Featured Snippet: Total Stack Height = (Layers x Layer Thickness) + Entry Thickness + Backup Thickness
Free PCB stack height calculator. Add layers, per-layer thickness, entry and backup board to get total stack height and aspect ratio versus your smallest hole.
Suitable for:
Enter stack build-up.
| Board thickness | -- mm |
| Total stack height | -- mm |
| Aspect ratio | -- : 1 |
Aspect ratio above ~10:1 is standard-limit; HDI pushes 15-20:1 with laser micro-vias. Verify against your drill capability.
Stack height is the total thickness being drilled - laminate plus your entry and backup board. It sets how far the bit engages per hole and bounds the hole aspect ratio you can hold. This tool totals the stack and reports the aspect ratio against your smallest hole so you can judge drillability before CAM release.
Taller stacks engage the bit longer per hole, raising heat and lowering hit count. The aspect ratio (stack height / smallest hole) is the real drillability gate: standard mechanical drilling holds roughly 10:1, while HDI uses laser drilling for micro-vias beyond that. Pick an entry/backup pair that supports the exit without adding unnecessary height - see our backup board range.
| Material | Feed Stability | Burr Control | Tool Life |
|---|---|---|---|
| UV Melamine backup board | ★★★★★ | ★★★★★ | ★★★★ |
| Phenolic backup board | ★★★★ | ★★★★ | ★★★ |
| Aluminum entry sheet | ★★★★★ | ★★★★★ | ★★★★ |
Stable feed rate and clean exits are what let you push hit count without micro-drill breakage. Pair the right board with the parameters from this tool — see our backup board range and aluminum entry boards.
| Material | RPM | Chip load | Feed (m/min) | Entry | Backup |
|---|---|---|---|---|---|
| FR4 (standard multilayer) | 90,000 | 0.012 | 2.16 | Aluminum entry sheet | HDF backup board |
| HDI / micro-via | 110,000 | 0.008 | 1.76 | Lubricant aluminum | UV melamine 880 backup board |
| Rogers (high-frequency) | 80,000 | 0.010 | 1.60 | Aluminum entry sheet | Phenolic backup board |
| PTFE / Teflon | 60,000 | 0.008 | 0.96 | Aluminum entry sheet | Phenolic backup board |
| IC substrate (ABF) | 120,000 | 0.006 | 1.44 | Lubricant aluminum | UV melamine 950 backup board |
| Ceramic PCB | 50,000 | 0.008 | 0.80 | Aluminum entry sheet | Phenolic backup board |
| Aluminum PCB (IMS) | 40,000 | 0.010 | 0.80 | Aluminum entry sheet | Phenolic backup board |
| Copper-core PCB | 30,000 | 0.010 | 0.60 | Aluminum entry sheet | Phenolic backup board |
Figures are qualified starting points cross-checked with published fabrication guidance and supplier benchmarks — validate on your own panels.
Panels per stack (standard 1.6 mm core)
Representative field benchmarks for a 0.20 mm drill on standard FR4; actual results vary with stackup, machine and consumables — validate on your own panels.
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| Copper weight | Thickness (mm) | Thickness (µm) |
|---|---|---|
| 0.5 oz | 0.018 | 18 |
| 1 oz | 0.035 | 35 |
| 2 oz | 0.070 | 70 |
| 3 oz | 0.105 | 105 |
Typical total stack heights: 2-layer ≈ 1.6 mm, 4-layer ≈ 1.6 mm (thinner cores), 6–8 layer ≈ 1.6–2.0 mm, 10–12 layer ≈ 2.0–2.4 mm. Use the stack height calculator above to model your exact build.
What is stack height in PCB drilling? Stack height is the total thickness drilled: laminate plus entry and backup board.
What is aspect ratio? Aspect ratio = total stack height / smallest hole diameter; it indicates drillability.
What aspect ratio can mechanical drilling hold? Roughly 10:1 for standard mechanical drilling; beyond that, laser micro-vias are used.
What aspect ratio is HDI? HDI often runs 15-20:1 using laser-formed micro-vias rather than mechanical bits.
How does stack height affect drilling? Taller stacks mean longer bit engagement, more heat and lower hit count.
What is an entry board? An entry board (aluminum) sits on top to centre and cool the bit on entry.
What is a backup board? A backup board under the stack supports exit, controls burr and protects the bit.
What is a multilayer PCB? A board with many inner layers of copper and dielectric built up as a stack.
What is prepreg? Prepreg is the pre-impregnated bonding sheet between layers in a multilayer build.
