PTH vs NPTH in PCB: Key Differences, Design Rules, and DFM Tips

PTH (Plated Through Hole) has copper on the hole wall for electrical connection and soldering. NPTH (Non-Plated Through Hole) has no wall copper and is primarily used for mechanical, clearance, tooling, or alignment purposes, and its hole wall does not provide conductive connection.

Choose PTH when the hole must provide electrical continuity, connect copper layers, support a soldered component lead, or intentionally bond hardware to ground. Choose NPTH when the hole is used only for mechanical clearance, alignment, tooling, or isolated mounting with no intended conductive barrel connection.

This guide covers the manufacturing differences, design rules, and common DFM mistakes for both hole types.

What Are PTH and NPTH?

PTH (Plated Through Hole)

A PTH is a drilled hole whose wall is metallized through a chemical copper deposition step followed by copper electroplating. The resulting conductive barrel can connect copper layers, support through-hole solder joints, or provide an intentional electrical bond such as chassis ground.

Key characteristics:

Wall material: Copper (electroless + electrolytic plating)
Electrical function: Yes, when assigned to a conductive feature or net
Size specification: Finished diameter (after plating)
Typical specified hole-wall copper thickness is around 20 μm for IPC Class 2 and 25 μm for IPC Class 3, depending on the fabrication standard and reliability target.

Common applications:

Through-hole component leads (resistors, capacitors, connectors)
Vias and plated slots
Grounded mounting holes (chassis ground, shielding)
Test points

NPTH (Non-Plated Through Hole)

An NPTH is a drilled hole with no conductive copper plating on the hole wall. The barrel itself does not provide electrical connection, and the hole is typically used where electrical isolation or purely mechanical function is required.

Key characteristics:

Wall material: Base laminate / substrate wall with no conductive barrel plating
Electrical function: No conductive barrel connection
Size basis: Often closer to the drilled size because there is no plating reduction in the hole barrel
Tolerance: Depends on the fabricator, hole size, and drawing convention; do not assume NPTH is always tighter than PTH

Common applications:

Screw and standoff clearance holes
Tooling and alignment holes
Mechanical location features
Isolated mounting (no ground connection)

Quick Comparison

Feature	PTH	NPTH
Wall structure	Metallized copper barrel	No conductive wall plating
Electrical role	Can provide electrical connection	No conductive barrel connection
Primary purpose	Electrical interconnect, soldering, sometimes grounded mounting	Mechanical clearance, tooling, alignment, isolated mounting
Hole size basis	Usually specified as finished hole size	Often closer to drilled size, depending on fab documentation
Tolerance	Varies by fabricator and finished-hole requirement	Varies by fabricator and hole type
Process flow	Drill, hole-wall preparation, chemical copper, copper plating, inspection	Non-plated drilling process, often handled separately in fabrication data
Relative cost	Usually higher due to metallization steps	May be lower, but not always, depending on fab flow and documentation

When to Use PTH vs NPTH

Use PTH When:

[ ] A through-hole component lead must be soldered into the hole
[ ] The hole must provide electrical continuity between copper layers
[ ] Mounting hardware needs chassis ground or shield connection
[ ] The hole is part of a plated slot for grounding

Example: A terminal block pin hole is PTH because the lead must solder and carry current. For designs that rely on soldered lead insertion and stable barrel connection, our through-hole assembly service explains the practical requirements for THT assembly and plated-hole reliability.

Use NPTH When:

[ ] The hole is used only for mechanical fastening, spacing, or support, with no intended conductive barrel function
[ ] The hole serves tooling or alignment purposes
[ ] No conductive connection through the hole barrel is allowed
[ ] The feature is purely mechanical clearance

Example: An M3 corner mounting screw hole is often NPTH when the screw is used only for mechanical retention and no grounding or shielding connection is intended.

Critical Decision: Mounting Holes

Mounting holes cause the most PTH/NPTH confusion. Use this rule. For related mechanical-hole decisions, see our guide to counterbore vs. countersink holes in PCB.

Hardware Type	Typical Choice	Reason
Plastic standoff	NPTH	No electrical contact needed
Metal screw + isolated board	NPTH	Prevent accidental grounding
Metal screw + chassis ground required	PTH	Intentional grounding path
Shield-can screw	PTH	EMI shielding connection

DFM Case: A designer specified NPTH for a shield-can mounting hole, assuming that mounting holes should never be plated. As a result, the metal hardware was not reliably bonded to ground, which contributed to poor shielding performance during EMC testing. The fix was to change the hole to PTH and connect it properly to the ground structure.

