PCB designers should normally specify the required finished hole diameter and tolerance; the PCB manufacturer should select the production drill size needed to achieve it after desmear, copper plating, surface finishing, and process variation.
A production drill is intentionally larger than the final diameter of a plated through hole. For non-plated holes, the drilled or routed diameter is usually much closer to the finished requirement.
Do not automatically add 0.10 mm to every plated hole. The correct production allowance depends on plating thickness, hole type, board thickness, aspect ratio, tolerance, surface finish, drill-tool availability, and the manufacturer’s controlled process.
What Is The Difference Between Drill Size And Finished Hole Size?
PCB drill size is the diameter of the mechanical drill, laser aperture, or routing tool used during fabrication.
Finished hole size is the measurable opening remaining after all relevant manufacturing processes are complete.
For a plated through hole, the sequence is approximately:
- Drill The Initial Opening
- Clean And Desmear The Hole
- Deposit Electroless Copper
- Electroplate Additional Copper
- Apply The Required Surface Finish
- Measure The Finished Diameter
Copper builds on both sides of the hole wall. Consequently, a plated hole normally finishes smaller than its production drill.
For an NPTH, there is no intentional hole-wall copper. Its final diameter is therefore much closer to the mechanical tool size, although tool tolerance, wear, material behavior, and routing conditions still affect the result.
Which Diameter Should The PCB Designer Specify?
The designer should normally specify the functional finished hole diameter.
That is the dimension controlling:
- Whether A Component Lead Fits
- Whether A Press-Fit Pin Works
- Whether A Fastener Passes Through
- Whether A Locating Pin Aligns
- Whether Wave Soldering Has Enough Clearance
- Whether The Finished Via Meets Electrical Requirements
The PCB manufacturer should normally choose the production drill because the manufacturer controls:
- Hole-Wall Copper Thickness
- Plating Distribution
- Desmear
- Drill-Tool Inventory
- Tool Wear Limits
- Process Compensation
- Surface Finish
- Finished-Hole Inspection
Molex connector specifications explicitly state that finished PCB hole size is the critical feature for compliant-pin performance and that the production drill may change according to the PCB manufacturer’s plating process. Molex Press-Fit PCB Specification
When Should The Designer Specify Both?
Specify both finished hole and reference drill only when:
- The Connector Manufacturer Requires Both
- A Qualified Construction Uses A Controlled Drill
- Military Or Customer Documentation Requires It
- A Press-Fit Application Specification Defines It
- A Test Coupon Must Reproduce A Specific Structure
- The Drill Diameter Is A Reliability-Controlled Parameter
When both are provided, identify which dimension is mandatory and which is reference information.
Why Is The Production Drill Larger Than The Finished PTH?
Copper plating grows inward from the entire circumference of the drilled hole.
A simplified relationship is:
Approximate Finished Diameter = Production Drill Diameter − 2 × Effective Hole-Wall Buildup
For example, consider a hypothetical 0.90 mm drilled hole with 0.025 mm of effective radial buildup on each side:
0.90 mm − 2 × 0.025 mm = 0.85 mm
The simplified finished diameter is approximately 0.85 mm.
This calculation demonstrates the geometry but should not be used by designers to select the production drill. Actual compensation may also account for:
- Drill Diameter Variation
- Tool Wear
- Hole-Wall Roughness
- Resin Smear
- Desmear Etchback
- Electroless Copper
- Electrolytic Copper
- Surface Finish
- Plating Distribution
- Measurement Method
The plated through hole manufacturing process explains why a final hole cannot be predicted from copper thickness alone.
Why The “Add 0.10 mm” Rule Is Not Universal
Many PCB articles recommend adding 0.10 mm to the required finished hole to obtain the production drill.
This can be a convenient preliminary estimate, but it is not a controlled manufacturing rule.
The required difference may change with:
- Required Hole-Wall Copper
- IPC Class
- Board Thickness
- Hole Aspect Ratio
- Pattern Or Panel Plating
- Plating Throwing Power
- Surface Finish
- Finished-Hole Tolerance
- Available Drill Increment
- Press-Fit Requirements
- Fabricator Process Capability
A designer who specifies both dimensions using an assumed 0.10 mm allowance may unintentionally prevent the fabricator from selecting the best tool and plating process.
