Project. Technical Overview

Transcription

1 Manhattan Project Technical Overview Carmine Meola et al ACI Technologies Pb-free Is Not Free!

2 Project Participants B2P COE Project Management: Carmine Meola Technical Project Leadership: Ed Morris (Lockheed Martin) & Jerry Aschoff (Boeing) Self-funded Meeting Moderator: Dr. Richard R. Reilly, Howe School of Technology Management, Stevens Institute of Technology SMEs: Dr. Peter Borgesen (Universal Instruments/Unovis) Lloyd Condra (Boeing) Dr. Carol Handwerker (Purdue University) Dr. Craig Hillman (DfR Solutions) Dave Hillman (Rockwell Collins) Dave Humphrey (Honeywell) Dave Locker (AMRDEC) Dr. Steph Meschter (BAE Systems) Dr. Mike Osterman (Univ. of Maryland CALCE) Dave Pinsky (Raytheon) Dr. Tony Rafanelli (Raytheon) Dr. Polina Snugovsky (Celestica) Fred Verdi (ACI) Dr. Paul Vianco (Sandia National Labs) Maureen Williams (NIST) Dr. Tom Woodrow (Boeing) Linda Woody (Lockheed Martin)

3 Discussion Topics Manhattan Project Overview Tin Whiskers Manufacturing Solder Reliability Components Printed Circuit Boards

4 Summary Approach for Aerospace & Defense (A&D) Pb-free Electronics Risk Reduction Manhattan Project A&D Project ONR Funded Phase 1: Best Practice Baseline Completed Manhattan Project JDMTP Funded Phase 2: Technology Roadmap In Work! 2009 Risk Reduction Program DoD plus Phase 3 Integrated Risk Reduction Projects Tin Whiskers Electronics Assembly Solder Joints Electronic Component Printed Circuit Boards Customers

5 Who Decided to Remove the Pb? Reduction of Hazardous Substances (RoHS) EU Directive banning placing on market new electronic equipment containing specific levels of the following after July 1, 2006 RoHS covers Lead, Cadmium, Mercury, hexavalent chromium, polybrominated biphenyl (PBB), polybrominated diphenyl ether (PBDE) flame retardants Waste Electrical and Electronic Equipment Directive (WEEE) EU directive aims to minimize the impact of electronic waste Encourages and sets criteria for collection, treatment, recycling Makes the producer responsible Related legislation in place in China, Japan, & Korea Lead-free brings new and re-emerging failure modes in electronics

6 Why Is Pb Currently Used in Electronics? Added to improve electronics reliability Improved Solderability Inexpensive Solution Lower the solder melt temperature for improved component reliability Stronger Solder Joints (Mechanical and Electrical Properties) Essentially eliminated the growth of tin whiskers that cause failures Tin Whiskers Growing on a Pure Tin Component Photo Source: NASA Goddard Losing 50+ Years of Proven & Predictable Performance Using Tin-Pb Electronics

7 Where Is Pb Used in Electronics? Internal to components: Die Bonding Lead Finish DIE DIE DIE Solder Ball Array PWB / Component Interconnect Component Terminations PWB Surface Finish Plating of Hardware on and around Circuit Cards

8 What Is the Difference Between Pure Tin vs. Pb-Free Electronics? Main Area of Past Focus NiPd Hot-dipped SnAg Annealed Matte SnCu Sn over Ni SnAg Dominant Risk Area SnBiCu NiPdAu Reflowed Sn Pb-Free Matte Sn (Alloy with <0.1 wt % Pb) Pure Tin SnCu (Alloy with >97 wt % Sn) NiAu SnBi Concerns: Reliability Bright Sn Annealed Matte Hot-dipped SnCu Data Sn Hot Dipped Sn Hot-dipped SnAgCu Ag Supply Chain Concerns: Management / Tin Whiskers Matte Sn over Ag Configuration AgPd Tin Pest Control SnAgNi Manufacturing Complexity Field Support Pure Tin Requires Mitigation; Pb-Free Requires an Understanding of New Materials

