Plastic package reliability

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Today, plastic packaged integrated circuits are ubiquitous even for high-reliability applications. Reliability testing and standards play a key role in reliability engineering to achieve the......

Today, plastic packaged integrated circuits are ubiquitous even for high-reliability applications. Reliability testing and standards play a key role in reliability engineering to achieve the necessary reliability performance. Traditional stress-based standards are easy to use but often over- or under-stress units and don’t focus on key vulnerabilities, particularly moisture-related ones. Knowledge-based standards have evolved to fix this, but rely on knowledge of mechanisms, control of board manufacturing conditions, and understanding and specifying end use conditions. This motivates a survey of plastic package mechanisms and testing with particular focus on moisture-related mechanisms and testing. The moisture-related examples will cover HAST testing, and the “popcorn” mechanism.
Learning Objectives
1.Understand the philosophy and methods behind reliability testing of ICs as applied to plastic-packaged ICs.
2.Learn the historical development of the JEDEC temperature-humidity-bias (HAST) moisture reliability testing standard.
3.Get a practical overview of key thermal, thermo-mechanical, moisture (chemical), and moisture (“popcorn”) mechanisms.
4.Appreciate how transformation of environmental conditions to conditions at the site of failure in the package is used to “scale” reliability models.

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  • 1. Plastic Package  Reliability li bili C. Glenn Shirley ©2011 ASQ & Presentation Shirley Presented live on Aug  02~04th, 2011http://reliabilitycalendar.org/The_Reliability_Calendar/Short_Courses/Shliability Calendar/Short Courses/Short_Courses.html
  • 2. ASQ Reliability Division  ASQ Reliability Division Short Course Series Short Course Series The ASQ Reliability Division is pleased to  present a regular series of short courses  featuring leading international practitioners,  academics, and consultants. academics and consultants The goal is to provide a forum for the basic and  The goal is to provide a forum for the basic and continuing education of reliability  professionals.http://reliabilitycalendar.org/The_Reliability_Calendar/Short_Courses/Shliability Calendar/Short Courses/Short_Courses.html
  • 3. Plastic Package Reliability C. Glenn Shirley Integrated Circuits Design and Test Laboratory Electrical and Computer Engineering Portland State University Portland, Oregon http://web.cecs.pdx.edu/~cgshirl/ © C. Glenn Shirley
  • 4. Outline• Plastic Packages• Stress and Test Flows• Thermal Mechanisms• Moisture Mechanisms• Thermo-mechanical Mechanisms• Moisture-mechanical Mechanisms• Technology Update8/2-4/2011 Plastic Package Reliability 2 © C. Glenn Shirley
  • 5. Plastic-Encapsulated Microcircuits • The course covers plastic-encapsulated microcircuits. • Molding compound (MC) in PEMs comes in direct contact with the die and chip connections. Single Layer Copper Heat Slug Lead Frame Tape/Adhesive DielectricExpoxy Based Molding Metal Heat Sink PlateCompound Ag - Epoxy Adhesive Ag - Epoxy Adhesive BT Resin Multilayer PCB Epoxy Based Molding 1.27mm Grid Array Compound Solder Balls Solder Balls 8/2-4/2011 Plastic Package Reliability 3 © C. Glenn Shirley
  • 6. Plastic-Encapsulated Microcircuits• Die is mounted on a lead frame (A42 or Cu).• Bonds are made by. Alloy 42 Fe 58% Ni 42% alloy – Wirebond: Au or Al; mostly Au. with CTE matching Si. – TAB: Tape-Automated Bonding. – C4: Controlled Collapse Chip Connect.• Assembly is encapsulated in molding compound. – Molding compound is in direct contact with die, wire bonds, etc.• External leads are trimmed and solder plated.8/2-4/2011 Plastic Package Reliability 4 © C. Glenn Shirley
  • 7. Molding Compounds• MC is thermoset (curing) epoxy, typically novolac. – Cures at ~ 170-180C. – Silica “filler” controls CTE and increases thermal conductivity. – MCs are (now) free of ionic contaminants.• Glass Transition ~ 140C.• Moisture properties of MC: – Permeable to moisture. – Absorbs moisture. “Hygroscopic.” Note distinction between thermoset and thermoplastic.8/2-4/2011 Plastic Package Reliability 5 © C. Glenn Shirley
  • 8. Molding Compound Properties• At the glass transition (> 140 C).. MC strength decreases CTE increases L. T. Manzione “Plastic Packaging of Microelectronic Devices,” Van Nostrand Reinhold 1990.8/2-4/2011 Plastic Package Reliability 6 © C. Glenn Shirley
  • 9. Molding Compound Properties, ct’d• Molding compound strongly absorbs water. – Saturation uptake is proportional to RH, and independent of temperature. – Rate of uptake depends strongly on temperature. L. T. Manzione “Plastic Packaging of Microelectronic Devices,” Van Nostrand Reinhold 1990.8/2-4/2011 Plastic Package Reliability 7 © C. Glenn Shirley
  • 10. Outline• Plastic Packages• Stress and Test Flows• Thermal Mechanisms• Moisture Mechanisms• Thermo-mechanical Mechanisms• Moisture-mechanical Mechanisms• Technology Update8/2-4/2011 Plastic Package Reliability 8 © C. Glenn Shirley
  • 11. Life of an Integrated Circuit OEM/ODMAssembly Shipping Storage End-user Environment Assembly Temp DT Shipping Shock Temperature Bend Reflow Handling Temp, RH Power Cycle Cycle Bent Pins, SingulationDesktop Temp DT BAM! Shipping Shock Temperature Bend Reflow Handling Temp, RH User Drop Power Cycle Cycle & VibeMobile PC Bent Pins, Singulation DT BAM! Shipping Shock Temperature Bend Reflow Handling Temp, RH Keypad Cycle User Drop pressHandheld & Vibe 8/2-4/2011 Plastic Package Reliability 9 Source: Eric Shirley © C. Glenn Monroe, 2003 Slide by Scott C. Johnson.
