Download EIA-977 - Test Methods for Resistance to Environmental Sulfur

ANSI/EIA-977-2016
Approved:
EIA-977
EIA
STANDARD
Test Method – Electronic Passive
Components Exposure to
Atmospheric Sulfur
EIA-977
2016
Electronic Components Industry Association
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(From Standards Proposal No. 5317, formulated under the cognizance of the P-1
Committee on EIA National Resistive Devices Standards).
Published by
©Electronic Components Industry Association 2016
EIA Standards & Technology Department
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Herndon, VA 20170
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Contents
1.
SCOPE .................................................................................................................................................................1
2.
REFERENCED DOCUMENTS ........................................................................................................................1
3.
APPARATUS AND MATERIALS ....................................................................................................................1
4.
GENERAL PROCEDURE ................................................................................................................................3
5.
SPECIFIC TEST PROCEDURES ....................................................................................................................5
6.
DETAILS TO BE SPECIFIED ..........................................................................................................................7
7.
DOCUMENTATION ..........................................................................................................................................7
Table 1 – Resistance to Environmental Sulfur Test Conditions ..............................................................................4
Figure 1: Typical Test Setup .......................................................................................................................................3
i
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Test Method –
Electronic Passive Components Exposure to Atmospheric Sulfur
(From EIA Standards Proposal No. 5317, formulated under the cognizance of the P-1 Committee
on EIA National Resistive Devices Standards).
1. SCOPE
This standard defines options for testing electronic components for susceptibility to the
effects of environmental sulfur. Such susceptibility results in the corrosion of elemental
metals, such as silver, in the presence of sulfur compounds in a liquid or gaseous state,
potentially leading to component failure.
2. REFERENCED DOCUMENTS
The current revision of the referenced documents in effect at the date of agreement to the test
plan shall be used. Subsequent test plans will automatically use the latest revision of these
referenced documents.
2.1. ASTM B 809: Standard Test Method for Porosity in Metallic Coatings by Humid
Sulfur Vapor (“Flowers of Sulfur”).
3. APPARATUS AND MATERIALS
3.1. Test Specimen – The component to be tested, typically surface mount resistors or other
components containing silver.
3.2. Control Sample – A silver coupon to be suspended in the test container by means of a
non-corroding material such as nylon line. This control sample is used to confirm the
presence of a sulfur vapor in the test container.
3.3. Dish – A Petri or other shallow dish approximately 15 cm (6 in) in diameter to hold
powdered sulfur. If a large test vessel is used and the silver control coupon does not
blacken (tarnish) from exposure to sulfur within 24 hours, a larger diameter shallow
container may be needed to accommodate additional sulfur.
3.4. Reagent – Sulfur, Sublimed (“Flowers-of-Sulfur”) powder, CAS No. 7704-34-9, N.F.
or laboratory grade.
3.4.1. Sulfur placement in Petri dish – A layer of sulfur approximately 10 mm (approx.
0.39 in) thick shall be placed in the Petri dish such that it covers the entire bottom
surface of the container.
3.4.2. Reuse of reagent – It is recommended that the sulfur be replaced with fresh
material each test, however, the reagent may potentially be used for multiple tests
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by using the corrosion of the silver control specimen as an indicator that the
reagent must be replaced. If the control specimen does not blacken (tarnish) from
sulfur exposure within 24 hours (per the definition in Section 4.5), the reagent
must be replaced.
3.5. Test Container – Any conveniently-sized vessel of glass, polycarbonate, stainless steel
(or any other material) that is not affected by sulfur vapor and elevated temperatures
may be used as the test container. The size of the test samples will dictate the required
size of the container. For small components such as chip resistors, a glass desiccator of
9 to 10L capacity will be sufficient. The vessel does not need to be hermetically sealed
and may have a small vent opening (1 to 4 mm diameter hole) to allow equalization of
pressure when elevated temperatures are present.
3.5.1. Large test containers – Larger vessels may be required to accommodate test
boards and Printed Circuit Board Assemblies (PCAs). If a large test container is
used and the silver coupon does not blacken (tarnish) from sulfur exposure
within 24 hours (per the definition in Section 4.5), a larger diameter Petri dish and
additional sulfur may be needed (Sections 5.1 and 5.2).
3.6 Convection Oven or Hot Plate– A convection oven or hot plate may be used to maintain
the required temperature inside the test container.
3.7 Thermocouples – Thermocouples are used to monitor and control the temperature inside
the test container.
3.8 DC Resistance Test Setup – A resistance bridge or multi-meter and appropriate test
probes capable of providing resistance measurements within specified tolerances. This
setup shall not apply a voltage greater than a value that exceeds the smaller of 50 mW of
power or 5% of the test sample’s rated power.
