Reliability of RoHS-Compliant 2D and 3D 1С Interconnects

Reliability of RoHS-Compliant 2D and 3D 1С Interconnects John H. Lau, Ph.D. New York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan Seoul Singapore Sydney Toronto

Foreword Preface Acknowledgments xxi xxiii xxvii Introduction to RoHS-Compliant Semiconductor and Packaging Technologies 1 1.1 Introduction 1 1.2 Electronics Industry 1 1.3 1С Semiconductor Technology 2 1.4 3-D 1С Packaging Technology 5-1.4.1 Conventional 1С Packaging Technology 5 1.4.2 3-D 1С Packaging Technology 6 1.5 3-D 1С Integration Technology 9 1.5.1 FEOL, BEOL, and MEOL 9 1.5.2 More Than Moore 10 1.5.3 3-D 1С Integration Technology 10 1.5.4 Critical Issues of 3-D 1С Integration 11 1.5.5 TSV, With or Without RDL 12 1.5.6 Manufacturing Process for TSV 3-D 1С Integration 17 1.5.7 How to Improve TSV Manufacturing Yield? 22 1.5.8 Thin-Wafer Handling 25 1.5.9 Low-Cost, Lead-Free Solder Microbumps 27 1.5.10 Thermal Management of 3-D 1С Integration 28 1.5.11 3-D 1С Packaging versus 3-D 1С Integration 34 1.6 3-D Si Integration Technology 36 1.6.1 3-D 1С Integration versus 3-D Si Integration 36 1.6.2 W2W (Cu-to-Cu) Bonding 36 1.6.3 W2W (Si0 2 -to-si0 2 ) Bonding 38 1.6.4 Future Outlook of 3-D Si Integration 39 1.7 Who Is Going to Make the TSV for 3-D 1С Integration? 42 vii

VÜi Contents 1.8 Notes on TSV Manufacturing Costs 44 1.9 EU RoHS Update 44 1.9.1 EU RoHS -44 1.9.2 EU Restricted Substances 44 1.9.3 EU Product Category 45 1.9.4 EU Exemptions 45 1.10 China RoHS Update 45 1.10.1 China RoHS 45 1.10.2 China Standards 46 1.10.3 China's Product Catalogue 46 1.10.4 China Compulsory Certificate (CCC) 47 1.11 Impact of RoHS on the Electronics Industry 47 1.12 References 49 2 Reliability Engineering of Lead-Free Interconnects 89 2.1 Introduction 89 2.2 Reliability Basics 89 2.2.1 Definition of Reliability 89 2.2.2 Objective of Reliability Tests 90 2.2.3 Life Distributions 90 2.2.4 Reliability, Failure Rate, and MTTF... 91 2.2.5 Simple System Reliability 93 2.2.6 Ranking 94 2.2.7 True Weibull Slopes 94 2.2.8 True Characteristic Life 95 2.2.9 True Mean Life 96 2.2.10 Comparison of the MTTF of Two Different Sets of Samples 97 2.2.11 Accelerated Models 98 2.2.12 Acceleration Factors 101 2.3 Reliability Engineering of Lead-Free Interconnects 102 2.4 Reliability Testing and Data Analysis 103 2.5 Failure Analysis 104 2.5.1 Failure Analysis Methods 104 2.5.2 3-D X-ray Inspections and Analyses of PBG A Lead-Free Interconnects... 105 2.6 Design for Reliability (DFR) 115 2.6.1 Advantages of DFR 115 2.6.2 A Note on DFR 116 2.6.3 Material Properties of Lead-Free Solder Interconnects 116