  • 12. Stress/Test Flow From: JEP150 “Stress-Test-Driven Qualification of and Failure Mechanisms Associated with Assembled Solid State Surface-Mount Components” (JEDEC) Simulate shipping, storing, and Preconditioning OEM board mounting process. Simulate in-service end use Environmental Stress conditions. Electrical Test, Failure Determine pass/fail. Diagnose Analysis failures.8/2-4/2011 Plastic Package Reliability 10 © C. Glenn Shirley
  • 13. Industry Reliability Standards• International – ISO International Standard Organization – IEC International Electrotechnical Commission• Europe – CEN, CENELEC Comite Européen de Normalisation Électrotechnique• Japan – JIS Japanese Industrial Standard, EIAJ• US – MIL (US Department of Defense), EIA/JEDEC For US commercial products JEDEC standards have mostly superseded MIL standards.8/2-4/2011 Plastic Package Reliability 11 © C. Glenn Shirley
  • 14. PreconditioningEnvironmental StressElectrical Test, Failure Analysis Preconditioning • Preconditioning simulates board assembly. • Specified by – JESD22-A113F Preconditioning of Nonhermetic Surface Mount Devices Prior to Reliability Testing. – IPC/JEDEC J-STD-020D.01 Moisture/Reflow Sensitivity Classification for Nonhermetic Solid State Surface Mount Devices http://www.jedec.org/ Free downloads, registration required. 8/2-4/2011 Plastic Package Reliability 12 © C. Glenn Shirley
  • 15. PreconditioningEnvironmental StressElectrical Test, Failure Analysis Preconditioning Flow JESD22-A113F IPC/JEDEC J-STD-020D.01 Slide 50 8/2-4/2011 Plastic Package Reliability 13 © C. Glenn Shirley
  • 16. PreconditioningEnvironmental StressElectrical Test, Failure Analysis Environmental Test • Stress-based testing (traditional). To keep things simple, we’ll follow this approach. – Standards: JESD47, MIL-STD-883. – Pro: • Well-established standards. Lots of historical data. Good for comparisons. • Little information about mechanism or use is required. – Con: • Overstress: May foreclose a technology. • Understress: Misses a mechanism. – May not accurately reflect a use environment. • Knowledge-based testing. – Risk assessment of Use and Mechanism guides test. 8/2-4/2011 Plastic Package Reliability 14 © C. Glenn Shirley
  • 17. PreconditioningEnvironmental StressElectrical Test, Failure Analysis Knowledge-Based Test • Knowledge-Based Testing Use Condition Mechanism – Stress depends on knowledge of use conditions and mechanisms. Risk Assessment – Risk assessment, using methods Stresses • JEDEC: JESD94, JEP143, JEP148 • Sematech: “Understanding and Developing Knowledge-based Qualifications of Silicon Devices” #04024492A-TR – Pro: • Stresses fit the product and its use. May make a product feasible. – Con: • Easy to miss mechanisms in new technologies and overlook use conditions in new applications. • Tempting to misapply to “uprate” devices, relax requirements. 8/2-4/2011 Plastic Package Reliability 15 © C. Glenn Shirley
  • 18. PreconditioningEnvironmental StressElectrical Test, Failure Analysis JESD47 Example Note: TS (JESD22-A106) and AC (Steam) (JESD22-A102) are not recommended. Very different from use. 8/2-4/2011 Plastic Package Reliability 16 © C. Glenn Shirley
  • 19. PreconditioningEnvironmental StressElectrical Test, Failure Analysis Example Stress Flow Early life failure rate. Assumptions ELFR 168 hrs 168 h is equivalent to early life requirement JESD22-A108 SS computed from goal. eg. 3x611 = 1833 Focus of this course. Preconditioning. PC JESD22-A113 (Lots x Units) 3 x 77 3 x 25 3 x 25 3 x 25 HTOL HTSL (Bake) TC THB or HAST High temperature 1000 hrs 700 cycles 1000 hrs (85/85) operating life. JESD22-A103 3 cycles/hr JESD22-A101 168 -1000 hrs 233 hrs 96 hrs (130/85) JESD22-A108 JESD22-A104 JESD22-A110 Condition B or G (C is too severe) 8/2-4/2011 Plastic Package Reliability 17 © C. Glenn Shirley
  • 20. Sampling• JESD47 sample requirements are minimal. – Single “snapshot” is a crude validation of the reliability of the product. – Small SS does not generate failures to give clues to process weaknesses.• Risks. – Qualification hinges on single failures. • Moral hazard to “invalidate” a failure is high. – Lot-to-lot variation, excursions. • Incoming materials, fab lots, assembly lots, test lots.8/2-4/2011 Plastic Package Reliability 18 © C. Glenn Shirley
  • 21. PreconditioningEnvironmental StressElectrical Test, Failure Analysis Sampling, ct’d • Number of lots covers risks of machine-to machine, day-to-day, etc. variation. • Often minimum SS to validate a goal is chosen. – Pro: Saves $, and there are no failures to explain. – Con: Pass/fail of the qual is at the mercy of a single failure. • Verrry tempting to invalidate a failure. – Con: No mechanism learning. (Accept/Reject  0/1) • eg. To validate 500 DPM at ELFR using minimum SS at 60% confidence, 1833 units are required.  ln(1  cl ) – 500 DPM is a typical goal (see ITRS) SS  D Useful “mental furniture”  ln(1  0.6) 1833  500  106 8/2-4/2011 Plastic Package Reliability 19 © C. Glenn Shirley
  • 22. PreconditioningEnvironmental StressElectrical Test, Failure Analysis Sampling, ct’d • For environmental stress, 77 is a typical SS, why?  ln(1  cl )  ln(1  0.9)  ln(.1) 100 230.26 SS  ; 2    76.7 D 3 10 3 3 – So, 0/1 accept/reject validates, to 90% confidence, a failure rate less than 3% at the accelerated condition. • If the stress corresponds to the lifetime (eg. 7 years) then the average wearout failure rate is 3 102 FR   109  489 Fits 7  365  24 – This falls into the range of ITRS goals. 8/2-4/2011 Plastic Package Reliability 20 © C. Glenn Shirley
  • 23. PreconditioningEnvironmental StressElectrical Test, Failure Analysis Reliability Goals from ITRS 2009 http://www.itrs.net/reports.html Infant Mortality Wear-out Constant fail rate 8/2-4/2011 Plastic Package Reliability 21 © C. Glenn Shirley
  • 24. Example Data • Additional attributes enhance value of data. – Device type – Date code – Package type – Readouts – Failure analysisMaxim product reliability report RR-1H 8/2-4/2011 Plastic Package Reliability 22 © C. Glenn Shirley
