Solder Joint Reliability Summary Report

Transcription

Project Number: SJR
Tracking Code: TC0623-SEAF-SJR-1059
Requested by: Jeremy Wooldridge
Date: 05/20/2008
Product Rev: D (SEAF), C (SEAM)
Part #: SEAF-50-5.0-S-10-2-A/ SEAM-50-2.0-S-10-2-A
Lot #:
SEAF-50-6.5-S-10-1-A/ SEAM-50-3.5-S-10-1-A
SEAF-50-6.5-S-10-2-A/ SEAM-50-3.5-S-10-2-A
Part description: Single Ended Array Female/ Single Ended Array Male
Test Start: 10/23/2006
Tech: Troy Cook
Eng: Dave Scopelliti
Qty to test: 96
Test Completed: 04/23/2007
SOLDER JOINT RELIABILITY TEST SUMMARY
Solder Joint Reliability Summary Report
PART DESCRIPTION
SEAF-50-5.0-S-10-2-A mated with SEAM-50-2.0-S-10-2-A
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Part description: Single Ended Array
Part #: SEAF/ SEAM
CERTIFICATION
All instruments and measuring equipment were calibrated to National Institute for Standards and Technology (NIST)
traceable standards according to IS0 10012-l and ANSI/NCSL 2540-1, as applicable.
All contents contained herein are the property of Samtec. No portion of this report, in part or in full shall be
reproduced without prior written approval of Samtec.
SCOPE
To perform the following tests: Solder Joint Reliability and life expectancy predictions via Thermal Cycling of TinSilver-Copper (SAC) and Tin-Lead (SnPb).
SAMPLES TESTED
Three groups of SEAF/SEAM connectors were evaluated with stack heights of 7 or 10 mm:
• Group A: SAC, 7 mm stack (SEAF 5.0 mm + SEAM 2.0 mm)
• Group C: SAC, 10 mm stack (SEAF 6.5 mm + SEAM 3.5 mm)
• Group D: SnPb, 10 mm stack (SEAF 6.5 mm + SEAM 3.5 mm)
RELIABILITY PROJECTIONS
1. Life expectancy is calculated for field service conditions of 25ºC to 45ºC and 25ºC to 55ºC cycles
based on lower bound values of Weibull parameters.
2. Field use cycles are calculated at 6 (Cycles/Day) x 365.25 (Days/Year) = 2191.5 Cycles/Year.
TABLE 1a: Reliability projections under field use condition for Groups C & D (10mm mated pairs).
Condition: 25ºC to 45ºC, 6 cycles/day
Years to 0.01% Failed
Group C
SAC
Group D
SnPb
100+ years
99 years
TABLE 1b: Reliability projections under field use condition for Groups C & D (10mm mated pairs).
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Group C
SAC
Group D
SnPb
56 years
11.38 years
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TABLE 2a: Reliability projections under field use condition for Group A (7mm mated pairs).
Group A
SAC
100+ years
TABLE 2b: Reliability projections under field use condition for Group A (7mm mated pairs).
Group A
SAC
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56 years
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APPLICABLE DOCUMENTS
•
Industry Standard: IPC-9701A
•
Clech, J-P., "Acceleration factors and thermal cycling test efficiency for lead-free Sn-Ag-Cu assemblies", Proceedings,
SMTA International Conference, Chicago, IL, Sept. 25-29, 2005, pp. 902-917.
•
Clech, J-P., "An obstacle-controlled creep model for Sn-Pb and Sn-based lead-free solders", Proceedings, SMTA
International Conference, Chicago, IL, September 26-28, 2004.
•
Clech, J-P., “Review and Analysis of Lead-Free Solder Material Properties”, NIST report, on-line version can be viewed
under NIST's Metallurgy Division web site: http://www.metallurgy.nist.gov/solder/clech/
•
Clech, J-P., “Solder Reliability Solutions: a PC-based design-for-reliability tool”, Proceedings, Surface Mount International
Conference, Sept. 8-12, 1996, San Jose, CA, Vol. I, pp. 136-151. Also in Soldering and Surface Mount Technology, Wela
Publications, British Isles, Vol. 9, No. 2, July 1997, pp. 45-54.
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TEST SAMPLES AND PREPARATION
Sample preparation was performed in accordance with paragraph 4.2.3.1 and 4.3.1 of IPC-9701A and the following
test conditions:
1) All materials were manufactured in accordance with the applicable product specification.
2) All test samples were identified and encoded to maintain traceability throughout the test sequences.