9 What Are the Pb-Free Electronics Concerns? Manufacturing Prevailing Pb-free solder replacement (SnAgCu) has ~35 C higher reflow temperature Can affect components and board material Infant mortality / Latent failures Requalification? Solder joint reliability (durability) Pb-free alloys can fail in high stress/strain applications Intermetallics between solder and lead/pad Cross contamination of different alloys Changed / unacceptable wetting characteristics New qualification parameters Configuration Control Must prevent mixing of incompatible alloys Many components not uniquely identified Field Support/Depot Repair Logistical Nightmare Cracked Solder Joint Joint

10 Operating Environment vs. Operational Life-time Consequences of Failure Harshness of Service Environment (Humidity, Temperature, Shock, Vibration) High Low C Cell Phones A Medical Equipment Cars Tin Whiskers Network Servers Desktop PCs Satellites D Missiles A&D Risk Reduction Project Focus Major Home Appliances Operational Service Life (Years) Aircraft B

11 Current Technical Status No universally acceptable technical solutions in sight to replace SnPb in Aerospace & Defense (A&D) applications Conformal coatings only mitigate tin whiskers Pb-free solder joint reliability decreased for shock and has corrosion issues SAC305 solder dissolves copper, impacting rework and repair Conductive Anodic Filament (CAF) problem is re-emerging due to higher CCA processing temperatures using Pb-free solders Current technical approaches are all still mitigations and not elimination of the Pb-free electronics issues Conductive Anodic Filament (CAF) in Circuit Card Assembly (CCA) Ref: Lead Free PCB Projects Update, Wayne Jones, Advanced of Electronic Assemblies Consortium, February 2008

12 Risks Pb (Lead) inhibits the growth of tin whiskers Electrically conductive Can metal vapor arc Pb-Free Solders Less reliable in high shock & vibration environments Have higher melting temps Incompatibilities with SnPb Solder Less repairable assemblies Configuration Control Nightmare! Photo Source: NASA Space Shuttle Program Pb-Free Solder Joint Electromagnetic Relay Vapor Arc Damage

13 Phase 1 & 2 Observations 1. Serious technical gaps exist for Pb-free electronics that have to be overcome for use in A&D harsh environment 2. Quantification of degraded reliability and lifetimes is a significant gap 3. The three-year Pb-Free Electronics Risk Reduction Program schedule is aggressive, but realistic 4. Phase 3 execution will require and draw on the best available talent in the A&D community 5. Phase 3 will benefit any A&D or commercial product that relies on Pb-free COTS electronics and operates in extreme or harsh environments Phase 1 Baseline Practices & Knowledge Gaps Design Manufacturing Sustainment Testing Reliability Phase 2 & 3 Risk Reduction Project Areas Tin Whiskers Assembly Solder Joints Printed Circuit Boards Components

14 Critical ASAP Steps Completed and In Work Team Benchmarking & Roadmapping Study Phase 1: Identify current best practices to deal with Pb-free electronics (2 Weeks, 20 April to 1 May 2009) Completed! Funded by Navy ManTech Benchmarking & Best Practices Center of Excellence Report available for download at the B2P COE Website ( and the Defense Acquisition University Lead-free Website ( Phase 2: Define the Risk Reduction Roadmap to address the gaps (2 Weeks, August 2009) In Work! Funded by Joint Defense Manufacturing Technology Panel (JDMTP) Met for two weeks in August and developed a 36-month Risk Reduction Roadmap for Phase 3 execution Report with Roadmap and ROM cost estimates being drafted targeting early 2010 release 1/28/10 Pb-Free Is Not Free! 14

15 Recommended Roadmap for A&D Risk Reduction Coordinated approach proposed to achieve technical consensus Individual companies figuring out unique solutions will result in configuration, contractual and logistics nightmares High cost if each individual company figures this out on their own DoD readiness and sustainment will be severely impacted by a noncoordinated approach 72 integrated project tasks have been defined Organized under the six major project areas 15 intermediate project groups Durations between 6 and 36 months Most projects estimated to require between $500k and $1M Projects typically collaborate with at least five other concurrent projects