  • 25. PreconditioningEnvironmental StressElectrical Test, Failure Analysis Test and Failure Analyis 48 HOUR TEST WINDOW • Moisture-related tests Functional Test Fail (unvalidated failure) Pass Return to Stress (85/85, HAST, Steam) Validate Using Functional Test Pass Invalid Failure (Censor sample or return to stress) Fail have specific test/FA Diagnostic Functional Test Including raster scan, electrical analysis Pass for electrical location of defect reqt’s. – Test must be done while All Other Failures Fail by Invalid Mechanism (eg. package defect in die-related certification) unit contains moisture. • Within 48 hr. VALID FAILURE – Units must not be “wet”. Bake + Diagnostic Functional Test • Wet = liquid water. Fail Irreversible Damage (eg. corrosion) Pass Reversible (eg. leakage path thu moisture films) • Diagnostic Bake. Non-Destructive F/A (visual, X-Ray, CSAM) • Risk decision before Risk Decision (based on likely mechanism) destructive analysis. Chemical Decapsulation (to observe mechanical defects such as cracks) Mechanical Decapsulation (to observe chemical defects such as residues) 8/2-4/2011 Plastic Package Reliability 23 © C. Glenn Shirley
  • 26. HAST versus 85/85• Moisture MUST be non-condensing. (RH < 100%).• Both require about < 1% fail. Typical SS ~ 100.• 130/85 HAST duration is 10x less than 85/85 duration. We’ll see how this was justified.• 85/85 (JESD22-A101) 6 week bottleneck in information turns.• HAST (JESD22-A110) 10x less time 33.3  14.2 1 atm = 14.2 psi  1.34 atmospheres  Pressure vessel required. 14.28/2-4/2011 Plastic Package Reliability 24 © C. Glenn Shirley
  • 27. Example: Comparison of HAST Stds Intermittent Bias Test and Failure Analysis Window From Sony Quality and Reliability Handbook http://www.sony.net/Products/SC-HP/tec/catalog/qr.html8/2-4/2011 Plastic Package Reliability 25 © C. Glenn Shirley
  • 28. HAST System• Large vessel (24” dia) requires forced convection. C. G. Shirley, “A New Generation HAST System”, Non-proprietary Report to Intel, Despatch Industries, and Micro- Instrument Corp. describing learnings during development of NG HAST. December, 1994.8/2-4/2011 Plastic Package Reliability 26 © C. Glenn Shirley
  • 29. HAST System8/2-4/2011 Plastic Package Reliability 27 © C. Glenn Shirley
  • 30. HAST System8/2-4/2011 Plastic Package Reliability 28 © C. Glenn Shirley
  • 31. HAST Development Team8/2-4/2011 Plastic Package Reliability 29 © C. Glenn Shirley
  • 32. HAST Ramp Up Requirements• Ramp Up: Avoid condensation on load.8/2-4/2011 Plastic Package Reliability 30 © C. Glenn Shirley
  • 33. HAST Ramp-Down Requirements• Mechanical pressure relief must be slow (3 h).• Vent when pressure reaches 1 atm.• Hold RH at test value. – Units must retain moisture acquired during test. ~ 3.5 atm 1 atm8/2-4/2011 Plastic Package Reliability 31 © C. Glenn Shirley
  • 34. Vapor Pressure and Relative HumidityLog scale 10 4 Coexistence of liquid and vapor Q = 0.42 eV 2 1 .4 Pressure (Atm) .2 Liquid Water .1 Water Vapor .04 .02 .01 200 160 120 100 80 60 40 20 0 Linear in 1/T (K), Temperature in deg C (Arrhenius Scale) with ticks placed at T (C). 8/2-4/2011 Plastic Package Reliability 32 © C. Glenn Shirley
  • 35. Vapor Pressure and Relative Humidity Actual water vapor pressure at temperature T H Saturated water vapor pressure at temperature T or PH2O  H  Psat (T ) Important. What is Psat?  lM   QP  klM Psat (T )  P0 exp   P0 exp  QP   0.42 eV  RT   kT  R Where l = 2262.6 joule/gm (latent heat of vaporization) M = 18.015 gm/mole, R = 8.32 joules/(mole K), k = 8.617x10-5 eV/K This is a fair approximation. The main benefit is physical insight.8/2-4/2011 Plastic Package Reliability 33 © C. Glenn Shirley
  • 36. Vapor Pressure and Relative Humidity An accurate formula for Psat (in Pascals) is  3  Psat (T )  1000  exp  an  x , x  n 1  n 0  273  T ( C) a0  16.033225, a1  35151386  103 , . a2  2.9085058  105 , a3  5.0972361 106 which is accurate to better than 0.15% in the range 5 C< T < 240 C. 1 atm = 101325 pascals This is an accurate formula.8/2-4/2011 Plastic Package Reliability 34 © C. Glenn Shirley
  • 37. Vapor Pressure and Relative Humidity• Relative humidity at “hot” die in steady state. – Partial pressure of water vapor is the same everywhere: PH2O (die)  PH2O (ambient ) – So RH at die is given by: H(die)  Psat (Tambient  DTja )  H(ambient )  Psat (Tambient ) – Where the ratio, h is defined as: H(die)  h  H(ambient ) Psat (Tambient ) h Psat (Tambient  DTja )8/2-4/2011 Plastic Package Reliability 35 © C. Glenn Shirley
  • 38. Vapor Pressure and Relative Humidity 1.00 0 2 0.80 4 0.784 6 0.60 8 R 10 0.40 15 20 30 0.20 40 Curves labelled with Tja 0.00 0 20 40 60 80 100 120 140 160 180 200 T(ambient) Example: At 20/85 and Tja = 4 C, the die is at 24/(0.784x85) = 24/67.8/2-4/2011 Plastic Package Reliability 36 © C. Glenn Shirley
  • 39. Outline• Plastic Packages• Stress and Test Flows• Thermal Mechanisms• Moisture Mechanisms• Thermo-mechanical Mechanisms• Moisture-mechanical Mechanisms• Technology Update8/2-4/2011 Plastic Package Reliability 37 © C. Glenn Shirley
  • 40. Focus Topic: Acceleration• Acceleration between two stresses is the ratio of times (or cycles) to achieve the same effect.• The “same effect” could be the same fraction failing. – eg. The ratio of median (not mean!) times to failure in different stresses is the Acceleration Factor (AF). • AF is proportional to 1/MTTF MTTF1 Q   1 1   AF (2 |1)   exp     Thermal MTTF2  kB   T1 T2    Q   1 1       exp C V2  V1  MTTF1 AF (2 |1)   exp  Thermal and Voltage MTTF2  kB   T1 T2     Q  1 1  m MTTF1  a  bV2   RH 2    AF (2 |1)     exp      Moisture ("Peck") MTTF2  a  bV1   RH1   k B  T1 T2     m MCTF1  DT2  AF (2 |1)    Thermal Cycle ("Coffin-Manson") MCTF2  DT1 8/2-4/2011 Plastic Package Reliability 38 © C. Glenn Shirley
  • 41. Thermal Mechanisms Early life failure rate. ELFR 168 hrs JESD22-A108 Preconditioning. PC JESD22-A113 HTOL HTSL (Bake) TC THB or HASTHigh temperature 1000 hrs 700 cycles 1000 hrs (85/85)operating life. JESD22-A103 3 cycles/hr JESD22-A101168 -1000 hrs 233 hrs 96 hrs (130/85)JESD22-A108 JESD22-A104 JESD22-A110 Condition B or G (C is too severe)8/2-4/2011 Plastic Package Reliability 39 © C. Glenn Shirley
  • 42. Gold-Aluminum Bond Failure• Gold and Aluminum interdiffuse. – Intermetallic phases such as AuAl2 (“Purple Plague”) form. – Imbalance in atomic flux causes Kirkendall voiding. – Bromine flame retardant is a catalyst.• Kirkendall voids lead to – Bond weakening - detected by wire pull test. – Resistance changes in bond - detected by Kelvin measurement of bond resistance.8/2-4/2011 Plastic Package Reliability 40 © C. Glenn Shirley
  • 43. Thermal (Ordinary) Purple Plague Cross-section of gold ball bond on aluminum pad after 200 hours at 160C8/2-4/2011 Plastic Package Reliability 41 © C. Glenn Shirley