The safer practice is:
Specify The Functional Finished Hole And Tolerance, Then Let The Approved Fabricator Determine The Production Drill.
PTH, NPTH, Via, Press-Fit, And Slot Requirements
Different hole functions need different documentation.
| Hole Type | Dimension That Usually Controls | Main Concern |
|---|---|---|
| Component PTH | Finished Diameter | Lead Fit And Soldering |
| Via | Finished Diameter Or Minimum Finished Diameter | Plating And Annular Ring |
| NPTH Mounting Hole | Finished Diameter | Mechanical Fit |
| Locating Hole | Finished Diameter And Position | Assembly Alignment |
| Press-Fit Hole | Connector-Specified Finished Diameter | Contact Force And Reliability |
| Plated Slot | Finished Width And Length | Connector Or Tab Fit |
| Non-Plated Slot | Finished Width And Length | Mechanical Clearance |
| Tooling Hole | Finished Diameter And Position | Fixture Accuracy |
| Filled Via | Drill And Finished Structure | Filling And Planarity |
| Back-Drilled Hole | Primary Hole Plus Back-Drill Diameter And Depth | Stub Removal |
Using the same hole tolerance for every category can increase cost without improving product function.
How Should Component PTH Size Be Selected?
A component hole must accept the largest possible lead while preserving adequate soldering conditions.
The calculation should consider:
- Maximum Lead Diameter
- Lead Shape
- Lead Manufacturing Tolerance
- PCB Hole Negative Tolerance
- Component Placement Accuracy
- Lead Position Tolerance
- Required Assembly Clearance
- Soldering Process
A useful starting relationship is:
Nominal Finished Hole ≥ Maximum Lead Dimension + Required Assembly Clearance + Hole Negative Tolerance
Example For A Round Lead
Assume:
- Maximum Lead Diameter: 0.60 mm
- Required Assembly Clearance: 0.15 mm
- Finished-Hole Negative Tolerance: 0.075 mm
The nominal finished hole should be at least:
0.60 + 0.15 + 0.075 = 0.825 mm
A designer may select an appropriate manufacturable nominal size above 0.825 mm after reviewing soldering and component requirements.
This example is a tolerance calculation, not a universal clearance rule.
Rectangular Leads Need Special Attention
For a rectangular or square lead, the maximum diagonal may control insertion if the component can rotate relative to the hole.
Using only the lead width can produce a hole that is too small.
Connector drawings may instead define a specific plated-hole geometry. Those product requirements should take priority over a generic diagonal calculation.
How Does Finished Hole Size Affect Through-Hole Soldering?
A hole that is too small can cause:
- Component Insertion Failure
- Bent Leads
- Damaged Hole Plating
- Component Seating Problems
- Automated Insertion Stops
- Pressing Force On The PCB
A hole that is excessively large can produce:
- Greater Solder Demand
- Inconsistent Solder Fill
- Component Movement
- Poor Lead Centering
- Increased Flux Entrapment
- Reduced Process Repeatability
Solder fill also depends on board thickness, internal plane connections, surface finish, flux, preheating, solder temperature, dwell time, and lead condition.
Hole diameter should therefore be selected as part of the complete through-hole assembly process rather than from the component lead alone.
What Is Different About Via Hole Sizes?
A via does not normally need to accept a component lead. Its hole size primarily affects:
- Plating Capability
- Aspect Ratio
- Current Capacity
- Annular Ring
- Routing Density
- Thermal Reliability
- Fabrication Cost
For ordinary vias, a designer may specify a nominal or minimum finished diameter while allowing the manufacturer greater process flexibility.
However, the manufacturing drawing must not allow the supplier to reduce a via hole if its final diameter affects:
- Current-Carrying Requirement
- Thermal Performance
- Via Filling
- Controlled Impedance
- Test-Probe Access
- Press-Fit Or Component Use
- Safety Spacing
A small hole intended for a component lead must not be automatically classified as a via merely because of its diameter.
How Does Hole Size Affect Annular Ring?
The pad must remain large enough around the production hole after accounting for drilling and layer-registration variation.
A pad that appears adequate around the nominal finished hole may be inadequate around the larger production drill.
