Transcript 3-11g IPC Fall meeting Sept 2016x

Status
• MFG test status
• Phase 3 tests planned (Cl2 in situ monitoring)
• FOS test method review for joint EIA standard
• Primary review of EIA 977 complete
• Feedback to be provided to governing ECIA committee
• FOS test status
• Trying to locate known “bad” parts for Phase 2 testing
Mixed Flowing Gas
Phase 1 Modified MFG Tests
• Goal: Reliably reproduce published corrosion results in MFG test with
very high H2S
• Three different MFG chambers
• Alcatel-Lucent
• CALCE
• Battelle
• Identical test conditions, coupons and materials
• Tightly specified MFG operating procedures
• Experienced PIs
Phase 1 Test Results
• All three test chambers observed minor creep corrosion
• But far less than the severe creep corrosion observed in other MFG testing and field failures
• CALCE saw most creep corrosion, Battelle least, ALU’s between but closer to
CALCE
• Surprisingly, there was a large difference in Cu coupon corrosion rate between
the three labs
• Battelle (1065nm/5d, 1860nm/10d)
• ALU (3380nm/5d)
• CALCE (~4200nm/5d, ~7000nm/10d)
Phase 2 Tests
• Goal: Use test coupons to investigate root cause of
differences in corrosion between chambers
Phase 2 Test Results
• Ag and Cu coupons tested in each
MFG chamber
• Cu corrosion rates similar
• Ag corrosion rates very different
• Investigation showed Cl2 levels to be
primary correlation with differences
between Ag corrosion rates
Phase 3 (planned): In situ Cl2 monitoring
• Next step: implement in situ Cl2
monitoring and control, then run
another set of Cu and Ag coupons in
the chambers
• Not all chambers may be able to
monitor and control adequately
EIA-364-65B Class IIIA Specifies Cl2 level to +/- 5ppb
Flowers of Sulfur
Alternative: Flowers of Sulfur based on ASTM B 809
High temperature sublimes solid sulfur. Sulfur gas reacts with metal.
• Dependent on
temperature
• Independent of
humidity.
• Accelerated test
• 2 days = 1 year (@
65°C)
Corrosion
determination:
AFM, XPS, visual cross
section, microbalance
Samples
Sulfur (g)
Sulfur (s)
Standard Test Method Development
• ECIA developed EIA 977 Flowers of Sulfur test method for passive
electronic components
• Based on Delphi and IBM conditions
• Similar to FoS test being developed by 3-11g committee
• Detail review conducted
• Input to be provided to ECIA committee
• Goal: create a joint standard
Phase 1 Test: Validate FoS for Resistor Testing
Conditions
• 0402 10K resistors mounted on PCBs
• Normal and corrosion resistant
• 105C for 20days
• Aggressive, based on IBM results
• No applied biased
Phase 1 Test Results
Preliminary Results
• No failures
Next Steps
• Locate “known bad” parts
– Order high risk parts and test
many types unmounted
• Extend test period
Next Steps
Next Steps
• MFG
• Phase 3: Test another set of Cu and Ag coupons in the chambers with in situ
monitoring and control
• Capture experimental results from all MFG tests
• Document findings
• Recommend best practices
• FOS
• Provide feedback to ECIA on EIA 977 Flowers of Sulfur test method and move
toward joint standard
• Identify “known bad” components and repeat FOS test
Backup
Background
Corrosion Failures in the Field
• Growing number of corrosion failures
observed in the field
• More products are being used in ISA
G2-GX environments
• Available tests were not sufficiently
predictive for PCBs and PCAs
• Need more predictive corrosionresistance test for PCBs and PCAs
Creep Corrosion
Mixed Flowing Gas (MFG)
Mixed Flowing Gas Test Chamber
EIA-364-65B for Connectors
• Test to determine the reaction of
plated or unplated connector
surfaces when exposed to
corrosive atmospheres
MFG and Finished PCAs
Connectors vs PCAs
• Standard MFG testing is
predictive and useful for
connectors
• But extended testing of
finished PCAs in Class IIIA
conditions did not produce
failures found in the field,
especially creep corrosion
Test Conditions from EIA-364-65B
Extending MFG
• Alcatel-Lucent published results in 2007/2009
• Using a modified MFG tests on PCBs and PCAs they were able to form creep
corrosion on samples
ALU
International
H2S
SO2
NO2
Cl2
1700 ppb*
200 ppb
200 ppb
20 ppb
• 3-11g task group began investigating the Alcatel-Lucent modified
MFG test as a possible creep corrosion test
*Normally 100 or 200ppb for test
Goal
• Identify or create a test method to differentiate and predict corrosion
resistance of components and PCAs in the field
• Develop a next generation corrosion test using a modified mixed flowing gas
test method for predicting field life of electronic assemblies and materials in
G1-GX environments as defined by ISA 71.04-1985
• Investigate other corrosion tests, including Flowers of Sulfur, as alternatives
to mixed flowing gas tests
Modified MFG Tests
• Three different MFG chambers
• Alcatel-Lucent
• CALCE
• Battelle
• Identical test conditions, coupons and materials
• Tightly specified MFG operating procedures
• Experienced PIs
Reproducing Alcatel-Lucent Results
• Conditions from APEX2007 paper:
ALU
International
H2S
SO2
NO2
Cl2
1700 ppb*
200 ppb
200 ppb
20 ppb
• Unbiased (no applied voltage)
• Keep same parameters from first test
• 40C, 70-75% RH
*Normally 100 or 200ppb for test
Test Coupons
Alcatel-Lucent test coupons
(same as 2009, includes PTH)
• Controls:
• Bare copper
• SnPb HASL
• Test samples:
• OSP
• Immersion silver
• ENIG
Preconditioning
• Precondition with solder assembly processes
• SMT print and reflow
• Wave solder
• RO and OR fluxes
• Masked areas to create interfaces
Sample Analysis (after testing)
1.