jx 2.6.4 Effects of Halogen on Solderability and Reliability of SAC Solder Pastes... 117 2.6.5 Creep, Young Modulus, CTE, and Poisson's Ratio of SnAgCu and Other Solders 123 2.6.6 Isothermal Fatigue Tests of WLCSP Lead-Free Interconnects 129 2.6.7 Isothermal Fatigue Tests of PBGA Lead-Free Interconnects at 6CPC... 138 2.6.8 Thermal-Fatigue Life Predictions of Lead-Free Interconnects 146 2.7 Quality of Lead-Free Solder Interconnects... 150 2.8 References 151 3 Notes on Failure Criteria 153 3.1 Introduction 153 3.2 Failure Criteria 153 3.3 Resistance Measurements 157 3.4 Three-Cycle Moving Average (TCMA) Method 158 3.5 Summary and Recommendations 165 3.6 References 165 4 Reliability of 1657-Pin CCGA Lead-Free Solder Joints 173 4.1 Introduction 173 4.2 Design for Reliability of the 1657CCGA with Lead-Free Solder Paste 174 4.2.1 The Structure 174 4.2.2 Material Properties 177 4.2.3 Temperature Boundary Conditions 179 4.2.4 Simulation Results 179 4.2.5 Thermal-Fatigue Life Prediction... 185 4.2.6 Summary and Recommendations... 187 4.3 Reliability Testing and Data Analyses of the 1657CCGA with Lead-Free Solder Paste... 187 4.3.1 Component and Test Boards 187 4.3.2 Test Chamber and Temperature Cycling Condition 188 4.3.3 Data Acquisition System and Failure Criterion 190 4.3.4 Statistical Analysis of 1657CCGA Solder Joints 191 4.3.5 Summary and Recommendations... 198

4.4 Failure Analyses of 1657CCGA Assemblies 199 4.4.1 Failure Analyses of CCGA with SAC and SnPb Solder Pastes 199 4.4.2 Summary and Recommendations... 206 4.5 References 206 5 Reliability of PBGA Lead-Free Solder Joints (With and Without Underfills) 209 5.1 Introduction 209 5.2 Reliability of PBGA SAC Solder Joints With and Without Underfills under Thermal Cycling Condition 211 5.2.1 Components, Test Board, and Underfills 211 5.2.2 Design for Reliability 214 5.2.3 Test Chamber and Temperature-Cycling Profile 214 5.2.4 Data Acquisition, Failure Criterion, and Data Extraction 215 5.2.5 Weibull Slope, Characteristic Life, and MTTF from Test Samples 216 5.2.6 True Characteristic Life 216 5.2.7 True MTTF 219 5.2.8 True Weibull Slope 220 5.2.9 Comparison of MTTF from Two Sets of Test Samples 221 5.2.10 Failure Analyses 223 5.2.11 Summary 224 5.3 Reliability of PBGA SAC Solder Joints With and Without Underfills under Drop Condition 225 5.3.1 Drop Test Setup, Data Acquisition, and Drop Profile 226 5.3.2 Failure Criterion 229 5.3.3 Strain Time-History During Drop Impact 229 5.3.4 Weibull Slope, Characteristic Life, and MTTF from Test Samples 231 5.3.5 True Characteristic Life 232 5.3.6 True MTTF 235 5.3.7 True Weibull Slope 235 5.3.8 Effects of Aging and Underfill on the Reliability of PBGA Interconnects under Drop Impacts 236

5.3.9 Failure Analysis 238 5.3.10 Summary 239 5.4 References 241 Reliability of LED Lead-Free Interconnects 245 6.1 Introduction 245 6.2 LED Seven-Segment Display Family 247 6.3 Lead-Free Wave Soldering of LED Displays 248 6.3.1 PCB 248 6.3.2 Flux and Solder Bar 248 6.3.3 Lead-Free Wave-Soldering Thermal Profiles 249 6.4 Thermal Cycling Test of LED Display Assemblies 250 6.5 85 C/85%RH Test of LED Display Assemblies 251 6.6 Creep Analysis of the LED Display Lead-Free Solder Joints 252 6.6.1 The Structure 252 6.6.2 Material Properties Constitutive Equations 252 6.6.3 Boundary Conditions 253 6.6.4 Deformation of the LED Assembly 255 6.6.5 Stress and Creep Strain Distributions 256 6.6.6 Stress Time-History 256 6.6.7 Creep Strain Time-History 256 6.6.8 Hysteresis Loops and Creep Strain Energy Density 256 6.6.9 Thermal-Fatigue Life of LED Solder Joints 260 6.7 Summary and Recommendations 260 6.8 3-D LED and 1С Integration 261 6.8.1 3-D LED and 1С Integration Packages 264 6.8.2 Manufacturing Process of 3-D LED and 1С WLP 265 6.8.3 Thermal Management of 3-D LED and 1С Integration System 268 6.8.4 Summary and Recommendations 270 6.9 References 272