  • 44. Gold-Aluminum Bond FailureLog scale 1E4 1 year (!) (8760h) 1E3 100 Hours 10 1 Source: S. Ahmad, Intel 0.1 380 340 300 260 220 200 180 160 Linear in 1/T Temperature (deg C, Arrhenius Scale) (K), with ticks Arrhenius plot of time to 10% of wire pull failure. placed at T (C). Activation energy (Q) = 1.17 eV. 8/2-4/2011 Plastic Package Reliability 42 © C. Glenn Shirley
  • 45. Gold-Aluminum Bond Failure • Kelvin resistance Log{ Resistance Change (milliohms)} measurements. 1.4 • Resistance increase of 1.45 1.2 2.7 Au bonds to Al pads vs 0.8 bake time. 1.0 0.5 • Bake at 200 C. 0.8 • Various levels of Br flame-retardant in 0.6 molding compound. Weight % Bromine 0.4 • Br catalyzes Au-Al intermetallic growth. 0.2 Source: S. Ahmad, et al. “Effect of Bromine in Molding Compounds on Gold-Aluminum Bonds,” • Br flame retardants IEEE CHMT-9 p379 (1986) are being phased out 0 20 40 60 80 100 120 140 today. Bake Time, hours8/2-4/2011 Plastic Package Reliability 43 © C. Glenn Shirley
  • 46. Thermal Degradation of Lead Finish• Only an issue for copper lead frames (not Alloy 42).• Cu3Sn or Cu6Sn5 inter-metallic phases grow at the interface between solder or tin plating.• Activation energy (Q) for inter-metallic phase growth is 0.74 eV.• If inter-metallic phase grows to surface of solder or tin plate, solder wetting will not occur.• Main effect is to limit the number of dry-out bakes of surface mount plastic components.8/2-4/2011 Plastic Package Reliability 44 © C. Glenn Shirley
  • 47. Thermal Degradation of Lead Finish Solder Solder Lead Cu6Sn5 intermetallic Copper Copper Post-plating solder plate Post burn-in solder plate showing copper-tin intermetallic8/2-4/2011 Plastic Package Reliability 45 © C. Glenn Shirley
  • 48. Thermal Degradation of Lead Finish X-section of solder-plated lead X-section of solder-coated lead8/2-4/2011 Plastic Package Reliability 46 © C. Glenn Shirley
  • 49. Outline• Plastic Packages• Stress and Test Flows• Thermal Mechanisms• Moisture Mechanisms• Thermo-mechanical Mechanisms• Moisture-mechanical Mechanisms• Technology Update8/2-4/2011 Plastic Package Reliability 47 © C. Glenn Shirley
  • 50. Example Stress Flow Early life failure rate. ELFR 168 hrs JESD22-A108 Preconditioning. PC JESD22-A113 HTOL HTSL (Bake) TC THB or HASTHigh temperature 1000 hrs 700 cycles 1000 hrs (85/85)operating life. JESD22-A103 3 cycles/hr JESD22-A101168 -1000 hrs 233 hrs 96 hrs (130/85)JESD22-A108 JESD22-A104 JESD22-A110 Condition B or G (C is too severe)8/2-4/2011 Plastic Package Reliability 48 © C. Glenn Shirley
  • 51. H2O Diffusion/Absorption in MC MODEL Surface exposed to ambient. Zero flux or "die" surface 2L Surface exposed to ambient. ACTUAL Plastic Molding Compound (MC) L A8/2-4/2011 Plastic Package Reliability 49 © C. Glenn Shirley
  • 52. H2O Diffusion/Absorption in MC Diffusion Coefficient: Saturation Coefficient:  Q  Q D  D0 exp   d  S  S0 exp  s   kT  See slide 13.  kT D0  4.7 105 m 2 / sec Qd  0.50 eV S0  2.76 104 mole/m3 Pa Qs  0.40 eV Source: Kitano, et al IRPS 1988 Henry’s Law: Msat  PS  HPsat S See slide 33. H2O vapor pressure. Key Observation: Saturated moisture content of molding compound is nearly independent of temperature, and is proportional to RH.  (Qs  Qp )  M sat  HP0 S0 exp   Qs  Qp  0.02 eV  kT  Nearly zero!8/2-4/2011 Plastic Package Reliability 50 © C. Glenn Shirley
  • 53. H2O Diffusion/Absorption in MC 1.00 0.80 Total Weight Gain (M) (C-Cinit)/(Ceq-Cinit) or 0.60 (M-Minit)/(Meq-Minit) 0.40 Concentration at Die Surface (C) 0.20 0.8481 0.00 0.00 0.20 0.40 0.60 0.80 1.00 Fourier Number = Dt/L^28/2-4/2011 Plastic Package Reliability 51 © C. Glenn Shirley
  • 54. Response to Step-Function Stress Typical Use Saturation Times Hours 1K DIP, PLCC (50 mils) Package Moisture 400 Time Constant 200 (time to 90% saturation) 100 PQFP (37 mils) t (sat )  20 L2  Qd  10 TSOP (12 mils) 0.8481 exp  D0  kTmc  4 2 L 1 220 180 140 100 60 40 20 130 T (deg C)Typical 130/85 HAST SaturationTimes Normal Operating Range 8/2-4/2011 Plastic Package Reliability 52 © C. Glenn Shirley
  • 55. Cyclical Stress One-Dimensional Diffusion Equation Solutions 8 hours on, 16 hours off cycling for PDIP CjMoles/m3 Moles/m3 520540 0 440 0 460 360 380 mils mils 280 0 0 20 40 50 20 40 50 Hours 60 Hours 60 T(ambient) = 100 C T(ambient) = 60 C t(sat) = 28 hours t(sat) = 153 hours Moisture concentration at the die is constant if Period << t(sat) 8/2-4/2011 Plastic Package Reliability 53 © C. Glenn Shirley
  • 56. Peck’s Acceleration Model• Fundamental environmental parameters are T, H and V, at the site of the failure mechanism. – If the die is the site, this is denoted by “j”.• A frequently used acceleration model is due to Peck AF  (a  b V )  H m  exp( Q / kT j ) j• Find a, b, m, Q from experiments with steady-state stress and negligible power dissipation.• Typically a is small or zero: Bias is required.• Requires H > 0 for acceleration: Moisture is required.8/2-4/2011 Plastic Package Reliability 54 © C. Glenn Shirley
  • 57. Moisture: MM Tape Leakage Leadframe Power Plane Ground Plane8/2-4/2011 Plastic Package Reliability 55 © C. Glenn Shirley
  • 58. Moisture: MM Tape Leakage MM Leakage vs 156/85 Biased HAST Time 156/85 HAST of MM Tape Candidates 1000 0.15 800 "A" 0.1 600Leakage 1/MTTF mA 400 (hrs) 0.05 200 "B" 50 0 10 20 30 40 0 Biased HAST Stress Time (HR) 1 2 3 4 5 6 7 8 Bias (Volts) Experimental Tape Data: Tape m Q eV Acceleration factor is proportional to bias. “A” >12 0.74 AF  “B” 5 0.77 Source: C. Hong, Intel, 1991 Constant  V  H m exp(Q / kT ) 8/2-4/2011 Plastic Package Reliability 56 © C. Glenn Shirley
  • 59. Moisture: Internal Metal Migration• TAB Inter-lead Leakage/Shorts – Accelerated by voltage, temperature and humidity – Seen as early as 20 hrs 156/85 HAST – Highly dependent on materials & process-+ - Copper dendrites after 40 hours of biased 156/85 HAST8/2-4/2011 Plastic Package Reliability 57 © C. Glenn Shirley
  • 60. Lead-Stabilizing Tape Leakage• A vendor process excursion.• Leakage observed after 336 hours of steam.• Re-activated by 48 hours at 70C/100% RH• No leakage seen between leads not crossed by tape• Rapid decay for leads crossing end of tape – Tape dries from exterior inwards Tape provides mechanical stability Die Lead Stabilizing Tape to long leads during wirebond.8/2-4/2011 Plastic Package Reliability 58 © C. Glenn Shirley
  • 61. Lead-Stabilizing Tape Leakage 1E-5 Pins Crossed by Tape 1E-6 1E-7 Leakage Pin 2-3 Current (A) 1E-8 Pin 3 -4 1E-9 1E-10 1E-12 Pins NOT crossed by tape 1E-13 10 100 1000 Recovery Time (Minutes) Source: S. Maston, Intel8/2-4/2011 Plastic Package Reliability 59 © C. Glenn Shirley
