Laser micro drilling is a three-dimensional material-removal process. Unlike two-dimensional laser cutting, a drilled feature carries coupled requirements for diameter, depth, taper, roundness, recast, position, and surface condition. A stable result starts by defining those variables together rather than treating diameter as the only critical dimension.
This technical guide explains how hole geometry, laser strategy, material response, and measurement method interact. Use it to define a process window before committing a design, sample plan, or production specification.
The Hole Is a 3D Object: Six Variables, Not One
Diameter Is the Easy One
Hole diameter at the entry surface is the dimension drawings emphasize most, and the easiest to hold. On 304 stainless between 0.1mm and 0.5mm thick, our routine entry diameter tolerance on micro laser drilling is ±5µm to ±10µm — tighter on holes under 50µm, looser above 200µm where roundness becomes the harder spec.
Aspect Ratio Sets the Real Limits
The depth-to-diameter ratio determines whether a feature is producible at all. For nanosecond fiber laser micro drilling, aspect ratios of 5:1 are routine, 10:1 is achievable with optimized parameters, and beyond 15:1 the process becomes unstable — debris cannot evacuate and beam attenuation reduces ablation efficiency. Picosecond and femtosecond sources push the practical limit to 30:1, and helical drilling can reach 50:1 on certain materials, but each step costs setup time, cycle time, and per-part rate.
The implication: a 0.05mm hole through 1mm material is a 20:1 drilling problem, not a 1mm cutting problem. Cost and feasibility scale with aspect ratio, not part size.
Taper Is Predictable but Often Unspecified
A laser-drilled hole is not a cylinder. The exit diameter is smaller than the entry because the focused beam has finite Rayleigh length and ablated material attenuates the beam through the hole. Typical taper on percussion-drilled holes runs 2°–6° per side. With trepan or helical strategies and beam waist repositioning, taper drops below 1°. Most drawings don't specify taper at all — and that ambiguity is where field failures originate.
Roundness, Position, and Hole-to-Hole Consistency
Roundness on percussion-drilled holes runs ±2µm to ±5µm under stable conditions. Hole position relative to a datum is held to ±10µm on commercial galvo-stage systems, ±3µm on linear stages with thermal compensation. Hole-to-hole consistency across an array — often more critical than absolute diameter for fluidic applications — is verifiable only by full-array CMM scanning.
Burr and Recast: The Invisible Quality Variables
Entry burr from melt expulsion runs from negligible (under 5µm) on optimized picosecond drilling to 30µm or more on aggressive nanosecond parameters. Recast layer inside the hole wall is what medical and aerospace customers care about most: a 5–15µm resolidified-melt layer can crack under thermal cycling, harbor contamination, and act as a fatigue initiation site. Picosecond and femtosecond drilling reduce recast under 2µm; nanosecond produces 5–20µm.
Drilling Strategies and When Each Applies
Percussion Drilling
Percussion drilling fires a stationary beam at a fixed point, producing a hole through repeated pulses. It is the fastest strategy — typical cycle times of 5–50ms per hole on thin material — and the most cost-effective for high-volume work where geometry tolerances are moderate. We use percussion on the 26 low-power precision stations dedicated to thin-foil work under 0.6mm.
Trepan Drilling
Trepan drilling moves the focused beam in a circular path to "cut out" the hole rather than ablate from the center. The result is much better roundness, controlled taper (below 1° with proper compensation), and consistent diameter independent of total drilling time. The trade-off is cycle time — typically 5–10× longer than percussion — and a minimum hole diameter set by spot size plus trepan radius (around 50µm for fiber, 25µm for picosecond UV).
Helical Drilling
Helical drilling combines trepan motion with controlled Z-axis descent, spiraling the beam down through the material. It is the strategy for high aspect ratio holes (above 20:1), thick stacks, and applications where wall geometry matters as much as entry diameter.
How a Real Job Routes
A medical device customer asks for a 25-hole array of 30µm holes through 0.15mm 316L stainless at 50µm pitch, with under 3µm recast. Impossible on percussion (recast spec rules it out) and impossible on basic trepan (diameter at the lower bound, pitch leaves no room for trepan radius). It runs on picosecond UV with helical drilling. The price difference between that part and the same array specified at 50µm holes with 10µm recast is roughly 4×.