tents Reliability of VCSEL Lead-Free Interconnects... 277 7.1 Introduction 277 7.2 Lead-Free Interconnect Reliability of a VCSEL under Transient and Steady-State Loadings 281 7.2.1 The Structure 281 7.2.2 Materials 282 7.2.3 Heat-Transfer Analysis and Results 286 7.2.4 Thermal-Stress Analysis and Results 289 7.2.5 Summary and Recommendations... 295 7.3 Lead-Free Interconnect Reliability of a VSCEL on an Optical PCB 295 7.3.1 Optical Design and Analysis 298 7.3.2 Thermal Design and Analysis 300 7.3.3 Lead-Free Interconnect Reliability 304 7.3.4 Summary and Recommendation... 308 7.4 References 309 Reliability of Low-Temperature Lead-Free (SnBiAg) Solder Joints 313 8.1 Introduction 313 8.2 Benefits of Using SnBiAg Low-Temperature Alloy 313 8.2.1 Cost Reduction 314 8.2.2 Product Reliability 314 8.2.3 Design Flexibility 314 8.3 Concerns with Use of Bismuth-Based Solders 314 8.3.1 Brittleness 314 8.3.2 Availability 315 8.3.3 Environmental Impact 315 8.3.4 Recyclability 316 8.3.5 Lead Contamination 316 8.4 Design for Reliability 316 8.4.1 Problem Definition 316 8.4.2 Material Properties 317 8.4.3 Temperature Condition 318 8.4.4 Results and Discussion 319 8.5 Reliability Testing and Data Analyses 320 8.5.1 Components and Test Board 320 8.5.2 Board Assembly Process 320 8.5.3 Post-Assembly Inspection 322

xiü 8.5.4 Air-to-Air Temperature Cycling (АТС) Tests 323 8.5.5 Results of АТС Tests 326 8.5.6 Shock (Drop) Tests and Results... 331 8.5.7 Vibration Tests and Results 332 8.6 Failure Analyses 333 8.7 Summary and Recommendations 336 8.8 References 337 9 Reliability of Lead-Free (SACX) Solder Joints 339 9.1 Introduction 339 9.2 SACC 339 9.3 Material Properties of SACC 340 9.3.1 Bulk Solder Test Specimen 340 9.3.2 Tensile Test Procedures 341 9.3.3 Tensile Test Results 341 9.3.4 Equations for Young's Modulus and Yield Stress 344 9.3.5 SnAgCu (SAC) versus SnAgCuCe (SACC) 347 9.3.6 Creep Test and Data 348 9.3.7 Summary and Recommendations 355 9.4 Intermetallic Compounds of SACC 357 9.4.1 Sample Preparation 357 9.4.2 Tests and Measurements 357 9.4.3 IMC on OSP Surface Finish 358 9.4.4 IMC on NiAu Surface Finish 361 9.4.5 SnAgCu (SAC) versus SnAgCuCe (SACC) 361 9.4.6 Summary and Recommendations... 364 9.5 Process Development of SACC with Various Packages 364 9.5.1 Components and PCBs 364 9.5.2 Printing Characteristics 365 9.5.3 Reflow Temperatures 368 9.5.4 Voids 368 9.5.5 Four-Point Bending Fatigue Tests.. 369 9.5.6 Summary and Recommendations... 376 9.6. Mechanical Pull Test of PQFP with SACC Solder Joints 376 9.6.1 Mechanical Pull Test Setup 376 9.6.2 Pull Test Results 377 9.6.3 Failure Analyses 377

