Tin Whisker Phenomenon, Mitigation And Testing Overview V2
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Tin Whisker Phenomenon, Mitigation And Testing Overview V2

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Everything you really need to know about Tin Whiskers. A literature and scientific review.

Everything you really need to know about Tin Whiskers. A literature and scientific review.
- by Patrick Neyman, PhD.

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    Tin Whisker Phenomenon, Mitigation And Testing Overview V2 Tin Whisker Phenomenon, Mitigation And Testing Overview V2 Presentation Transcript

    • Tin Whiskers Properties P ti Risk Factors Mitigation Industry Perspective JEDEC Test Requirements - Patrick Neyman y
    • Outline•Ti TinWhiskers Fundamentals Whi k F d t l •Physical & Electrical Properties •Growth and Accelerated Growth Factors •Risk Factors •Mitigation t gat o - Conformal Coating Update •The Role of Intermetallics•Industry Perspective - Consumer, Telecom, Automotive - Supplier and Customer•JEDEC Testing Requirements•Test Flow: Ni-Underplated devices with 4/less leads•Reference List Information is Patrick Neyman Confidential & Proprietary page 2 / Do Not Reproduce or Distribute - Patrick Neyman
    • Tin Whiskers Basics•TinWhiskers are single-crystal Sn filaments that extrudefrom the Sn surface via grain boundary diffusion•Grain boundary diffusion occurs due to compressivestresses at tin grain boundaries•Tin whiskering is a stress relief mechanism•TinWhisker mitigation techniquesare stress relief mechanisms Information is Patrick Neyman Confidential & Proprietary page 3 / Do Not Reproduce or Distribute - Patrick Neyman
    • Tin Whisker ExamplesWhisker with striations Whisker with rings g Smooth Whisker with a consistent cross section. Information is Patrick Neyman Confidential & Proprietary page 4 / Do Not Reproduce or Distribute - Patrick Neyman
    • Physical and Electrical Properties•Diameter: ~1 – 5 microns•Length: up to ~1 mm 1•Fusing Current: ~5 mA•LinearResistance: 0.5 Ohm/micron (for (f 2 micron di i diameter) t )•~700 G required tobreak-offbreak off from surface note: G Gold plating required for electrical contact f Oxide difficult to breach with whisker (7 G force required to breach oxide) Information is Patrick Neyman Confidential & Proprietary page 5 / Do Not Reproduce or Distribute - Patrick Neyman
    • Typical Time to Whiskering• iNEMI h d t has determined rough t i l ti i d h typical time t whiskering f various h idit to hi k i for i humidity & temperature conditions• Matte Tin over Copper, 150 °C anneal – NO UNDERPLATE• No Corrosion on measured regionsTemperature Humidity Tin Thickness Time to Whisker85 °C C 85% RH 3 micron ~ 2000 hours 10 micron ~ 2000 hours60 °C 87% RH 3 micron ~ 2000 – 4500 hours 10 micron ~ 4500 – 7000 hours60 °C 60% RH 3 micron ~ 7000 – 10,000 hours 10 micron ~ 7000 – 10,000 hours30 °C 90% RH 3 micron ~ 11,000 hours45 °C C 60% RH 10 micron ~ 10 000 hours 10,000 Information is Patrick Neyman Confidential & Proprietary page 6 / Do Not Reproduce or Distribute - Patrick Neyman
    • Information is Patrick Neyman Confidential & Proprietary page 7 /Do Not Reproduce or Distribute - Patrick Neyman
    • Tin Whisker Risk Factors•Mechanical Processing •Compressive stress at bending and singulation points•IntermetallicFormation •Cu6Sn5 volume is greater than 6Cu+5Sn •Compressive stress forms at the Cu6Sn5 – Sn interface•Surface Oxidation •SnO burrows into the Sn layer during oxidation •SnO volume is greater than Sn + O•CTE Mismatch (Coefficient of Thermal Expansion) •Compressive stress at solder fillet / device interface. interface•Plating Conditions •Organic Contamination ( g (internal compressive stresses) p ) Information is Patrick Neyman Confidential & Proprietary page 8 / Do Not Reproduce or Distribute - Patrick Neyman