  • 62. Aluminum Bond Pad Corrosion Fe++ AF Lead CorrosionMicrogap Ni++ Cl- Constant  V  H m exp(Q / kT ) Source m Q (eV) Peck (a) 2.66 0.79 Moisture Moisture Hallberg&Peck (b) 3.0 0.9 (a) IRPS, 1986; (b) IRPS, 1991. Pins 1 Shortest path has highest failure rate. Source: P.R. Engel, T. Corbett, and W. Baerg, “A New Failure Mechanism of Bond Pad Corrosion in Plastic-Encapsulated IC’s Under Temperature, Humidity and Bias Stress” Proc. 33rd Electronic Components Conference, 1983. 8/2-4/2011 Plastic Package Reliability 60 © C. Glenn Shirley
  • 63. Passivation in Plastic Packages• Passivation is the final layer on the die.• Passivation has two main functions: – Moisture Barrier • Molding compound is not a moisture barrier. • Silicon oxides are not good moisture barriers. • PECVD silicon nitride or silicon oxynitride film is a good barrier. • Film must be thick enough to avoid pinholes, coverage defects. – Mechanical Protection • Silicon nitride films are brittle. • Polyimide compliant film protects silicon nitride. • Polyimide can react with moisture (depending on formulation).8/2-4/2011 Plastic Package Reliability 61 © C. Glenn Shirley
  • 64. Polyimide/Au Bond Failure• Bonds overlapping passivation don’t necessarily violate design rules.• But can activate polyimide-related “purple plague” failure mechanisms in combination with moisture.• Acceleration modeling showed no field jeopardy. Polyimide PECVD Oxynitride/Nitride Metal Bond Pad Other films Silicon8/2-4/2011 Plastic Package Reliability 62 © C. Glenn Shirley
  • 65. Wire Bond Pull Test8/2-4/2011 Plastic Package Reliability 63 © C. Glenn Shirley
  • 66. Moisture-Related Gold Bond Degrad’n Effect of 80 hours of 156/85 HAST vs 156/0 Bakeand Centered vs Off-Centered Bonds on Wire Pull Test Data 99.99 99.9 99 90 70 HAST 50 OFF-CENTER %30 10 HAST CENTERED 1 BAKE BAKE OFF-CENTER 0.1 CENTERED 0.01 0 2 4 6 8 10 12 14 16 18 20 Pull Force (gm) Source: G. Shirley and M. Shell, IRPS, 19938/2-4/2011 Plastic Package Reliability 64 © C. Glenn Shirley
  • 67. Moisture-Related Gold Bond Degrad’nWire Pull Strength of Polyimide vs No Polyimide and Centered vs Off-Centered Bonds after 40 hours of 156/85 HAST 99.99 99.9 99 90 70 50 %30 POLYIMIDE OFF-CENTER 10 1 NO-POLYIMIDE 0.1 POLYIMIDE CENTERED: SQUARE CENTERED OFF-CENTER: TRIANGLE 0.01 0 2 4 6 8 10 12 14 16 18 20 Pull Force (gm) Source: G. Shirley and M. Shell-DeGuzman, IRPS, 1993 8/2-4/2011 Plastic Package Reliability 65 © C. Glenn Shirley
  • 68. Moisture-Related Purple Plague Cross-section of gold ball bond on aluminum pad after 80 hours at 156C/85%RH8/2-4/2011 Plastic Package Reliability 66 © C. Glenn Shirley
  • 69. Moisture-Related Gold Bond Degrad’n 121/100 17hr 156/85 + x 156/65 b  112.7 gm 135/85 156/85 100 a0  113  1010 (gm - hrs) -1 . 80 m  0.98; Q  115 eV .F50 1(gm) F50  40 (at ) 2  1 / b 2 a  a0  h m  exp( Q / kT ) 20 FP  F50  exp(   Z P ) 20 40 100 200 400 1E3 2E3 Hours   0.17 Source: G. Shirley and M. Shell-DeGuzman, IRPS, 1993 8/2-4/2011 Plastic Package Reliability 67 © C. Glenn Shirley
  • 70. Circuit Failure Due to Passiv’n Defects 10m Site of failing bit. SRAM after HAST stress. Courtesy M. Shew, Intel8/2-4/2011 Plastic Package Reliability 68 © C. Glenn Shirley
  • 71. Circuit Failure Due to Passiv’n Defects 2m 2m Etch-decorated cross-section of passivation. Note growth seams.8/2-4/2011 Plastic Package Reliability 69 © C. Glenn Shirley
  • 72. Circuit Failure Due to Passiv’n DefectsSRAM VOLTAGE THRESHOLD MAP FOR CELL PULLUP TRANSISTOR(Baseline threshold is 0.89 V. Passivation is 0.6 m nitride, no polyimide.)Vthreshold Vthreshold Row Row Column Column After 120 h 156/85. 4 2 bits recover after further 2 hr failed bits with Vt > 2.5 V bake at 150 C Source: C. Hong, Intel 8/2-4/2011 Plastic Package Reliability 70 © C. Glenn Shirley
  • 73. Acceleration Model Fit of HAST Data SRAM HAST and 85/85 Bit Failures (No Polyimide) 90 85/85, standby 70 140/85, standby 140/85, no bias 50 156/85, standby % 156/85, active 30 156/85, no bias Model: 85/85 standby Model: 140/85 standby 10 Model: 140/85 no bias Model: 156/85 standby Model: 156/85 active Model: 156/85 no bias 1 Notes: 0.5 • “Standby” = 5.5V bias, low power 30 100 1E3 1E4 • “Active” = 5.5V bias, high power Hours • 156/85: non-standard, limit ofAF  Constant  ( a  bV )  H m  exp( Q / kT ) pressure vessel. • Source: C. G. Shirley, C. Hong. Intela  0.24 b  014 m  4.64 Q  0.79 eV . 8/2-4/2011 Plastic Package Reliability 71 © C. Glenn Shirley
  • 74. Peck Model Parameters Hours of Q/m < 130/85 Mechanism Q(eV) m Q/m 0.42eV? 1kh 85/85 ReferenceMM Tape A 0.74 12 0.06 Yes 69 2MM Tape B 0.77 5 0.15 Yes 62 2Single Bit SRAM 0.79 4.6 0.17 Yes 57 3Corrosion, THB (early Peck) 0.79 2.66 0.30 Yes 57 4Corrosion, THB (later Peck) 0.90 3 0.30 Yes 39 5Bond Shear 1.15 0.98 1.17 No 16 6 Yes/No: Increasing power dissipation at die, slows/accelerates the moisture mechanism. 1. Kitano, A. Nishimura, S. Kawai, K. Nishi, "Analysis of Package Cracking During Reflow Soldering Process," Proc. 26th Ann. Intl Reliability Physics Symposium, pp90-95 (1988) 2. S. J. Huber, J. T. McCullen, C. G. Shirley. ECTC Package Rel. Course, May 1993. Package tape leakage acceleration data courtesy C. Hong. 3. G. Shirley and C. Hong, "Optimal Acceleration of Cyclic THB Tests for Plastic-Packaged Devices," in Proc. 29th Ann. Intl Reliability Physics Symposium, pp12-21 (1991) 4. S. Peck, "Comprehensive Model for Humidity Testing Correlation," in Proc. 24th Ann. Intl Reliability Physics Symposium, pp44-50 (1986). 5. Hallberg and D. S. Peck, "Recent Humidity Accelerations, A Base for Testing Standards," Quality and Reliability Engineering International, Vol. 7 pp169-180 (1991) 6. G. Shirley and M. Shell-DeGuzman, "Moisture-Induced Gold Ball Bond Degradation of Polyimide-Passivated Devices in Plastic Packages," in 31st Ann. Intl Reliability Physics Symposium, pp217-226 (1993). 8/2-4/2011 Plastic Package Reliability 72 © C. Glenn Shirley
  • 75. HAST versus 85/85, ct’d• For all mechanisms surveyed, 1000 hours of 85/85 is equivalent to < 96 hr of 85/85.• For packages < 10 mils covering die, moisture saturation occurs within 10 h at 130/85.• For Tj-Ta > 10C, most mechanisms (with Q/m < 0.42 eV) can be more accelerated with cyclical bias.• 85/85 – JESD22-A101• HAST – JESD22-A1108/2-4/2011 Plastic Package Reliability 73 © C. Glenn Shirley