XJV Contents 9.7 Thermal Cycling Test of SACC Solder Joints 381* 9.7.1 Components and Test Boards Э81 9.7.2 Thermal Cycling Test 381 9.7.3 Thermal Cycling Test Results 382 9.7.4 Finite-Element Analysis and Results 385 9.7.5 Summary and Recommendations 389 9.8 References 390 10 Chip-to-Wafer (C2W) Bonding and Lead-Free Interconnect Reliability 393 10.1 Introduction 393 10.2 3-D Packaging (PoP) with AuSn Interconnects 393 10.3 Test Vehicle and Fabrication 393 10.3.1 Test Vehicle 393 10.3.2 Test Vehicle Fabrication 395 10.4 C2W PoP Assembly 399 10.4.1 Bump Height Coplanarity 400 10.4.2 Alignment Accuracy 400 10.5 C2W Design of Experiments (DOE) 403 10.5.1 Three-Factor DOE 403 10.5.2 DOE Results 404 10.6 Reliability Tests and Results 405 10.7 Summary and Recommendations 406 10.8 3-D Packaging (PoP) with SnAg Interconnects 407 10.9 Low-Temperature C2W (InSnAu) Bonding for 3-D 1С Chip Stacking 410 10.9.1 How Does Low-Temperature Bonding with Solder Work? 410 10.9.2 Solder Design 411 10.9.3 Test Vehicle 412 10.9.4 3-D 1С Chip Stacking with InSnAu Low-Temperature Bonding 414 10.9.5 SEM, ТЕМ, XDR, and DSC of the InSnAu IMC 415 10.9.6 Young's Modulus and Hardness of the InSnAu IMC 417 10.9.7 Three-Time Reflows of the InSnAu IMC 417 10.9.8 Shear Strength of the InSnAu IMC 418

XV 10.9.9 Electrical Resistance of the InSnAu IMC 420 10.9.10 When Does the InSnAu IMC Become Unstable? 421 10.9.11 Summary and Recommendations... 422 10.10 References 422 Wafer-to-Wafer (W2W) Bonding and Lead-Free Interconnect Reliability 427 11.1 Introduction 427 11.2 Low-Temperature W2W Bonding with Snln Solder on CuTiAu Metallization Pads 427 11.2.1 The Test Vehicle 427 11.2.2 Test Vehicle Fabrication 428 11.2.3 Low-TemperatureW2WBonding... 429 11.2.4 C-SAM Inspection 430 11.2.5 Microstructure by SEM/EDX/ FIB/ТЕМ 431 11.2.6 Helium Leak Rate Tests and Results 436 11.2.7 Reliability Tests and Results 436 11.2.8 Summary and Recommendations... 439 11.3 W2W Bonding with AuSn Solder and TiCuNiAu Metallization Pads 440 11.3.1 The Test Vehicle 440 11.3.2 Test Vehicle Fabrication 442 11.3.3 W2W Bonding 444 11.3.4 Electrical Performance 444 11.3.5 Quality and Reliability 444 11.3.6 Summary and Recommendations... 448 11.4 References 450 Through-Silicon-Via (TSV) Interposer Reliability 453 12.1 Introduction 453 12.2 DFR of the Cu Thickness in Toshiba's TSV 454 12.2.1 Finite-Element Modeling 454 12.2.2 Modeling Results and Analyses 455 12.2.3 Other Considerations 457 12.3 TSV Reliability Due to Local Thermal Expansion Mismatch 458 12.3.1 Boundary-Value Problems 458 12.3.2 DFR Results 460

tents 12.3.3 TSV with Redistribution Layer 463 12.3.4 Summary and Recommendations... 468 12.4 TSV Reliability Due to Global Thermal Expansion Mismatch 468 12.4.1 2-D Boundary-Value Problem 469 12.4.2 Summary and Recommendations... 470 12.4.3 3-D Boundary-Value Problem 472 12.4.4 3-D Analysis Results 472 12.4.5 Summary and Recommendations... 472 12.5 Reliability Test and Failure Analysis of a 2.5D 1С Integration SiP with a TSV Interposer 476 12.5.1 Underfill Materials 476 12.5.2 Thermal Cycling Test and Results 476 12.5.3 Failure Analysis 478 12.5.4 Summary and Recommendations 479 12.6 Thermal-Enhanced and Cost-Effective 3-D 1С Integration SiP with a TSV Interposer 479 12.6.1 Introduction 480 12.6.2 Design Philosophy 483 12.6.3 The New Designs 483 12.6.4 A 3-D 1С Integration SiP Design Example for Demonstration 486 12.6.5 Modeling of the 3-D 1С Integration SiP Design Example 486 12.6.6 Thermal Analyses and Results of the 3-D 1С Integration SiP 491 12.6.7 Nonlinear Stress Analyses and Results of the 3-D 1С Integration SiP 493 12.6.8 Summary and Recommendations... 500 12.7 References 501 Electromigration of Lead-Free Microbumps for 3-D 1С Integration 505 13.1 Introduction 505 13.2 Test Vehicles and Methods 505 13.2.1 Solder Bumps 505 13.2.2 Test Methods 506 13.3 Test Procedures 506 13.4 Microstructures of Samples Before Tests 508 13.5 Samples Tested at 140 C C with Low Current Density 509

