GORE® EMI Shielding

Transcription

GORE® EMI Shielding

GORE EMI Shielding
®
MATERIALS
Technical Note
Performance Testing - GS8000 Series
Executive Summary
This report describes the performance testing conducted on GORE® EMI Shielding Materials – GS8000 Series (hereafter referred
to as GS8000) and another material (Sample A) and compares the results. Both materials are based on conductive foam and
have a similar appearance. The materials were tested simultaneously using the same protocols. Test results showed that GS8000
performed well over a wide gap range, with recoverability and stable performance over time. In comparison, the test results showed
that Sample A did not provide the same performance.
For a grounding pad to have a wide working range, it must provide a low DC resistance path over a wide gap range. The test results
showed that GS8000 provided less than a 250 milliohm DC resistance over the entire gap range that was tested. The DC resistance
values for Sample A fell below 250 milliohms only within a narrow range of gap distances. Thus, GS8000 demonstrated a much
wider working range than Sample A.
For grounding pads to maintain performance after open/close cycling, they must recover from compression. The test results
showed that GS8000 rebounded from the recommended compression height approximately 2 to 8 times more than Sample A.
In this testing, Sample A materials took a very severe compression set, which could lead to performance issues after open/close
cycling.
To compare performance over time, Accelerated Life Testing was conducted using a standard humidity chamber test. Through this
testing, GS8000 maintained or even reduced its DC resistance with exposure. However, DC resistance of Sample A increased in
a highly variable manner. Thus, it is expected that GS8000 would deliver more consistent performance through service life than
Sample A.
Testing Methods
The following tests were performed to characterize both GS8000 and Sample A:
• Force-Displacement-Resistance (FDR) Testing, per Modified EM2 WI-10502 (see Appendix A)
• Recoverability Testing, per ASTM D395 Method B, "Compression Set Under Constant Deflection in Air"
• Accelerated Life Testing (ALT) for DC Resistance
To ensure comparable results among the tests, 5 mm x 5 mm pads of both materials were used in each test:
Gore: GS8000-03X
GS8000-063
GS8000-126
Sample A: 0.7 mm thick
1.5 mm thick
3.0 mm thick
W. L. Gore & Associates, Inc.
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GORE EMI Shielding Materials
®
Performance Testing GS8000 Series
Force-Displacement-Resistance (FDR) Testing
1. Test Equipment
• Keithley Model 580 Micro-ohmmeter
• Gold-Plated Anvils with 4-point Probe Connected (see Appendix B for photo)
• Instron Single Column Tabletop Universal Test Machine Model 5542
2. Test Procedure
See Appendix A for a detailed description of the test procedure used: Modified EM2 WI-10502 Rev A, SMT - Supersoft
Compression Resistance Test Method.
In previous testing, the recommended compression stop of GS8000 grounding pads was determined as shown in Figure 1:
Recommended Compression Stop
Material
(mm)
(in)
GS8000-03X
0.30
0.012
GS8000-063
0.60
0.024
GS8000-126
1.40
0.055
Figure 1: GS8000 recommended compression stop
The working ranges of Sample A were determined by reading the height data from the FDR curves at the 5 psi and 100 psi
points. An average of these 2 points was calculated to identify a proposed recommended compression stop as shown in Figure 2:
Recommended Compression
Stop
100 psi
Material
5 psi
(mm)
(in)
(mm)
(in)
(mm)
(in)
0.7 mm Sample A
0.19
0.007
0.31
0.012
0.43
0.017
1.5 mm Sample A
0.35
0.014
0.61
0.024
0.86
0.034
3.0 mm Sample A
0.39
0.015
0.65
0.025
0.90
0.035
Figure 2: Sample A observed working range and calculated recommended compression stop
3. Test Results
The following graphs show the results of the FDR testing. Each pairing of materials represents the most closely matched
set of working ranges associated with the thickness of the samples. This pairing allows comparison of materials for the gap
range, and upper and lower compression limits of a specific application; a concept Gore refers to as fitness for use.