  • 76. Steady Power Dissipation• Superimpose log(H) vs 1/T contour plots of – Peck model for THB acceleration factor. – Partial pressure of water vapor, Psat.• Contours are straight lines: – Peck model: Iso-acceleration contours with slope proportional to Q/m. – Psat: Isobars with slope proportional to Qp = 0.42 eV.• Depends on: In steady state, the partial pressure of H2O is the same in the ambient and at the die. Reference: C. G. Shirley, “THB Reliability Models and Life Prediction for Intermittently- Powered Non-Hermetic Components”, IRPS 19948/2-4/2011 Plastic Package Reliability 74 © C. Glenn Shirley
  • 77. Steady Power Dissipation Iso-acceleration contours for example mechanism (m = 4.6, Q = 0.8 eV) superimposed on water vapor pressure isobars. 5 atm 4 3 2 1 atm 0.1 atm 0.01atm 100 100K 1K X Typical Climate RH (%) at Die Hj Increasing steady-state(log scale) 100 dissipation (X to Y). Follows isobar. 10 40 1 Relative slope Y 0.01 Q/m < 0.42 eV: Deceleration Q/m > 0.42 eV: Acceleration. 30 180 140 100 80 60 40 20 0 Tj at Die (deg C) (Arrhenius (1/TK) Scale, marked with TC) 8/2-4/2011 Plastic Package Reliability 75 © C. Glenn Shirley
  • 78. Example: Comparison of HAST Stds Non-steady-state requirements From Sony Quality and Reliability Handbook http://www.sony.net/Products/SC-HP/tec/catalog/qr.html8/2-4/2011 Plastic Package Reliability 76 © C. Glenn Shirley
  • 79. Time-Varying Power Dissipation• Most moisture-related mechanisms.. – Have slow or zero rates at zero bias (V=0). AF  V  H  exp(Q / kT ) m j j – Have Q/m < 0.42 eV so, in steady-state, depressed die humidity due to power dissipation slows the rate.• There is an optimum duty cycle which maximizes the effective acceleration.8/2-4/2011 Plastic Package Reliability 77 © C. Glenn Shirley
  • 80. JEDEC 85/85 and HAST Req’ts • Tj-Ta 10C: 100% duty cycle. Assumptions: • 85/85 • Tj-Ta > 10C, 50% duty cycle. • Peck Model m = 4.64, Q = 0.79 eV • AF = 0 for V = 0. • MC thickness 50 mils • Kitano et. al MC properties. Effective EffectiveAcceleration Acceleration Factor Factor Tj – Ta = 20C G. Shirley and C. Hong, "Optimal Acceleration of Cyclic THB Tests for Plastic-Packaged Devices," in Proc. 29th Ann. Intl Reliability Physics Symposium, pp12-21 (1991) 8/2-4/2011 Plastic Package Reliability 78 © C. Glenn Shirley
  • 81. Outline• Plastic Packages• Stress and Test Flows• Thermal Mechanisms• Moisture Mechanisms• Thermo-mechanical Mechanisms• Moisture-mechanical Mechanisms• Technology Update8/2-4/2011 Plastic Package Reliability 79 © C. Glenn Shirley
  • 82. Thermomechanical Mechanisms Early life failure rate. ELFR 168 hrs JESD22-A108 Preconditioning. PC JESD22-A113 HTOL HTSL (Bake) TC THB or HASTHigh temperature 1000 hrs 700 cycles 1000 hrs (85/85)operating life. JESD22-A103 3 cycles/hr JESD22-A101168 -1000 hrs 233 hrs 96 hrs (130/85)JESD22-A108 JESD22-A104 JESD22-A110 Condition B or G (C is too severe)8/2-4/2011 Plastic Package Reliability 80 © C. Glenn Shirley
  • 83. Key Material Properties• Material properties which drive temperature cycling- induced failure mechanisms. Material Thermal Coeffic’t Youngs Thermal of Expansion Modulus Conductivity (ppm/°C) “TCE” (GPa) (W/m °C)Copper 17 119 398Alloy 42 5 Match! 145 15 Low!Silicon 3 131 157Molding Compound 21 18 0.6Alumina 6.5 25 25 PC Board 15-17 11 258/2-4/2011 Plastic Package Reliability 81 © C. Glenn Shirley
  • 84. Cracking Due to Temperature Cycle Bond and TFC damage Void & cracks CrackShearStress With crack Without crackZeroNormal Die EdgeStress With crackZero Without crack 8/2-4/2011 Plastic Package Reliability 82 © C. Glenn Shirley
  • 85. Crack Propagation in Test Conditions• Tensile Test of Notched Samples – Measure crack growth rate for sinusoidal load: Crack Load a Load Notch – Sample geometry and load determine stress intensity factor, K. – Plot crack growth rate da/dN versus K on log-log plot to determine Coffin-Manson exponent, m:8/2-4/2011 Plastic Package Reliability 83 © C. Glenn Shirley
  • 86. Crack Propagation in Test Conditions 1E-1 Encapsulant A 1E-2 Slope of lines on log-log plotCrack Growth Rate 25C da/dN 1E-3  Const  DK  mm/cycle da m 1E-4 150C dN -55C m  20 1E-5 Source: A. Nishimura, et. al. “Life Estimation for IC Packages Under Temperature Cycling Based on Fracture Mechanics,” IEEE Trans. CHMT, Vol. 10, 1E-6 p637 (1987). 0.5 1 2 3 Stress Intensity Factor Amplitude K (MPa m)8/2-4/2011 Plastic Package Reliability 84 © C. Glenn Shirley
  • 87. Crack Propagation in Package• The rate of crack propagation is also given by  Const  DK  da m dN• But in plastic packages under temperature cycling, the stress concentration factor is Important DK  Const  ( moldingcompound   silicon )  Tmin  Tneutral • α is the TCE of MC. DT in temperature cycling-driven models is the temperature difference between the neutral (usually cure) temperature, and the minimum temperature of the cycle. Tmax is less important.8/2-4/2011 Plastic Package Reliability 85 © C. Glenn Shirley
  • 88. Package Cracking and Delamination.. ..damages Wires, Bonds, and Passivation Films. Wire Shear Normal (tensile) Crack Shear Au Substrate Damage Silicon Thin-Film Cracking8/2-4/2011 Plastic Package Reliability 86 © C. Glenn Shirley
  • 89. Bond Damage: Wires and Ball Bonds• Cracks can intersect wires, TAB leads.• Bonds can be sheared at the bond/pad interface• Shear and tensile normal stress can break wires at their necks.• Substrate cracks induced during bonding can propagate and cause “cratering” or “chip-out”.8/2-4/2011 Plastic Package Reliability 87 © C. Glenn Shirley
  • 90. Wire Damage (Open) Wires sheared by wire crack8/2-4/2011 Plastic Package Reliability 88 © C. Glenn Shirley
  • 91. Bond Damage Sheared Bond Unfailed Bond 20 m Die Corner Ball bonds in plastic package after temperature cycle.8/2-4/2011 Plastic Package Reliability 89 © C. Glenn Shirley
  • 92. Bond Damage Necking Damage8/2-4/2011 Plastic Package Reliability 90 © C. Glenn Shirley
  • 93. Bond Damage Necking fracture8/2-4/2011 Plastic Package Reliability 91 © C. Glenn Shirley
  • 94. Bond Damage Delamination induced down bond fail after temperature cycle8/2-4/2011 Plastic Package Reliability 92 © C. Glenn Shirley
  • 95. Bond Damage Cratering damage on bond pads8/2-4/2011 Plastic Package Reliability 93 © C. Glenn Shirley
  • 96. Bond Damage Die Bond shear at die corners after temperature cycle8/2-4/2011 Plastic Package Reliability 94 © C. Glenn Shirley
