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Conductive Anodic Filament Growth Failure

Conductive Anodic Filament Growth Failure. Electro Migration of Copper Across Two Oppositely Biased Copper Conductors Failure Modes Hole to Hole Line to Line Through Hole to Line Layer to Layer Hole to Hole Is Most Common Failure Mode. CAF.

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Conductive Anodic Filament Growth Failure

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  1. Conductive Anodic Filament Growth Failure

  2. Electro Migration of Copper Across Two Oppositely Biased Copper Conductors Failure Modes Hole to Hole Line to Line Through Hole to Line Layer to Layer Hole to Hole Is Most Common Failure Mode CAF

  3. Step 1: Degradation of the Resin Glass Interface - Reversible Step 2: Actual Filament Growth - Irreversible Time to Failure Is Believed to Be a Function: - Hole to Hole Spacing - Temperature - Voltage Bias - Humidity The Temperature Relationship Can Be Looked As an Arhennius Relationship While Power Laws Approximate the Other Relationships Mechanism

  4. Electro-Chemical Reactions + - ThroughHole to Through Hole • At the Anode: • Cu Cun + ne- • H20 1/2 O2 + 2 H++2e- • At the Cathode: • H20 +e- 1/2 H2 +2 OH- • The Enthalphy of formation - Copper ion = 64.8 KJ/Mo

  5. Mechanism • The Ionic Mobility and the Electromigration Process Are a Function of • The Conductivity of the Electrolyte. • For a Resistance of 109ohms at 100 V Current I= 100/109 = 10-7 A or 0.1 Micro Amps Vs 0.1 Ma at 106 Ohms • Current Density - For Copper on Copper a Limiting Value Is Needed 0.4 -1.0 Ma/cm2 • IR Is a Key Factor Influencing CAF • The PH of the Electrolyte

  6. Pourbaix Diagram Equilibrium Potential vs PH

  7. Thermal History CTE Mismatch Voids Dryness Chemical Attack with Water - Hydrolysis Drilling - Fractured Glass Degradation / Debonding

  8. Voltage Bias Glass Finish Resin Systems Grain Direction Hole to Hole Spacing Mask Temperature and Humidity at 85 °C 85 % Variables Explored

  9. CAF Test Vehicle

  10. CAF Test Vehicle Schematic V • Equidistant Holes • Adjacent Holes Oppositely Biased • Greater than 125 Opportunities for Failure • Test Voltage 100 V • Bias Voltage Varied

  11. CAF Test Vehicle Circuit V • For N Resistors in Parallel • Overall Resistance R = 1/N * RP • Resistance Across Parallel Paths RP=N * R • A Decade Drop in IR = 2.4 Decade Drop in Individual Resistor for 25 Resistors • Failure Criteria Needs to Be Defined Based on the Number of Resistances in II As Well As Geometries

  12. Test Conditions 13.5 Volt Bias 24 Mil Hole to Hole Spacing 100 V Testing at 2 Test Conditions 85/85 and 23/50 Variables Treating Conditions and Resin Systems Glass Finishes Mask Experiments- Low Bias Testing

  13. Insulation Resistance No Solder Mask Ohms 1.00E+13 1.00E+12 1.00E+11 1.00E+10 1.00E+09 1.00E+08 1.00E+07 1.00E+06 1.00E+05 0 164 328 492 656 820 984 1148 1312 1476 1640 1804 1968 2132 Hours -23°C/50% RH

  14. Insulation Resistance Ohms Hours -23°C/50% RH With Solder Mask

  15. Insulation Resistance 0 164 328 492 656 820 984 1148 1312 1476 1640 1804 With Solder Mask Ohms 1.00E+09 1.00E+08 1.00E+07 1.00E+06 1.00E+05 1.00E+04 1.00E+03 1.00E+02 1.00E+01 1.00E+00 -85°C/85% RH Hours

  16. Insulation Resistance 0 164 328 492 656 820 984 1148 1312 1476 1640 1804 No Solder Mask Ohms 1.00E+10 1.00E+09 1.00E+08 1.00E+07 1.00E+06 1.00E+05 Hours -85°C/85% RH

  17. No Actual Failures Were Seen Mask Causes Erratic IR Results Resin System a Major Factor in IR - One Resin System Out Performed Others Glass Finish a Marginal Factor No Major Differences in the Warp and Weft Treating Conditions Marginal Effect (Good Wetout) Results

  18. Test Conditions 100 V Bias Test 12 Mil Hole to Hole Spacing,13.5 Mil Holes 100 V Testing Variables 3 Resin Systems 3 Glass Finishes Experiments Low Spacing High Bias

  19. Ohms 1.00E+11 1.00E+10 1.00E+09 1.00E+08 1.00E+07 1.00E+06 600 100 200 300 400 500 700 800 900 1000 1100 1200 1300 1400 1500 -85°C/85% RH Hours • Effect of Resin System on Resistance Drop

  20. Ohms 1.00E+11 1.00E+10 1.00E+09 1.00E+08 1.00E+07 1.00E+06 600 100 200 300 400 500 700 800 900 1000 1100 1200 1300 1400 1500 Hours • Effect of Glass Finish on Resistance Drop -85°C/85% RH

  21. No Actual Failures Were Seen Resin System a Major Factor in IR - One Resin System Out Performed Others Glass Finish a Major Factor in This Experiment - One Finish Out Performed Others Results of High Bias Low Spacing Experiments

  22. CAF Solution Lies in Preventing the Primary Step of Degradation of IR or Debonding Through: Robust Resin Systems Resistant to Chemical Attack Robust Glass Resin Interface / Robust Finish Drilling Parameters Understanding and Avoiding other Fab Related Causes such as Thermal Shock / Stress Conclusions

  23. Design Experiments to Understand the Effect of Process Parameters Drilling Thermal Stress New Coupon Design Look at the Effect of Glass Styles Next Steps

  24. Standardized Test Vehicle Spacing Bias Test Conditions Define Failure Criteria Magnitude IR or Drop in value Industry Needs

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