Relevant dimensions include:
- Finished Hole Diameter
- Production Drill Diameter
- Pad Diameter
- Drill Position Tolerance
- Layer Registration
- Required Internal Annular Ring
- Required External Annular Ring
The basic geometric relationship is:
Nominal Annular Ring = (Pad Diameter − Hole Diameter) ÷ 2
The correct hole diameter used in a design calculation depends on whether the requirement evaluates the drilled opening, finished hole, or plated barrel.
Our PCB annular ring article explains how drill wander and registration affect the remaining copper.
Why Press-Fit Holes Need Separate Control
Press-fit connectors rely on controlled interference between a compliant pin and a plated through hole.
If the finished hole is too small:
- Insertion Force Can Become Excessive
- The Pin Can Deform
- The PCB Can Crack
- Hole Plating Can Be Damaged
- Pads Can Lift
- Inner-Layer Connections Can Be Stressed
If the hole is too large:
- Retention Force Can Be Insufficient
- Contact Resistance Can Increase
- Vibration Reliability Can Decrease
- The Connector Can Move
- Gas-Tight Contact May Not Form
There is no universal press-fit finished hole or tolerance. Use the connector manufacturer’s application specification.
TE Connectivity, for example, publishes connector-specific PCB end-hole requirements rather than one dimension for all press-fit products. TE Press-Fit Technology
Our press-fit PCB assembly article covers compliant pins, insertion force, PCB support, inspection, and connector qualification.
Should A Press-Fit Drawing Include The Production Drill?
The finished hole remains the primary functional dimension.
A connector supplier may publish a reference drill that produced the qualified finished hole. However, the PCB fabricator may need a different drill because of its plating process.
A robust press-fit drawing should define:
- Finished Hole Diameter
- Upper And Lower Limits
- Hole-Wall Copper Requirement
- Surface Finish
- Pad Diameter
- PCB Thickness
- Hole Position
- Connector Part Number
- Applicable Connector Drawing
- Inspection Method
- Sampling Plan
If a reference production drill is included, label it clearly as reference unless strict reproduction of the qualified construction is required.
How Are NPTH Sizes Different?
A non-plated through hole does not intentionally receive conductive hole-wall plating.
NPTHs are commonly used for:
- Mounting Screws
- Locating Pins
- Plastic Support Posts
- Tooling
- Mechanical Alignment
- Component Retention Features
Because there is no intentional copper buildup, the production tool and finished diameter may be close.
They are still not automatically identical. Final size may be affected by:
- Drill-Tool Tolerance
- Tool Wear
- Router Runout
- Material Burrs
- Laminate Springback
- Deburring
- Plated-Finish Encroachment
- Measurement Pressure
A locating hole may require tighter diameter and position control than an ordinary mounting clearance hole.
Why PTH And NPTH Must Be Clearly Separated In The Files
An ambiguous drill file can cause a mechanical hole to be plated or an electrical hole to remain unplated.
Good documentation can use:
- Separate PTH And NPTH Drill Files
- Hole-Type Attributes In Intelligent Data
- A Controlled Drill Table
- Fabrication Drawing Symbols
- Clear Plating Notes
- Slot Identification
Do not rely only on the presence or absence of a copper pad. Some NPTHs have surrounding copper, while some production holes may not have conventional outer-layer pads.
IPC-2614 establishes documentation requirements for printed-board fabrication. IPC-2615 addresses dimensioning and tolerancing practices. IPC Board Design Standards
How Should Plated Slots Be Specified?
A plated slot requires at least:
- Finished Slot Width
- Finished Slot Length
- Plated Or Non-Plated Status
- Slot Position
- Slot Orientation
- End Shape
- Dimensional Tolerance
- Copper Requirements
The router or drill used to create the slot must be larger than or compatible with the final geometry before plating.
A slot’s width may be reduced by plating on both sidewalls. The end radius is also limited by the production tool.
Do not represent a slot only as overlapping round holes unless the manufacturer has approved that construction. Overlapping drill hits can create rough walls, tool breakage, dimensional variation, and unreliable plating.
How Does PCB Thickness Affect Drill Selection?
A small hole through a thick board is more difficult to drill, clean, metallize, and plate uniformly.
