conformal coating evaluation for improved...
TRANSCRIPT
Conformal Coating Evaluation for Improved Environmental Protection
Project Leaders: Prabjit Singh (IBM)Chen Xu (Nokia)iNEMI Staff: Haley FuMarch 25 & 27, 2019
The recording of this webinar is available at:
https://inemi.webex.com/inemi/lsr.php?RCID=1e9dff30b0d84d45b810ce3edfd88f2a
It will be accessible for six months following the date of the webinar.
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• Introduction of Project Chairs • iNEMI Project Development Process• Companies Involved in Planning
• Project Briefing• Objectives• Previous Related Work• Scope• Timeline
• How to Join• Q&A
Agenda
Note: All phones will be on mute until the end of the presentation
Introduction of Project Chairs
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Dr. Chen Xu (Nokia Bell Labs)Job title: Distinguished member of technical staff
Experience: 1. Extensive experience with reliability issues
associated with equipment installation in challenging environments and developing methodologies for mitigating environmental impact on electronic equipment.
2. BS Degree in Chemistry from Tongji University in Shanghai, China; Ph.D. in Physical Chemistry from Ruhr-University Bochum, Germany
3. ~110 publications, ~40 presentations, 3 book chapters, 18 issued and pending patents.
4. Participated in various industrial consortium efforts in resolving industry-wide reliability issues.
Dr. Prabjit Singh (IBM)Job title: Senior Technical Staff Member
Experience:1. 40 years of metallurgical engineering and failure
analysis of computer power, packaging and cooling.
2. IBM Master Inventor with 72 issued patents.3. B.Tech from IIT Kharagpur, MS and PhD
Stevens Institute of Technology, and two recent MS in electrical engineering.
4. Numerous publications in IPC, SMTA, iTHERM, and other conferences. Authored the 2nd edition of the ASHRAE book on data center gaseous and particulate contamination.
INPUT
SELECTION
DEFINITION
PLANNING
EXECUTION / REVIEW
CLOSURE
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iNEMI Project Development Process - 5 Steps
“ Project”Limited to committed Members
“ Initiative”Open for Industry input
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------------------- iNEMI Technical Committee (TC) Approval Required for Execution
iNEMI Project Management Policy
• Two governing documents for projects• SOW (statement of work): sets out project scope,
background, purpose, benefits, and outlines required resources, materials, processes, project schedule, etc.
• Project Statement (PS): signed by participating companies to secure commitment on resource and time contributions.
• iNEMI Project requires iNEMImembership• Signed membership agreement
• Commitment to follow iNEMI By-laws and IP policy
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Conformal Coating Evaluation for Improved Environmental Protection
Project Formation Participants
Project Briefing
Project Background
• Electronic hardware can be susceptible to corrosion and electrochemical migration (ECM) related failures in geographies with high concentrations of gaseous and particulate contamination.
• It may be necessary to conformally coat susceptible hardware to prevent corrosion-related hardware failures.
• Conformal coatings are presently tested by determining the time to failure of coated SMT resistors. While the test has been successful in weeding out resistors with poor reliability, the test has many disadvantages:• The test is done in dry sulfur environment at 105oC. The mode of failure at
this high temperature may be very different from that at the 40-70oC application temperature. The high-temperature test may also be rejecting robust, reliable parts. A lower temperature test is therefore required.
• The test environment has no moisture and no gas besides sulfur. As a result, there is no synergistic effect of gas mixtures common in corrosion mechanisms.
• The test time of many months is too long to be a practical test. Supply chain disruption to a manufacturing process requires a quick test, less than a week in duration, to qualify an alternate conformal coating.
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Project Objectives & Impact
• Develop a more convenient and effective conformal coating qualification test.• Test should be able to qualify conformal coatings in less than
a week under test environmental conditions similar to the application conditions.
• Test should be capable of quantitative measurement of the protection provided by the conformal coating.
• Quantitative measurement can help optimize the conformal coating parameters, such as type of coating, application methods and thickness.
