Sulfur Corrosion Failure Mechanisms and the Test Methods Developed to Mitigate Catastrophic Events ACKNOWLEDGEMENT: Randy Schlueller, Dell Inc. provided much field data and photographs. Randy presented his paper “Creep Corrosion On Lead - Free Printed Circuit Boards In High Sulfur Environments” at the 2007 SMTA conference. Sulfur Corrosion Test 1 ASTR 2008 Oct 1 – Oct 3, Portland, Oregon David Rahe September 16, 2016
Outline Overview – Sulfur Corrosion Product Risk and Factors PCB Finish Methods Extent of the Impact Mitigation: • Design Recommendations • Sulfur Corrosion Testing Test Results Conclusion Supporting Information ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
Overview: Sulfur Corrosion “Sulfur Gas at the Parts per Million Level Can Cause Computer Systems to Fail Within 2 Months of Use.” Hewlett - Packard Case Study : Separately, HP and Dell recently experienced dramatic product failures within first 2 weeks of installation at multiple automotive design labs. Replacement systems failed similarly. Conclusion : Airborne sulfur from modeling clay corroded immersion silver PCB trace finish. Failure Mechanism: Galvanic reaction with electrode potential between Copper and Silver when copper is exposed to high levels Sulfur and >50% Humidity . ‘Creep Corrosion’ Copper Sulfide (Cu2S) ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
Products at Risk Pb Initiatives Have Resulted in Sudden and Drastic Increases in Sulfur Corrosion Vulnerable Product: Immersion silver (ImAg) PCB finish in corrosive environment applications Presentation Focus: IT Hardware Absorbs Surface active moisture sulfur Electrolyte transfers CU, reacts with S & deposits CU 2 S ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
Corrosion Factors Pb Initiatives Have Resulted in Sudden and Drastic Increases in Sulfur Corrosion • Aggressive dendritic formation growth in all directions • Causes low resistance trace paths • Voltage not required (not electrochemical migration) • Thermal cycling induced: Cu2S created/dissolved in moisture layer; forms dendrites when moisture dries • Increased airflow (fans) accelerates sulfur exposure, failures ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
Sulfur Environments 8.8 Mil Tons of Sulfur Produced in the US Annually Majority of Failures Occur within 2 to 4 Months Rapid Failure Environments • • Rubber manufacturing Vehicle exhaust fumes present • Water treatment • Adhesives • Paper mills • Desiccant • Fertilizer production • Sewage/waste-water treatment • Petrochemical • Farms/cattle yards • Automotive design (clay modeling lab) • • Swamps/bogs/wetlands Packaging areas ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
PCB Finish Materials ‘Finish’ Protects PCB Cu from Oxidation and Deterioration PB Free Methods • Immersion Silver (ImAg) • Hot Air Solder Leveling (HASL) • Organic Solder Preservative (OSP) • Electroless-Nickel Immersion Gold (ENIG) • White Tin Industry-Accepted ImAg Benefits • Only cosmetic tarnishing expected Paper Mill • Studies indicated electrochemical creep corrosion not a problem Recent Reports of Creep Corrosion in OSP Material (Paper mill industry) “While ENIG process has largest market penetration, last year more ImAg process lines were installed in PCB facilities than any other finish” . (Multicircuits, Inc. ) ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
Extent of the Impact Failures Most Frequently Occur in Desktop/Storage Computers & HDDs, Rather Than Laptops Supplier contamination ruled out: Creep corrosion found on PCBs supplied by 5 different vendors HDDs with OSP in same sulfur environments did not show signs of corrosion Dell study compared ImAg, OSP, ImSn, ENIG. Concluded ImAg, ENIG could not survive ISA G2 environment. Alcatel-Lucent ImAg testing (ISA Class G2 equivalent MFG at 69% RH) confirms creep corrosion in surface finish ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
Extent of the Impact Impact of RH Factor Determined by Duration of Exposure ‘ Time of Wetness’ • Defined as: Hrs/yr where temp >0 ° C, and RH >80% • 6 Catagories 1 to 6 • Critical Zone: ≥ 10%/yr Time of Wetness and Pollution Degree combined with ANSI/ISAS17-07 standard ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
