Step Drill / Controlled Depth Drilling
Multiple-diameter and depth-controlled holes for special mechanical and electrical needs.
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Step Drill / Controlled Depth Drilling — Process Capabilities & DFM Guide
Controlled-depth drilling shapes the z-axis of your interconnects: stable press-fit seats, precise countersinks, thermal counterbores, and selective backdrill to minimize stubs—without over-processing the entire panel.
Process Capability Matrix（Core Specs）
|
Type |
Typical Use |
Drill Ø Range (mm) |
Step Height / Depth |
Depth Tolerance |
Registration (XY) |
Board Thickness |
Notes |
|
Step Drill (Counterbore) |
Screw seats, thermal pads |
0.80–6.50 |
≥0.20 mm step |
±0.05–0.10 mm |
≤±50 µm |
≤4.0 mm |
Flat bottom seat; copper keep-out needed |
|
Countersink (Chamfer) |
Screw/connector heads |
1.00–6.50 |
60°/82°/90° |
±2° angle, depth ±0.10 |
≤±60 µm |
≤4.0 mm |
Angle per fastener standard |
|
Controlled-Depth Blind Drill |
Cavity, pad relief |
0.20–0.50 |
To target dielectric |
±0.05–0.08 mm |
≤±40 µm |
≤3.2 mm |
Laser/Mech hybrid by stack-up |
|
Selective Backdrill |
Stub reduction |
0.20–0.45 |
Residual stub ≤0.20 mm |
±0.05–0.10 mm |
≤±50 µm |
≤4.0 mm |
Per net, one-side program |
|
Multi-Step Hole |
Press-fit tuning |
1.00–3.20 |
Dual steps ≥0.20/step |
±0.08–0.10 mm |
≤±60 µm |
≤3.2 mm |
Hole wall quality controlled |
DFM & Package Rules
- Copper keep-out: ≥0.25–0.35 mm radial around counterbore/countersink to avoid exposed planes.
- Annular ring: For stepped pads, maintain ≥0.10–0.15 mm after etch compensation.
- Stack-up datum: Specify drilling from TOP or BOT; depth referenced to layer index (e.g., stop above L3).
- Mask strategy: Keep mask clearance around step rim 0.10–0.15 mm to avoid chipping.
- Press-fit: Match hole class (plated/unplated). For plated press-fit, set finished Ø & insertion force target; consider step seat for head support.
- Thermal seats: Use counterbore to thin dielectric path; connect to copper pour with spokes if solderability is needed.
- Backdrill: Define start/stop layers and max residual stub (e.g., ≤0.20 mm critical, ≤0.30 mm non-critical).
Manufacturing Flow & Controls
Tooling & datum → Pilot drill / peck cycle → Z-depth calibration (contact probe) → Controlled-depth drilling (spindle encoder) → Deburr & wall inspection → PTH / pattern plate (if plated) → Counterbore/countersink verification → Mask/finish → Metrology (CMM, pin gauge, cross-section).
Quality & Verification
|
Item |
Method |
Criteria (Typical) |
Note |
|
Depth accuracy |
Contact gauge / CMM |
±0.05–0.10 mm |
Per program side |
|
Angle accuracy |
Optical protractor |
±2° |
60°/82°/90° options |
|
Residual stub |
Cross-section / X-ray |
≤0.20 mm critical nets |
Backdrill lots |
|
Wall quality |
Endoscope / Cross-section |
No delam/burr/cracks |
After plating if PTH |
|
Pad concentricity |
Vision AOI |
≤0.10 mm |
For stepped pads |
Typical Applications
- Press-fit connectors: stepped seats for head support; controlled interference in plated holes.
- Screw & standoff seats: counterbore/countersink for mechanical clearance.
- Thermal counterbores: shorten dielectric path to copper heatsink.
- Selective backdrill: minimize stubs on high-speed through vias near BGAs or connectors.
- RF shielding: countersunk holes for shield can frames to sit flush.
Common Issues → Countermeasures
- Exposed plane → Increase copper keep-out; re-reference depth to stop above target layer.
- Burrs / fiber pull-out → Optimize peck cycle and tool; apply post-drill deburr; verify wall before PTH.
- Depth overshoot → Re-calibrate Z; reduce feed near target; use pilot pocketing.
- Stub too long → Tighten backdrill stop; verify start layer; add fiducial witness.
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