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0.95
0.90
Sample A Stress
0.85
GS8000-03X Stress
0.80
Sample A DCR
1.00
0.75
2200
(319.1)
2090
(304.6)
1980
(290.1)
1870
1760
2200
1650
GS8000-03X DCR
0.95
0.70
DC Resistance (Ohms)
Material Force Displacement Resistance (FDR)
Testing Done with 5 x 5 mm Ground pads
Sample A Material, Gore GS8000-03X Material
2090
1540
0.90
0.65
Sample A Stress
0.85
0.60
GS8000-03X Stress
1870
1320
0.80
0.55
Sample A DCR
1760
1210
0.75
0.50
1980
1430
1650
1100
GS8000-03X DCR
0.70
0.45
1540
990
0.65
0.40
1430
880
0.60
0.35
1320
770
0.55
0.30
1210
660
0.50
0.25
1100
550
0.45
0.20
990
440
0.40
0.15
880
330
0.35
0.10
770
220
0.30
0.05
660
110
0.25
0.00
mm
0.200.70
0.65
.028
in.0.15
0.60
0.55
0.50
.024
0.45
.020
0.40
.016
0.10
0.35
0.30
0.25
0.20
.012
Compressed Gap
0.15
.008
0.10
0.05
.004
110
0.65
in. .028
0.60
0.55
0.50
.024
0.45
0.40
.020
.016
0.35
0.30
0.25
0.20
.012
Compressed Gap
0.15
.008
0.10
0.05
.004
(261.1)
(246.6)
(319.1)
(232.1)
(304.6)
(217.6)
(290.1)
(203.1)
(275.6)
(188.5)
(261.1)
(174.0)
(246.6)
(159.5)
(232.1)
(145.0)
(217.6)
(130.5)
(203.1)
(116.0)
(188.5)
(101.5)
(174.0)
(87.0)
(159.5)
(72.5)
(145.0)
(58).0
(130.5)
(43.5)
(116.0)
(29.0)
(101.5)
(14.5)
(87.0)
550
0
(72.5)
0.00440 mm
(58).0
.000 330 in.
(43.5)
220
(29.0)
0.05
0.00
mm 0.70
(275.6)
Stress kPa
(PSI)
1.00
Stress kPa
(PSI)
Sample A Material, Gore GS8000-03X Material
®
0
0.00
.000
(14.5)
mm
in.
Figure 3: FDR curves of GS8000-03X vs. 0.7 mm Sample A
Sample A Material, Gore GS8000-063 Material
0.90
0.85
0.80
1.00
0.75
0.95
0.70
0.90
0.65
0.85
0.60
0.80
0.55
0.75
0.50
0.70
0.45
0.65
0.40
0.60
0.35
0.55
0.30
0.50
0.25
0.45
0.20
0.40
0.15
0.35
0.10
0.30
0.05
0.25
0.00
0.20
1.50
mm
0.15
in.
.059
0.10
GS8000-063 Stress
Sample A DCR
GS8000-063 DCR
Sample A Stress
GS8000-063 Stress
Sample A DCR
GS8000-063 DCR
1.40
1.30
.051
1.20
.047
1.10
.043
1.00
.039
0.90
.035
in.
.059
0.70
.028
0.60
.024
0.50
.020
0.40
.016
0.30
.012
0.20
.008
0.10
.004
Compressed Gap
0.05
0.00
1.50
mm
0.80
.031
1.40
.055
1.30
.051
1.20
.047
.039
.035
.031
.028
Compressed Gap
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(304.6)
1980
(290.1)
.024
.020
.016
.012
0.20
.008
0.10
.004
(275.6)
(261.1)
1760
(319.1)
2200 (246.6)
1650 (304.6)
2090 (232.1)
1540 (290.1)
1980 (217.6)
1430 (275.6)
1870 (203.1)
(261.1)
1320 (188.5)
1760
(246.6)
1210 (174.0)
1650
(232.1)
1100 (159.5)
1540
(217.6)
(145.0)
990
1430
(203.1)
(130.5)
880
1320 (188.5)
(116.0)
770
1210 (174.0)
(101.5)
660
(159.5)
1100 (87.0)
550
(145.0)
990
(72.5)
440
(130.5)
880
(58).0
330
(116.0)
(43.5)
770
(101.5)
220
(29.0)
660
(87.0)
110
(14.5)
550
(72.5)
0
440
0.00 mm(58).0
330
in. (43.5)
.000
220
(29.0)
110
1.10
1.00
0.70
0.60
0.50
0.30
Figure
4:
FDR0.90
curves0.80
of GS8000-063
vs. 1.5
mm0.40
Sample
A
.043
(319.1)
2090
1870
Sample A Stress
.055
2200
(14.5)
0
0.00 mm
.000
in.