XVÜ 13.5.1 Samples Tested at 140 C with Current Density of 2.04 x 10 4 A/cm 2 509 13.5.2 Microstructures of Samples Tested at Low Current Density 510 13.6 Samples Tested at 140 C with High Current Density 511 13.6.1 Samples Tested at 140 C with Current Density of 4.08 xlo 4 A/cm 2 511 13.6.2 Microstructures of Samples Tested at High Current Density 511 13.7 Failure Mechanism of the Multiphase Solder-Joint Interconnect 514 13.8 Summary and Recommendations 515 13.9 References 516 Effects of Dwell Time and Ramp Rate on SAC Thermal Cycling Test Results 519 14.1 Introduction 519 14.2 Effects of Dwell Time on the Thermal-Fatigue Life of SnAgCu (SAC) Solder Joints 519 14.2.1 The Structure, Material Properties, and Simulations 519 14.2.2 Temperature Loading Conditions 520 14.2.3 Creep Hysteresis Loops 520 14.2.4 Shear Stress Time-History 521 14.2.5 Shear Creep Strain Time-History... 521 14.2.6 Creep Strain Energy Density Time-History 522 14.2.7 Summary and Recommendations... 524 14.3 Effects of Ramp Rate on the Thermal- Fatigue Life of SAC Solder Joints 525 14.3.1 Temperature Loading Conditions... 525 14.3.2 Maximum Stress/Strain Location... 526 14.3.3 Creep Hysteresis Loops 527 14.3.4 Shear Stress Time-History 530 14.3.5 Shear Creep Strain Time-History 531 14.3.6 Creep Strain Energy Density Time-History 532 14.3.7 Summary and Recommendations... 533 14.4 References 534

tents Effects of High Strain Rate (Impact) on SAC Solder Balls/Bumps 537 15.1 Introduction 537 15.2 Angled High-Speed Ball Shear Test of SnAgCu Solder Balled/Bumped Package... 537 15.2.1 Apparatus Setup with High-Speed Shear Tester 537 15.2.2 Test Specimens and Sample Preparation 540 15.2.3 Test Results 541 15.2.4 Characterizations of Failure Samples 543 15.2.5 Comparison of SAC305 and SAC105 547 15.3 Finite-Element Analyses of Angled High-Speed Ball Shear of the SnAgCu Solder-Balled Package 547 15.3.1 Finite-Element Modeling 547 15.3.2 Finite-Element Analysis and Results 547 15.4 Summary and Recommendations 551 15.5 References 552 Effects of Voids on Solder Joint Reliability 555 16.1 Introduction 555 16.2 Effects of Voids on BCC-H- Solder Joint Reliability 556 16.2.1 The BCC-H-Package and Structure 556 16.2.2 Finite-Element Analyses 557 16.2.3 Analysis Results 561 16.2.4 Effects of Voids on Crack Growth... 563 16.2.5 J-Integral Evaluation around a Crack Tip 563 16.2.6 J-Integral for Various Crack Lengths without Voids 564 16.2.7 J-Integral for a Fixed Crack Length with Various Void Sizes 566 16.2.8 J-Integral for Various Crack Lengths and Void Sizes 566 16.2.9 2-D versus 3-D Solutions 568 16.2.10 Summary and Recommendations... 569 16.3 Effects of Voids on WLCSP Solder Joint Reliability 572 16.3.1 The Structure and Simulations 572

xix 16.3.2 Effects of Cracks on the Reliability of WLCSP Solder Joints 573 16.3.3 Effects of Voids on the Reliability of WLCSP Solder Joints 575 16.3.4 2-D versus 3-D Solutions 576 16.3.5 Summary and Recommendations... 578 16.4 References 580 Index 583