3.9 Microscope – An optical microscope capable of up to 50X magnification.
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Figure 1: Typical Test Setup
4. GENERAL PROCEDURE
4.1. Choice of test procedure – The user and supplier must agree as to which of the two sets
of test conditions will be applied, A or B.
4.2. Mounting – Unless otherwise specified in the individual specification or by customer
request, samples shall be mounted to a printed wiring test board. If the components are
to be placed as loose samples inside the test container, the surface of interest (typically
those containing silver) should have unobstructed exposure to the sulfur environment.
4.3. Test sample documentation – All relevant parameters from the component placement
and soldering operation shall be recorded, including but not limited to: solder and flux
materials, soldering temperature or profile, and component placement method.
4.4. Test sample cleaning – After the components are soldered to the printed wiring board,
the test specimens shall be cleaned in order to remove contamination that might affect
the corrosion resistance results of the component itself. Cleaning requirements and
conditions shall be adequate to remove all residual flux and ionic contamination. The
cleaning requirements and conditions may be AABUS (as agreed by user and supplier).
4.5. Control sample – A silver coupon sample shall be suspended in the test container by a
nylon line or other non-corroding material during the test to confirm the severity of the
environment.
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4.6. Initial Measurements – Unless otherwise specified, initial measurements of the samples
to be tested shall be made and recorded. It is expected that the initial measurement of
each sample unit will be within the specified nominal tolerance.
4.7. Exposure – The samples shall be placed in the test container and subjected to the test
conditions according to Condition A (Section 5.1) or B (Section 5.2) chosen from Table
I below. The parameters given for each test condition are default parameters.
Deviations to the given parameters shall be as agreed by user and supplier and shall be
documented in the test report.
Table 1 – Resistance to Environmental Sulfur Test Conditions
Test Conditions
Test Parameters
Temperature
Humidity
Duration
Reagent
Amount of Reagent
Component Sample Size
Sample Nominal
Resistance Value
Sample Tolerance
Mounted on PCB
Failure Criteria
1.
A1
60 ± 2°C (140°F±3.6°F)
Not applicable
480 Hours
Sulfur, Sublimed (Flowers of Sulfur, or FoS).
The sulfur shall be placed on a tray at the bottom of the
chamber or on the base of the chamber. Cover the tray or
base of the chamber with a bed of sulfur to 10 mm depth
minimum. The greater the amount of sulfur placed in the
chamber, the faster the sulfur in the chamber air will reach
equilibrium.
22 units. The case size to be qualified will be 0402 or
smallest size available larger than 0402 or AABUS (As
Agreed By User and Supplier).
B
105°C ± 2°C (221°F±3.6°F)
Not applicable
750 hours
Sulfur, Sublimed (Flowers of Sulfur, or FoS).
The sulfur shall be placed on a tray at the bottom of the
chamber or on the base of the chamber. Cover the tray or
base of the chamber with a bed of sulfur to 10 mm depth
minimum. The greater the amount of sulfur placed in the
chamber, the faster the sulfur in the chamber air will reach
equilibrium.
15 units each from 3 different production lots (of the same
style, termination design and manufactured under the
same process and conditions with the same materials. )
The case size to be qualified will be 0402 or smallest size
available larger than 0402 or AABUS (As Agreed By User and
Supplier).
Lowest available resistance value for the series being
qualified or AABUS
Nominal tolerance to be qualified.
Yes
Lowest available resistance value for the series being
qualified or AABUS
Nominal tolerance to be qualified.
Yes
A) Using 50X magnification, any Ag2S growth present at the
interface between any end termination and the protective
Shift in resistance (ΔR) greater than nominal tolerance.
overcoat, OR B) Shift in resistance (ΔR) greater than
Thus a resistance shift of > ±1% for a 1% tolerance
nominal tolerance. Thus a resistance shift of > ±1% for a
component or > ±5% for a 5% tolerance component .
1% tolerance component or > ±5% for a 5% tolerance
component .
Test conditions based on modification of ASTM B 809.
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5. SPECIFIC TEST PROCEDURES
5.1. Test Condition “A”
5.1.1. Test Container Temperature Control
5.1.1.1.
It is recommended that the test container temperature be controlled by
placing it in a larger convection oven.
5.1.1.2.
Thermocouples connected to the temperature controller should be placed
in close proximity to the test samples.
5.1.1.3.
Properly placed flat heating elements (hot plate heaters) may be used on
the exterior of the test container if the test container temperature can be
controlled to ±2°C consistently throughout the test container.
5.1.1.4.
It is highly recommended that proportional temperature controllers with
safety temperature limit shutoff be used for heating larger test containers.
5.1.2. Test container humidity is not actively controlled because the formation of silver
sulfide (Ag2S) occurs independent of the relative humidity.
5.1.3. Samples shall be exposed for 480 hours in the test container maintained at
60°C±2°C (140°F±3.6°F).
5.1.4. Monitoring control sample
5.1.4.1.
