Press Fit Hole in PCB: Complete Guide to Design, Tolerances & Assembly

After 15 years working in PCB design and manufacturing, I’ve seen press fit hole technology evolve from a niche telecom solution into an essential technique used across automotive, industrial, and high-reliability applications. This guide covers everything I’ve learned about designing, specifying, and assembling press fit holes—based on real production experience and industry standards.

What is a Press Fit Hole?

A press fit hole is a plated through-hole (PTH) in a printed circuit board with significantly tighter tolerances than standard holes. Unlike conventional through-hole technology where components are soldered to the board, press fit technology uses mechanical force to push specially designed pins into these holes, creating a gas-tight electrical and mechanical connection without any solder.

The principle behind press fit connections dates back to the 1970s when it was first developed for telecommunications equipment. The technique works like a blade-and-socket connector, but with reversed roles: the press fit pin (or “compliant pin”) has flexible sections that deform during insertion, while the PCB hole remains rigid.

When the pin is pressed into the hole, the compliant section compresses and creates contact points against the copper-plated hole wall. This forms what engineers call a “cold weld”—a gas-tight zone where the contact materials bond at the molecular level without heat.

How Press Fit Technology Differs from Traditional Soldering

The fundamental difference between press fit and soldering lies in how the electrical connection is established. With wave soldering or reflow, molten solder creates the conductive path. Press fit connections rely entirely on mechanical interference between the pin and hole wall.

This distinction has major implications for manufacturing. Press fit assembly eliminates thermal stress, removes flux residues from the equation, and avoids common soldering defects like cold joints, bridging, and insufficient wetting. For boards that already have heat-sensitive components or require secondary assembly operations, press fit technology offers a compelling alternative.

Press Fit Hole Tolerances and Specifications

Getting the tolerances right is probably the most critical aspect of press fit design. I’ve seen projects fail because designers applied standard PTH tolerances to press fit holes without understanding the precision requirements.

Standard vs Press Fit Hole Tolerance Comparison

Parameter	Standard PTH	Press Fit Hole
Finished Hole Tolerance	±0.10mm (±4 mil)	±0.05mm (±2 mil)
Typical Drill Tolerance	±0.075mm (±3 mil)	±0.05mm (±2 mil)
Copper Plating Thickness	20-25 μm minimum	20-25 μm (controlled)
Hole Wall Quality	Standard inspection	Enhanced inspection required

Finished Hole Size (FHS) Requirements

The connector manufacturer always specifies the finished hole size requirements. This is non-negotiable. If your connector datasheet calls for a 1.02mm finished hole with ±0.05mm tolerance, that’s exactly what you need to achieve.

Here’s the tricky part: the PCB fabricator needs to drill a larger hole to account for copper plating buildup. A typical calculation looks like this:

Drill Size = Finished Hole Size + (2 × Copper Plating Thickness) + Process Allowance

For a 1.02mm finished hole with 25μm copper plating: Drill Size = 1.02mm + 0.05mm + 0.03mm ≈ 1.10mm

Common Press Fit Hole Sizes by Pin Type

Pin Type	Typical Pin Diameter	Recommended Hole Size	Tolerance
ACTION PIN (TE Connectivity)	0.60mm	1.02mm	±0.05mm
Multispring	0.64mm	1.02mm	±0.05mm
NanoMultispring	0.40mm	0.65mm	±0.05mm
Eye of Needle (EON)	Various	Per manufacturer	±0.05mm

Always reference the specific connector manufacturer’s datasheet. These values serve as general guidance, but production specifications may vary based on PCB thickness, surface finish, and application requirements.

Types of Press Fit Pins

Understanding pin types helps you make better design decisions and communicate effectively with your connector suppliers.

Compliant (Flexible) Pins

Compliant pins feature an elastic section that deforms during insertion. The “Eye of the Needle” (EON) design is the most common configuration, featuring two opposing beams that compress when entering the hole and spring back to create consistent contact pressure.

