Short answer: For standard PCB drilling (holes ≥0.20 mm, 2–24 layers), 1100 H18 aluminum at 0.18 mm thickness is the default. Deviate from this only when your hole size, layer count, surface sensitivity, or thermal requirements call for a different alloy, temper, or coated option. Below is a seven-factor framework that CAM engineers and production managers can use to evaluate any entry board — whether you are sourcing from YUESHAN or comparing multiple suppliers.
Why the entry board matters more than you think
The aluminum entry board sits on top of the PCB stack and performs four distinct jobs simultaneously:
- Drill guidance: Centres the bit at the point of entry, preventing wander and ensuring positional accuracy within ±0.02–0.05 mm.
- Heat dissipation: 1100 aluminum has a thermal conductivity of ~220 W/(m·K) — over 10× that of FR-4 — drawing heat away from the cutting edge.
- Burr prevention: Absorbs the deformation at drill exit, keeping burr height ≤0.03 mm on standard stacks.
- Surface protection: Shields the top copper layer from pressure foot marks, scratches, and indentations.
Choosing the wrong entry board — wrong thickness, wrong temper, or wrong alloy — degrades all four functions simultaneously. The seven factors below help you avoid that.
Factor 1: Alloy — why 1100 dominates
Over 90% of PCB drilling entry boards are made from AA1100 (≥99.0% commercial-pure aluminum). The reasons are thermal and mechanical:
- High thermal conductivity (~220 W/m·K) rapidly pulls heat from the drill tip.
- Low flow stress means the bit penetrates cleanly without a large axial-force spike.
- Good formability at thin gauges (0.15–0.20 mm) without cracking.
Alternatives exist — 3003 (Al-Mn, slightly harder) and 5052 (Al-Mg, for structural use) — but they are rarely specified for entry boards. The higher hardness of 3003 reduces entry surface conformability, and the cost premium offers no drilling benefit. 1100 is the standard for a reason.
For detailed 1100 H18 specifications, chemical composition, and mechanical properties, see the dedicated guide.
Factor 2: Temper — H18 vs alternatives
H18 (full-hard) is the default temper for entry boards. It provides the surface rigidity needed to resist top-side burr without being so hard that it accelerates bit wear.
Typical mechanicals for 1100 H18 entry foil: tensile strength >170 MPa, elongation ≥2%, Brinell hardness ~20 HB. The H18 temper delivers the best balance of surface stability (holds the bit on entry) and drill-friendliness (does not blunt the cutting edge).
Temper H14 (half-hard) is sometimes used for very thin entry foils (0.07–0.10 mm) where flexibility is needed to conform to uneven stack surfaces, but it is rare in mainstream production.
Factor 3: Thickness — matching to hole size and stack
Three standard thicknesses cover the vast majority of production:
| Drill Ø (mm) | Recommended thickness | Best for |
|---|---|---|
| 0.20–0.30 | 0.15 mm | Fine-pitch, thin panels, flex |
| 0.30–0.45 | 0.18 mm | Standard multilayer — the default |
| 0.45–0.60 | 0.20 mm | Thick stacks, larger drills, high rigidity |
Using too thin an entry board for large drills risks the bit punching through before reaching full guidance; too thick for fine drills increases the axial load and snap risk. For a full treatment of this trade-off, see 0.15 vs 0.18 vs 0.20 mm: which thickness for your stack.
Factor 4: Flatness — the invisible spec
Flatness is the most overlooked entry board spec because it is invisible until the drill misses target. A bowed or warped entry sheet shifts the Z-zero reference across the panel, creating inconsistent stub lengths and positional drift.
Spec flatness at ≤0.10 mm for standard entry boards. For back-drill applications where the entry sheet doubles as a Z-reference, tighter flatness (≤0.05 mm) is required. The entry board's flatness is not a "nice to have" — it is the mechanical reference the entire drilling cycle depends on.
Factor 5: Surface quality and cleanliness
Surface defects on the entry board transfer directly to hole quality. Check for:
- Oil residue — rolling oil left on the surface can contaminate the hole wall and interfere with subsequent PTH plating.
- Scratches and die marks — create local thickness variations that shift the drill's entry point.
- Edge burrs — from slitting or shearing, these can embed in the stack and cause registration errors.
A reputable supplier specifies surface roughness (Ra ≤0.28 μm), certifies oil-free delivery, and ships with edge protection. If the surface spec is not in the TDS, ask for it.
Factor 6: Coating — when plain aluminum is not enough
Plain 1100 H18 is the right choice for holes ≥0.20 mm on standard FR-4 and high-Tg laminates. When the hole drops below 0.15 mm, or when drilling polyimide, RF substrates, or IC substrate materials, the entry board needs a lubricating coating to reduce friction and control temperature.
Our lubricated entry (LE) sheet applies a 3–5 µm thermoset coating that melts at ~220°C, reducing drill tip temperature by 30–50°C. The decision framework: use plain 1100 H18 for standard work; step up to LE sheet when microvia accuracy, resin smear prevention, or bit life extension becomes the priority. See the standard vs lubricated cost comparison for the financial trade-off.
Factor 7: Supplier consistency — the hidden variable
The first six factors are spec-sheet items. The seventh is whether the supplier actually delivers those specs lot after lot. A supplier with documented process capability (CpK ≥1.33 on thickness and flatness) will produce consistent results; one without it will ship material that meets spec "on average" but varies panel to panel.
Questions to ask any entry board supplier:
- Do you publish thickness CpK with each lot?
- What is your flatness measurement method — and what is the Cpk?
- Can you provide a 3rd-party certificate of analysis for alloy composition?
- How is the material packaged to prevent edge damage and moisture absorption during transit?
YUESHAN publishes ISO 9001:2015 certification, thickness CpK data, and full TDS/MSDS with every shipment. Free samples with documented specs are available for side-by-side comparison against your current entry board.
Selection summary table
| Your condition | Recommended entry board | Why |
|---|---|---|
| Holes ≥0.20 mm, 2–12 layer FR-4 | 1100 H18, 0.15–0.18 mm | Standard spec, lowest cost |
| Holes ≥0.20 mm, 12–24 layer | 1100 H18, 0.18–0.20 mm | Extra rigidity for thicker stack |
| Holes 0.15–0.20 mm, HDI | 1100 H18, 0.15 mm or LE Sheet | Evaluate cost vs temperature benefit |
| Holes ≤0.15 mm, microvia | LE Sheet (coated) | 30–50°C temperature reduction needed |
| RF / high-frequency laminate | LE Sheet (thermoset, 220°C) | Resin smear prevention critical |
| Back-drill pass, controlled depth | Back-drill aluminum (HW600/HW900) | Z-reference flatness needed |
FAQ
Can I use 3003 aluminum instead of 1100 for entry boards? Technically yes, but 3003 is harder (Al-Mn alloy), which increases the axial load on micro-drills and reduces bit life. Stick with 1100 unless a specific customer spec requires 3003.
Is 0.15 mm thick enough for 0.50 mm drills? No — the bit's cutting edge can punch through a 0.15 mm entry before reaching full guidance. Use 0.20 mm for drills ≥0.45 mm.
Does oily surface residue on entry boards affect drilling? Yes. Oil residue can migrate into the hole wall and interfere with electroless copper deposition (PTH). Specify oil-free delivery in your purchase order.
How do I verify supplier flatness claims? Place the sheet on a granite surface plate and measure the gap with a feeler gauge at nine points (centre + 8 edges). The maximum gap should not exceed the supplier's stated flatness spec.