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Previous Related Work
Qualification test for creep corrosion using FOS (2013-2017)
The project successfully developed a cost-effective and convenient creep corrosion qualification test that suppliers can use to satisfy their customers that their products will survive moderately corrosive environments.
White Paper: A Cost-Effective & Convenient Approach to Creep Corrosion Testing (August 2018)
iNEMI FoS chamber conditions
• An acrylic cube with a paddle wheel can hold 8 boards rotating at 20 rpm
• 50oC chamber temperature
• 200 g sulfur
• %RH controlled by salt solution in the 11 to 90% range
• 100 ml 8.25% sodium hypochlorite Clorox®
is used to introduce chlorine gas that would work in synergy with sulfur
• Cu and Ag foils are included for Cu and Ag corrosion rate measurement
• The corrosion rate of Cu and Ag should be 500-1500 and 400-1200 Å/day, respectively. The rate of formation of AgCl should be 50-500 Å/day.
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iNEMI FoS chamber
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• The challenge is to have the Clorox release chlorine gas into the chamber but not upset the relative humidity.
• The saturated salt controls the relative humidity to its deliquescence value.
• The moisture coming off the Clorox is throttled and forced to flow over the saturated salt.
n Ag serpentine thin films, 770-nm thick, were evaporated on 15x15 mm SiO2 on Si dies.
n The corrosion rates of thin films can be measured using 4-point resistance measurements.
n The corrosion protection provided by a conformal coating was determined by comparing the corrosion rates of coated and uncoated Ag thin films.
Previous Related Work – continued
“Characterization of conformal coating,” by P. Singh, SMTA International, Sept 2015
Bare Ag
Time, days0.0 0.2 0.4 0.6 0.8 1.0
Ag fi
lm th
ickn
ess,
nm
0
200
400
600
800
FP04
FP08
Test Coupon for This Project
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§ The above structure enables accurate measurement of film resistance using the 4-point method.
§ L shaped pins are soldered to the PCB and silver epoxied to the thin films. § Connector pins are soldered to the PCB.§ Jumper wires are soldered to the L shaped pin ends and the connector pin ends.§ The connector pin conical tops provide good contact surfaces for the ohm meter to make
reproducible resistance measurements without disturbing any connections to the thin films.
BC AD
Serpentine thin film on SiO2
Silver epoxy cured at 150 C
Solder joints
Scope of Work
• The rates of Cu and Ag foil corrosion will be compared with that of Cu and Ag serpentine thin films using the resistance and the coulometric methods.
• Similar testing in MFG (mixed flowing gas) test chamber and NSS (neutral spraying salt) testing will be done depending on the resource availability and team concurrence.
• Serpentine thin films of Cu and Ag, 800 nm thick, will be coated with the conformal coatings under test.
• Characterize various conformal coatings using the iNEMI FoStest chamber. Evaluate the effectiveness of selected conformal coatings at different thicknesses and accelerated aging conditions.
• The effect of the 3D nature of PCBA surfaces being coated may be studied using an novel approach involving measuring the corrosion rates of silver thin films as a function of distance from the silicon chip edge.
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Timeline
Tasks Months
Tasks 1 2 3 4 5 6 7 8 9 10 11 12
1. Serpentine thin film resistance measurement
Fabricate serpentine thin films X X X
Build & Test the setup for measuring thin film resistance
X X X X X X
Finalize resistance measurement setup X X X X
Make final test runs at chamber with 81%RH and 30oC.
X X X
2. FOS test runs of coated and uncoated thin films at 81%RH and 30oC.
X X X
3. MFG test of coated and uncoated thin films X X X
4. NSS test of coated and uncoated thin films X X X
5. Summary & Final report X X
How to Join
Sign-Up Due on April 31, 2019
• iNEMI membership is required to join the project• Download SOW and PS from iNEMI web:• https://community.inemi.org/content.asp?admin=Y&contentid=620
• Sign the PS• Signature of representative of participants• Signature of manager approval• Send scanned PS to [email protected]• iNEMI Vice President of Technical & Project Operations will
sign and approve your participation and send you back the completed PS with acceptance
• Join iNEMI membership, or questions, contact Haley Fu ([email protected])
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