Advantages of compliant pins:

• Lower insertion force reduces stress on the PCB
• Greater tolerance for hole size variations
• Less likely to damage hole plating
• Can be extracted and reinserted (typically up to 3 times)
• Suitable for a wide range of PCB thicknesses

The dual-beam design creates two contact points per pin, providing redundancy and maintaining connection integrity even if one contact point degrades over time.

Solid (Rigid) Pins

Solid pins maintain their shape during insertion, relying entirely on the interference fit between pin and hole for connection stability. While less common in modern designs, solid pins offer advantages in specific applications.

When to consider solid pins:

• High current applications requiring maximum contact area
• Multi-layer PCBs where vertical alignment is critical
• Applications where the connection must never be disturbed

The tradeoff is tighter tolerance requirements and higher insertion forces, which can damage the PCB plating if not carefully controlled.

Pin Material Considerations

Most press fit pins use copper alloys for their combination of electrical conductivity and mechanical properties. Common materials include:

Material	Properties	Typical Applications
Phosphor Bronze (CuSn4, CuSn6)	Good spring properties, corrosion resistant	General purpose connectors
Copper-Nickel-Silicon (C7025)	Higher strength, good conductivity	Automotive, high-reliability
Beryllium Copper	Excellent fatigue resistance	High-cycle applications

PCB Design Guidelines for Press Fit Holes

Successful press fit implementation starts at the design stage. Here are the key considerations I’ve learned to check on every project.

Hole Construction Requirements

The plated through-hole construction is equally as important as the hole diameter. The PTH must have:

Proper copper thickness: Maintain 20-25μm minimum copper in the hole barrel. Too thin, and the copper can delaminate during pin insertion. Too thick, and you’ll struggle to meet finished hole size tolerances.

Uniform plating: Variations in plating thickness around the hole circumference create inconsistent contact pressure. Request plating uniformity specifications from your fabricator.

Clean, burr-free holes: Any burrs or debris in the hole can damage the pin during insertion or create weak contact points. Specify enhanced hole cleaning if your fabricator offers it.

Annular Ring and Pad Design

Press fit holes typically require larger annular rings than standard PTH to withstand insertion forces without pad lift. A minimum 0.25mm annular ring is common, but check your fabricator’s capability.

The pad design should also account for:

• Sufficient copper connection to internal layers
• Thermal relief patterns (if connected to planes)
• Clearance for the press tool

PCB Material Selection

Not all PCB materials are suitable for press fit applications. The laminate must withstand mechanical stress during insertion and maintain dimensional stability across operating temperatures.

Parameter	Requirement	Reason
Glass Transition Temperature (Tg)	>130°C for general, >170°C for automotive	Prevents softening during operation
Z-axis CTE	<60 ppm/°C	Maintains hole integrity during thermal cycling
Peel Strength	>1.0 N/mm	Prevents pad lift during insertion

For automotive applications, high-Tg materials like FR-4 with Tg >170°C or polyimide are often specified. The PCB’s glass transition temperature should exceed the maximum operating temperature by a comfortable margin.

Design for Manufacturability Tips

Based on production experience, here are practical tips that improve yield:

Separate press fit holes in your design files. Most CAD tools allow you to define press fit holes on a separate layer or with distinct attributes. This helps the fabricator apply the correct drilling and plating parameters.

Include connector datasheets with your fabrication package. Don’t assume the fabricator knows which connector you’re using. The datasheet provides critical information about hole sizes, tolerances, and any special requirements.

Consider hole aspect ratio. Very thick boards (>3mm) with small holes create high aspect ratios that make plating uniformity difficult. If your aspect ratio exceeds 10:1, discuss capabilities with your fabricator early.

Surface Finish Recommendations

The surface finish affects both the insertion process and long-term connection reliability. This is an area where I’ve seen engineers make costly mistakes.