16 Phase 1 Report Content Executive Summary 1.0 Introduction 2.0 Pb-Free Electronics Overview 3.0 Design Current baseline* Issues/Misconceptions/Gaps Conclusion Recommendations 4.0 Manufacturing 5.0 Sustainment 6.0 Test 7.0 Reliability 8.0 Conclusions 9.0 Recommendations Appendices Post-Release Peer Review Phase 1 Report to Be a Living Document Open Request for Critical Review and Corrections & Additions * Current Baseline Practice: A practice that describes the current state-of-theart as a baseline against which future improvement can be measured

17 Recommended Roadmap for A&D Risk Reduction (Cont d) Year 1 Year 2 Tin Whiskers Manufacturing and Repair Processes Solder Joint Reliability Component Issues Year 3 Tin Whisker Risk Mitigation Interconnection Reliability PCB Issues Program Management/Coordination KEY DELIVERABLES Risk Reduction Detailed Design Guidelines Validated Life-Prediction Models Assembly and Repair Process Definitions Methodologies for Assessing New Materials 17

18 Any Recent Failures? SAC BGA Rework Head in Pillow (HiP) Defect Problem: Intermittent ATC open failure after rework (2000 I/O BGA with 1 open joint) Lab Analysis: Metallurgical analysis found head-on-pillow and differential cooling between balls and paste Result: SAC process requires regular calibration of reflow heaters Other Causes: BGA ball contamination, warpage BGA Ball Open (HiP) 3D X-ray Reconstruction Photos Provided by Celestica Paste & SAC Ball Not Wetted Large Sn Dendrite Indicates Slower Cooling at Component Side SAC Paste Resolidified Before Wetting to BGA 1/28/10 18 Pb-Free Is Not Free!

19 Any Recent Failures? (Cont d) A Recent Industry Disclosure: 1. A board assembly house working on an Defense development Contract who was successfully soldering lead-free BGAs of around 1000 balls onto a tin lead PCB got into a problem recently. 2. The board assembler developed an oven profile which soldered the SAC 305 BGAs and the tin-lead with out damaging temperature sensitive components. 3. Everything was going along well until the manufacturer of the BGAs switched from SAC 305 to SAC 105 because of concerns about solder fracture during drop testing from commercial customers. 4. The BGA had the same lead-free logos on it indicating it was RoHS compliant. The markings did not reflect the alloy change of the BGA solder balls. 5. SAC 305 has a melting temp of around 221C. SAC105 has a melting temperature of 228C. 6. The profile that melted the SAC 305 BGAs did not fully melt all the SAC 105 BGA solder balls. 7. The problem was missed until an intermittently functioning BGA was found during trouble shooting. The BGA passed automated X-ray inspection. The connections were in the middle of the package and not optically inspectable. 8. Unfortunately some of the product escaped into the field and had to be recalled. 1/28/10 Pb-Free Is Not Free! 19

20 Tin Whiskers 20

21 What Is a Tin Whisker? Tin whisker effects documented since the 1940 s Tin Whiskers Occur on nearly all tin alloys Few microns to ½ inch + Electrically conductive Hardware Tin plated nuts, bolts, covers, card guides, etc. also at risk Whisker Induced Failures: Short Circuit: Bridges two adjacent pins 1/3 inch Photo Source: NASA Space Shuttle Program Metal vapor arc: Voltage and atmospheric conditions can result in plasma arc capable of catastrophic damage FOD: Whisker breaks off and interferes with mechanical, optical, or MEMS component

22 12/3/09 Pb-Free Is Not Free! 22

23 Have Tin Whiskers Caused Failures? Multiple Documented Occurrences (NASA/Industry/Academic Publications) Nuclear Utilities 7 Satellites ($100M Boeing Loss) Patriot (PAC-2) 6 Missile Programs Heart Pacemaker F-15 Radar Military Airplane Telecom. Equip. $1B Worth of Satellites, Missiles & Other Equipment Catastrophic Damage Due to Tin Whisker Induced Metal Vapor Arc NOTE: Electromagnetic Relay Was Purchased to MIL Spec Prohibiting Pure Tin Finish Inside, But IT WAS Pure Tin Ref:

