How to Choose the Right Aluminum Entry Board for PCB Drilling

This article covers entry board selection for the through-hole drilling pass. For entry board use in back-drilling, see Back-Drilling Principle and Stub Control. For the full burr-control picture including backup board pairing, see Exit Burr Control Guide.

What an entry board does — and why it is not optional

The entry board sits on top of the copper foil layer and serves three distinct functions that together determine hole quality:

1. Bit guidance: The entry board stabilises the drill bit at the first point of contact. A flat, burr-free entry surface prevents the bit from walking before it reaches the copper. This single function determines hole-location accuracy across the entire panel.
2. Heat management: The friction between the drill bit and the entry board generates heat. The entry board material must conduct heat away from the bit tip, reducing peak temperature and extending bit life.
3. Burr suppression: A clean entry board produces a clean entry burr — or no burr at all. A rough or uneven entry board creates an entry burr that can interfere with subsequent plating.

Despite these well-understood roles, entry boards are the most commonly mis-specified consumable in PCB drilling. Many factories use a single entry-board type for all products, leaving performance on the table for their most demanding jobs.

The three types of aluminum entry board

1. Plain aluminum entry (1100 H18)

This is the standard entry board: a sheet of 1100-grade aluminum in the H18 (full-hard) temper. It is cost-effective, widely available, and sufficient for the majority of standard multilayer drilling.

Key specifications:

• Alloy: 1100 (99.0% min. aluminum)
• Temper: H18 (full hard)
• Thickness options: 0.15 mm, 0.18 mm, 0.20 mm
• Flatness: ≤0.10 mm
• Surface: degreased, scratch-free

Best for:

• Standard multilayer boards (2–24 layers)
• Hole sizes ≥0.20 mm
• High-volume production where cost per hole is the primary metric
• Pairs with: HDF 880/950 or UV Melamine backup boards

Limitation: Plain aluminum provides no lubrication. At high spindle speeds (>150 krpm) or with small drills (Ø<0.20 mm), the friction can cause bit overheating and reduced life. For these cases, a coated entry board is the better choice.

2. Thermoset coated aluminum (thermoset-coated)

This is plain aluminum with a thermoset resin coating applied to the top surface. The coating melts at approximately 220°C during drilling, creating a lubricating film that reduces friction and heat. The coating also seals the aluminum surface, preventing aluminium debris from contaminating the hole wall.

Key specifications:

• Base: 1100 H18 aluminum, 0.08–0.15 mm
• Coating: thermoset resin, 220°C melt point
• Total thickness: 0.10–0.20 mm
• CPK: ≥4.3 (coating uniformity)

Best for:

• HDI microvia (≤Ø0.15 mm)
• BGA and IC substrate drilling
• High spindle speeds (>180 krpm)
• Any application where bit life is the primary cost driver
• Pairs with: UV Melamine 950 or Phenolic PHE backup boards

This is the product that competes directly with L.C.O's coated aluminum entry. For a detailed comparison, see L.C.O vs YUESHAN Coated Lubricant Aluminum.

3. Water-soluble coated aluminum

A variation of the coated entry board where the coating is water-soluble rather than thermoset. The lubricating mechanism is similar, but the coating washes off in the cleaning cycle instead of remaining as a residue. This is advantageous for boards that require extremely clean hole walls before plating.

Best for:

• General HDI (holes >Ø0.10 mm)
• Boards with strict cleanliness requirements before desmear
• Lines that prefer not to manage thermoset residues

Thickness selection guide

The correct thickness depends primarily on the smallest hole size in the panel:

Smallest hole Ø	Entry board type	Recommended thickness
≥0.30 mm	Plain 1100 H18	0.20 mm
0.20–0.30 mm	Plain 1100 H18	0.18 mm
0.15–0.20 mm	Plain 1100 H18 or coated	0.15 mm
0.10–0.15 mm	Thermoset coated	0.10–0.15 mm base
<0.10 mm	Thermoset coated	≤0.10 mm base

A thicker entry board provides more bit guidance but generates more friction heat. A thinner entry board reduces heat but provides less guidance. The table above balances these trade-offs for typical production conditions.

Parameter considerations

Switching entry board types may require parameter adjustments. The coated entry board's lubricating effect allows higher feed rates and/or higher spindle speeds compared to plain aluminum:

Parameter	Plain 1100 H18	Thermoset coated	Water-soluble coated
Max spindle speed	180 krpm	250+ krpm	220+ krpm
Feed rate (0.20 mm hole)	1.2–1.5 m/min	1.5–1.8 m/min	1.4–1.7 m/min
Bit life improvement vs plain	—	+30–50%	+20–40%

The exact gain depends on your stack, hole count and coolant method. Run a side-by-side trial before changing parameters in production.

Common entry board mistakes

• Using the same entry for all jobs: A factory that runs both 2-layer automotive boards and 20-layer HDI boards with the same entry is leaving yield on the table for one of the two product types — possibly both.
• Reusing entry boards: An entry board that has been drilled once has raised burrs around every hole. Reusing it guarantees poor location on the second pass.
• Storing entry boards vertically: Aluminum sheets stored leaning against a wall develop permanent bow within days. Store flat on a pallet.
• Skipping the entry board entirely: Some low-cost operations run without an entry board. This saves a few cents per panel but increases drill breakage, reduces location accuracy, and raises burr — the net cost is almost always negative.

How to test a different entry board grade

1. Measure current bit life (hits before first regrind) and entry burr height.
2. Request a sample of the candidate grade — contact YUESHAN for free samples of plain 1100 H18 or thermoset coated entry.
3. Run a side-by-side trial with the same program, same panel design and same drill bits. Switch only the entry board.
4. Measure burr, bit wear and hole location for both entry types. The data will tell you which is correct for that product.

For full specifications of plain and coated entry boards, see 1100 H18 Aluminum Entry Board and Lubricant Aluminum Entry Board.

Market Snapshot: What Domestic Suppliers Are Shipping

The Chinese-language market gives a useful read on where entry-board specs are heading. Foshan-based — a domestic drilling-materials maker that benchmarks itself against leading Western coated-aluminum brands — publishes a composite aluminum entry board built as a "0.06 mm Al foil + pure-fibre core" sandwich at 0.35 ±0.02 mm total, citing thermal conductivity ≥ 200 W/(m·K), hole-position deviation within ±0.01 mm, and a double-roll-coated surface at Ra ≤ 0.2 µm for sub-0.15 mm drills. It also claims its composite entry runs 15–20% cheaper per unit area than imported product while extending drill life 25%+.

One variant worth knowing: a hard-coating anti-burr (防批锋) aluminum entry sheet. coats the backside with a 7–9H polymer layer that it says holds burr height ≤ 18 µm (vs 35–50 µm for bare aluminum), sheds coolant (contact angle > 110°), and lasts > 5,000 holes vs < 1,500 for plain Al. That is a different product from a lubricant entry sheet — coating for burr suppression, not lubrication — but it sits in the same "engineered entry board" family. (We do not yet have a standalone article on anti-burr entry sheets; tell us if that belongs on your roadmap.)

Related Resources