Manufacturing Differences

1. Hole Size Specification

PTH: Usually specified by finished hole diameter, because copper plating reduces the final opening size. Additional process factors such as drill wear, desmear, and final finish may also affect the finished result.

A connector pin needs 1.00 mm clearance. If the expected plated wall thickness is about 25 μm per side, the drill size may need to be approximately 1.05 mm, subject to the fabricator’s process compensation.

Approximation:
Drill Size ≈ Target Finished Size + (2 × Expected Wall Plating Thickness) + Fabricator Compensation

NPTH: The final size is often closer to the drilled size because there is no conductive wall plating. However, the exact size convention still depends on the fabricator’s documentation rules and tolerance policy.

An M3 screw needs 3.2 mm clearance. The hole may be drilled near 3.2 mm, with the final size controlled according to the board shop’s mechanical drilling tolerance.

2. Process Flow

Typical PTH Manufacturing:

Mechanical drilling
Hole-wall cleaning / desmear
Electroless copper deposition (seed layer)
Electrolytic copper plating (build-up)
Subsequent imaging / etching steps as required

Typical NPTH Manufacturing:

Mechanical drilling in a non-plated drill stage
Mechanical quality control such as burr control and dimensional verification
No conductive wall metallization

Key difference: PTH adds hole-wall preparation and metallization steps that NPTH does not require. You can also review our PCB fabrication service for a broader look at bare-board process control, drill handling, and inspection capability.

3. Tolerance Control

Aspect	PTH	NPTH
Diameter tolerance	Depends on finished-hole requirement and fabricator capability	Depends on hole size and fabricator capability
Primary variation source	Plating thickness, drill wear, process compensation	Drill accuracy, wear, burrs, positioning
Location tolerance	Depends on board shop capability and drawing requirement	Depends on board shop capability and drawing requirement
Aspect ratio concern	Important for plating uniformity and reliability	Less affected by plating, but drilling quality still matters in thick boards

Note: High aspect ratio PTHs are harder to plate uniformly and may create higher reliability risk in thick boards with small holes.

4. Quality Inspection

PTH inspection points:

Hole-wall copper thickness
Plating voids or insufficient coverage
Barrel or corner cracking under thermal stress
Registration and internal layer connection quality

NPTH inspection points:

Diameter accuracy
Position relative to copper features
Burr removal quality
Edge distance and breakout risk

Design and DFM Guidelines

Drill File Preparation

Best practice: Provide separate drill files for plated and non-plated holes whenever possible.

File	Content	Naming Example
Plated drill	All PTH, vias, plated slots	`pcbname_pth.drl`
Non-plated drill	All NPTH, tooling holes	`pcbname_npth.drl`

Why separate files: Separate drill outputs reduce ambiguity and help CAM engineers avoid inferring intent from pads, copper clearance, or layer count. If your production package still depends on CAM interpretation, a formal PCB DFM review can catch drill-file and fabrication-note issues before release.

Common Design Mistakes

Mistake 1: Confusing Drill Size with Finished Size

Error: Specifying a 1.00 mm drill when the design actually requires a 1.00 mm finished plated hole.

Result: After hole-wall plating and process variation, the finished hole can be smaller than required, so the pin may not fit properly.

Fix: Specify the required finished hole size for PTH features and let the fabricator determine the drill size based on its plating process and tolerance rules.

Mistake 2: Insufficient Copper Clearance Around NPTH

Error: NPTH placed too close to copper traces or planes.

Risk: If an NPTH is too close to copper, drilling tolerances, burrs, or breakout can damage nearby copper features or reduce isolation margin.

Guideline: Keep adequate copper clearance around NPTH features according to the fabricator’s design rules. As a practical shop-floor rule, some manufacturers recommend about 0.30 mm minimum drill-to-copper clearance, with larger margins preferred in high-reliability designs.

Mistake 3: Wrong Mounting Hole Type

Error: All mounting holes default to NPTH without checking grounding requirements.

Risk: Floating metal hardware, degraded shielding performance, unintended grounding behavior, or grounding function not working as intended.