Compatible Surface Finishes

Surface Finish	Compatibility	Notes
Immersion Tin (Chem Tin)	Excellent	Recommended for gold-plated pins
HASL (Lead-Free)	Good	Acceptable, may have thickness variation
ENIG	Good with caution	Avoid with gold-plated pins (gold-on-gold)
OSP	Limited	Short shelf life, humidity sensitive

The Gold-on-Gold Problem

Here’s something that catches many engineers: combining gold-plated pins with ENIG (gold) surface finish creates problems. The gold-gold interface lacks the “slippage” needed for smooth insertion, resulting in higher insertion forces and potential damage.

The solution? If your connector uses gold-plated pins, specify a tinned surface finish on the PCB (immersion tin or HASL). The tin provides the lubricity needed for reliable insertion. This recommendation comes directly from major connector manufacturers like TE Connectivity and is backed by production experience.

Press Fit Assembly Process

Understanding the assembly process helps designers avoid creating boards that are difficult or impossible to assemble reliably.

Assembly Methods

Manual Insertion: Suitable for prototypes or low-volume production. Uses hand-held press tools or arbor presses. The operator controls the insertion force, which requires training and introduces variability.

Semi-Automated Press: Desktop or benchtop machines with controlled force and speed. Provides force-distance monitoring for quality feedback. Typical cost range: $10,000-30,000.

Fully Automated Press: Servo-electric press systems that handle high volumes with consistent quality. Can integrate with automated optical inspection (AOI) for inline verification. Investment typically exceeds $30,000, but provides the best process control.

Critical Process Parameters

Parameter	Typical Range	Control Method
Insertion Force	20-100N per pin	Force monitoring
Insertion Speed	5-25 mm/s	Servo control
Final Position	±0.1mm	Distance monitoring
Support Pressure	Board-specific	Fixture design

The insertion force is particularly important. Too little force and the pin doesn’t seat properly. Too much force and you risk damaging the hole plating or cracking the board. Modern press equipment monitors force versus distance curves to detect anomalies in real time.

Common Assembly Defects and Prevention

Bent pins: Usually caused by misalignment between connector and PCB. Prevention includes optical verification before pressing and proper fixture design.

Insufficient insertion depth: Results from inadequate force or PCB support. Use force-distance monitoring to verify complete insertion.

Hole damage: Occurs when insertion force exceeds hole wall strength. Ensure hole specifications match connector requirements and consider compliant pin designs.

PCB cracking: Often related to PCB material properties or inadequate support during pressing. Specify appropriate materials and design fixtures to support the board around press fit areas.

Quality Inspection Methods

Press fit connections are notoriously difficult to inspect because the critical contact zone is hidden inside the hole. Unlike solder joints that can be visually examined, the actual metal-to-metal contact in a press fit connection occurs below the PCB surface. This makes quality assurance both more important and more challenging. Here are the methods I’ve used successfully in production, ranging from simple visual checks to sophisticated automated systems.

Visual and Optical Inspection

Automated Optical Inspection (AOI) can verify pin presence and alignment at the top surface, but cannot see the actual contact zone inside the hole. Use AOI for:

• Pin true position verification
• Missing or damaged pins
• Connector seating height
• Visible damage to surrounding pads

Force-Distance Monitoring

The most reliable production inspection method is real-time force-distance monitoring during insertion. A good insertion creates a characteristic curve that can be compared against acceptable limits.

Abnormal curves indicate problems like:

• Undersized holes (higher than expected force)
• Oversized holes (lower than expected force)
• Burrs or debris (force spikes)
• Plating defects (irregular curve shape)

X-Ray Inspection

For critical applications, X-ray inspection can verify pin position within the hole. This is particularly valuable for:

• Double-sided press fit assemblies where pins from opposite sides share a hole
• Thick boards where pin tails aren’t visible
• Quality audits and failure analysis

Electrical Testing

After assembly, electrical testing verifies connection integrity:

• Contact resistance measurement (typically <200 μΩ)
• High-potential (hipot) testing for insulation
• Continuity verification across the connection

For production environments, automated test equipment can measure contact resistance across all pins in a connector and flag any connections exceeding specified limits. This provides a final quality gate before shipping assembled boards to customers.

