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Low-Cycle Fatigue Behavior of Lead-Free Solder EM388F Final Presentation Kuan (Gary) Lu Materials Science & Engineering April 30 2008.

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Presentation on theme: "Low-Cycle Fatigue Behavior of Lead-Free Solder EM388F Final Presentation Kuan (Gary) Lu Materials Science & Engineering April 30 2008."— Presentation transcript:

1 Low-Cycle Fatigue Behavior of Lead-Free Solder EM388F Final Presentation Kuan (Gary) Lu Materials Science & Engineering April

2 Outline Introduction –Solder Alloys –Fatigue behavior of Solder Case study –Frequency effect –Temperature effect –Solder composition –Solder joint

3 Introduction: Solder in Microprocessor Solder provides electrical, mechanical and thermal interconnects. Thermal-mechanical fatigue of solder joints during normal usage. (Strain controlled fatigue) Silicon Chip Plastic substrate Solder bump Underfill CTE: 2.6ppm/ o C for Si; ~15ppm/ o C for PCB

4 Introduction: Solder Alloys Eutectic solders: –63Sn-37Pb –96.5Sn-3.5Ag (Pb-free) Small addictives: Cu, Bi, Sb, Zn,... Some Thermal-mechanical properties: –High homologous RT (~0.6T m ); –Time dependent creep deformation; –Low-Cycle Fatigue (N f <10 4 ).

5 Solder under Cyclic Load (strain control) Strain softening in the beginning: –Stress amplitude approaches a steady state. Stress drops dramatically at the end of fatigue life. Coffin-Manson eqn.: J.A. Bannantine, Fundamentals of Metal Fatigue Analysis C. Andersson, Mater. Sci. Eng.A

6 General Approaches in Solder Fatigue Study Strain controlled (0.1~10% total strain); Bulk solder (regulated by ASTM) or solder joints; Isothermal fatigue test or TMF test; Failure criteria: 25% or 50% of stress drop; Variables to study: Solder composition, Temperature, frequency, solder joint geometry and metallization,…. Strain-N f log plot, derive Coffin-Manson coefficients; Failure analysis. Dogbone bulk solder (unit: mm)

7 Case Study: Frequency Effect Bulk 96.5Sn-3.5Ag Isothermal (20 o C) C. Kanchanomai, Mater. Sci. Eng.A

8 Case Study: Frequency Effect Coffin-Manson relationship: C. Kanchanomai, Mater. Sci. Eng.A

9 Case Study: Frequency Effect Eckel relationship: Frequency-modified Coffin-Manson relationship: C. Kanchanomai, Mater. Sci. Eng.A

10 Case Study: Temperature Effect Bulk 96.5Sn-3.5Ag Isothermal (20 o C, 85 o C, 120 o C) Frequency: 0.1Hz C. Kanchanomai, Mater. Sci. Eng.A

11 Case Study: Temperature Effect C. Kanchanomai, Mater. Sci. Eng.A

12 Case Study: Solder composition Bulk solder Isothermal (RT) 3.5Ag C. Andersson, Mater. Sci. Eng.A

13 Case Study: Solder Joint Shear RT; Hourglass shape solder joint; Cu/Ni/Au metallization; Frequency: 0.2Hz. (mm) C. Andersson, Mater. Sci. Eng.A

14 Case Study: Solder Joint Low strain levelHigh strain level C. Andersson, Mater. Sci. Eng.A

15 Complexity of Solder Joint Study Sample geometry effect; Intermetallic compound (IMC); Crack path may depend on: –Solder composition; –Under bump metallization (UBM); –Strain range.


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