2.
3.
4.
Visual inspection
Mass change measurement of witness coupon
Determination of chemical composition of corrosion products
Removal of corrosion products followed by additional surface
inspection
5. Measurement of corrosion rate in angstroms
Different Types of Corrosion Observed
Discoloration
Discoloration
[Bare Copper –day 5]
Fiber assisted corrosion
[Immersion Silver–day 5
Creep
Creep
[Immersion Silver–day 5]
Flaking
Flaking
[Immersion Silver–day 20]
White Patina
Green Patina
White Patina
[Bare Copper –day 10]
Green Patina
[Bare Copper –day 5]
Creep Corrosion Results - CALCE
Results
Board Type
Discoloration
Day 5
Creep
Day 10
Green
Day 15
Flaking
White
Day 20
Cu
Cu-OR
Cu-RO
SnPb
SnPb-OR
SnPb-RO
OSP
OSP-OR
OSP-RO
ImAg
ImAg-OR
ImAg-RO
ENIG
3 out of 3
ENIG-OR
2 out of 3
ENIG-RO
1 out of 3
Results
Board Type
Discoloration
Day 5
Creep Corrosion Results - Battelle
Creep
Green
Flaking
Day 10
Day 15
White
Day 20
Cu
Cu-OR
Cu-RO
SnPb
SnPb-OR
SnPb-RO
OSP
OSP-OR
OSP-RO
ImAg
ImAg-OR
ImAg-RO
ENIG
ENIG-OR
ENIG-RO
3 out of 3
2 out of 3
1 out of 3
Results
Board Type
Creep Corrosion Results – Alcatel-Lucent
Discoloration
Creep
Green
Flaking
Day 5
Day 10
Day 15
White
Day 20
Cu
Cu-OR
Cu-RO
SnPb
SnPb-OR
SnPb-RO
OSP
OSP-OR
OSP-RO
ImAg
ImAg-OR
ImAg-RO
ENIG
3 out of 3
ENIG-OR
2 out of 3
ENIG-RO
1 out of 3
Flowers of Sulfur
Alternative Test: Flowers of Sulfur
• Flowers of sulfur is another type of corrosion test that may be useful
to differentiate corrosion performance of certain components
• Narrow scope of investigation to look at resistors only
Sulfidation of Ag-Containing Resistors
Resistors and Sulfur Corrosion
• Ag-containing
resistors are a type
of component that can fail in high
sulfur environments
• Not all Ag-containing resistors are susceptible
• Construction and process control are key
• It may be helpful to develop a
simpler and more focused test to
screen this common component
Typical Thick Film Resistor Construction
• Thick film resistors use Ag alloy as
the first layer of the termination
structure
• Provides contact to the thick film
resistive element
• Covered with Ni and Sn to provide a
solderable surface
• An open seam can allow
atmospheric sulfur to access Ag
electrode material
(4) Coating/glaze
(3) Resistive layer
(6) Sn (plated)
(5) Ni (plated)
(2) Ag conductive layer
(1) Substrate (alumina/silica)
Sulfur Ingress from the Environment
• Nickel is supposed to overlap the
glass to limit gas diffusion to the Ag
underlayer
• If overlap is not large enough or if
the seal is not sufficient, sulfur
gases can penetrate to the Ag
• Sulfur reacts with Ag to form Ag2S
• Corrosion continues until the
resistance increases and/or
becomes an open
(4) Coating/glaze
(3) Resistive layer
Sulfur
(6) Sn (plated)
(5) Ni (plated)
(2) Ag conductive layer
(1) Substrate (alumina/silica)
Flowers of Sulfur testing—based on ASTM B
809
High temperature sublimes solid sulfur. Sulfur gas reacts with metal.
• Dependent on
temperature
• Independent of
humidity.
• Accelerated test
• 2 days = 1 year (@
65°C)
Corrosion
determination:
AFM, XPS, visual cross
section, microbalance
Samples
Sulfur (g)
Sulfur (s)
Flowers of Sulfur Test Apparatus
Polycarbonate box
within a heating
oven; attached fan
for air circulation.
Samples
Sulfur (s)
Tests
Conditions
• 0402 10K resistors mounted on PCBs
Preliminary Results
• No failures
• Normal and corrosion resistant
• 105C for 20days
• Aggressive, based on IBM results
• No applied biased
Next Steps
• Extend test period
• Locate “known bad” parts
– Order high risk parts and test
many types unmounted