Aluminum entry-board thickness: 0.18 mm is the default for 90% of lines; use 0.15 mm for fine holes (0.20-0.30 mm) and thin panels; use 0.20 mm for larger drills (at or above 0.45 mm) and thick stacks (at or above 16 layers). The right gauge is the thinnest that still guides your smallest drill.
Short answer: 0.18 mm is the default thickness for 90% of PCB drilling lines. Use 0.15 mm for fine holes (Ø0.20–0.30 mm) and thin panels; use 0.20 mm for larger drills (≥0.45 mm) and thick stacks (≥16 layers). The wrong thickness costs you positional accuracy on one side and bit life on the other — here is the data to get it right.
How thickness affects drilling performance — the trade-off
The entry board thickness is a trade-off between two competing requirements:
- Thinner entry (0.15 mm): Lower axial load on the bit at penetration, less heat generation from the entry surface, and lower cost per sheet. But less surface rigidity means the bit may wander before reaching the copper foil.
- Thicker entry (0.20 mm): More surface rigidity to centre the bit, better Z-reference stability for controlled-depth drilling, and more heat dissipation capacity. But higher axial load increases snap risk for sub-0.20 mm drills, and higher cost per sheet.
The "right" thickness is the thinnest gauge that still provides sufficient guidance for your smallest drill diameter.
Three-standard comparison table
| Parameter | 0.15 mm | 0.18 mm | 0.20 mm |
|---|---|---|---|
| Optimal drill Ø range | 0.20–0.30 mm | 0.30–0.45 mm | 0.45–0.60 mm |
| Max stack height (FR-4) | ≤3.2 mm (8 layers) | ≤4.8 mm (12 layers) | ≤6.4 mm (16+ layers) |
| Bit snap risk (sub-0.20 mm drill) | Low | Medium | High |
| Surface rigidity / wander control | Moderate | Good | Excellent |
| Z-reference stability | Moderate | Good | Excellent |
| Cost per sheet (relative) | −15% vs 0.18 | Baseline | +15% vs 0.18 |
When to use 0.15 mm
Best for fine-pitch HDI, flex, and thin panels. The thinner entry reduces the axial-force spike when the bit first contacts the surface, which is critical for sub-0.30 mm drills where the flute volume is already limited.
Typical use cases:
- Ø0.20–0.30 mm via drilling on 2–8 layer HDI
- Flex and rigid-flex PCB — the thinner entry conforms better to uneven stack surfaces
- Panels ≤1.6 mm total thickness where entry load must be minimised
Limitation: 0.15 mm does not provide enough guidance for drills ≥0.40 mm. The bit can push through the entry before reaching full rotational stability, leading to oval holes and positional deviation.
When to use 0.18 mm — the default
Best for the widest range of standard multilayer production. 0.18 mm covers the majority of FR-4 boards from 4 to 12 layers with drill diameters from 0.30 to 0.45 mm.
Typical use cases:
- Standard 4–12 layer FR-4, high-Tg, and mid-range telecom boards
- Automotive PCBs (where the stack is typically 4–8 layers)
- Most general-purpose drilling where no special thermal or mechanical requirements exist
Why 0.18 mm became the standard: It provides sufficient rigidity for the most common drill range (0.30–0.35 mm) while keeping bit load low enough for reliable tool life. The industry converged on 0.18 mm through decades of production experience — it is the thickness that fails least often across the widest range of jobs.
When to use 0.20 mm
Best for thick stacks, large drills, and back-drill applications. The extra 0.02 mm provides measurable improvements in surface rigidity and heat dissipation capacity.
Typical use cases:
- Ø0.45–0.60 mm through-hole drilling on 16+ layer stacks
- Thick panels (≥3.2 mm) where the entry board must carry more of the thermal load
- Back-drill applications where the entry sheet doubles as a Z-reference — the thicker gauge provides more stable depth control
Limitation: 0.20 mm significantly increases snap risk for sub-0.20 mm drills. Do not use 0.20 mm entry for HDI microvia drilling (Ø ≤0.15 mm) — this is where a lubricated entry (LE) sheet at 0.15–0.18 mm is the correct choice, not thicker plain aluminum.
Cost comparison: thickness vs cost per good hole
The cost difference between thicknesses is small on a per-sheet basis (±15%) but compounds across volume:
| Thickness | Cost / 1000 sheets | Typical hits / bit | Cost per 10,000 holes (incl. bits) |
|---|---|---|---|
| 0.15 mm | −15% vs baseline | 18,000 | Baseline −8% |
| 0.18 mm | Baseline | 20,000 | Baseline |
| 0.20 mm | +15% vs baseline | 22,000 | Baseline +5% |
The slightly higher bit life on 0.20 mm (the bit experiences less vibration at entry due to the more rigid surface) offsets part of the material cost premium. However, this advantage disappears if the thickness is mismatched to the drill size — using 0.20 mm with a 0.20 mm drill reduces bit life by 30–50% due to increased snap frequency.
Decision matrix: thickness by job type
| Job type | Smallest drill | Max layers | Recommended thickness |
|---|---|---|---|
| Fine-pitch HDI | 0.15–0.20 mm | 8 | 0.15 mm (or LE Sheet) |
| Standard multilayer | 0.30–0.35 mm | 12 | 0.18 mm |
| Thick multilayer | 0.35–0.45 mm | 16+ | 0.18–0.20 mm |
| Large through-hole | 0.45–0.60 mm | 20+ | 0.20 mm |
| Back-drill (controlled-depth) | 0.30–0.50 mm | 16+ | 0.20 mm (back-drill grade) |
| Flex / rigid-flex | 0.20–0.30 mm | 6 | 0.15 mm |
For the full decision framework covering alloy, temper, flatness, and supplier consistency, see How to Choose Aluminum Entry Board: 7 Factors Explained. For detailed 1100 H18 alloy specs and what each number means, see the 1100 H18 Specifications Guide.