24 How Can We Mitigate Tin Whiskers? Design Practices Eliminate exposed conductive surfaces Conformal Coating Material Selection Avoid Use of Tin Plating Greater than 97% Purity Component & Assembly Processes Re-flow of Pure Tin Plated Surfaces Solder Dip / Strip & Re-plate Terminations Annealing Handling Practices Provide Stable Storage Environment Temperature/Humidity Provide Protection From Mechanical Damage Mitigation Elimination Tin Whisker Examples Growing on Capacitor Growing on Reworked Component Lead

25 12/3/09 Pb-Free Is Not Free! 25 25

26 Manufacturing and Repair 26

27 The Pb-free Impact on the Manufacturing Process Flow DFM (4.2) Manufacturing Flow (Staging 4.3) Purchase and Store Parts/Boards Incoming Inspection Kit and Issue to Production Paste Print (4.4) Chip Adhesive Application (4.5) Part Placement (4.5) Convection Reflow (4.7) Vapor Phase Reflow (4.7) Wave Solder (4.7) (Solder Formation 4.6) Selective Solder (4.7) Depanel (4.8) Clean & Mark (4.9) Underfill (4.10) Inspect (4.11) Rework (4.12) Conformal Coating (4.13) Test (in circuit) (4.14) Test (ESS) (4.14) Conformal Coating (4.13) Pack & Ship (4.15) No Impact Low Impact High Impact 12/3/09 Pb-Free Is Not Free! 27

28 Solder Process Requires Higher Temperature Profiles 12/3/09 Pb-Free Is Not Free! 28

29 Current Baseline Practices Aerospace & Defense Manufacturing Processes which use Lead-free require tighter process controls and detailed process validation Critical process parameters requiring tighter control include reflow profiles, cleaning requirements, and damage control margins due to higher processing temperatures. Process variations may have a greater impact on resulting solder joint integrity Master manufacturing facility layout strategy required for coexistence or segregation of SnPb and Lead-free processes. Marking strategies and tighter inventory controls need to be adopted to distinguish SnPb from Lead-free (IPC-609). Basic understanding of metallurgy of different solder alloys and subsequent solder joint integrity required Operator training is critical for process and inspection techniques 12/3/09 Pb-Free Is Not Free! 29

30 Solder Reliability 30

31 Solder Joint Reliability Majority of electronic part (memory, logic, passives, etc.) manufacturers have converted parts construction to comply with government regulations (i.e. EU RoHS). While some still provide tinlead terminations, obtaining originally manufactured parts with tinlead terminals is becoming increasingly difficult. For solder joint reliability, the greatest issue with maintaining tin-lead soldered assemblies is the increased use of area array packages which are no longer available with tin-lead solder bumps. Mixed solder (lead-free area array bumps and tin-lead solder paste) joints have known reliability issues which are dependent on the solder assembly process. This issue is further complicated by continued changes to solder composition by electronic part manufacturers. Conversion to full lead-free assemblies raises long-term reliability concerns. Again, this issue is further complicated by continued changes by electronic part manufacturers. 12/3/09 Pb-Free Is Not Free! 31

32 Solder Joint Project Area Solder Joint Reliability Models Effects Issue Resolution Underfill, Staking, and Coating Models Solder Selection Guidelines Insertion Mount Issue Resolution Handling Guidelines 12/3/09 Pb-Free Is Not Free! 32

33 Solder Joint Reliability Models Provide (i) credible models for assessing life expectancy of solder interconnects formed with a set of prevalent solder combinations and (ii) optimized test methodology to qualify new solder combinations. Create common test vehicles Create common material database Create common failure database Temperature cycling Vibration Drop and Shock Combined Loads Create models based on common material and failure database 12/3/09 Pb-Free Is Not Free! 33

34 Mixed (lead-free bumped array assembled with Tinlead solder paste) Solder A SAC BGA was assembled in a conventional Sn37Pb solder process. Failure in temperature cycling (-55 to 125 o C) occurred in less than 150 cycles. This type of defect could escape current screening practices and result in aborted or failed missions. Hillman, D., Wells, M., and Cho, K., The Impact of Reflowing a Pb-free Solder Alloy Using A Tin/Lead Solder Alloy Reflow Profile on Solder Joint Reliability Last Accessed 1/22/ /3/09 Pb-Free Is Not Free! 34