3) All components were preconditioned prior to soldering at 125 C for 24 hours.
4) All test PCB’s were preconditioned prior to soldering at 105 C for 24 hours.
5) All samples tested were preconditioned after soldering prior to testing at 100 C for 24 hours.
6) Samtec Test PCBs used: PCB-100504-TST-0X (IS410), IS410, 0.093 inches thick, 6-layer with 70 Cu
coverage on layers 2 and 4, 40% Cu coverage on layers 3 and 5. The pads are finished with Electroless
Nickel Immersion Gold.
TEST BOARD ASSEMBLY
FIGURE 1: Soldering profile for SnPb samples.
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FIGURE 2: Soldering profile for SAC samples.
1) SnPb samples used Kester HM531 Type 3 Solder Paste containing Sn63 Pb37, 90% metal, 325 mesh.
2) SAC samples used Kester R520A Type 3 Solder Paste containing Sn96.5 Ag3.0 Cu0.5, 89.5% metal, 325
mesh.
3) For both SnPb and SAC, stencil thickness was 0.006 inches with aperture diameter of 0.04 inches.
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THERMAL CYCLING:
Thermal Cycling was performed in accordance with Table 4-1 of IPC-9701A and the following test conditions:
1) Thermal Limits: Low Temperature = 0° C +0/- 3° C; High Temperature = 100° C + 5/- 0° C
2) Dwell Time at Thermal Limits: Ten (10) minutes
3) Ramp Time to Thermal Limits: Ten (10) minutes
FIGURE 3: Accelerated thermal cycling profile.
Figure 3 above is a picture of a Thermotron 2 hour temperature graph. Thermocouples are placed in the air of the
chamber and attached to PCB on 5 random samples. The solid line represents the chamber air temperature and the
dotted line represents the temperature on a sample.
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CONFIGURATION
FIGURE 4: Groups A, C, & D consists of 32 mounted mated pair samples each. Group B was mounted but not
tested. Signal routing is daisy-chained through all positions on each sample facilitating 100% contact monitoring.
EVENT DETECTION:
1) Events are established in accordance with Paragraph 4.3.3.3 of IPC-9701A and Table 4-4.
2) An event is defined as a Signal Interruption exceeding 1000 Ω lasting for greater than 200 nanoseconds.
FAILURE CRITERIA:
1) Failures were established in accordance with Paragraph 4.3.3.3 of IPC-9701A and Table 4-4
2) A failure was defined as 10 events within an elapsed time of 10% of the thermal cycles to the initial
event. I.e. if the first event happens at cycle 1000, 9 more events need to happen by cycle 1100.
3) Thermal Cycling was terminated when ≥62% of the product fails or 6000 cycles are completed. This test
was stopped at 5929 cycles because the cooling compressor on the Thermotron chamber failed at that
cycle.
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FLOWCHART
Thermal Cycling for SJR (0 - 100 degrees C)
32 mated assemblies
32 mated assemblies
32 mated assemblies
GROUP A (SE Array)
GROUP C (SE Array)
GROUP D (SE Array)
Lead-Free Paste
Lead-Free Paste
Leaded Paste
IPC-9701A, 32 samples
10 Min Ramp
10 Min dwell at T-Limits
10 Min Ramp
10 Min Ramp
01
Etch ID# on each component
02
Component Conditioning
03
PCB Conditioning
PCB Conditioning
PCB Conditioning
04
Solder components to PCB's
05
Assembly Conditioning
06
X-Ray Analysis of Assemblies
07
Mate and # mated assemblies
08
Measure assembly resistance
09
Solder lead wires to assemblies
10
Orient samples in test chamber
11
Measure assembly resistance through cable/connector
12
Begin thermal cycling
13
Start event detection
14
Cycle chamber 6000x
Cycle chamber 6000x
Cycle chamber 6000x
15
TEST
STEP
16
Cross-Section Analysis of 3 samples Cross-Section Analysis of 3 samples Cross-Section Analysis of 3 samples
from each group
from each group
from each group
FIGURE 5: Flowchart for SJR test.
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RESULTS
Group A (SAC, 7 mm stack assemblies):
Four failures out of 32 monitored daisy chains at 5929 test cycles
Failure Percentage ------------------------------------------------------12.5%
• Failure#1--------------------------------------------------------4919
• Failure#2--------------------------------------------------------5027
• Failure#3--------------------------------------------------------5470
• Failure#4--------------------------------------------------------5752
The Weibull shape parameter was determined using the same β as for SnPb assembly, i.e. β = 4.736
Characteristic life was then estimated from Weibull equation:
% Fail at 1st failure = 1/32 = 1-exp[ -(6917 / α )^4.736 ]
which gives α = 14,331 .