    • Tin Whisker Mitigation Techniques•Plating Conditions •!!! No other techniques work if this is not right !!! •Eliminate / reduce organics,...•M tt Tin ( f no Ni underplate: min 7 micron, 10 nominal. With Ni: thinner is better) Matte Ti (if ) •Larger grains result in larger free volume (void volume) •Free volume allows short-range stress relief•U d Underplate with Ni k l (min 0.5 micron, 1.27 recommended) l t ith Nickel •Ni protects Sn from Cu •Ni3Sn4 intermetallic forms tensile stress regions •Relieves compressive stress from oxides or damage on thin (<<10 μm) Sn•Anneal @ 150 C for 1 hr within 24 hrs of plating •Stress relaxation•Fuse in hot oil above Tmelt(Sn) within 24 hrs of plating (time varies) •Sn flows to fill in voids and cool to non-stressed state•Alloy with Lead •Telecom and Automotive current (JUN07) method of choice Information is Patrick Neyman Confidential & Proprietary page 9 / Do Not Reproduce or Distribute - Patrick Neyman
    • Conformal Coating NOT a mitigator• No coatings yet found to mitigate whisker growth• Conformal coatings CAN protect against intrusion by whiskers from neighboring components Information is Patrick Neyman Confidential & Proprietary page 10 / Do Not Reproduce or Distribute - Patrick Neyman
    • Tin Whiskers & Intermetallics•IntermetallicFormation•Cu6Sn5 takes up more volumethan 6Cu+5Sn•Compressive stress forms at theCu6Sn5 – Sn interface Sn Deposit Cu6Sn5 Cu Substrate Information is Patrick Neyman Confidential & Proprietary page 11 / Do Not Reproduce or Distribute - Patrick Neyman
    • Tin Whiskers & Intermetallics•Occasionally, a whisker extrudes•The extrusion die is thepath of least resistance Information is Patrick Neyman Confidential & Proprietary page 12 / Do Not Reproduce or Distribute - Patrick Neyman
    • Tin Whisker Formation Questions ??? Information is Patrick Neyman Confidential & Proprietary page 13 / Do Not Reproduce or Distribute - Patrick Neyman
    • Outline•Ti TinWhiskers F d Whi k Fundamentals t l •Physical & Electrical Properties •Growth and Accelerated Growth Factors •Risk Factors •Mitigation t gat o - Conformal Coating Update •The Role of Intermetallics•Industry Perspective - Consumer, Telecom, Automotive - Supplier and Customer•JEDEC Testing Requirements•Test Flow: Ni-Underplated devices with 4/less leads•Reference List Information is Patrick Neyman Confidential & Proprietary page 14 / Do Not Reproduce or Distribute - Patrick Neyman
    • Telecom / Automotive (AEC Jun07)• Sn Pb components preferred by most Sn-Pb – Pb-free being forced by suppliers and customers• Long-term reliability concern – Uncertain if Whisker Growth is Limited / Unlimited• 3% Sn Pb requirement being pushed by some Sn-Pb• Whisker-Risk labeling on Pb-free parts under debate• Majority going with JEDEC for testing requirements – Telecom pushing for new Class 2A• Periodic recertification may be dropped• Ambient conditions storage may be dropped• Sn Pb component price increasing significantl Sn-Pb significantly Information is Patrick Neyman Confidential & Proprietary page 15 / Do Not Reproduce or Distribute - Patrick Neyman
    • Consumer Electronics (IPC, Dec06)– Tin Whiskers viewed as small source of problems– Largest Pb-Free concern is solder-joint reliability– OEM manufacturers concerned as devices grow smaller– Old plating techniques now known to be a problem– Cleanliness an issue for many (smaller?) shops– Confusion in general about best methods Information is Patrick Neyman Confidential & Proprietary page 16 / Do Not Reproduce or Distribute - Patrick Neyman
