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Preventing Micro-Damage in Dielectric Layers During Drilling of Ultra-Low Loss Substrates

2025-06-22

Ultra-Low Loss Substrate.jpeg

1. Drilling Damage Mechanisms

  • Stress Concentration:

    • Axial force >50N causes resin mICro-cracks (depth >10μm)

    • CTE mismatch (5.4 vs 60 ppm/°C) induces fiber-resin delamination

  • Thermal Damage:

    • Friction heat >300°C at >180krpm leads to resin carbonization (conductivity ↑1000×)

2. Drill Bit Specifications

Parameter Optimal Value Damage Control Principle
Point Angle 130°±2° Reduces axial stress
Margin Width ≤5% drill dia. (e.g., 5μm for 0.1mm bit) Lowers friction heat
Coating Diamond nanocomposite (2μm) Hardness↑30%, conductivity↑50%
Flute Helix 30°~35° Improves chip evacuation

3. Process Window

  • Dynamic Speed Control:

  • Key Parameters:

    • Drilling time: 0.8~1.5ms/μm board thickness

    • Retract speed: ≥15m/min (prevents re-SCRatching)

    • Peck depth: ≤1/3 board thickness (e.g., 0.03mm for 0.1mm board)

4. Dielectric Material Enhancement

  • Nano-Modified Resin:

    • 20~40nm silica additives (↑50% crack resistance)

    • Flat glass fiber (thickness variation <0.5μm)

  • Copper InteRFace Treatment:

    • Brown oxide roughness Rz≤1.5μm (vs. 3~5μm traditional)

5. Auxiliary Process Innovations

Technique Implementation Effect
Ultrasonic Drilling 40kHz vibration (5μm amplitude) ↓35% drilling force, ↓40°C
Cryogenic Cooling -50°C N₂ jet (0.3MPa) Wall temperature <150°C
Vacuum Extraction Bottom suction (-90kPa) ↓80% resin residue

6. Damage Detection & Evaluation

Method Resolution Failure Criteria
SAM (Scanning Acoustic Microscopy) 10μm Delamination <5% hole area
Laser Confocal Microscopy Surface Ra≤0.8μm No >2μm resin cracks
Df Test @10GHz ΔDf≤0.0001 Insertion loss delta <0.02dB/cm
Cross-section Dye penetration + 500× microscopy Crack depth <5μm

7. Equipment Precision Requirements

  • Spindle Runout: ≤3μm TIR (dynamic)

  • Positioning Accuracy: ±2μm (X/Y), ±1μm (Z)

  • Drill Life: Mandatory replacement after ≤500 holes (for 0.1mm bits)