Relevant risks include:
- Drill Deflection
- Tool Breakage
- Hole-Wall Roughness
- Resin Smear
- Incomplete Desmear
- Thin Copper At Hole Center
- Plating Voids
- Barrel Cracking
- Increased Cost
The PCB thickness selection should therefore be reviewed with minimum hole size and plating capability.
A 0.20 mm hole through a thin board and a 0.20 mm hole through a thick multilayer board are not equivalent manufacturing requirements.
Which Diameter Is Used For PCB Aspect Ratio?
PCB industry sources do not always use the same denominator when discussing aspect ratio.
Two calculations may appear:
Drilled Aspect Ratio = Board Thickness ÷ Production Drill Diameter
Finished Aspect Ratio = Board Thickness ÷ Finished Hole Diameter
For drilling and plating capability, many manufacturers use production drill diameter. Other published capability tables use finished hole diameter.
The difference becomes important for small plated holes.
Example:
- Board Thickness: 1.60 mm
- Production Drill: 0.30 mm
- Finished Hole: 0.25 mm
Drilled aspect ratio:
1.60 ÷ 0.30 = 5.33:1
Finished-hole ratio:
1.60 ÷ 0.25 = 6.40:1
Both numbers describe the same hole but are not directly comparable.
When reviewing a PCB supplier’s capability, ask which diameter is used in its aspect-ratio calculation.
How Does Aspect Ratio Affect Plating?
A high-aspect-ratio hole is difficult to plate because copper ions and plating solution must reach the center of a deep, narrow opening.
Potential results include:
- Thin Copper At The Hole Center
- Uneven Barrel Thickness
- Plating Voids
- Reduced Thermal-Cycling Life
- Higher Electrical Resistance
- Longer Plating Time
- Excessive Surface Copper
Reducing the finished hole diameter without changing board thickness can therefore increase manufacturing difficulty and cost.
The supplier should review board thickness, production drill, finished hole, copper requirement, plating chemistry, and inspection method together.
How Does Surface Finish Affect Finished Hole Size?
The effect depends on the selected finish and whether it is deposited inside the hole.
Potential processes include:
- OSP
- ENIG
- ENEPIG
- Immersion Tin
- Immersion Silver
- HASL
- Hard Gold
- Selective Finishes
The finished hole requirement should apply after the relevant fabrication and surface-finishing processes unless the drawing explicitly states otherwise.
Press-fit connectors are particularly sensitive because additional metal or uneven finish inside the barrel can change insertion and retention force.
The connector drawing and PCB fabrication drawing should identify both the final diameter and allowed surface finish.
Why Published Hole Tolerances Differ Between Suppliers
Hole tolerance is a manufacturing capability and commercial requirement, not one universal value.
For example, Eurocircuits publishes a standard tolerance of ±0.10 mm for many plated holes up to 4.00 mm, while Summit Interconnect describes typical component-hole and press-fit tolerances in inches that differ by hole function. Eurocircuits PCB Tolerances, Summit PTH Specification Q&A
These are supplier examples, not universal IPC requirements.
Actual capability depends on:
- Hole Type
- Nominal Diameter
- Board Thickness
- Aspect Ratio
- Plating Thickness
- Surface Finish
- Production Volume
- Inspection Method
- Required Process Capability
Confirm the tolerance with the selected manufacturer before releasing a tight mechanical design.
Should Hole Tolerance Be Bilateral Or Unilateral?
A bilateral tolerance permits variation in both directions.
Example:
0.80 mm ±0.08 mm
Acceptable range:
0.72 mm To 0.88 mm
A unilateral tolerance may better represent a functional fit.
Example:
0.80 mm +0.10/−0.00 mm
Acceptable range:
0.80 mm To 0.90 mm
Unilateral control may be useful when:
- A Lead Must Always Fit
- A Fastener Must Pass Through
- Minimum Clearance Is Critical
- Oversize Is Less Harmful Than Undersize
Press-fit holes are different because both the upper and lower limits may be critical.
Do not use zero tolerance. Every manufactured dimension requires an achievable tolerance and inspection agreement.
How Are Finished Hole Sizes Measured?
Common measurement methods include:
- Go/No-Go Pin Gauges
- Plug Gauges
- Tapered Hole Gauges
- Optical Measurement
- Coordinate Measuring Equipment
- Cross-Section Measurement
- Automated Inspection Systems
The inspection method should match the function.
