Technical Challenges of RoHS Compliance

1. Technical Challenges of RoHS Compliance by Leo Lambert EPTAC Corp, Manchester, NH for Implementing Lead-Free Electronics Workshop February, 28, 2006

2. Design and Manufacturing Impacts • Component identification • Component lead plating • Component selection • Board designs from the perspective of selecting solderable coatings • Immersion silver or Tin • Gold ENIG • OSP • Manufacturing process changes

3. Design and Manufacturing Impacts • Higher heat profiles • Laminates • Number of thermal cycles • Components and compatibility of those components to the new thermal profiles • Bake cycles and double sided mounting on assemblies • Reflow processes • Higher temperatures and longer dwell times

4. Laminates • Must have lead free solderable coatings • Must comply with list of identified RoHS materials • Must be able to meet new thermal excursion temperatures. • Users must understand Tg and Td • Review CAF (Conductive Anodic Filament) resistance

5. Laminate Requirements for Lead Free Processes • Recommend Temperature of Decomposition (ASTM D-3850 test method) testing using the 2 percent weight loss for reporting the performance characteristics of more thermally robust laminate materials. • Recommend all laminate material data sheets report T288°C (Time to delamination at 288°C) as well as T260°C • Time to Delamination test results better indicate performance in higher temperature lead free assembly

6. Laminate Requirements for Lead Free Processes • Recommend CAF (Cathodic Anodic Filament) testing per IPC TM-650 Section 2.6.25. • Recommend reporting 5X Thermal Shock at 260°C results as a key indicator of material performance in higher temperature lead free assembly applications. • Most non-dicy cured FR-4 laminate materials made using Novolac-type catalyst are more thermally robust and should be part of this testing. • Several non-dicy FR-4 laminate materials using Novolac-type catalyst have now been developed (with T288°C Time to Delamination data) Adapted from Lead-free Reflow Oven and Rework Machine Status by Jaspir Bath, Solectron, 2004

7. CAFConductive Anodic FilamentGrowth

8. CAF • First identified by Bell Labs in 1976 • Conductive, subsurface filament growth from the anode in high voltage (400V) boards, exposed to high humidity, i.e. greater than 80% Rh. • Will cause failures if shorting between anode and cathode. Adapted from “Conductive Anodic Filament (CAF) Formation by Laura Turbini, W. Jud Ready and Brian A. Smith of Georgia Institute of Technology

9. Conductive Anodic Filament CAF Found most likely to occur at following locations: • PTH to PTH • Line to Line • PTH to Line • Layer to Layer Standardizing a Test Method for Conductive Anodic Filament Growth Failure By Clarissa Navarro, Isola Laminate Systems.

10. Conductive Anodic Filament CAF Factors driving concerns: • Increased operating temperatures • Under the hood applications. • High density of holes • High Humidity (80%Rh) • High voltage (~3 – 8 V/mil) • Multiple thermal cycles • Soldering Flux Standardizing a Test Method for Conductive Anodic Filament Growth Failure By Clarissa Navarro, Isola Laminate Systems.

11. Conductive Anodic Filament CAF Conductive anodic filament (CAF) failure is the growth or electromigration of copper in a PCB. Standardizing a Test Method for Conductive Anodic Filament Growth Failure By Clarissa Navarro, Isola Laminate Systems.

12. What does Pb-Free mean to electrochemical migration (ECM)? New plating materials New interconnect materials New flux chemistries ECM and alternative platings ENIG and ImSn dependent upon plating quality ImAg dependent upon electric field Sn-Based Alloys Use environment likely to be acidic with the presence of oxygen and halides Potential for order of magnitude increase in corrosion rate Electrochemical Migration in the Age of Pb-Free

13. Components Lead free components will require: • An awareness of moisture sensitivity • Meeting new temperature excursion profiles • Identification of parts relative to solderable coating • Providing proper storage containers and environments • Training of material handling personnel

