If you specify "1100 H18 aluminum entry board" on a purchase order, here is exactly what each part of that description means — the chemical composition limits, the mechanical properties the H18 temper guarantees, and the dimensional tolerances that separate a consistent entry board from one that varies lot to lot.
What "1100" means — the alloy system
The AA (Aluminum Association) 1xxx series designates commercially pure aluminum — ≥99.0% aluminum content with no intentional alloying elements. The last two digits ("00") indicate the minimum purity: 1100 means a minimum of 99.0% Al.
The chemical composition of AA1100 is tightly specified:
| Element | Content (%) | Role |
|---|---|---|
| Al | ≥99.0 | Base — provides thermal conductivity and formability |
| Si + Fe | ≤0.95 | Trace impurities from smelting |
| Cu | 0.05–0.20 | Minor strengthening without reducing conductivity |
| Mn | ≤0.05 | Trace grain refiner |
| Zn | ≤0.10 | Trace impurity |
| Others (each) | ≤0.05 | Individual impurity limit |
| Others (total) | ≤0.15 | Total impurity limit |
Why does purity matter for PCB drilling? Higher aluminum content means higher thermal conductivity. AA1100 measures approximately 220 W/(m·K) — more than 10× the thermal conductivity of FR-4. This is what allows the entry board to act as a heat sink during drilling.
What "H18" means — the temper system
H18 is a strain-hardened temper designation. The "H" indicates the material has been work-hardened (cold-rolled) to increase strength. The first digit "1" means strain-hardened only (no thermal treatment). The second digit "8" indicates the hardest commercially practical level — equivalent to approximately 75% cold reduction.
The mechanical properties guaranteed by H18 temper in 1100 entry foil:
| Property | Typical value | Why it matters |
|---|---|---|
| Tensile strength (UTS) | >170 MPa | Surface rigidity resists top-side burr |
| Elongation | ≥2% | Enough ductility to conform without cracking |
| Hardness (Brinell) | ~20 HB | Hard enough to guide the bit, soft enough not to dull it |
| Surface roughness (Ra) | ≤0.28 μm | Smooth surface prevents contamination transfer |
H18 temper is the most common choice because it offers the best balance for entry boards: the hardness to hold the bit at entry without the brittleness that can cause edge cracking during slitting or shearing.
Thickness tolerance — the real spec
A nominal thickness of "0.18 mm" on a quote means almost nothing without the tolerance. Entry board thickness tolerance directly determines Z-reference stability and therefore hole depth consistency.
Industry-standard tolerances for 1100 H18 entry foil:
| Thickness | Standard tolerance | Premium (documented CpK) |
|---|---|---|
| 0.15 mm | ±0.01 mm | CpK ≥1.33 on lot |
| 0.18 mm | ±0.01 mm | CpK ≥1.33 on lot |
| 0.20 mm | ±0.01 mm | CpK ≥1.33 on lot |
A consistent ±0.01 mm tolerance is achievable from any competent rolling mill. The differentiator is whether the manufacturer measures and documents the CpK for each lot — and whether they can prove that the tolerance holds across the full sheet width and length, not just at the edges.
Flatness — the unspoken differentiator
Flatness is the most commonly ignored spec in entry board procurement because it is not visible on a certificate of analysis. It is, however, the spec that most directly affects drilling accuracy.
Flatness is typically measured as the maximum deviation from a reference surface (granite plate). Standard spec for PCB entry board flatness: ≤0.10 mm across the sheet diagonal. For back-drill or precision microvia applications: ≤0.05 mm.
Warpage (curvature across the sheet) should be ≤0.6% of the diagonal dimension. For a standard 940 × 1245 mm sheet, that means warpage ≤8.7 mm across the diagonal — a spec that most mills meet easily, but one worth verifying if you are processing high-layer-count stacks.
Grade variations within 1100 H18
Not all 1100 H18 entry foil is identical. Three grade levels exist in practice:
| Grade | Thickness tolerance | Flatness | Surface | CpK documented |
|---|---|---|---|---|
| Standard commercial | ±0.015 mm | ≤0.15 mm | General purpose | No |
| PCB-grade | ±0.01 mm | ≤0.10 mm | Oil-free, Ra ≤0.28 μm | On request |
| Premium (YUESHAN) | ±0.01 mm | ≤0.10 mm | Oil-free, Ra ≤0.28 μm, edge-protected | Per lot |
The difference between "standard commercial" and "PCB-grade" is not the raw material — it is the selection and inspection that removes out-of-tolerance sheets before they reach your line. A premium supplier like YUESHAN ships with documented CpK per lot, oil-free surface certification, and edge-protected packaging.
Quick spec check when evaluating entry board suppliers
- Request the thickness gauge tolerance in writing — not just nominal.
- Ask for flatness measurement — max deviation across the sheet diagonal.
- Confirm oil-free delivery — ask for the surface cleanliness spec.
- Request CpK data for the last 5 production lots (≥25 measurements each).
- Verify edge condition — burr-free slitting matters for automated stacking.
For the full 7-factor selection framework that includes alloy, temper, coating, and supplier consistency, see the pillar guide. For the 1100 H18 entry board spec, including downloadable TDS, see the plain aluminum entry board page.