Featured Snippet: Ra (um) = base(material) x feedFactor x wearFactor / supportFactor
Free PCB hole wall roughness calculator. Estimate hole-wall roughness (Ra, um) from feed, RPM, material and drill wear, then read a plating-class verdict.
Suitable for:
Estimate hole-wall roughness (Ra).
| Est. Ra | -- um |
| Plating verdict | -- |
Relative estimate - confirm with profilometry on your panel.
Hole wall roughness (Ra) decides how cleanly a hole plates. Rough walls trap chemistry and weaken via reliability. Roughness is driven by feed, drill wear, material abrasiveness and support. This tool estimates Ra (um) and a plating-readiness verdict so you can tune before production.
Rough walls trap plating chemistry and can leave voids that hurt via reliability. Stay in the stable feed band, keep the bit sharp, and use a melamine backup board for support - aim for Ra below ~1.6 um on standard FR4. See the 2026 backup board comparison.
Hole wall roughness comes from the interaction between the drill and the laminate. The five levers below are exactly the inputs the calculator above uses, so a rough reading usually traces back to one of them:
| Cause | What it does to the hole wall | Calculator input it maps to |
|---|---|---|
| Drill wear | A worn bit ploughs and smears resin instead of shearing it, raising peak-to-valley height | Drill wear (new / mid-life / worn) |
| Feed rate outside the stable band | Too high tears the wall; too low rubs and generates heat | Feed rate (mm/min) |
| Spindle RPM mismatch | Chip load drifts away from the material's sweet spot | Spindle RPM |
| Backup board support | Poor support lets the bit vibrate at entry and exit | Backup board selection |
| Board material | High glass content and hard laminates resist shearing | Board material (FR4, HDI, PTFE, ceramic) |
Entry boards matter on the same lever: the entry sheet stabilizes first contact so the bit reaches the panel straight. Pair the calculator result with entry board material selection when roughness stays high after feed and wear are corrected.
Roughness is quantified after drilling, most commonly by cross-section analysis of a Coupon hole under microscopy; the wall profile is then reduced to standard height parameters:
| Parameter | Definition | Typical use |
|---|---|---|
| Ra (arithmetic mean) | Average absolute deviation of the profile from its mean line | General spec sheets and this calculator's estimate |
| Rz | Mean of individual peak-to-valley heights over sampling lengths | Drawing notes that care about worst valleys |
| Rmax | Single largest peak-to-valley height found | Screening for isolated deep scratches |
Units differ between datasheets, and a unit mix-up is a classic source of rejected panels. The conversions are exact:
| From | in μm | in mil | in μin |
|---|---|---|---|
| 1 μm | 1 | 0.0394 | 39.4 |
| 1 mil | 25.4 | 1 | 1000 |
| 1 μin | 0.0254 | 0.001 | 1 |
So a fab drawing note such as “hole wall roughness ≤ 1.2 mil” means ≤ 30.48 μm. Compare that against your calculator reading and the plating-class verdict before releasing the stack to production.
| 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.
Hole wall Ra (FR4)
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.
Specs quote roughness in two units and both survive in requirements documents: hole wall roughness of 1.2 mil written as a maximum is the same limit as about 30 µm, so a supplier sheet in µm and a customer spec in mil are not disagreeing. What drives the number is heat at the wall — resin smear, debris and an off-band chip load all roughen the surface before plating ever sees it — which is why roughness belongs in the same conversation as chip load and thermal load rather than as a standalone incoming check.
What is hole wall roughness? Surface roughness (Ra) inside the drilled hole.
Why does roughness matter? Rough walls trap chemistry and weaken plating and via reliability.
What is a good Ra? Below ~1.6 um on standard FR4 is a common plating target.
What raises roughness? High feed, low RPM, worn bit, abrasive material, poor support.
What is drill wear? Edge dulling that raises heat and roughness over a bit's life.
What is via reliability? Long-term via integrity; clean, smooth walls support it.
What is desmear? Removing resin smear after drilling to restore the hole wall.
What backup board helps? UV melamine 880/950 give the cleanest, most supported exit.
What is burr control? Limiting exit burr via correct feed and board support.
What is resin smear? Melted dielectric on the wall from heat; desmear manages it.
What is the difference between mechanical and laser? Laser micro-vias avoid bit wear but need laser capex.
How do I lower roughness? Trim feed, match RPM, resharpen the bit, use melamine backup.
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.
Schmoll — PCB drilling machines ↗
Wicking note: drilling parameters on the wicking in high aspect ratio holes surface as resin smear and wall roughness together. Feed that is too aggressive for the stack leaves rougher walls and deeper wicking channels at the same time, so a rising roughness reading is the early signal to re-check the stack before plating rejects accumulate.
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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