14. Marking Categories Pb-free category : • Identifies the general family of materials used for the 2nd level interconnect including solder paste, lead/terminal finish, and terminal material/alloy solder balls • e1: SnAgCu • e2: Other Sn alloys – no Bi or Zn (SnCu, SnAg, SnAgCu…) • e3: Sn • e4: Pre-plated (Ag, Au, NiPd, NiPdAu, (no Sn) • e5: SnZn, SnZnX (no Bi) • e6: Contains Bi • e7: Low Temperature solder (<150oC) containing indium but no bismuth • e8, e9 unassigned categories Adapted from Courtesy IPC-1066

15. e1 = SnAgCu (i.e. solder balls) e2 = Other Sn alloys (i.e. SnCu, SnAg) e3 = Sn (i.e. matte Sn) e4 = pre-plated (i.e. NiPdAu, NiPd) Component Markings

16. Marking Symbols Pb-free Symbol • Can be used as an option to replace the phrase “lead-free” on labels or wherever practical on components/devices, boards, assemblies, etc. Pb-free Category Symbol Marking Hierarchy • If two or more solder alloys are used, the reflow category will be shown first, then the wave solder category alloy will follow. Adapted from Courtesy of Cogiscan

17. Moisture Sensitivity Levels

18. Impact of Lead Free on MSD

19. Impact of Lead Free on MSD Ref : Pb-free IC Component Issues and IPC/JEDEC Specification Update, Rick Shook, Agere Systems Adapted from Courtesy of Cogiscan

20. Reliability

21. What do we know? Many Lead-Free studies were conducted Typical Findings: • High quantities of failure were found to be cracking of ceramic chip capacitors when flexing the circuit board. • Pb-Free solder resulted in solder joints that were more rigid than those of Sn/Pb.

22. Types of Capacitor Failures1

23. SnAgCu Flex Crack Examples1

24. SnAgCu Flex Crack Examples1

25. Acknowledgements The previous slides were adapted from the following papers. • Robustness of Surface Mount Ceramic Capacitors Assembled with Pb-Free Solder, by Nathan Blatau, Patrick Gormally, Vin Iannaccone, Laurence Harvilchuck and C. Hillman • Robustness of Surface Mount Aluminum Electrolytic Capacitors When Subjected to Lead Free Reflow, by C. Wiest, N. Blatau, J. Wright, R. Schatz, and C. Hillman

26. Where Does It Happen? • Flexing (Mechanical Stress) occurs in following areas: • Manufacturing • Soldering Handling • Board separation • Connector installation • Mechanical standoff installation • In-circuit testing • Customer usage

27. Flex Cracking Examples Adapted from “AVX MLCC Flexiterm Guarding Against Capacitor Crack Failures” by Mark Stewart, Technical Information

28. Solder Joint Cracking

29. Tin/Lead Solder Joint Failure Crack starts at the toe of the solder joint and propagates to the component. Grain coarsening may be an area of high stress. Adapted from: “A Comparison of the Isothermal Fatigue Behavior of Sn-AG-Cu to Sn-Pb Solder” By Nathan Blattau and Craig Hillman, DfRSolutions

30. Sn/Ag/Cu Solder Joint Failure • In this figure the crack starts in the fillet and goes toward the component. • The crack start further up the fillet then it does with Sn/Pb solder. • Next slide provides another example Adapted from: “A Comparison of the Isothermal Fatigue Behavior of Sn-AG-Cu to Sn-Pb Solder” By Nathan Blattau and Craig Hillman, DfRSolutions

31. Sn/Ag/Cu Solder Joint Failure Adapted from: “A Comparison of the Isothermal Fatigue Behavior of Sn-AG-Cu to Sn-Pb Solder” By Nathan Blattau and Craig Hillman, DfRSolutions

32. Lead as an impurity goes to the last area of the joint to cool. This forms a pocket and disturbs the grain structure. The resultant lead rich areas have a lower melting temperature and could cause dewetting during soldering Lead Contamination Adapted from “A Study of Lead-Contamination In Lead-free Electronics Assembly And Its Impact on Reliability” by Karl Seeling and David Suraski, AIM, Inc.