Material Behavior and What Changes the Drilling Strategy
Stainless Steel: The Workhorse
304 and 316L stainless from 0.05mm to 1.0mm thickness covers the majority of our laser micro drilling metal volume. Nanosecond fiber percussion handles routine work at high throughput; picosecond UV handles the medical-grade subset where recast and HAZ are specified. Aspect ratios up to 10:1 are routine; above that, helical drilling on picosecond is required.
Nitinol, Platinum-Iridium, and Other Medical Alloys
Nitinol drilling for drug-eluting stents and implantable sensors requires HAZ minimization to preserve transformation temperature and superelastic behavior. We drill nitinol exclusively on picosecond UV, with measured HAZ under 5µm and recast under 2µm verified by metallographic cross-section. Platinum-iridium and other refractory medical alloys behave similarly — fiber sources are not used.
Polymers, Glass, and Aerospace Superalloys
Polyimide film drilling for flexible electronics is high-volume work where UV picosecond produces clean walls at 25–200µm hole diameters. Glass and sapphire micro drilling — for optical and sensor packaging — requires UV nanosecond with controlled fluence or femtosecond pulses to avoid microcracking; aspect ratios above 5:1 in sapphire are research-grade today. For advanced packaging ultra-precision drilling solutions, refer to Inno Laser's ultra-precision drilling equipment.
Cooling holes in turbine components — drilled into Inconel 718, CMSX-4, and similar single-crystal superalloys — drove laser micro drilling development. Hole diameters of 200–600µm at 20°–35° angles, in 1–3mm walls, with specified recast and oxide layer limits.
Tolerance, Recast, and Verification
What "±5µm" Actually Covers
A ±5µm callout on a hole spec, without further qualification, refers to entry diameter only. It does not bound exit diameter, taper, position, roundness, or recast. A vendor estimating that tolerance has not committed to anything about the hole's three-dimensional geometry. For function-critical drilled features, the spec needs to call out at least entry diameter, exit diameter or taper, position relative to datum, and recast/HAZ allowance.
Routine tolerances on our mid-power fiber line for percussion drilling 0.1mm holes through 0.3mm 304 stainless: entry diameter ±8µm, exit diameter ±15µm, position ±10µm, roundness within 5µm.
Recast Specification and Measurement
Recast layer thickness is verified by metallographic cross-section — there is no shortcut. The hole is sectioned, polished, etched if needed, and imaged on SEM or calibrated optical microscope. For medical and aerospace work, recast specs of "≤5µm" or "≤10µm" are common, and the process route must provide cross-section evidence rather than verbal assurance.
Verification on Production Lots
For production-grade laser micro drilling, every lot is dimensionally verified on optical CMM with sub-micron resolution. First-article includes destructive cross-sectioning to verify exit diameter, taper, and recast. The quality control data is linked per-lot to laser parameters, material certificate, and operator — without that traceability, a passed inspection on Tuesday tells you nothing about Wednesday.
Cost Drivers Specific to Drilling
Why Drilling Cost Is Not Linear in Hole Count
A part with 100 holes does not cost 100× a part with one hole — setup, fixturing, and first-article amortize across the array. But each hole adds cycle time, and on high-aspect-ratio work that cycle time dominates. A 200-hole array of 50µm holes through 0.3mm material on percussion runs roughly 30 seconds total drilling time; the same array on helical picosecond runs 8–12 minutes. That order-of-magnitude gap is the dominant cost variable on most drilling jobs.
Aspect Ratio as a Cost Multiplier
The premium for high-aspect-ratio work compounds: 5:1 runs at routine fiber rates; 10:1 adds 30–50%; above 15:1 the work shifts to picosecond helical drilling at 2–4× the per-hour rate; above 25:1 it is commonly costed per feature.
Recognizing an Unrealistic Process Assumption
High-aspect-ratio drilling requires the process route to match the geometry. A result is at risk when percussion drilling is substituted for trepan or helical drilling, when a nanosecond source is used where ultrafast pulses are needed, or when the material-and-parameter combination has not been validated. These choices commonly appear as excess taper, recast, or unstable hole-to-hole variation at production scale.
Honest Limitations
Laser micro drilling is not optimal for every drilled hole spec. When diameters exceed 0.5mm in production volumes, mechanical micro drilling and EDM may be more cost-effective without recast. Aspect ratios above 30:1 on most materials may require EDM or photochemical processes as the only viable option. Similarly, glass or sapphire with above 5:1 aspect ratio in production sits at the edge of repeatable laser micro drilling capability.