    • Industry Perspective - Suppliers Joint Fi di J i t Findings: Philips, Infineon, STMicroelectronics, Freescale Semiconductor• Reflow Mitigates Tin Whiskering – matches RCP initial findings• Plating improvement efforts ceased / very limited – JEDEC: any change to bath requires re testing re-testing• JEDEC inspection procedures seen as impractical• Corrosion is found to be a significant cause of whiskering in practical use, but is a JEDEC exemption• Preconditioning does not cause increased whiskering, but adds 66% workload• Grandfathered parts fail JESD201 testing – Surface finishes with long field history of reliability exempt Information is Patrick Neyman Confidential & Proprietary page 17 / Do Not Reproduce or Distribute - Patrick Neyman
    • Industry Perspective - Customers Joint Fi di J i t Findings: Philips, Infineon, STMicroelectronics, Freescale Semiconductor• Very Few customers request Tin Whisker report – Mostly, no more questions after report submitted• Some customers ADD demands to JESD201• Some concern about JEDEC exception for terminations covered in solder during assembly• Customers are accepting the g p g grandfather clause on long- g established tin surface finish processes. – from JESD201 Section 6 (Acceptance Criteria): “data on long established tin surface finish manufacturing processes with data reliable field histories can be substituted with agreement between supplier and user”. – BUT, many of these components fail JESD201 testing y p g Information is Patrick Neyman Confidential & Proprietary page 18 / Do Not Reproduce or Distribute - Patrick Neyman
    • Outline•Ti TinWhiskers F d Whi k Fundamentals t l •Physical & Electrical Properties •Growth and Accelerated Growth Factors •Risk Factors •Mitigation t gat o - Conformal Coating Update •The Role of Intermetallics•Industry Perspective - Consumer, Telecom, Automotive - Supplier and Customer•JEDEC Testing Requirements•Test Flow: Ni-Underplated devices with 4/less leads•Reference List Information is Patrick Neyman Confidential & Proprietary page 19 / Do Not Reproduce or Distribute - Patrick Neyman
    • JEDEC Testing Requirements• Temp Cycle: – +85 C Tmax, -55/-40 C Tmin, 5-10 min soak, ~3 cyc/hr – Whi k Whiskers typically f t i ll form after 500 cycles ft l• High Temp/Hum Conditions: – 60 C / 87% RH for 4000 hours – Whiskers typically form after 1000-2000 hours• Room Conditions: – 30 C / 60% RH for 4000 hours – AEC and iNEMI driving to eliminate this condition from JEDEC• Calibration Standard and Equipment Certification required Information is Patrick Neyman Confidential & Proprietary page 20 / Do Not Reproduce or Distribute - Patrick Neyman
    • Sample Requirements for 2-Leads• Fi l as-mounted product. L Final t d d t Loose and R fl d Reflowed d – For parts without top-bottom symmetry: 3 total pre-conditions• Minimum 3 plating lots, at least one week apart, no more than ~1-2 months old at time of test – the older the samples, the more likely Whiskers will grow• Minimum 2 samples per lot for pre-condition for each test• Minimum 9 samples total per test – Due to minimum 18 measurable terminations – Measurable termination = able to measure top and 2 sides• Minimum 75 mm2 total inspection area per test• Minimum 25 mm2 total inspection area each sample – Including at least 2 edges with 3 mm total length• Minimum 96 total inspection areas – Must increase number of samples if cannot achieve 96 areas – Each inspection area should be > 0.85 mm2 (not including solder fillet) Information is Patrick Neyman Confidential & Proprietary page 21 / Do Not Reproduce or Distribute - Patrick Neyman
    • JEDEC Allowable Whisker Length Military Telecom Industrial Consumer Aerospace Automotive Electronics Electronics Information is Patrick Neyman Confidential & Proprietary page 22 / Do Not Reproduce or Distribute - Patrick Neyman
