PCB backup boards sit under the bottom panel to give the drill a clean exit landing, suppressing exit burr and preventing bit breakage. YUESHAN grades run 70 HD (HDF) to 90 HD (phenolic), hold 0.10 mm flatness and 0.05 mm burr, and cost about 20% less than melamine-laminate for the same hole quality.
Key Takeaways
- The backup board sits under the bottom panel and decides exit burr, drill-bit life and panels per stack.
- Wrong grade costs you in scrap and throughput long before it shows up as a "drilling problem."
- Our recommended default backup is UV Melamine 950 — its anti-deformation performance beats melamine-laminate board and it costs ~20% less, so most lines get cleaner holes for less. HDF (cost) and UV Melamine 840/880 cover the rest; Phenolic PHE is a specialty grade we keep available, not our primary push.
What a Backup Board Actually Does
The board gives back-face support that delivers exit burr suppression and drill bit breakage prevention by absorbing thrust at hole exit.
The backup board (also called a drilling backup material) sits under the bottom panel of your stack. As the drill pierces the last layer, the board gives it a clean landing pad. Without a dense, flat support, the bit exits into air — dragging copper and resin with it. That is your exit burr.
Three physical properties decide whether a board does its job:
- Hardness (HD): higher = less drill wander and sharper exit. Our grades run 70 HD (entry HDF) to 90 HD (phenolic, a specialty grade).
- Density (kg/m³): denser boards resist compression and stay flat. Tolerance held at ±30 kg/m³.
- Flatness (mm): we hold ≤0.10 mm across the sheet, protecting hole-location accuracy.
💡 Field note — how we recommend backup boards: Phenolic PHE is a great laminate, but it is not our core product, so we don't lead with it. For the density and hardness phenolic used to own, our melamine-laminate board was developed to match it — and our process now hits those numbers. Today the grade we actually recommend by default is UV Melamine 950: it resists warping better than melamine-laminate and costs about 20% less, so you get a flatter, cheaper board for the same hole quality. Phenolic stays in the catalogue for routing-machine worktables and a few specific IC jobs — just not as our headline.
Quick Grade Comparison
| Grade | Hardness | Core selling point | Upgrade signal |
|---|---|---|---|
| UV Melamine 950 ★ | 80 HD | Recommended default — anti-warp, ~20% below laminate cost | HDI / multilayer / most lines |
| HDF | 70 HD | Best cost-to-performance | 2–4 L, cost-first lines |
| UV Melamine 840 | 75 HD | Moisture-sealed surface | 6–16 L, humid / FPC |
| UV Melamine 880 | 80 HD | HDI & back-drill workhorse | HDI 1–2 step, 12–24 L |
| Phenolic PHE | 90 HD | Specialty (routing table / specific IC) | Available on request |
Pain × Solution Matrix
High exit burr and snapped bits both trace back to weak back-face support and wrong density grade selection.
| Your failure mode | Likely cause | YUESHAN fix |
|---|---|---|
| Exit burr too high | Soft / low-flatness board | Step up HD + flatness ≤0.10 mm |
| Drill-bit wears fast | Abrasive filler | Virgin-fiber HDF / Melamine |
| Can't raise stack height | Board compresses | Denser Melamine / Phenolic |
| Burr in humid season | Board absorbs moisture | Sealed Melamine 840 / Phenolic |
| HDI microvia scrap | Poor location accuracy | Melamine 880 / Phenolic PHE |
Grade Options
HDF Backup Board
Cost-to-performance workhorse · 70 HD · 100% virgin wood fiber
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| Grade | Hardness | Density | Thickness | Best for |
|---|---|---|---|---|
| HDF 840 | ~70 HD | 840±30 kg/m³ | 2.0 / 2.5 mm | 2–4 L, cost-first |
| HDF 880 | 75±2 HD | 880±30 kg/m³ | 2.0 / 2.5 mm | Standard 2–12 L |
| HDF 950 | ~76 HD | 950±30 kg/m³ | 2.5 mm | Thick, high density |
Technical highlights
- 100% virgin wood fiber — no recycled filler, stable exit burr.
- Internal bond strength > 0.8 N/mm² — resists drill breakthrough.
- Three density grades for cost-to-performance tuning.
Recommended pairing
Aluminum Entry 1100 H18
Standard entry for 2–12 L stacks.
Sizes & packaging
| Size (mm) | Thickness | Sheets / pallet | MOQ |
|---|---|---|---|
| 940 × 1245 | 2.0 / 2.5 mm | 300 | 100 sheets |
| 520 × 620 | 2.0 / 2.5 mm | 800 | 200 sheets |
Storage
Store flat at ≤25°C, relative humidity <50%, away from direct sunlight. Palletise or shelve on edge.
UV Melamine 840 Backup Board
Moisture-sealed surface · 80±5 HD · for humid lines & FPC
| Property | Spec |
|---|---|
| Base | 840 HDF |
| Surface | Melamine face, sealed |
| Hardness | 80±5 HD |
| Thickness | 2.0 / 2.5 mm |
Technical highlights
- Melamine face sealed against moisture absorption — stable in humid seasons.
- Lower smear than bare HDF on 6–16 L boards.
- Good drill-life balance for flex-rigid and FPC runs.
Recommended pairing
Aluminum Entry 1100 H18
Standard entry board.
Coated Aluminum
For finer holes / HDI.
