1. Foundational Aperture Design Rules

1.1 Aperture Size by Substrate

• Flexible Layers (Polyimide): Use 0.1–0.2mm laser microvias. Mechanical drills wander on soft polyimide; lasers (±0.01mm tolerance) fix this. Apple Watch uses 0.15mm microvias—no signal loss after 10,000+ bends. Samsung cut foldable phone failure rates from 15% to <1% by switching from 0.25mm to 0.12mm microvias.
• Rigid Layers (FR-4): 0.3–0.5mm for signal vias (fits 0.3mm pins with 0.1mm tolerance); 0.6–1.0mm for power/thermal needs. Bosch uses 0.8mm power vias in radar modules to prevent overheating.
• Cross-Layer Alignment: Keep ±0.03mm tolerance. Nitto Denko’s aerospace PCBs follow this, cutting cross-layer failures by 70%.

1.2 Aperture Spacing

• Between apertures: ≥2x diameter (0.8mm for 0.4mm vias) to avoid drill deflection.
• From board edges: ≥1.5x diameter (0.75mm for 0.5mm vias) to prevent delamination.
• High-frequency apps: ≥0.3mm between signal and power vias to reduce EMI.

2. Drilling Process Controls

2.1 Speed & Feed Rate

2.2 Alignment Tools

• Optical Markers: 0.5mm copper pads with white borders. LG Innotek reduced drift to <0.04mm.
• Registration Pins: 1.0–2.0mm steel pins for high-volume runs. Shennan Circuits uses them for insulin pump PCBs to align vias.

2.3 Drill Bits

• FR-4: Tungsten carbide (5,000 holes/bit).
• Polyimide: Diamond-coated carbide (3,000 holes/bit).
  Fujikura’s customers saw 35% less deviation with this schedule.

3. Post-Drilling Checks

• AOI: Scans for size, alignment, and burrs. Foxconn catches 98% of issues (e.g., 0.18mm vs. 0.15mm microvias).
• Cross-Sectional Testing: For critical apps (e.g., automotive). Bosch rejected a batch with 0.08mm tilt, avoiding radar errors.
• Electrical Tests: Network analyzers check 50Ω impedance for 5G—rejects boards with 60Ω drift.

4. Real-World Wins

• Samsung: Switched to 0.12mm laser microvias + AOI, cutting foldable phone failures to 0.1% (saving $50M).
• Tesla: Added pins + diamond bits, reducing radar via deviation to <0.03mm.

5. Conclusion