A Real Failure Mode
A first article on a 0.08mm hole through 0.4mm 316L for a medical fluidic application passed entry diameter and position, but cross-section showed asymmetric recast — 3µm on one side, 12µm on the other. Root cause was misalignment between beam axis and workpiece normal. Resolution: active normal-incidence verification was added to the fixture sequence, and the lot was re-run. Lesson: cross-section both sides of a sample hole on first article — asymmetric recast is invisible on top-down inspection.
DFM Rules: What Designers Should Know Before Releasing a Print
Specify the Hole, Not Just the Diameter
A drilled-feature print should call out: entry diameter and tolerance, exit diameter or maximum taper angle, hole position relative to datum, roundness, recast or HAZ allowance, and the inspection method that validates each. A drawing listing only "Ø0.1mm ±0.005" leaves every other variable open to interpretation.
Aspect Ratio Sanity Check
Before releasing a print, divide material thickness by hole diameter. If the result is above 10, the part is in the high-aspect-ratio regime and requires a documented process review before the print is final. Often a small change in material thickness or hole diameter — within the function envelope — moves the part from a 4× cost regime to routine cost.
Hole Spacing, Edge Distance, and Material Specification
Center-to-center hole spacing for parallel arrays should be at least 2× hole diameter for thin material and 3× for thick material — closer spacing produces thermal coupling that distorts geometry. Edge distance should be at least 2× hole diameter to prevent edge breakthrough. For thin foils, laser micro structuring services is sometimes a viable alternative when the function is fluidic permeability rather than discrete-hole geometry.
Specify material with realistic certification — alloy, condition, surface finish, and traceable lot if recast is critical. Stainless from two different mills can produce different recast at identical parameters.
Process Capability Review: From Beam Delivery to Measurement
The Cross-Section Test
A metallographic cross-section of a representative hole on the actual material is the most informative verification method for recast-critical drilling. It reveals sidewall condition, taper, recast, and heat effects that a top-down optical image cannot resolve.
Laser Source and Specification Match
Match pulse duration to the recast requirement. Recast below 5 µm typically calls for picosecond or shorter pulses on most metals; recast below 2 µm often requires femtosecond or carefully optimized picosecond processing. The measurement method must use the same boundary conditions as the drawing requirement.
Parameter Traceability and Lot Validation
A controlled drilling process records pulse energy, pulse duration, repetition rate, beam path, gas assist, fixturing, material condition, and inspection method. Evaluate a representative lot rather than a single hole so that hole-to-hole and lot-to-lot variation are visible before a process window is released.
Frequently Asked Questions
Laser micro drilling produces holes with diameters typically below 500µm using focused laser pulses. Aspect ratios of 5:1 are routine, 10:1 with optimized parameters, and 20–30:1 requires picosecond or femtosecond helical drilling. Above 30:1, EDM may be the better choice.
Very few materials are incompatible. Highly reflective metals like copper andaluminum require UV or ultrafast wavelengths for reliable energy coupling. Somepolymers, such as PTFE, decompose rather than ablate cleanly and need carefullycontrolled UV pulse energy.
Extremely thick sections (>25 mm) in metals may exceed practical laser penetrationwithout millisecond-range pulses, where EDM or mechanical drilling becomes moreeconomical
Mechanical micro drilling produces holes with no recast but is limited above 5:1 aspect ratio and below 100µm diameter. EDM produces clean geometry on conductive materials at any aspect ratio but is slow. Laser micro drilling is faster than both at small diameters, handles non-conductive materials, but produces recast that must be specified and verified.
Tolerances depend on pulse duration and material. Femtosecond systems hold +1-3um on metals and ceramics. Picosecond systems achieve +2-5 um.
Nanosecond fiber or UV lasers deliver +3-10 um, sufficient for PCB microvias andgeneral industrial holes. Position accuracy ranges from +1 um on ultrafast systemsto +10 um on high-volume industrial platforms over a 300 mm x 300 mm field.
Conclusion
Laser micro drilling is harder than laser micro cutting because every hole is a three-dimensional geometry with multiple interacting variables. A robust drilled feature is defined by aspect ratio, taper, recast, positional accuracy, and verification method—not by diameter alone.
Use the geometry, material, process-route, and measurement checks in this guide to set realistic requirements for a micro-drilled feature.