Sizes & packaging
| Size (mm) | Thickness | Sheets / pallet | MOQ |
|---|---|---|---|
| 940 × 1245 | 2.0 / 2.5 mm | 300 | 100 sheets |
| 520 × 620 | 2.0 / 2.5 mm | 800 | 200 sheets |
Storage
Store flat at ≤25°C, RH <50%. Keep carton sealed until use.
UV Melamine 880 Backup Board
HDI & back-drill main grade · 80±3 HD · UV melamine face
| Base | Hardness | Thickness | Best application |
|---|---|---|---|
| 880 | 80±3 HD | 2.0 / 2.5 mm | HDI 1–2 step · 12–24 L |
| 950 | 83±3 HD | 2.5 mm | HDI microvia, tighter tol |
| 980 | 80±5 HD | 2.5 mm | Back-drill · high layer count |
Technical highlights
- UV-cured melamine face — low smear, high location accuracy.
- Default grade for HDI microvia and multilayer 6–24 L.
- Pairs with thermoset-coated aluminum and back-drill sheets.
Recommended pairing
L.C.O Coated Aluminum
HDI / BGA / IC entry.
Back-drill Aluminum
For controlled-depth stubs.
Sizes & packaging
| Size (mm) | Thickness | Sheets / pallet | MOQ |
|---|---|---|---|
| 940 × 1245 | 2.0 / 2.5 mm | 300 | 100 sheets |
| 520 × 620 | 2.0 / 2.5 mm | 800 | 200 sheets |
Storage
Store flat at ≤25°C, RH <50%. UV face side protected from prolonged light.
UV Melamine 950 Backup Board ★ Recommended
Our default backup · 83±3 HD · anti-warp · ~20% below melamine-laminate cost
| Property | Spec |
|---|---|
| Base | 980±30 kg/m³ |
| Surface | UV-cured melamine, sealed |
| Hardness | 83±3 HD |
| Thickness | 2.5 mm |
| Anti-deformation | Beats melamine-laminate board |
Why we recommend 950 by default
- Resists warping better than melamine-laminate board, so holes stay located even on humid lines.
- Costs about 20% less than melamine-laminate at the same hole quality — lower cost per good hole.
- UV-sealed surface = low smear, stable CpK lot to lot.
Recommended pairing
Green L.C.O Coated Aluminum
HDI / BGA / IC entry.
Back-drill Aluminum
For controlled-depth stubs.
Sizes & packaging
| Size (mm) | Thickness | Sheets / pallet | MOQ |
|---|---|---|---|
| 940 × 1245 | 2.5 mm | 300 | 100 sheets |
| 520 × 620 | 2.5 mm | 800 | 200 sheets |
Storage
Store flat at ≤25°C, RH <50%. UV face protected from prolonged light.
Phenolic PHE Backup Board
Specialty grade · 90±5 HD · 1.50 mm · routing worktables & specific IC · not our primary push
| Property | Spec |
|---|---|
| Construction | Laminated phenolic |
| Hardness | 90±5 HD |
| Thickness | 1.50 mm |
| Decomp. temp | > 220°C |
Technical highlights
- Waterproof, moisture-proof — stable in any season.
- ROHS / E1 compliant, recyclable offcut.
- Best exit burr control (≤0.05 mm) for holes <Ø0.10 mm.
Recommended pairing
L.C.O Coated Aluminum
IC substrate entry.
Sizes & packaging
| Size (mm) | Thickness | Sheets / pallet | MOQ |
|---|---|---|---|
| 940 × 1245 | 1.50 mm | 360 | 100 sheets |
| 520 × 620 | 1.50 mm | 900 | 200 sheets |
Storage
Store flat at ≤25°C, RH <50%. Phenolic is dimensionally stable — long shelf life.
Applications
Backup boards are specified wherever hole quality and bit life matter. Pick the grade to your stack and target industry:
High-reliability boards
Traceable grades for aerospace & diagnostic PCB.
See Defense →Why Engineers Choose YUESHAN
Measurable specs
Hardness, density (±30 kg/m³) and flatness (≤0.10 mm) are stated and toleranced — not vague marketing claims.
Exit burr ≤0.05 mm
Grades tuned for clean holes, fewer scrub-backs and higher first-pass yield.
Free samples & TDS
Side-by-side comparison with your current grade, shipped in 5–7 days worldwide.
Stack-up advice
Send your hole size and stack — we recommend the right grade and pairing, free.
Packaging & Storage Overview
Tight moisture content control during storage prevents warpage that would ruin back-face support.
All grades ship on wooden pallets, edge-protected, in moisture-barrier cartons. Standard sheets 940×1245 mm; panel-size 520×620 mm for prototype lines. Store flat, ≤25°C, RH <50%.
Related Products & Resources
FAQ
What thickness backup board should I use for HDI drilling?
For HDI microvia, step up to **UV Melamine 950 (our recommended default)** or 880 at 2.0–2.5 mm. Pair with green L.C.O coated aluminum entry for sub-Ø0.15 mm vias. Phenolic PHE is available on request for specific IC jobs.
Why does flatness matter?
Flatness ≤0.10 mm keeps the bit's exit point consistent across the sheet, protecting hole-location accuracy on dense boards.
Can I get a sample before ordering?
Yes — free samples and full TDS/MSDS are sent for side-by-side comparison with your current grade. Contact Mr. Lucky Xu.