  • 97. Bond Damage and Delamination A8 Intermetallic fracture at bond due to shear displacement. 44 PLCC devices that failed after solder A7Pulse-echo acoustic image of mold compound/ die reflow and 1000 cycles (-40A9 125C) tointerface in four devices. Delamination is shown inblack. White boxes added to show locations of low Source: T.M.Moore, R.G. McKennabond wire pull strength results. and S.J. Kelsall, IRPS 1991, 160-166. 8/2-4/2011 Plastic Package Reliability 95 © C. Glenn Shirley
  • 98. Bond Damage (TAB) Cu Lead Cu Lead Ti barrier Au bump Au bump Etch Crater Al pad Substrate Crack Barrier crack and Au/Al intermetallic Silicon TAB cratering and diffusion barrier damage revealed by wet etch.8/2-4/2011 Plastic Package Reliability 96 © C. Glenn Shirley
  • 99. Bond Damage (TAB) TAB bonds Au/Al intermetallic formed at cracks in Ti barrier8/2-4/2011 Plastic Package Reliability 97 © C. Glenn Shirley
  • 100. Bond Damage (TAB) Crater under TAB bonds8/2-4/2011 Plastic Package Reliability 98 © C. Glenn Shirley
  • 101. Thin-Film Cracking (TFC) Wire Shear Normal (tensile) Crack Shear Au Substrate Damage SiliconThin-Film Cracking 8/2-4/2011 Plastic Package Reliability 99 © C. Glenn Shirley
  • 102. TFC - Plastic Conforms to Die Surface Die Surface Replica in Plastic8/2-4/2011 Plastic Package Reliability 100 © C. Glenn Shirley
  • 103. TFC – Effect on Thin Films Die Corner Aluminum Cracks Polysilicon A B Die center Shear stress applied to passivation Passivation Aluminum A Crack Crack B PSG SiO2 Channel Polysilicon8/2-4/2011 Plastic Package Reliability 101 © C. Glenn Shirley
  • 104. Thin-Film Cracking (TFC) 1 micron Source: K. Hayes, Intel Passivation delamination crack propagates into substrate.8/2-4/2011 Plastic Package Reliability 102 © C. Glenn Shirley
  • 105. Test Chip• Thin film cracking can be detected electrically by test structures in the corner of the die. – Sensitive to opens and to shorts.• Buss width is varied to determine design rule. Die edge (saw cut). TFC sensor Edge ring TFD TFC (20 um bus) Metal 5 TFC (40 um bus) Metal 4 Via 4 BOND PADS Minimum Minimum ATC X Minimum TFC (10 um bus) TFC (100 um bus) 100 microns X = 10, 20, 40, 100 microns8/2-4/2011 Plastic Package Reliability 103 © C. Glenn Shirley
  • 106. TFC – Effect of Buss Width Factors Affecting TFC: Buss Width EffectPolysiliconmeanders underbuss edge arevulnerable to No Contactscrack-inducedopens. 17 m contacts Buss Widths 3 m contacts 21 m 7m 105 m Source: Shirley & Blish, “Thin Film Cracking and Wire Ball Shear...,” IRPS 1987.8/2-4/2011 Plastic Package Reliability 104 © C. Glenn Shirley
  • 107. TFC – Effect of Buss Width, ct’d Factors Affecting TFC: Buss Width Effect 70 50 30 % Fail 105 micron bus, no slots or contacts 10 5 2 1 Busses with slots and/or contacts .1 10 100 1000 Cycles Narrow buss, or contacts, stabilizes buss, reduces incidence of TFC. Leads to buss width design rules, and buss slotting in die corners.8/2-4/2011 Plastic Package Reliability 105 © C. Glenn Shirley
  • 108. TFC – Effect of Temperature Cycle• Drivers: T/C conditions, and number of cycles.• Mimimum T/C temperature, not amplitude, is key aspect of stress. – Stress depends on difference between cure temperature (neutral stress) and minimum stress temperature. 95 -65 C to 150C Same amplitude! -40 C to 85 C 80 0 C to 125 C 60 125 C Amplitude Source: C. F. Dunn and J. W. McPherson, “Temperature- 40 Cycling Acceleration Factors for Aluminum Metallization Cum % Failure in VLSI Applications,” IRPS, 1990. Fail 20 10 5 2 1 10 100 1000 Cycles8/2-4/2011 Plastic Package Reliability 106 © C. Glenn Shirley
  • 109. TFC – Effect of Passivation Thickness 100• Fraction of PDIP- Source: A. Cassens, Intel packaged SRAM failing. 80• Post 1K cycle of T/C C.• No Polyimide die coat. 60 %• Thicker passivation is Failing 40 more robust. 20 0 0.5 0.6 0.7 0.8 0.9 1.0 1.1 Total Passivation Thickness in microns8/2-4/2011 Plastic Package Reliability 107 © C. Glenn Shirley
  • 110. TFC – Effect of Compliant Overcoat• SRAM in PDIP• Temperature Cycle Condition C• Polyimide Overcoat 200 cycles 500 cycles 1000 cycles No Polyimide 0/450 13/450 101/437 Polyimide 0/450 0/450 0/4508/2-4/2011 Plastic Package Reliability 108 © C. Glenn Shirley
  • 111. Theory of TFC• Shear stress applied to die surface by MC – Is maximum at die corners – Zero at die center. (At die Surface) Die8/2-4/2011 Plastic Package Reliability 109 © C. Glenn Shirley
  • 112. Theory of TFC, ct’d• Buss width effect: Okikawa et. al.• Passivation thickness effect: Edwards et al.• TFC occurs when and where 2 t  ( Passivation Surface)  K  E     L • K = dimensionless constant • E = Young’s modulus of passivation • t = Passivation thickness • L = Buss width Thicker passivation, and/or narrower busses implies less TFC. Sources: Okikawa, et al. ISTFA, Oct. 1983. Edwards, et al. IEEE-CHMT-12, p 618, 19878/2-4/2011 Plastic Package Reliability 110 © C. Glenn Shirley
  • 113. Outline• Plastic Packages• Stress and Test Flows• Thermal Mechanisms• Moisture Mechanisms• Thermo-mechanical Mechanisms• Moisture-mechanical Mechanisms• Technology Update8/2-4/2011 Plastic Package Reliability 111 © C. Glenn Shirley
  • 114. Thin Film Delamination• Saw cut exposes thin film edges to moisture.. Polyimide PECVD Oxynitride/Nitride Metal Bond Pad Other films Silicon• And shear stress tends to peel films. Shear stress Thin film delamination. Moisture Thin films Substrate (Si)8/2-4/2011 Plastic Package Reliability 112 © C. Glenn Shirley
  • 115. Test Chip• “Edge rings” are lateral moisture barrier.• Effectiveness of edge rings can be tested electrically by a TFD sensor on a test chip. Edge ring Die edge (saw cut). TFC (20 um bus) TFD Cross section of TFD sensor TFC (40 um bus) thin film#7 BOND PADS thin film#6 ATC thin film#5 thin film#4 thin film#3 thin film#2 TFC (100 um bus) thin film#1 TFC (10 um bus) substrate interconnect via8/2-4/2011 Plastic Package Reliability 113 © C. Glenn Shirley
  • 116. Thin-Film Delamination Edge ringTFD Sensor Source: C. Hong Intel Delamination at die edge after 168 hours of steam. 8/2-4/2011 Plastic Package Reliability 114 © C. Glenn Shirley
  • 117. Thin-Film Delamination Edge RingCrack breakscontinuity ofTFD sensor 10 m Source: C. Hong Intel Delamination at die edge after 168 hours of steam. 8/2-4/2011 Plastic Package Reliability 115 © C. Glenn Shirley
  • 118. Popcorn Mechanism Early life failure rate. ELFR 168 hrs JESD22-A108 Preconditioning. PC JESD22-A113 HTOL HTSL (Bake) TC THB or HASTHigh temperature 1000 hrs 700 cycles 1000 hrs (85/85)operating life. JESD22-A103 3 cycles/hr JESD22-A101168 -1000 hrs 233 hrs 96 hrs (130/85)JESD22-A108 JESD22-A104 JESD22-A110 Condition B or G (C is too severe)8/2-4/2011 Plastic Package Reliability 116 © C. Glenn Shirley