33. BGAs

34. Typical Over Molded PBGA Adapted from: PBGA Package Warpage and Impact on Traditional MSL Classification for Pb-Free Assembly By B.T. Vaccaro, R.L. Shook, E. Thomas, J.J. Gilbert, C. Horvath, A. Dairo and G.J. Libricz

35. BGA Concerns Due Higher Process Temperatures • Typical warpage due to increases in temperature Adapted from: PBGA Package Warpage and Impact on Traditional MSL Classification for Pb-Free Assembly By B.T. Vaccaro, R.L. Shook, E. Thomas, J.J. Gilbert, C. Horvath, A. Dairo and G.J. Libricz

36. BGA Concerns Due Higher Process Temperatures • As can be seen as the temperature increases the shape of the package changes which can cause excess forces on the molten solder creating shorts. Adapted from: PBGA Package Warpage and Impact on Traditional MSL Classification for Pb-Free Assembly By B.T. Vaccaro, R.L. Shook, E. Thomas, J.J. Gilbert, C. Horvath, A. Dairo and G.J. Libricz

37. What are they and how do they happen? Solidification process of SAC alloys causes shrink holes Slow cooling causes excessive shrinkage of the final eutectic solder phase just before solidification It does not seem to impact reliability It is not a crack and does not continue to grow under thermal or mechanical stresses Shrink Hole Voids

38. Forward Process/Component Compatibility • Forward Compatibility: • Using Sn/Pb components in Pb-free process • Reported of an increase in voiding in PBGA solder ball joint due to flux trapping. • Also reported is resulting lead contamination that may affect the solder joint structure and decrease its reliability. • Many component vendors including Intel do not recommend using their components in forward or backward compatible assemblies.

39. Backward Process/Component Compatibility Backward compatibility: • Using Pb free components in Sn/Pb process • Lead free BGAs are not recommended for Sn/Pb assembly using temperature below 220oC (428oF) because solder joints are poorly formed if the balls do not melt. • May impact 2nd level Interconnect reliability may be affected • Increase tin whisker growth

40. BGA Solder Joints Grain structure of alloy in BGA solder joint Adapted from photos from Bob Willis

41. Tin/ Silver /Copper, Sn/ Ag / Cu Reflow Temperature 219 -217

42. Tin Whiskers Columns Striations Rings Adapted from iNEMI Tin Whisker Test Project, September 25, 2003 Adapted from a publication of the National Electronics Manufacturing Center of Excellence

43. Tin Whiskers • Tin Whiskers Growing on the Portion of a Bright" Tin-Plated Lead of a Crystal Oscillator (see inset above)that was NOT Immersed in Sn/Pb Solder during Hot Solder Dip Preparation Prior to Mounting

44. NEMI Experimental Tests for Tin Whisker Growth Tests: • -55°C (+0, -10) / 85°C (+10, -0) air-air temperature cycle (20minutes/cycle) up to 3000 cycles (500 cycles check points) • 60°C, 90±5%RH temperature / humidity storage 9000 hrs (~1 year) with 1000 hr check points • Ambient storage (~23°C, ~60%RH) up to 18000 hours (~2 years) with 1000 hr check points

45. Copper Dissolution Example microsection produced as part of the evaluation showing copper erosion on the copper track. (IDEALS Lead Free Project) Adapted from Lead-free Wave Soldering Process Issues By Bob Willis

46. Good solder joint Fillet lifting on top side of joint Lead Free Solder Joints Adapted from Lead-free Wave Soldering Process Issues By Bob Willis

47. PTH Solder Joint Solder Lifting Off Pad. Solder Joint Cracking in Fillet

48. Corroded Solder Iron Tips

49. Step 1: Solder Pot - De-Alloying Problem 1. Lead free solder alloys cause corrosion and abrasion at the stainless-steel based solder pot, pumps and solder channels fragmentation at the solder shafts Supplied by SEHO USA

50. Step 1: Solder Pot - De-Alloying Protection of the contact zones To avoid problems caused by de-alloying of Fe, the replacement machine parts must be special coated which protects the parts against the aggressive solder alloy. composit-coatedpump wheels uncoated pump wheel after 6 month of use with Pb-free solder alloy Supplied by SEHO USA