Industry Applications

Press fit technology has found adoption across industries that value reliability and manufacturing efficiency.

Automotive Electronics

The automotive industry has embraced press fit technology extensively. Modern vehicles contain numerous PCBs controlling everything from engine management to infotainment systems. Press fit connections appear in:

• Engine control units (ECUs)
• Airbag control modules
• ABS/ESC brake systems
• Transmission controllers
• Dashboard electronics
• Power steering modules
• Electric vehicle battery management systems

Automotive applications demand connections that withstand extreme temperatures (-40°C to +125°C), vibration, and thermal cycling. The gas-tight nature of press fit connections provides the reliability these conditions require.

TE Connectivity introduced press fit technology to the automotive sector in 1988, and it has since become the preferred connection method for safety-critical systems. The technology’s ability to handle both signal-level and power connections makes it versatile enough for modern automotive architectures. With the rise of electric vehicles, press fit connections are increasingly important for high-current battery and motor control applications where thermal management and connection reliability are paramount.

Telecommunications Infrastructure

Telecommunications was the original domain for press fit technology. Network equipment like routers, switches, and base stations use large backplanes with thousands of press fit connections. The ability to assemble without thermal stress and achieve high reliability makes press fit ideal for infrastructure equipment expected to operate continuously for years.

Modern data center equipment relies heavily on press fit connections for backplane interconnects. A single high-speed networking switch may contain hundreds of press fit connectors, each with dozens of pins, creating thousands of individual connections per assembly. The technology supports the signal integrity requirements of high-speed data transmission while providing the mechanical stability needed for 24/7 operation.

The trend toward higher data rates and denser connectivity has driven innovation in press fit pin design. Manufacturers now offer pins optimized for high-speed signal transmission with controlled impedance and minimal signal reflections. This evolution allows press fit technology to support data rates exceeding 25 Gbps per channel.

Industrial Control Systems

Factory automation, process control, and robotics systems increasingly use press fit connections. The technology suits applications where:

• Equipment operates in harsh environments
• Long service life is expected
• Maintenance accessibility is limited

Medical Devices

Medical electronics require exceptional reliability and traceability. Press fit connections offer advantages for implantable devices and diagnostic equipment where solder-related contamination is unacceptable.

Advantages and Limitations

Before committing to press fit technology, consider both the benefits and constraints.

Advantages of Press Fit Connections

No thermal stress: The solderless process eliminates heat damage to sensitive components and adjacent circuitry.

Higher reliability: Gas-tight connections resist corrosion and maintain stable contact resistance over time. Failure rates (FIT values) can be 30 times better than comparable SMT solder joints.

Environmental benefits: No flux, no lead, no cleaning chemicals. Press fit assembly is inherently more environmentally friendly than soldering.

Reworkability: Compliant pins can be extracted and replaced without desoldering, simplifying repair procedures.

Design flexibility: Components can be mounted on either side of the PCB without wave soldering concerns.

Limitations to Consider

Tighter tolerances: The ±0.05mm hole tolerance requirement increases fabrication cost and may limit supplier options.

Initial equipment investment: Proper press equipment costs more than basic soldering tools, though the investment pays back in volume production.

Design constraints: Press fit holes require more PCB real estate than equivalent SMT connections.

Not suitable for all components: Only connectors and terminals with press fit terminations can use this technology.