35 Tin-Silver-Copper Solder Tin-Silver-Copper (SAC) alloys have gained market share as the leadfree replacement for tinlead solder. While select compositions (i.e sn ag0.5cu) have been extensively studied, reliability concerns have resulted in continued exploration of new compositions. E, CTE Bieler, 06 E, CTE Significant scatter expected in SAC properties because of heterogeneity & uniqueness caused by few large anisotropic Sn grains As-fabricated BGA SAC Joints Sundelin, μm Park et al,, 2008 Park et al,, /3/09 Pb-Free Is Not Free! 35

36 1 Overall Approach for Fatigue Life Prediction Constitutive laws Elastic ε el = σ/ε Plastic ε p = K p (T) σ n p(t) Creep ε cr = K c σ n c e -Δ Η / R Τ 2 Package Architecture / Loads Package Architecture Passivation layer Solder resist A B Silicon die Copper track FR4 board bondpad metallization Temp. (C) solder joint time 4 Energy density (MPa/cycle) Damage Assessment U e W p W c 3 shear stress (Mpa) Local Stress-Strain History Cycles Shear strain (%) N fe, N fp, N fc Output: Cycles to failure: *Figures and Images courtesy of CALCE, University of Maryland 1 N ftotal = 1 N fe N fp N fc

37 Fatigue Damage Evolution Sn37Pb *Images courtesy of CALCE, University of Maryland SAC Under cyclic stress tin-lead solder exhibits grain coarsening (enlargement), crack formation and growth. For lead-free SAC solder, the structure exhibits grain formation due to recrystalization which results in finer grains that separate at grain boundaries resulting in crack growth. Due to anisotropic behavior and random dispersion of intermetallic compounds in the solder, material behavior exhibits a greater degree of randomness than occurred with SnPb. 12/3/09 Pb-Free Is Not Free! 37

38 Effects Issues Electromigration Current densities of 10 4 A/cm 2 create structural changes in solder material. Current limits and impact on solder joint reliability need to be determined. Corrosion Impacts of corrosive environments on lead-free solder have been largely unexplored. Increased rate of damage due to corrosion may be a factor in extended service life. Board Finish Pad finish plays largely a secondary role but needs to be addressed to provide guidelines for designers. Solder Paste Evaluation Level of impact due to proprietary organics in solder pastes from different solder manufacturers not quantified. Wave Solder Contamination Visual defects may not be sufficient to determine acceptable contamination levels for wave solder. Life impact needs to be examined. Tin Pest Conversion of β-tin to α-tin. α-tin is highly brittle and falls apart under minimal loading. Transition known to occur a low temperatures (<13C). Factors that promote transitions and likelihood of issue remain unknown for long-term applications. 12/3/09 Pb-Free Is Not Free! 38

39 Effects Issue Resolution In addition to anticipated temperature cycling, mechanical shock and vibration, solder joints and their respective reliability can be expected to be influenced by other factors. With the use of new materials and combinations, it is necessary to quantify these impacts to qualify materials for use in A&D applications. Factors include: Electromigration Corrosion Board Finish Solder Paste Wave Solder Contamination Tin Pest SAC305 solder after treated with salt spray 5% wt% at 35 C for 96 hrs. Lui, B, Lee, T, Lui, K, Environmental Conditions Impact on Pb-Free Solder Joint Reliability, IMAPS 2009, San Jose, CA, Nov 31-5, /3/09 Pb-Free Is Not Free! 39

40 Testing Temperature Cycling Low strain rates, Low cycle Vibration High strain rates, High cycle Combined Mixed failure models produced by combination of low and high strain rates. Concerns with how to account for different combinations Drop and Shock Extremely high strain rates Creep Rupture Abrupt failure of joints under a fixed load. 12/3/09 Pb-Free Is Not Free! 40

41 Components 41

42 Components - Current Baseline Practices Component Pb-free process/materials compatibility characterized mainly for consumer applications Component Assembly Compatibility Moisture Sensitivity Level widely characterized for Pb-free SnPb finishes not characterized for Pb-free process temperatures Temperature Sensitivity per J-STD-075 not universal Storage of components not major concern for most current Pbfree applications No-clean processes for consumer items Component Finish Effects on Solder Joint Reliability Short term life generally sufficient for most finish materials 12/3/09 Pb-Free Is Not Free! 42