The silver coupon control sample shall be visually inspected (if possible,
from outside of the test container) 24 hours after a test is begun.
5.1.4.2.
The silver coupon must blacken (tarnish) from exposure to sulfur within
24 hours.
5.1.4.3.
If the silver coupon does not completely blacken (tarnish) from sulfur
exposure within 24 hours, additional or fresh sulfur shall be added and the test
shall be restarted.
5.1.4.4.
The silver coupon shall remain in the test container for the duration of the
test to avoid disrupting the equilibrium within the container.
5.1.5. Applied bias
5.1.5.1. Bias shall not be applied to any test sample during the test.
5.1.5.2. If resistance measurements are being used for sample monitoring and/or
inspection, the applied voltage must not cause local heating of the test
component because of the strong effect of temperature on the sulfuration
chemical reaction and local sulfur vapor concentration. The applied voltage
shall not be greater than a value that exceeds the smaller of 50 mW of power
or 5% of the test sample’s rated power.
5.1.6. Sample Inspection and Testing
5.1.6.1. After exposure, components shall be examined using a microscope with
adjustable magnifications to 50X.
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5.1.6.1.1. Higher magnifications may be necessary, including the use of scanning
electron microscope, for more critical applications.
5.1.6.1.2. Any observable growths of silver sulfide crystals (Ag2S) must be
recorded.
5.1.6.2. All components shall be tested for DC resistance and the measurements
recorded.
5.1.6.3. Failure criteria
5.1.6.3.1.
Microscopic inspection at 50X reveals the presence of any amount
of Ag2S crystals at the interface between any end termination and the
protective overcoat, or
5.1.6.3.2.
The change in DC resistance is greater than the nominal tolerance.
(For instance, a resistance shift (ΔR) of > ±1% for ±1% tolerance
component, or a shift of >±5% for ±5% tolerance.)
5.1.6.3.3.
A change in resistance due to printed wiring board degradation
shall not be considered a failure and shall be confirmed by directly
measuring the resistance of the test sample.
5.2. Test Condition “B”
5.2.1. Test Container Temperature Control
5.2.1.1.
It is recommended that the test container temperature be controlled by
placing it in a larger convection oven.
5.2.1.2.
Thermocouples connected to the temperature controller should be placed
in close proximity to the test samples.
5.2.1.3.
Flat heating elements (pancake heaters) may be used on the exterior of the
test container if the test container temperature can be controlled to ±2°C
consistently throughout the test container.
5.2.1.4.
It is highly recommended that proportional temperature controllers with
safety temperature limit shutoff be used for heating larger test containers.
5.2.2. Test container humidity is not actively controlled because the formation of silver
sulfide (Ag2S) occurs independent of the relative humidity.
5.2.3. Samples shall be exposed for 750 hours in a test container maintained at
105°C±2°C (221°F±3.6°F).
5.2.4. Monitoring control sample
5.2.4.1.
The silver coupon control sample shall be visually inspected (if possible,
from outside of the test container) 24 hours after a test is begun.
5.2.4.2.
The silver coupon must blacken (tarnish) from exposure to sulfur within
24 hours.
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5.2.4.3.
If the silver coupon does not completely blacken (tarnish) from sulfur
exposure within 24 hours, additional or fresh sulfur shall be added and the test
shall be restarted.
5.2.4.4.
The silver coupon shall remain in the test container for the duration of the
test to avoid disrupting the equilibrium within the container.
5.2.5. Applied bias
5.2.5.1. Bias shall not be applied to any test sample during the test.
5.2.5.2. If resistance measurements are used for sample monitoring and/or
inspection, the applied voltage must not cause local heating of the test
component because of the strong effect of temperature on the sulfuration
chemical reaction and local sulfur vapor concentration. The applied voltage
shall not be greater than a value that exceeds the smaller of 50 mW of power
or 5% of the test sample’s rated power.
5.2.6. Sample Inspection and Testing
5.2.6.1. All components shall be tested for DC resistance and the measurements
recorded.
5.2.6.2. Failure criterion
5.2.6.2.1.
The change in DC resistance is greater than the nominal tolerance.
(For instance, a resistance shift (ΔR) of > ±1% for ±1% tolerance
component, or a shift of > ±5% for ±5% tolerance.)
6. DETAILS TO BE SPECIFIED
The following details shall be specified in the referencing document:
6.1. Test condition to be used (A or B)
6.2. Number of samples
6.3. Sample nominal resistance value
6.4. Sample tolerance
6.5. Mounted on PCB or not
6.6. Failure criteria
7. DOCUMENTATION
Documentation shall contain the details specified and any exceptions:
7.1. Title of the test
7.2. Specimen description, including test fixturing if applicable (photographs may be used)
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7.3. Test equipment used, and date of last and next calibration
7.4. The test condition used
7.5. Values and observations
7.6. Name of operator and test date
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