Shake the flask vigorously to liberate the spores
from the fruiting bodies and to break the spore clumps.
5.1.8.5
Filter the dispersed fungal spore suspension through
a 6 mm layer of glass wool contained in a glass funnel and
collect into a sterile flask. This process should remove large
mycelial fragments and clumps of agar which could interfere
with the spraying process.
5.1.8.6
Centrifuge the filtered spore suspension and discard
the supernatant liquid.
5.1.8.7
Resuspend the residue in 50 ml of sterile water and
centrifuge.
5.1.8.8
Wash the spores obtained from each of the fungi in
this manner three times.
5.1.8.9
Dilute the final washed suspension with sterile
mineral-salt solution such that the resultant spore suspension
contains 1,000,000 ± 200,000 spores per ml as determined
with a colony counter.
5.1.9
Repeat the steps in 5.1.8 for each organism used in
the test and blend equal volumes of the resultant spore sus-
pension to obtain the final mixed spore suspension. The spore
suspension may be prepared fresh each day or may be held
at 6 ± 4 °C [43 ± 7 °F] for not more than seven days.
5.2 Viability of Inoculum Control
With each daily group
of tests, place one piece of sterilized filter paper, 2.5 cm [1.0
in] square, on hardened mineral-salt agar in three separate
Petri dishes. Inoculate these dishes with the spore suspension
by spraying the suspension from a sterilized atomizer until
initiation of droplet coalescence. Incubate these at 30 ± 1 °C
[86 ± 2 °F] at a relative humidity not less than 85% and exam-
ine them after seven days of incubation. There shall be copi-
ous growth on all three of the filter paper control specimens.
Absence of such growth requires repetition of the test.
5.3 Control Items
5.3.1
In addition to the viability of inoculum control, known
susceptible substrates shall be inoculated along with the test
item to insure that proper conditions are present in the incu-
bation chamber to promote fungus growth.
5.3.2
The control items shall consist of 284.5 g/m
2
[8.25-oz]
bleached, scoured, 5 cm [2 in] long cotton duck strips, that
have been dipped into a solution containing 10% glycerol,
0.1% potassium dihydrogen orthophosphate (KH
2
PO
4
), 0.1%
ammonium nitrate (NH
4
NO
3
), 0.025% magnesium sulfate
(MgSO
4
7H
2
O), and 0.05% yeast extract (pH 5.3), from which
the excess liquid has been removed.
5.3.3
The strips should be hung to air dry before being
inoculated and placed into the chamber.
5.4 Inoculation of Test and Control Item
5.4.1
Mount the test and control items on suitable fixtures or
suspend from hangers. No cleaning of the test item shall be
permitted for 72 hours prior to the beginning of the fungus
test. Equipment handling prior to and during the fungus test
shall be accomplished without contamination of the equip-
ment.
Number
2.6.1
Subject
Fungus Resistance of Printed Board Materials
Date
03/07
Revision
G
IPC-TM-650
Page
2
of
3