investigation of factors that influence creep corrosion
TRANSCRIPT
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Agenda
Phase 1: Industrial survey
Phase 2: Primary factors influencing creep corrosion
Phase 3: Mixed flowing-gas test
Scope
Experimental setup and corrosion uniformity
Test matrix
Results, discussion and summary
Project leaders: Xiadong
Jiang (Alcatel-Lucent), Mason Hum (Cisco) and Simon Lee (Dow).
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iNEMIiNEMI
project members phases 1 and 2project members phases 1 and 2
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Phase 1
Survey to collect data on creep corrosion failures and related factors in the electronics industry.
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Phase 1: Survey of creep corrosionPhase 1: Survey of creep corrosion
45 respondents: 67% of them have experienced creep corrosion failures.
Industrial and automotive
Telecom + high end servers
Computers and peripherals
Consumer products
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Phase 1: Survey Phase 1: Survey --
Time to failure Time to failure due to creep corrosiondue to creep corrosion
s s
< 1
year
1-3
year
3-5
year
> 5
year
I ndust r i alTel ecomComput erConsumer
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Phase 1: Survey Phase 1: Survey --
ComponentsComponentsA
ctiv
e
Pas
sive
Inte
rcon
nect
I ndust r i alTel ecomComput erConsumer
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Phase 1: Survey Phase 1: Survey ––
Solder typeSolder type
I ndust r i alTel ecomComput erConsumer
Lead free Pb-Sn
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Phase1: Survey Phase1: Survey --
SummarySummary
Creep corrosion was a common failure mode in the four product types mentioned in the survey.
Most of the creep corrosion failures occurred in less than 3 years. Electrical shorting was the major failure mode.
Failures were reported globally.
Large number of responses correlated failures to air pollution levels/industrial areas.
Some respondents
correlated failures to high sulfur environments.
Some reported failures in indoor office areas.
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Phase1: Survey Phase1: Survey --
SummarySummary
Typical failure locations were the exposed copper areas on PCBs and areas with improper touchup solder.
Corrosion of silver terminals on passive components was also reported, both on Pb-Free and Sn-Pb
soldered
PCBs.
ImAg
surface finish was most frequently reported for creep corrosion.
Failures observed on PCB’s with OSP surface finish in harsh environments.
None of the failures were induced by overly aggressive design features.
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Technical findings from Telephonic Interviews
All the respondents agreed that creep corrosion is an environmentally driven phenomenon.
Presence of sulfur and humidity are the main contributing factors leading to creep corrosion.
The role of flux is unclear.
Half the respondents (4/8) mentioned there is no detrimental affect of flux residue.
The other half (4/8) acknowledged that aggressive fluxes could accelerate creep corrosion.
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Phase 1: Technical findings from telephonic interviews
No known, agreed to standard test method to test for creep corrosion.
Standard mixed-flowing gas test unable to recreate creep corrosion on a consistent basis.
Clay test and modified mixed-flowing gas test are being evaluated.
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The challenge
To develop a test that suppliers of Pb-free PCB assemblies can use to satisfy their customers that their products will survive environments high in sulfur-bearing gaseous contamination.
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Phase 3: Investigation of Factors Phase 3: Investigation of Factors That Influence Creep CorrosionThat Influence Creep Corrosion
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Phase 3: Investigation of Factors Phase 3: Investigation of Factors That Influence Creep CorrosionThat Influence Creep Corrosion
Perform laboratory-based experiments to investigate the affects of:
surface finish,
flux,
solder mask geometry,
solder paste coverage,
reflow and wave soldering and
mixed-flowing gas test conditions.