What is core material? Core material is the rigid laminate base (e.g. FR4) around which layers are built.
What is copper foil? Copper foil is the conductive layer etched into traces; thickness adds to stack height.
What is microvia drilling? Microvia drilling forms tiny vias (often by laser) for HDI interconnects.
What is laser drilling? Laser drilling (UV/CO2) ablates micro-vias without a mechanical bit, beating aspect-ratio limits.
What is the difference between inner and outer layer? Inner layers are buried in the stack; outer layers are surface planes etched and plated.
What is hole wall roughness? Inside-hole roughness; long engagements in tall stacks can worsen it without good support.
What is via reliability? Long-term via integrity; controlled aspect ratio and clean holes support it.
How thick is a typical 4, 5 or 12-layer PCB? A 4-layer board is commonly about 1.6 mm total; a 5-layer stack around 1.8-2.0 mm; a 12-layer board typically 2.0-2.4 mm depending on copper weight and prepreg count. Minimum thickness for a 12-layer board with 2 oz copper is usually above 2.0 mm.
How many mm is 1 oz copper? 1 oz copper foil is about 0.035 mm (35 micrometres) thick; 2 oz copper is about 0.070 mm (70 micrometres).
How do I calculate core thickness for a 1.6 mm PCB with 1 oz copper? Subtract the copper and prepreg from the total: a standard 1.6 mm two-layer build uses a roughly 1.5 mm FR4 core plus two 1 oz foils (about 0.035 mm each) and thin surface prepreg. Enter those layers into the stack height calculator to get the exact core thickness.
What is 2 oz copper thickness in mm, and how thick an aluminum base for a 2.0 W/mK MCPCB? 2 oz copper is about 0.070 mm (70 micrometres). For a 2.0 W/mK MCPCB with 2 oz copper, the aluminum base is usually 1.0-3.0 mm depending on the power-density and mechanical requirement.
How do I convert copper weight (oz/ft2) to thickness (mm)? Divide ounces per square foot by about 1.37 to get thickness in mils, then multiply by 0.0254 for mm: 1 oz/ft2 is about 0.035 mm and 2 oz/ft2 about 0.070 mm. The copper weight thickness calculator applies this to each layer of your stack.
The fundamental relationship — Feed (mm/min) = RPM × chip load × flutes — governs heat generation, burr formation, and tool wear. For micro-drills below 0.2 mm, keep chip load between 0.005–0.012 mm/tooth to avoid drill breakage. Validate on your stack with a sample before committing to production.
Proto-Electronics — PCB drilling process ↗
Stack height and aspect ratio (hole depth ÷ diameter) interact directly with feed parameters. High aspect ratio holes (> 10:1) require reduced feed to maintain chip evacuation and avoid resin smear. Pairing a lubricated entry board with a UV melamine backup board supports higher stacks without quality degradation.
NCAB Group — HDI / microvia design ↗
Tool life is maximised when feed rate keeps the cutting edge loaded (not rubbing). A stable feed of 6–12 mm/min for 0.2 mm drills on FR4 typically yields 3,000–4,000 hits per bit. Worn bits increase burr height and hole wall roughness — monitor both as end-of-life indicators.
IPC — rigid PCB standards (IPC-6012) ↗
The entry board material directly affects parameter stability. Standard aluminum entry sheets provide consistent centering for most builds; lubricated aluminum entry sheets reduce drill wander on micro-vias below 0.15 mm and enable higher feed rates by lowering frictional heat.
YUESHAN — What is an entry board
The backup board absorbs exit energy and controls burr. UV melamine boards (880/950 grades) offer the best surface hardness for HDI and fine-pitch work; HDF is cost-effective for standard FR4; phenolic suits back-drilling and rigid-flex applications.
YUESHAN — What is a backup board
The total cost per hole includes drill bit cost, entry/backup board cost, machine time, and scrap. Optimising parameters to increase hit count by even 20% often has a higher ROI than reducing consumable cost per sheet. Use the tools on this site to model the trade-offs.
Process and CAM engineers use these numbers across demanding builds:
The right entry and backup board is what actually lets you hold a stable feed rate without breakage. Explore the product lines:
HDF, UV melamine and phenolic backup boards for stable exits and burr control.
Product Page →Plain and coated aluminum entry boards, including lubricated grades for micro-holes.
Product Page →Self-lubricating entry sheets that cool and center the bit on HDI / micro-via drilling.
Product Page →Coated back-drill entry sheets built for controlled-depth second-pass accuracy.
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