Extent of the Impact 2009 EU Directive for the Energy Performance of Buildings : Energy reduction via circulation of outside air. (EU Data Centre Code of Conduct, Section 3) Impact: Significantly greater exposure to corrosive gasses with varying humidity environments. Result : Greater events of creep corrosion failures ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
Mitigation: Sulfur Corrosion Testing Standard Test Methods Don’t Capture Creep Corrosion Failures Many corrosion failures undetected by electrical testing Corrosion causes electrical shorting; various symptoms result (depending on which conductors are the first to bridge) Resistance decrease measured during re-exposure of corroded product to high humidity: >10 Mohm to < 1 Mohm ISA Standard "Environmental Conditions for Process Measurement and Control Systems: Airborne Contaminants” ISA-S71.04-1985 ISA S71.04-1985 OnGuard Correlation Effects Class GX >2000 Å/30 Class GX >66 Å/24 Hours Electronic/electrical equipment not expected Days to survive due to corrosive attack. Class G3 <2000 Å/30 Class G3 <66 Å/24 Hours High probability that corrosive attack will Days occur. Probable effect on equipment reliability in less than 5 years. Class G2 <1000 Å/30 Class G2 <33 Å/24 Hours Effects of corrosion are measurable and are a Days factor in equipment reliability. Possible effects in less than 5 years. Class G1 <300 Å/30 Class G1 <10 Å/24 Hours Corrosion is not a factor in determining Days equipment reliability. ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
Mitigation: Sulfur Corrosion Testing “ The industry requires a test method that will consistently produce creep corrosion on ImAg control samples in a way as is observed in high sulfur environments.” Dell, inc. Historical test methods for MFG (Mixed Flow Gas) • IEC • EIA • Telecordia • Battelle Does not properly produce creep corrosion Does not provide a usable acceleration factor to determine proper test duration to simulate 1 year, 2 years or product life ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
Mitigation: Design Changes Design Recommendations: • Plugging all non-test vias with soldermask • Use of non-soldermask defined test vias and pads • Spacing vias and pads sufficiently to prevent bridging • Solder paste to cover all remaining metal features on the PCB • Discontinue use of ImAg surface finish • Test product samples ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
Mitigation: Sulfur Corrosion Testing Clay Test Method • Early development by Randy Schueller, Dell, Inc. • Utilizes high content (30-50% elemental sulfur) sulfur modeling clay • Wetted/heated clay placed in sealed container • Pre-cooled PWA samples placed in container with no direct clay contact • Exposed to the sulfurous environment for approximately 12 hours • Repeated process four times, measure corrosion Creep corrosion typically visible after 2 days, pronounced after 5 days ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
Mitigation: Sulfur Corrosion Testing Clay Test Results 3 day exposure ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
Conclusion Failures Have Occurred, Products are at Risk Design/Mfg Process Must Consider Corrosive Customer Environments ImAg Poses Highest Known Risk Testing Methods Now Available Future Work • Refinements to the clay test method Improve control of humidity, temperature, sulfur levels and include airflow • Research other test methods • Standard test method adoption ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
Thank ank You ou David Rahe 512-775-4001 drahe@dlinnovations.com 3201 Industrial Terrace, Suite 120, Austin, TX 78758 www.dlinnovations.com ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
Sources Article: Accelerated Corrosion of Printed Circuit Boards due to High Levels of Reduced Sulfur Gasses in Industrial Environments, Paul Mazurkiewicz, Ph.D. Hewlett-Packard Company, Fort Collins, Co, USA (http://www.multicircuits.com/pcb/tech/surface_finishes.html) ASTR 2008 Oct 1 – Oct 3, Portland, Oregon September 16, 2016 David Rahe, DLi Labs
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