Stress kPa
(PSI)
0.95
Stress kPa
(PSI)
1.00
®
0.95
0.90
0.85
0.80
0.75
0.70
2200
2090
Sample A Stress
1980
1870
GS8000-126 Stress
1760
Sample A DCR
1650
1540
GS8000-126 DCR
0.65
1430
0.60
1320
0.55
1210
0.50
1100
0.45
990
0.40
880
0.35
770
0.30
660
0.25
550
0.20
440
0.15
330
0.10
220
0.05
110
0.00
0
mm 2.4 2.3 2.2 2.1 2.0 1.9 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0
.091 .087 .083 .079 .075 .071 .067 .063 .059 .055 .051 .047 .043 .039 .035 .031 .028 .024 .020 .016 .012 .008 .004 .000
in.
(319.1)
(304.6)
(290.1)
(275.6)
(261.1)
(246.6)
(232.1)
(217.6)
(203.1)
(188.5)
(174.0)
(159.5)
(145.0)
(130.5)
(116.0)
(101.5)
(87.0)
Stress kPa
(PSI)
1.00
(72.5)
(58).0
(43.5)
(29.0)
(14.5)
mm
in.
Compressed Gap
Figure 5: FDR curves of GS8000-126 vs. 3.0 mm Sample A
4. Summary
GS8000 grounding pads have a much more consistent performance over a wider range of gap heights. As demonstrated by all
3 FDR comparisons, the DC resistance of GS8000 was already low at the initial test points in the curve. These results indicated
that GS8000 performed as intended with very little compression, effectively broadening the design gap range as well as the
acceptable tolerance of this proposed gap. This versatility can provide engineers more flexibility to meet design requirements.
Recoverability Testing
Recoverability is the inverse of compression set. For EMI shielding materials, recoverability is a measure of the material's ability
to fill the gap following a release of a load that has compressed the material. Filling the gap ensures that the electrical path is
maintained when compression is removed and then reestablished, which is indicative of an open/close cycle. If the electrical
device will be tuned during initial production or serviced with hardware upgrades and field repairs, the ability of the gap-filling
material to rebound and create a consistent connection following an open/close cycle is critical to performance requirements.
1. Test Equipment
• ASTM D395B Compression Fixtures (see Appendix B for photo)
• Aloma Stainless Steel Precision Shims
• VWR Scientific Products Model 1670 HAFO Series Oven
• Mitutoyo Model ID-C1012CEX, Low Measuring Force Digimatic Indicator (see Appendix B for photo)
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2. Test Procedure
ASTM D395 B "Standard Test Methods for Rubber Property, Test Method B – Compression Set Under Constant Deflection in Air"
a) The free height of each test sample was measured using a low force digital indicator.
b) Compression fixtures were prepared with precision shims to set the gap distance to the recommended compression stop.
c) Test samples were inserted into the compression fixtures, and the bolts were tightened to a defined torque providing
consistent clamping force.
d) Two sets of samples were aged as follows:
• One set at 70˚C dry heat for 22 hours
• One set at 70˚C dry heat for 70 hours
e) Upon removal from the oven, the samples were immediately removed from the compression fixtures and allowed to stand at
room temperature for 30 minutes.
f) The height of each sample was re-measured and compared to its initial height to characterize recoverability.
3. Test Results
Figures 6–8 show the recovery percentage for the different material sets at the two durations specified in the test protocol.
Recoverability Test, ASTM D395 B
GS8000-03X vs. 0.7 mm Sample A
Compressed to RCS
Sample A 0.7 mm
GS8000-063
8%
14%
7%
12%
6%
Percent Recovery
Percent Recovery
GS8000-03X
GS8000-063 vs. 1.5 mm Sample A
Compressed to RCS
5%
4%
3%
2%
10%
8%
6%
4%
1%
2%
0%
0%
22 hrs
70 hrs
Sample A 1.5 mm
22 hrs
70 hrs
Duration
Duration
Figure 6: Recoverability of GS8000-03X and 0.7 mm Sample A
Figure 7: Recoverability of GS8000-063 and 1.5 mm Sample A
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®
GS8000-126 vs. 3.0 mm Sample A
Compressed to RCS
GS8000-126
Sample A 3.0 mm
20%
18%
Percent Recovery
16%
14%
12%
10%
8%
6%
4%
2%
0%
70 hrs
22 hrs
Duration
Figure 8: Recoverability of GS8000-126 and 3.0 mm Sample A
4. Summary
Sample A took a severe set compared to GS8000. It could be seen that GS8000 recovered approximately 2 to 8 times greater
than Sample A. This ability to recover is significant because the devices using these grounding pads have the potential for
multiple open/close cycles over their lifetime.