43 Components - Knowledge Gaps Assembly Process Temperature sensitivity Corrosion sensitivity Flux and cleaning compatibility Finish effects on solder joint reliability Solderability requirements Refinishing cost and schedule impacts Storage requirements for solderability maintenance Protocols for finish material verification Uncertainties for Aerospace and Defense Applications 12/3/09 Pb-Free Is Not Free! 43

44 Components - R&D Approach Recommended Projects Component Characterization Temperature exposure limits Receiving/incoming inspection requirements Storage requirements for unassembled components Component properties database Fluxes/cleaning process compatibility with components Component Refinishing/Reprocessing Temperature Sensitivity Capability Improvement Component Finish Finish Solder Joint Effect Solderability Component Corrosion Corrosion Acceleration Factors Corrosion Mitigation 12/3/09 Pb-Free Is Not Free! 44

45 Printed Circuit Boards 45

46 Current Baseline Practices Military/Aerospace Electronic Products Characterization: Life Critical & Flight Critical Applications Extremely Stable Qualified Material Lists Significant Use Life ~ Years Not Uncommon Manufacturing Mode: High Mix/Low Volume Design Cycle Mode: Deliberate and Long ~ 12 Months Customer Certification The printed circuit board is the foundation for the entire printed circuit assembly if the PCB integrity is questionable, then all other efforts are a moot point 46

47 Knowledge Gap #1 Printed Circuit Board Copper Structures: Pad Design/ Stencil Design Assessment and Confirmation What pad patterns and stencil designs are required for the creation of High Performance solder joint geometries? Copper Requirements and Copper Dissolution What are the minimum copper plating requirements for High Performance harsh environment integrity? Acceptance Test Methods for Void Formation associated with Aging of Solder/Copper Plated Structures What test methods provided an assessment of void formation in solder/copper plated structures 47

48 Knowledge Gap #1 Copper Dissolution of Plated Thru Hole 48

49 Knowledge Gap #2 Printed Circuit Board Laminate Materials: Thermal Robustness of Laminate Material What level of laminate robustness is required to avoid thermally induced degradation in High Performance PCB laminates? Pad Cratering How do we characterize, assess and design for a new failure mode in High Performance PCB laminates? Conductive Anodic Filament (CAF) How do we characterize, assess and design for this failure mode in High Performance PCB laminates? Development of New Laminate Material Application of High Performance PCB laminate key characteristics for laminate development 49

50 Knowledge Gap #2 Pad Cratering Defects (Courtesy of Celestica) 50

51 Knowledge Gap #3 Printed Circuit Board Surface Finishes: Surface Finish Evaluation What Assembly Robustness, Corrosion, Solderability and Tin Whisker characteristics are necessary requirements for High Performance Assembly Processes Surface Finish Test Methods What test methods exist for understanding surface finish characteristics relating to harsh long storage and fielded environments Development of New PCB Plating Materials Development of new plating materials that meets the assembly, reliability, and cost expectations of High Performance products Sporadic Brittle Failure of Pb-Free Solder Due to Nickel Plating How do we characterize, assess and design for a new failure mode in High Performance PCB laminates 51

52 Knowledge Gap #4 Printed Circuit Board Database and Design Rules: Heuristic rules used by electrical and mechanical designers based on experience with SnPb programs may be insufficient to ensure reliability of Pb-free product. Provide a database of new and future materials attributes and compatibilities resulting in design rules for PCBs used in Pb-free assembly of High Performance products. 52

53 Summary Pb-free electronics are fundamentally and drastically changing the way electronic products for A&D are designed, procured, manufactured, tested, and supported Need a coordinated, proactive DoD-wide Risk Reduction Program to deal with the issues and ensure highest quality, best value electronic products for the Warfighter The Cultural Issues for are as challenging as the Technical Issues, making it more difficult to obtain risk reduction funding Good News: The concept has been validated as a viable approach to deal with complex issues that demand a radical approach A focused team of Government and Industry Subject Matter Experts is recommended!