    • JEDEC Testing Requirements• Whisker length chosen by established lead spacing requirements. spacing• Saturation debate (Telecom): – Original allowable length was 65 micron – R d Reduced t 40 micron since classified with d to i i l ifi d ith automotive in JEDEC – Move to separate infrastructure from human safety – form Class 2A Information is Patrick Neyman Confidential & Proprietary page 23 / Do Not Reproduce or Distribute - Patrick Neyman
    • Outline•Ti TinWhiskers F d Whi k Fundamentals t l •Physical & Electrical Properties •Growth and Accelerated Growth Factors •Risk Factors •Mitigation t gat o - Conformal Coating Update •The Role of Intermetallics•Industry Perspective - Consumer, Telecom, Automotive - Supplier and Customer•JEDEC Testing Requirements•Test Flow: Ni-Underplated devices with 4/less leads•Reference List Information is Patrick Neyman Confidential & Proprietary page 24 / Do Not Reproduce or Distribute - Patrick Neyman
    • Test Flow Example Tin Whisker Test Flow for Ni-Underplated Passive Components with Four or Less Terminals Plating Lot C Plating Lot A Plating Lot B Lot (plated >1 week after lot B) (test finished parts) (plated >1 week after lot A) (plated <4? weeks after lot A) 3-5 per condition for each test No Precondition: No Precondition:Cond Precondition: Glued in Normal Glued in “Deadition Reflow Configuration Bug” Configuration 27-45 parts goto ::: each test ::: ~300-500 parts total (80-140 if re-use) Information is Patrick Neyman Confidential & Proprietary page 25 / Do Not Reproduce or Distribute - Patrick Neyman
    • Test Flow Example, stress tests Information is Patrick Neyman Confidential & Proprietary page 26 / Do Not Reproduce or Distribute - Patrick Neyman
    • Test Flow Example, examination Information is Patrick Neyman Confidential & Proprietary page 27 / Do Not Reproduce or Distribute - Patrick Neyman
    • Reference List• Annotated Tin Whisker Bibliography and Anthology George T Galyon IEEE Trans Anthology, T. Galyon, Trans. Elec. Pack., 28 (1), 94-122 (January 2005)• Role of Intrinsic Stresses in the Phenomena of Tin Whiskers in Electrical Connectors, Sudarshan Lal and Thomas D. Moyer, IEEE Trans. Elec. Pack., 28 (1), 63-74 (January 2005)• An Integrated Theory of Whisker Formation: The Physical Metallurgy of Whisker Formation and the Role of Internal Stresses, George T. Galyon and L. Palmer, IEEE Trans. Elec. Pack., 28 (1), 17-30 (January 2005) ( ) ( y )• An Electrical Characterization of Tin Whisker, Robert Hilty, Ned Corman, MRS Spring Meeting, San Francisco (2007)• Tin Whisker Reliability Assessment by Monte Carlo Simulation, Robert Hilty, Ned Corman, Corman IPC/JEDEC Lead Free Symposium San Jose (2005) Symposium,• Accelerated Tin Whisker Test Committee Update Phase 5, Heidi L. Reynolds, ECTC Tin Whisker Workshop, Reno, NV, (May 29, 2007)• Matte Sn Electroplating in Mass Production and Testing According to JESD201, P Oberndorff, Ditt Ob d ff M Dittes, P Crema, H Si C Siegel, P S ECTC Ti Whi k W k h l Su, Tin Whisker Workshop, R Reno, NV, (May 29, 2007)• Evaluation of Conformal Coatings as a Tin Whisker Mitigation Strategy, Part II, Tom Woodrow, , Reno, NV, (May 29, 2007) Information is Patrick Neyman Confidential & Proprietary page 28 / Do Not Reproduce or Distribute - Patrick Neyman
    • Reference List• JESD22A121: Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes (May 2005)• JP002: Current Tin Whiskers Theory and Mitigation Practices Guideline (March 2006)• JESD201: Environmental Acceptance Requirements for Tin Whisker Susceptibility of Tin and Tin Alloy Surface Finishes (March 2006) Information is Patrick Neyman Confidential & Proprietary page 29 / Do Not Reproduce or Distribute - Patrick Neyman