Accelerated Life Testing (ALT) for DC Resistance
1. Test Equipment
• Keithley Model 580 Micro-ohmmeter
• Gold-Plated Anvils with 4-point Probe Connected (see Appendix B for photo)
• FR4 Test Boards with Open Gold Trace (see Appendix B for photo)
• Aloma Stainless Steel Precision Shims
• Blue M Electric Humid Flow Humidity Chamber, Model: AC-7602TDA-4-A
2. Test Procedure
a) 5 mm x 5 mm pads were affixed to the gold traces of test boards and placed on base compression blocks.
b) Shims were placed on the alignment posts to provide a compression stop at the recommended compression distance.
c) A mating test board was placed onto the base compression block with the gold trace contacting the pad.
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®
d) The upper compression block was placed on the alignment posts, and the screws were tightened to 40 in-lbs.
e) 4-point probes were placed on each of the traces of the test boards to measure the DC resistance through the traces and the
pad. These DCR measurements were recorded as the pre-ALT measurements.
f) The compression block assemblies were placed into a humidity chamber for 5 days at 85˚C and 85% relative humidity.
g) The compression block assemblies were removed and allowed to cool for 30 minutes.
h) The DC resistance was measured in the same way as for the initial DCR measurements and recorded as the post-ALT
measurements.
i) Analysis was performed to determine the change between the initial and the final DCR measurements.
3. Test Results
Figure 9 shows the results of the Accelerated Life Testing (ALT) performed for the 6 samples. The variability was determined as
the percentage of change between the pre-ALT and post-ALT measurements.
Variability Chart for % DCR Change over ALT
Figure 9: Variability for DCR Change of GS8000 and Sample A before and after ALT testing
4. Summary
The variability demonstrated in the testing of Sample A materials was significant. While the DC resistance of GS8000 remained
stable with little change over time and temperature, the DC resistance of Sample A materials degraded. Because of the
variability of the degradation, the performance of Sample A would be expected to get worse by an indeterminate amount for
any application.
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®
Conclusion
When designing electrical devices, it is important to consider the performance of the components over time. When comparing test
results of GS8000 with a similar material (Sample A), GS8000 clearly demonstrated performance advantages. GS8000 provided
very good DCR over a much wider gap range, enabling very low DCR connections with a larger allowable tolerance range of the
mating surfaces. In addition, the data showed that GS8000 remained consistent over time and temperature, allowing devices to
reach their life expectations without performance degradation. Finally, GS8000 recovered from compression significantly better
than the Sample A material did. Overall the tests proved that GS8000 performed significantly better than Sample A, with better
electrical performance over gap range, recoverability, and performance over time.
GORE and designs are trademarks of W. L. Gore & Associates ©2012 W. L. Gore & Associates, Inc. TNGS8000-20120502
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®
Appendix A:
Force-Displacement-Resistance (FDR) Testing, per Modified EM2 WI-10502 Rev A,
SMT - Supersoft Compression Resistance Test Method
Assembling Test Fixture
Install the test fixture by bolting the fixture base to the machine base and inserting the upper probe into the tool mount.
Calibrating Load Cell
1. Ensure that the proper load cell is mounted in the Instron.
2. Run the calibration program to ensure proper set-up of the machine.
Testing Parts
1. Set the gauge length for parts to 2.6 mm.
a. Balance (zero) the load cell.
b. Bring the anvils close together using the jog button. Then use the fine-position adjustment until the load is just touching.
Use the fine-position to separate one "click" so the anvils are sitting just before there is a load.
c. Reset the gauge length to zero.
d. Jog the anvils apart until they read 2.6 mm. Then reset the gauge length to zero.
2. Place the test part in the center of the anvil bottom, adhesive side down.
3. Click Start Test.
4. The Instron will slowly lower and return data points for Ohms and Force.
5. Remove and discard the tested piece.
6. Continue to the next part testing until samples are completed.
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®
Appendix B: Test Equipment
FDR Testing
Recoverability Testing
Gold-Plated Anvils with 4-point Probe Connected
Mitutoyo Model ID-C1012CEX, Low Measuring
Force Digimatic Indicator
Accelerated Life Testing for DC Resistance
FR4 Test Boards with Open Gold Trace
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ASTM D395B Compression Fixtures
Page 10

GORE® EMI Shielding

Transcription

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