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Experimental PlanExperimental Plan
Chamber Uniformity Test (3 runs)
Formal MFG Test(3 runs planned)
H2
S = 1700 ppb; NO2
= 200 ppb; Cl2
= 20 ppb; SO2
= 200 ppb; 40, RH 70-75%, 5 days
H2
S = 500 ppb; NO2
= 200 ppb; Cl2
= 20 ppb; SO2
= 200 ppb; 40, RH 70-75%, 5 days
H2
S = 1000 ppb; NO2
= 200 ppb; Cl2
= 20 ppb; SO2
= 200 ppb; 40, RH 70-75%, 5 days
H2
S = 1200 ppb; NO2
= 200 ppb; Cl2
= 20 ppb; SO2
= 200 ppb; 40, RH 70-75%, 20 days
H2
S = 1200 ppb; NO2
= 200 ppb; Cl2
= 20 ppb; SO2
= 200 ppb; 40, RH 70-75%, 20 days
H2
S = 1200 ppb; NO2
= 200 ppb; Cl2
= 20 ppb; SO2
= 200 ppb; 40, RH 70-75%, 20 daysTo be determined
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Test chamber setup for mixedTest chamber setup for mixed-- flowing gas testflowing gas test
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Silver corrosion product thicknessSilver corrosion product thickness weight gain vs. weight gain vs. coulometriccoulometric
reductionreduction
Ag 2 Ag 3 Ag4 Ag 5 Ag 6Ag2
S thickness by wt gain, angstroms 630 910 580 1170 720
Ag2
S thickness by coulometeric
reduction, angstroms
513 538 535 546 636
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Copper corrosion product thicknessCopper corrosion product thickness weight gain vs. weight gain vs. coulometriccoulometric
reductionreduction
Cu 2 Cu 3 Cu 4 Cu 5 Cu 6 Cu 7 Cu 8
Thickness bywt gain, angstroms
17410 15880 15630 15060 17840 17790 18990
Thickness by Coulometeric
reduction, angstroms
-- 14603 20361 14127 20574 16574 22181
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Corrosion rates in mixed-flowing gas chamber
0
5
10
15
20
25
30
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0 500 1000 1500 2000Hydrogen sulfide, ppb
Ag
corro
sion
rate
, nm
/day
0
200
400
600
800
1000
1200
1400
1600
1800
0 500 1000 1500 2000
Hydrogen sulfide, ppb
Cu
corro
sion
rate
, nm
/day
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Corrosion product Corrosion product ––
Cu couponCu coupon
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MFG test matrix MFG test matrix ––
11stst runrun
H2
S = 1200 ppb; NO2
= 200 ppb; Cl2
= 20 ppb; SO2
= 200 ppb; 40, RH 70-75%, 20 days
ID Finish Flux
I-R ImAg
(Immersion silver) Rosin fluxI-O ImAg
(Immersion silver) Organic acid flux
O-R OSP (Organic solderability preservative) Rosin fluxO-O OSP (Organic solderability preservative) Organic acid fluxH-R Pb-free HASL (Hot air solder leveling) Rosin fluxH-O Pb-free HASL (Hot air solder leveling) Organic acid flux
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Creep Corrosion: Copper creep corrosion is when the corrosion products spread onto the solder mask beyond the edge of the pad or via.
Creep Corrosion: Copper creep corrosion is when the corrosion products spread onto the solder mask beyond the edge of the pad or via.
Edge Corrosion: Corrosion products only along the edges of the pads and vias.
Edge Corrosion: Corrosion products only along the edges of the pads and vias.
Corrosion: Corrosion products on pad and via surfaces.
Corrosion: Corrosion products on pad and via surfaces.
Creep Corrosion: Creep corrosion is the spread of the corrosion product onto the FR4 and the solder mask surfaces.
Creep Corrosion: Creep corrosion is the spread of the corrosion product onto the FR4 and the solder mask surfaces.
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MFG test result summary: 1MFG test result summary: 1stst
runrun
Finish and flux Corrosion Edge corrosion
Creep corrosion
Creep corrosion severity
ImAg, organic acid flux Yes No Yes High
ImAg, rosin flux Yes No No ---
OSP, organic acid flux Yes No Yes Low
OSP, rosin flux Yes No Yes Low
Pb-free HASL, organic acid flux No Yes Yes
High(isolated areas)
Pb-free HASL + rosin flux No Yes No ---
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Electrical short detection and Electrical short detection and resistance measurementresistance measurement
L1 L2 L3 L4 L5 L6 L7 L8 L9 L10 L11 L12 L131-I-R-11-I-R-21-I-R-31-I-O-1 4.7K Ω 38K Ω 3.55K Ω1-I-O-2 600 Ω 48K Ω1-I-O-3 1.5K Ω 9.8K Ω1-O-R-11-O-R-21-O-R-31-O-O-11-O-O-21-O-O-31-H-R-11-H-R-21-H-R-31-H-O-1 36K Ω1-H-O-21-H-O-3
PCB 20th day - Short Detected on the patterns of the TVs
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ImAgImAg, 20 days MFG, bottom side, 20 days MFG, bottom side
ImAg, rosin flux ImAg, organic acid flux
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ImAgImAg, organic acid flux, 20 Days MFG , organic acid flux, 20 Days MFG
Creep corrosion in the soldered and boundary
areas
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ImAgImAg, rosin flux, 20 days MFG , rosin flux, 20 days MFG No significant creep corrosion. General tarnish.
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OSP, organic flux, 20 days MFG OSP, organic flux, 20 days MFG
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OSP, rosin flux, 20 days MFG OSP, rosin flux, 20 days MFG Minor creep corrosion, non solder or flux location
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PbPb--free HASL, Organic Flux, After 20 free HASL, Organic Flux, After 20 Days MFG TestingDays MFG Testing
Creep corrosion and edge corrosion due to poor HASL coverage
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PbPb--free HASL, rosin flux, 20 days MFG free HASL, rosin flux, 20 days MFG No creep corrosion
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SummarySummary
MFG test conditions of the 1st
formal run were chosen to reach the target of about 500nm/day copper corrosion rate.
Creep corrosion was observed on all the finish types tested (ImAg, OSP and Pb-free HASL):
However more creep corrosion was occurred on boards with organic acid flux.
Most severe creep corrosion was observed on ImAg boards with organic acid flux.
Most serious creep corrosion locations have obvious flux residue. Most creep corrosion occurred in solder boundary area.