Featured Snippet: Thickness rule: hole <=0.15 mm -> 0.15-0.25 mm; 0.15-0.30 mm -> 0.30 mm; >0.30 mm -> 0.50 mm; dense HDI -> thinner coated
Free PCB entry board thickness calculator. Recommend entry sheet thickness (mm) from drill diameter, hole density and material, with a thickness-vs-wander note.
Suitable for:
Get a recommended entry thickness.
| Recommended thickness | -- mm |
| Wander note | -- |
Recommendation is a starting point - match to your stack and qualify on a sample.
Entry sheet thickness trades support against flexibility: too thin and it deflects (more drill wander), too thick and it adds stack height and cost. This calculator recommends a thickness from your drill diameter, hole density and material, with a wander note so you can balance.
Thinner sheets (0.15-0.25 mm) suit micro-holes where a lubricant aluminum coating already centres the bit; 0.30 mm is the standard for most FR4 holes; 0.50 mm suits larger drills and harder stacks but adds stack height and can raise aspect ratio concerns. See our aluminum entry boards.
| Material | Density (kg/m³) | Surface Hardness (HD) | Best For |
|---|---|---|---|
| UV Melamine 950 | 980 ± 30 | 80 ± 5 | IC Substrate, HDI micro-via |
| UV Melamine 880 | 950 ± 30 | 80 ± 5 | HDI, high-layer-count FR4 |
| HDF 880 | 880 ± 30 | 70 ± 2 | Standard FR4 multilayer |
| Phenolic (standard) | 750 ± 40 | 55 ± 5 | Back-drilling, rigid-flex |
| Aluminum entry sheet | N/A (metal foil) | N/A | Universal entry protection |
| Lubricated aluminum (LE) | N/A (coated foil) | N/A | Micro-via, HDI, high-Tg |
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.
Entry thickness (0.20 mm)
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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What is an entry board? A sheet on top of the stack that centres and cools the bit on entry.
Why does thickness matter? Too thin deflects (more wander); too thick adds height and cost.
What is drill wander? Lateral bit deflection on entry; thickness and coating control it.
What thickness for micro-holes? 0.15-0.25 mm, often a coated lubricant sheet.
What thickness for standard holes? 0.30 mm is the common balanced choice for FR4.
What thickness for large drills? 0.50 mm suits larger holes and harder stacks.
What is a lubricant entry sheet? Coated entry that cools and centres micro-holes.
What is stack height? Total drilled thickness; entry adds to it and bounds aspect ratio.
What is aspect ratio? Stack height / smallest hole; thickness choices affect it.
What is drill registration? Hole position accuracy; entry support keeps it tight.
What backup board should I pair? UV melamine 880 for HDI/clean exits, HDF for cost FR4, UV melamine 950 for thick/hard, phenolic for Rogers/PTFE/ceramic.
What is burr control? Limiting exit burr via correct feed and board support.
Standard aluminum 1100 H18 entry foil (0.15–0.20 mm) is the universal choice for FR4 and back-drilling. Lubricated aluminum entry sheets (LE/CAE) add a thermoset coating that phase-change cools the drill tip by 15–22%, reducing resin smear and drill breakage on HDI and micro-via work. Water-soluble coated entry boards offer an alternative for rigid-flex where residue cleanliness is critical.
UV melamine 950 (980 kg/m³, 80±5 HD) is the premium choice for IC substrate and HDI where exit burr must be near zero. UV melamine 880 (950 kg/m³) suits high-layer-count FR4. HDF 880 (880 kg/m³, 70±2 HD) balances cost and performance for standard multilayer. Phenolic boards are preferred for back-drilling and rigid-flex due to their machinability.
1100 H18 (99% Al) is the industry standard for entry foil. 3003 and 5052 alloys offer higher strength for thicker entry boards but may increase drill wear. The choice of alloy affects chip load stability and burr formation on the entry side.
Kyocera Precision Tools — PCB drilling ↗
Thermoset-coated (LE/CAE) entry boards provide lubrication through phase-change cooling at 120–180°C. Water-soluble coated boards dissolve in cleaning. Uncoated aluminum relies purely on mechanical centering. The coating choice directly affects drill temperature, chip evacuation, and hit count.
YUESHAN — LE Sheet drill temperature data
Drill tip temperature can exceed 300°C on standard FR4 without proper consumables. The entry board absorbs 20–30% of frictional heat; the backup board dissipates exit heat. Lubricated entry systems reduce peak temperatures by up to 30%, directly reducing resin smear and hole wall roughness.
Rogers Corp — RO4000 laminates ↗
Micro-drill breakage is most often caused by chip clogging in the flute, not by mechanical overload. Lubricated entry boards eliminate the chip adhesion failure mode. A worn entry board (excessive hits per sheet) increases drill wander risk — replace entry sheets at the same interval as drill change.
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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