Group C (SAC, 10 mm stack assemblies):
One failure out of 32 monitored daisy chains at 5929 test cycles
• Failure#1--------------------------------------------------------2666
Two-parameter Weibull analysis of failure cycles gives:
Characteristic life: α = Cycles to 63.2% Failures = 11270 cycles
Shape parameter (slope of Weibull distribution): β = 4.736
Group D (SnPb, 10 mm stack assemblies):
Two failure out of 32 monitored daisy chains at 5929 test cycles
• Failure#1--------------------------------------------------------4254
• Failure#2--------------------------------------------------------5691
Two-parameter Weibull analysis of failure cycles gives:
Characteristic life: α = Cycles to 63.2% Failures = 11270 cycles
Shape parameter (slope of Weibull distribution): β = 4.736
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DETERMINING ACCELERATION FACTOR
The acceleration factors were determined in Calculations for Solder Joint Reliability Summary
Report, which is located in the same Mechanical Test Reports section as this report.
MEASURED PATH RESISTANCES OF SAMPLES
Group A Path Resistances, Ω
Minimum
Maximum
Average
St. Dev.
Before Test
3.6
4.6
4.15
0.26
Δ Passed
Samples
0.0
0.7
0.2
0.17
Δ Failed
Samples
0.2
22.0
5.7
10.85
Group D Path Resistances, Ω
Minimum
Maximum
Average
St. Dev.
Before Test
4.2
4.8
4.45
0.16
Δ Passed
Samples
0.0
0.6
0.25
0.15
Δ Failed
Samples
0.0
23.8
11.9
16.83
Group C Path Resistances, Ω
Minimum
Maximum
Average
St. Dev.
Before Test
3.8
4.7
4.34
0.23
Δ Passed
Samples
0.0
0.4
0.1
0.10
Δ Failed
Samples
0.1
0.1
0.1
N/A
FIGURE 7: Path resistances of daisy-chained samples through 18 ft. lead wires.
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CROSS SECTION ANALYSIS
1. Cross sectional metallographic evaluation was performed on all 3 groups of SJR samples. Revealing the
microstructure of the solder joints depicts the cracks that caused failures in samples.
2. Cross sections were taken on:
i. Group A: Three failure samples of SAC, 7 mm stack
ii. Group C: One failure and two passing samples of SAC, 10 mm stack
iii. Group D: Two failures and one passing sample of SnPb, 10 mm stack
FIGURE 8: Sectioning pattern used for Metallographic Evaluation
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FIGURE 9: Photomicrograph showing failed solder joint of Sample #42, Row 1 (7mm Lead-free, failed)
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FIGURE 12: A partial crack showing on a passed solder joint of Sample #81, Row 1 (10mm Lead, passed)
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FIGURE 13: Photomicrograph showing on a failed solder joint of Sample #99, Row 1 (10mm Lead, failed)
FIGURE 14: Photomicrograph showing on a failed solder joint of Sample #105, Row 1 (10mm Lead, failed)
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FIGURE 15: Photomicrograph showing a solder joint of Sample #123, Row 1 (10mm Lead-free, passed)
FIGURE 16: Photomicrograph showing a solder joint of Sample #129, Row 1 (10mm Lead-free, failed)
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FIGURE 17: Photomicrograph showing a solder joint of Sample #148, Row 1 (10mm Lead-free, passed)
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EQUIPMENT AND CALIBRATION SCHEDULES
Equipment #: MM-01
Description: Digital Multimeter
Manufacturer: Fluke
Model: 87 III
Serial #: 74660176
Accuracy: See Manual
… Last Cal: 06/14/07, Next Cal: 06/14/08
Equipment #: THC-02
Description: Temperature/Humidity Chamber
Manufacturer: Thermotron
Model: SE-1000-6-6
Serial #: 31808
Accuracy: See Manual
… Last Cal: 09/21/07, Next Cal: 09/21/08
Equipment #: ED-01
Description: STD Series Event Detector
Manufacturer: Analysis Tech
Model: 256
Serial #: 1010425
Accuracy: See manual
… Last Cal: 06/18/07, Next Cal: 06/18/08
…
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Solder Joint Reliability Summary Report

Transcription

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