Pin Gauges
Pin gauges are effective for confirming whether a finished opening accepts or rejects a controlled diameter.
Optical Measurement
Optical systems can measure diameter and identify irregular shape, but surface reflections and plated-hole geometry must be controlled.
Microsectioning
Microsectioning is destructive and normally used to evaluate:
- Hole-Wall Copper
- Plating Voids
- Barrel Shape
- Inner-Layer Connections
- Resin Smear
- Cracks
It is not the most efficient method for checking every finished hole diameter.
What Happens When Drill And Fabrication Files Disagree?
Common conflicts include:
- Drill File Says 0.80 mm While Drawing Says 0.85 mm Finished
- Drill Table Marks A Hole As NPTH While Pads Suggest PTH
- Metric And Inch Dimensions Are Mixed
- Slot Width Differs Between Gerber And Drill Data
- Connector Drawing Requires A Different Press-Fit Hole
- Via Sizes Differ Between CAD And PDF Notes
- Old Revision Drill Files Are Included
The manufacturer should issue an engineering question rather than silently choosing one value.
The customer should provide a controlled order of precedence, such as:
- Approved Customer Change Notice
- Fabrication Drawing
- Intelligent PCB Dataset
- NC Drill File
- Gerber Data
- Informal Reference Documents
The exact hierarchy must be agreed by the customer and supplier.
Our PCB assembly file requirements explain how revision control prevents conflicting manufacturing instructions.
Common PCB Hole Specification Mistakes
Specifying The Drill Instead Of The Finished PTH
This transfers plating compensation to the designer and may produce the wrong final opening.
Applying One Tolerance To Every Hole
Component, via, mounting, locating, and press-fit holes have different functional requirements.
Not Separating PTH And NPTH
The manufacturer may need clarification and production can be delayed.
Ignoring Maximum Component Lead Size
A nominal lead dimension does not include lead tolerance or deformation.
Using Lead Width For A Square Pin
The pin diagonal may control insertion.
Using A Generic Press-Fit Hole
Connector-specific requirements should control.
Over-Tolerancing Ordinary Vias
Tight via-hole tolerances may increase cost without improving function.
Ignoring Surface Finish
The final connector interface may differ after finishing.
Comparing Aspect Ratios With Different Definitions
One supplier may use production drill while another uses finished diameter.
Forgetting Hole Position
Correct diameter does not guarantee alignment with connectors, tooling, or enclosures.
PCB Hole Specification Decision Table
| Application | What The Designer Should Provide | What The Fabricator Should Determine |
| Soldered Component Lead | Finished Hole And Tolerance | Production Drill And Plating Compensation |
| Ordinary Via | Finished Or Minimum Hole Requirement | Production Drill And Process Optimization |
| Press-Fit Connector | Connector-Controlled Finished Hole Limits | Drill And Plating Process |
| NPTH Mounting Hole | Finished Diameter And Position | Production Tool |
| Locating Hole | Finished Diameter, Position, And Datum | Tool And Inspection Plan |
| Plated Slot | Finished Width, Length, And Tolerance | Router Tool And Plating Compensation |
| Filled Via | Finished Structure And Fill Requirement | Drill, Plate, Fill, And Planarization Process |
| Back-Drilled Via | Primary Hole And Stub Requirement | Back-Drill Tool And Depth Compensation |
This division keeps functional responsibility with the designer and process responsibility with the fabricator.
PCB Drill And Finished Hole DFM Checklist
Before releasing the design, confirm:
Hole Function
- Is Every Hole Classified As PTH Or NPTH?
- Are Component Holes Separated From Vias?
- Are Press-Fit Holes Identified?
- Are Tooling And Locating Holes Defined?
- Are Plated And Non-Plated Slots Separated?
Dimensions
- Is Finished Hole Size Specified?
- Is An Achievable Tolerance Included?
- Are Unilateral Tolerances Used Only When Necessary?
- Does The Largest Component Lead Fit?
- Are Square-Pin Diagonals Considered?
- Is Hole Position Controlled Where Required?
Manufacturing
- Has The Fabricator Selected The Production Drill?
- Is Hole-Wall Copper Included?
- Is Aspect Ratio Calculated Using A Defined Diameter?
- Is The Annular Ring Manufacturable?
