An anti-burr aluminum entry board adds a high-hardness polymer coating (7-9H pencil, grade-0 adhesion) to plain foil, holding exit burr at 18 micrometres or less versus 35-50 micrometres on bare aluminum. Bench data shows under 2% scratch rate versus over 30%, more than 5,000 holes per sheet versus under 1,500, and about 80% less deburring labor.
Exit burr — the ragged lip of aluminum left around a drilled hole — is one of the most expensive "small" defects in PCB drilling. Left unchecked it scratches dry-film in lamination, causes skimmed or false solder joints, and forces manual deburring that eats labor and cycle time. The anti-burr aluminum entry board (a hard-coated cover sheet) is the material fix most high-density mills now spec to keep burr inside tolerance without touching drilling parameters. This guide covers what it is, how it works, the measured numbers, and how to choose one.
What Is an Anti-Burr Aluminum Entry Board?
An entry board is the sheet placed on top of the panel stack before drilling — it steadies the bit on first contact and pulls heat away. A plain (bare) aluminum foil does that job acceptably until hole density and burr budget tighten. An anti-burr coated sheet adds a single-component high-hardness polymer coating on the panel-facing side. That coating is the whole trick: it raises surface hardness from the soft-aluminum baseline to a 7–9H support plane that resists the drill's shear and stops the aluminum from smearing into a burr at the exit.
The coating also sheds coolant and oil (contact angle >110°, so cleaning drops from minutes to under 30 seconds per sheet) and stays put at grade-0 adhesion, so it does not flake into the hole as a secondary contaminant.
How an Anti-Burr Coated Sheet Suppresses Exit Burr
Burr forms because bare aluminum is soft: the rotating drill shears the foil at the hole mouth and the aluminum flows outward into a lip. Three things stop it:
- Rigid support plane. The 7–9H coating gives the bit a hard, flat reference instead of a yielding surface, so the aluminum deforms far less at exit.
- Shear resistance. With less material flow, the exit edge stays crisp. Bench data shows surface-scratch incidence falling below 2% versus over 30% on plain foil under the same condition.
- Paired second-pass cut. On demanding stacks, the coated sheet is used together with a controlled back-drill (stub-removal) pass that severs any residual barrel/burr, pushing hole-wall integrity above 99.7%.
Anti-Burr Coated vs Plain Aluminum: The Numbers
Published bench tests on a 2-up stack (≈110k rpm, 0.06 mm/rev feed) put the two head-to-head:
| Metric | Anti-burr coated sheet | Plain aluminum foil |
|---|---|---|
| Exit burr height | ≤18 µm | 35–50 µm |
| Surface scratch rate | <2% | >30% |
| Coolant/oil clean time | <30 s/sheet | >2 min/sheet |
| Holes per sheet | >5,000 | <1,500 |
| Downstream rework rate | 2.8% | 24.5% |
The gap is not marginal — it is the difference between a pass and a scrap/rework loop.
Why Mills Specify Anti-Burr Coated Entry
Burr inside tolerance
Exit burr held at or below 18 µm keeps lamination and assembly clean, cutting skimmed-joint and short-circuit risk.
3x+ sheet life
Hard, scratch-resistant coating runs past 5,000 holes versus under 1,500 for plain foil — fewer sheet changes, less downtime.
15–20% lower total cost
Rework drops from ~25% to under 3% and deburring labor falls ~80%, so the slightly higher sheet price pays for itself per panel.
Drop-in, no re-qualification
Keeps aluminum's heat sink and drill guidance, so it replaces plain entry foil with no drilling-parameter rewrite.
Selection Matrix: Pick by Stack and Burr Budget
| Condition | Recommendation | Why |
|---|---|---|
| HDI / IC substrate, <0.15 mm | Anti-burr coated + second-pass cut | Burr budget tightest; finish drives yield |
| RF / high-frequency laminates | Anti-burr coated | Clean hole wall protects Tg-sensitive resin |
| Thick multilayer (≥8 L) | Anti-burr coated | 3x life offsets frequent sheet change |
| Standard 4–6 L, >0.20 mm | Plain aluminum sufficient | Burr rarely binding; cost first |
Anti-Burr vs Lubricant (LE Sheet): Which Do You Need?
They are complementary, not competing. An anti-burr coated sheet attacks exit burr and edge finish. A lubricant (LE Sheet) attacks drill-bit temperature, bit life, and resin smear on micro-holes. On dense HDI and RF lines it is common to run both — anti-burr on entry for finish, LE Sheet when bit life or smear is the binding constraint. If your pain is burr and deburring labor, start with anti-burr; if it is bit snapping or smear, start with our LE Sheet guide.
FAQ
What is an anti-burr aluminum entry board?
It is an aluminum cover sheet with a high-hardness coating on the panel side. The 7–9H coating forms a rigid support plane that resists the drill's shear, so aluminum deforms far less at exit and burr stays at or below 18 µm instead of the 35–50 µm typical of plain foil.
How much can an anti-burr coated sheet reduce exit burr?
Bench tests on 2-up stacks at ~110k rpm show exit burr dropping from 35–50 µm on plain aluminum to 18 µm or less on a coated sheet, with hole-wall integrity above 99.7% when paired with a controlled second-pass cut. Validate on a sample for your exact stack.
Does switching to an anti-burr sheet require process changes?
No. It keeps aluminum's thermal mass and drill-guiding behavior, so it drops into existing drilling programs as a direct replacement for plain entry foil — no parameter rewrites.
Anti-burr coated vs lubricant (LE Sheet) — which do I need?
Different problems: anti-burr for exit burr and finish; LE Sheet for bit temperature, life, and smear. Many HDI/RF lines run both. See our LE Sheet guide for the temperature mechanism.
How long does one anti-burr sheet last?
Typically past 5,000 holes per sheet versus under 1,500 for plain foil in the same condition, because the hard coating resists scratch and wear. That 3x+ life plus an ~80% drop in burr-rework labor drives the 15–20% lower total cost per panel.
Internal links (verified live on www.yueshanpcb.com)
- Pillar: /products/entry-boards/ · /products/lubricant-aluminum/
- Definitions: /resources/what-is-entry-board/ · /resources/what-is-coated-aluminum/ · /resources/exit-burr-control/
- Same-topic published: lubricant (LE Sheet) guide · choose an aluminum entry board · aluminum vs phenolic for back-drill
- Related: standard vs lubricated · back-drill guide
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Anti-Burr Coated Aluminum
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