  • 119. Popcorn Mechanism Moisture Absorbtion a During Storage t Moisture Vaporization During Solder Pressure Dome Delamination Void Pressure in Void = P Bond Damage Plastic Stress Fracture Package Crack Collapsed Voids Plastic package cracking due to “popcorn” effect during solder reflow8/2-4/2011 Plastic Package Reliability 117 © C. Glenn Shirley
  • 120. Popcorn Damage Plastic package cracking due to “popcorn” effect during solder reflow8/2-4/2011 Plastic Package Reliability 118 © C. Glenn Shirley
  • 121. Popcorn Damage B-Scan line A8 SEM of cross section Pulse-echo acoustic image through back of 68PLCC that developed popcorn A7 cracks during solder reflow A9Source: T.M.Moore, R.G. McKenna and S.J. Kelsall,in “Characterization of Integrated Circuit PackagingMaterials”, Butterworth-Heinemann, 79-96, 1993. Acoustic B-scan 8/2-4/2011 Plastic Package Reliability 119 © C. Glenn Shirley
  • 122. Popcorn Damage Pulse-echo acoustic Acoustic time-of-flight Real-time x-ray image showing image through top image indicating deformation in wires where (delamination in black) package crack they intersect the crack 132 lead PQFP which was damaged Source: T.M.Moore, R.G. McKenna and S.J. Kelsall, in “Characterization of Integrated Circuit Packaging during solder reflow. Materials”, Butterwoth-Heinemann, 79-96, 1993.8/2-4/2011 Plastic Package Reliability 120 © C. Glenn Shirley
  • 123. Factors Affecting Popcorning• Peak temperature reached during soldering.• Moisture content of molding compound.• Dimensions of die paddle.• Thickness of molding compound under paddle.• Adhesion of molding compound to die and/or lead frame.• Mold compound formulation. Not on this list: Pre-existing voids in the plastic package.8/2-4/2011 Plastic Package Reliability 121 © C. Glenn Shirley
  • 124. Popcorn Model• A crack propagates to the surface when maximum bending stress max exceeds a fracture stress characteristic of the molding compound  max   crit (Treflow )• crit depends on MC formulation, and on temperature (see next slide). Source: I. Fukuzawa, et. al. “Moisture Resistance Degradation of Plastic LSIs by Reflow Solder Process,” IRPS, 19888/2-4/2011 Plastic Package Reliability 122 © C. Glenn Shirley
  • 125. Popcorn Model, crit 100 80 Source: Kitano, et al. Molding Compound IRPS, 1988 Strength (MPa) 60 40 20 0 50 100 150 200 250 Temperature (deg C) crit is proportional to molding compound strength.8/2-4/2011 Plastic Package Reliability 123 © C. Glenn Shirley
  • 126. Popcorn Model, max• Maximum bending stress occurs at center of long edge of die and is given by: 2 a  max  6 K   P t – a is the length of the die edge. – t is the thickness of the molding compound over the die. – K is a geometrical factor (K = 0.05 for square pad). – P is the internal pressure. Depends on • Moisture content of molding compound. – Depends in turn on RH and T of previous soak ambient. • Peak temperature during reflow.8/2-4/2011 Plastic Package Reliability 124 © C. Glenn Shirley
  • 127. Popcorn Model, Internal Pressure Impermeable Surface Cavity Molding Compound Ambient Before m ( x, t ) Shock (T0) After  (t ) Shock (T1) Time = t x = -l x=w m ( x , t )  Concentration Profile in Molding Cpd.  (t )  Moisture Concentration in Cavity Pcav (t )  R  T1   (t )  Cavity Pressure m 0  H0  Psat (T0 )  S (T0 )  Initial Moisture Conc. In Mold. Cpd. For t  0 the boundary condition at x  0 is: m (0, t ) Pcav (t )  Henry’s Law S (T1 )8/2-4/2011 Plastic Package Reliability 125 © C. Glenn Shirley
  • 128. Popcorn Model, Internal Pressure m ( , f )  T1 S1   2  c  exp( n2 f ) sin[ n (1   )]  1  1   m0  T0 S 0  n1 ( n2  c 2  c) sin  n  S1    2  ( n2  c 2 ) exp( n2 f ) sin[ n (1   )]    1  1     S 0   n1 ( n  c  c) n 2 2  RT1S1 where c  and  n are roots of  tan   c Dt x Ref. H. S. Carslaw and J.C. Jaeger, and f  12 (Fourier Number);   “Conduction of Heat in Solids,”Oxford w w 2nd ed. (1986) pp128-129.8/2-4/2011 Plastic Package Reliability 126 © C. Glenn Shirley
  • 129. Popcorn Model, Internal Pressure Water Concentration Profile Cavity = 0.05 mm, Precond = 25/85, Tsolder = 215 C Package Thickness = 0.60 mm Cavity Water Vapor Concentration Moisture conc. in MC >>Moisture conc. in cavity. 0.1 1 350 Time 10 250 (sec) 150 Mole/m^3 100 50 1000 -0.05 0.15 0.35 0.55 (mm) 0 (Mold cpd/cavity interface)8/2-4/2011 Plastic Package Reliability 127 © C. Glenn Shirley
  • 130. Popcorn Model, Internal Pressure S (T0 ) Pcav  0) H0  Psat (T0 )   l 0; w  ( or t  S (T1 ) Delamination pressure exists even with no physical void. Example: • Unit preconditioned in 85/85 for a long time, then subjected to 215 C solder shock. • Saturation coefficient has activation energy of 0.4 eV. (eg. Kitano et. al.) • Steam table pressure at 85 C is 0.57 atm.  0.40 eV  1 1  Pcav  0.85  0.57  exp     8.62  10 eV/ K  273  85 273  215  -5  15.3 Atmospheres Wow!!8/2-4/2011 Plastic Package Reliability 128 © C. Glenn Shirley
  • 131. “Popcorn” Design Rules 400 Package Cracking 300 Pad Size, a (mils) 200 100 No Package Cracking a/t = 4.5 0 0 10 20 30 40 50 60 70 80 Plastic Thickness, t (mils) Cracking sensitivity of PLCC packages after saturation in 85/85 followed by vapor-phase reflow soldering at 215 oC8/2-4/2011 Plastic Package Reliability 129 © C. Glenn Shirley
  • 132. Outline• Plastic Packages• Stress and Test Flows• Thermal Mechanisms• Moisture Mechanisms• Thermo-mechanical Mechanisms• Moisture-mechanical Mechanisms• Technology Update8/2-4/2011 Plastic Package Reliability 130 © C. Glenn Shirley
  • 133. Package Anatomy OEM’s heat sink OEM’s TIM Intel’s TIM Integrated Heat Spreader (IHS) Silicon chipMade Underfill by C4 bumpsIntel Substrate A “land” Land Grid Array connectors Socket pin OEM’s socket • This is an example of a packaged part as it might be used in a product Slide: Scott C. Johnson 8/2-4/2011 Plastic Package Reliability 131 © C. Glenn Shirley
  • 134. Package Anatomy C4 bumps Silicon chip Conductive traces and vias (yellow) Polymer insulating layers (green) Substrate core A “land” OEM socket pin• This is a close-up of the package substrate showing the many layers of conductors and insulators Slide: Scott C. Johnson8/2-4/2011 Plastic Package Reliability 132 © C. Glenn Shirley
  • 135. Location: Silicon (vs. Package) “Back end” = interconnects “Front end” = transistors Interlayer dielectric (ILD) Gate Channel Gate Metal Oxideinterconnect Source Drain Le Via Transistor Slide: Scott C. Johnson 8/2-4/2011 Plastic Package Reliability 133 © C. Glenn Shirley