- Is Surface Finish Included In The Final Dimension?
- Are Tight Tolerances Supported By Inspection Capability?
Documentation
- Do The Drawing And Drill File Agree?
- Are Units Clearly Stated?
- Are PTH And NPTH Files Separated?
- Are Slots Defined With Width And Length?
- Is The Connector Application Specification Included?
- Does Every File Use The Same Revision?
These checks should be completed during a PCB DFM review rather than after components fail to fit.
What Should Buyers Include In A Hole-Size RFQ?
Provide:
- PCB Part Number And Revision
- Fabrication Drawing
- Drill Files
- PTH And NPTH Identification
- Finished Hole Table
- Hole Tolerances
- Slot Requirements
- Board Thickness
- Layer Count
- Copper Weight
- Surface Finish
- Minimum Production Quantity
- Applicable IPC Class
- Press-Fit Connector Part Numbers
- Component Lead Dimensions
- Hole-Wall Copper Requirements
- Inspection Method
- First-Article Reporting Requirements
If the production drill is not controlled by the product design, do not lock it unnecessarily. Allow the manufacturer to compensate for its qualified plating process.
Frequently Asked Questions About PCB Drill And Finished Hole Size
Is PCB Drill Size The Same As Finished Hole Size?
Not for a plated hole. Copper and surface finishing reduce the opening. For an NPTH, the two dimensions are usually closer.
Should I Add 0.10 mm For Hole Plating?
Use 0.10 mm only as a preliminary estimate when appropriate. Specify the finished hole and let the fabricator determine the required production drill.
Does A PCB Drill File Contain Finished Hole Sizes?
It depends on the fabrication agreement and data format. The drawing should clearly state whether listed diameters represent finished holes or production tools.
What Size Hole Should I Use For A Component Lead?
Use the maximum lead dimension plus assembly clearance and the PCB hole’s negative tolerance. Consider the diagonal for square or rectangular leads.
What Size Hole Should I Use For A Press-Fit Connector?
Use the connector manufacturer’s finished-hole range and application specification. Do not apply a generic through-hole tolerance.
Are Via Sizes Finished Or Drilled?
CAD systems and suppliers may use different conventions. Define the requirement explicitly in the fabrication drawing.
Why Did The PCB Manufacturer Change My Via Drill?
The supplier may compensate for plating, available drill sizes, annular ring, aspect ratio, or manufacturing yield. Functional finished-hole requirements must still be met.
Does Thicker Copper Make The Finished Hole Smaller?
Greater hole-wall buildup reduces the internal diameter unless the production drill is adjusted.
Does ENIG Change The Finished Hole Size?
ENIG deposits metal on exposed copper, including applicable hole-wall surfaces. The final diameter should be evaluated after all required finishes.
Can A Hole Be Too Large For Wave Soldering?
Yes. Excessive clearance can increase solder demand and reduce component stability. Hole size must be coordinated with the complete soldering process.
Should NPTHs Be In A Separate Drill File?
Separate files or reliable hole-type attributes reduce ambiguity. The fabrication drawing should still identify plating status.
Which Hole Size Is Used For Aspect Ratio?
Confirm the supplier’s definition. Some use production drill diameter, while others report finished-hole diameter.
Final Recommendations
The most important rule is:
The Designer Controls The Functional Finished Hole; The PCB Manufacturer Controls The Production Drill Needed To Manufacture It.
For reliable fabrication and assembly:
- Define Every Hole By Function.
- Specify Finished PTH Diameter And Tolerance.
- Separate PTH And NPTH Requirements.
- Use Component Maximum Dimensions, Not Nominal Dimensions.
- Follow Connector-Specific Press-Fit Requirements.
- Avoid Applying One Plating Allowance To Every Hole.
- Allow The Fabricator To Select Production Drill Compensation.
- Review Hole Size With Board Thickness And Aspect Ratio.
- Calculate Annular Ring From The Correct Hole Reference.
- Include Surface Finish In The Final Requirement.
- Resolve Drawing And Drill-File Conflicts Before Production.
- Inspect Critical Holes During First Article Approval.
Correct hole documentation prevents component insertion failures, damaged press-fit connectors, weak annular rings, plating defects, soldering problems, assembly delays, and unnecessary PCB cost.