Fix: Review every mounting hole's electrical intent. Mark grounded holes clearly in fabrication notes.

Mistake 4: Ambiguous Plated Slot Callouts

Error: Slot shown in mechanical layer without specifying plated or non-plated.

Risk: If the slot is not clearly identified, the CAM engineer may need to infer intent or raise a query, which can cause delay or incorrect interpretation.

Fix: Explicitly label "PLATED SLOT" or "NON-PLATED SLOT" in drill file and fabrication drawing.

Fabrication Documentation Checklist

Include in your fab notes:

[ ] Separate PTH and NPTH drill files (or clear layer coding)
[ ] Required finished hole sizes for plated holes where fit or assembly is critical
[ ] Clearly defined NPTH hole sizes according to the fabricator’s preferred documentation method
[ ] Plated slot callouts with dimensions
[ ] Mounting hole grounding intent (which holes tie to ground)
[ ] Special tolerance requirements (if any)
[ ] Hole-to-edge minimum distances

Reliability and Cost Considerations

PTH Reliability Risks

Barrel cracking: Thermal cycling stress can crack the copper barrel, especially in high aspect ratio holes.

Plating voids: Incomplete copper coverage creates weak points.

Z-axis expansion: CTE mismatch between copper and FR4 causes stress at hole corners.

Mitigation:

Keep aspect ratio within the fabricator’s reliable plating capability
Specify the required minimum hole-wall copper thickness based on the product class
Avoid unnecessarily small drilled holes in thick boards, and consult the fabricator for high-aspect-ratio or high-reliability designs

NPTH Reliability Risks

Copper breakout: If the hole is too close to copper, drilling variation can break into a trace or plane.

Burr-related contact: Poor hole quality can leave burrs or reduce insulation margin near adjacent copper features.

Misalignment: Tight-tolerance NPTH features can create assembly or mechanical fit problems if the hole position drifts.

Cost Impact

Factor	PTH	NPTH
Process complexity	Higher due to hole-wall preparation and metallization	Lower because no conductive barrel plating is required
Inspection focus	More emphasis on metallization quality and hole reliability	More emphasis on mechanical accuracy, burr control, and clearance
Main yield risk	Plating-related defects	Mechanical tolerance, breakout, or interpretation errors
Tight-tolerance impact	Can add cost significantly, depending on hole size and reliability class	Can also add cost significantly, depending on mechanical precision requirements

Rule: Do not choose NPTH solely to reduce cost. Choose the hole type by function. Using NPTH where a conductive or grounded hole is required can create failures that are far more expensive than the added plating process.

PTH vs NPTH Quick Reference

Decision Point	Choose PTH	Choose NPTH
Component lead soldering	✓	✗
Layer-to-layer electrical connection	✓	✗
Chassis ground or shielding connection	✓	✗
Pure mechanical mounting with no intended grounding	✗	✓
Electrical isolation required	✗	✓
Tooling or alignment only	✗	✓

Need DFM review? If you want a second check on your Gerber package, drill files, and fabrication notes, see our PCB layout support and DFM review service.

+++FAQ+++

Is every through hole plated?

No. "Through hole" describes geometry (hole passes through board). It can be plated (PTH) or non-plated (NPTH).

Are mounting holes always NPTH?

No. Many are NPTH, but mounting holes can be PTH when the hardware must connect to ground or shielding.

Why specify finished size for PTH?

Copper plating reduces the final internal diameter, so plated holes are usually specified by required finished size rather than raw drill size.

Can NPTH connect to a circuit?

Not through the hole wall. If conductive barrel connection is required, use PTH; if only surface contact is needed, define that separately in the pad/copper design.

Do all through-hole components need PTH?

For standard electrical through-hole components, yes. Soldered leads and press-fit leads normally require a properly designed plated hole to provide reliable mechanical and electrical contact. Non-electrical locating or mechanical features are a different case.

Why separate PTH and NPTH drill files?

Clarity. Separate drill files reduce CAM interpretation, prevent ambiguity between conductive and non-conductive holes, and lower the risk of manufacturing errors.

Is NPTH always cheaper?

Usually, but tight tolerances or difficult positioning can add cost. Function should drive the choice, not cost alone.

What is the most common PTH design error?

Specifying drill diameter instead of finished plated diameter, causing component fit failures.