Relevant Standards and Resources

IPC Standards

Standard	Description
IPC-2221	Generic PCB Design Standard (includes hole requirements)
IPC-9797	Press-Fit Standard for Automotive and High-Reliability Applications
IPC-A-610	Acceptability of Electronic Assemblies (inspection criteria)
IPC-J-STD-001	Requirements for Soldered Electrical and Electronic Assemblies

International Standards

Standard	Description
EN IEC 60352-5	Solderless Connections – Press-In Connections – General Requirements
DIN EN 60352-5	German adoption of IEC 60352-5
SAE/USCAR-2	Performance Specification for Automotive Electrical Connector Systems

Manufacturer Resources

Major connector manufacturers provide detailed application guides:

• TE Connectivity: Press-Fit Technology White Paper, ACTION PIN and Multispring design guides
• Molex: Press-Fit Connector Selection Guide
• Wurth Elektronik: REDCUBE Press-Fit Design Guide
• Positronic: Press-Fit Connector Technical Documentation

These resources typically include specific hole size recommendations, insertion force data, and application notes for their products.

Frequently Asked Questions

What is the typical tolerance for press fit holes in PCBs?

The standard tolerance for press fit holes is ±0.05mm (±0.002 inches), which is twice as tight as standard plated through-holes at ±0.10mm. This precision is necessary to ensure proper interference between the compliant pin and hole wall. The connector manufacturer’s datasheet always takes precedence—if they specify a different tolerance, follow their recommendation. Note that achieving these tight tolerances requires specialized drilling equipment and enhanced process controls, which is why press fit capable fabrication typically costs more than standard PCB production.

Can press fit connectors be reused or repaired?

Yes, compliant press fit pins can typically be extracted and reinserted up to three times without damaging the PCB or significantly degrading connection quality. This is a major advantage over soldered connections, which require desoldering and risk thermal damage during rework. However, each insertion/extraction cycle does wear the hole plating slightly, so limit rework operations when possible. For production repairs, always use new connectors rather than reinserting removed ones. Solid press fit pins are generally not suitable for multiple insertions due to their rigid construction.

How does press fit compare to soldering for high-current applications?

Press fit technology excels in high-current applications for several reasons. First, the solid metal-to-metal contact creates lower resistance than typical solder joints—often below 200 μΩ per connection. Second, press fit connections don’t suffer from the thermal degradation that affects solder joints under continuous high-current loads. The contact area extends the full height of the compliant zone rather than just the solder fillet area. For these reasons, manufacturers like Wurth Elektronik offer press fit terminals rated for currents up to 500A. The key is specifying connectors designed for high-current service, with appropriate contact cross-sections and material selections.

What surface finish should I use with gold-plated press fit pins?

Use a tinned surface finish (immersion tin or HASL) when your connector has gold-plated pins. Combining gold-plated pins with ENIG (electroless nickel immersion gold) creates a gold-on-gold interface that lacks sufficient lubricity for smooth insertion. This can increase insertion forces and damage the hole plating. The tin surface provides the “slippage” needed during the pressing operation while still forming reliable cold-weld connections. This recommendation comes from connector manufacturers including TE Connectivity and Multi Circuit Boards. If you must use ENIG for other components on the same board, discuss options with your fabricator—selective surface finishes may be possible.

How do I specify press fit holes in my PCB design files?

The best practice is to define press fit holes on a separate drill layer or with distinct attributes in your CAD tool. Include a note in your fabrication drawing specifying “Press-fit holes per [connector part number] datasheet” and attach the relevant datasheet pages. Key information to communicate includes: finished hole size, tolerance (typically ±0.05mm), copper plating thickness requirements, and surface finish. Some designers create a separate drill file for press fit holes, which helps ensure the fabricator applies appropriate process controls. If using ODB++ format, the press fit designation can be embedded in the data automatically. Always confirm your fabricator’s capabilities and preferred specification method before releasing production files.

Conclusion

Press fit hole technology represents a mature, reliable approach to PCB interconnection that eliminates many challenges associated with soldering. Success requires attention to tolerances, material selection, and process control—but the payoff is connections that maintain integrity across demanding operating conditions.

The key points to remember:

• Specify hole tolerances of ±0.05mm and always reference the connector manufacturer’s datasheet
• Choose surface finishes carefully, avoiding gold-on-gold combinations
• Use compliant pin designs for most applications
• Invest in proper pressing equipment and process monitoring for production volumes
• Work with fabricators experienced in press fit capable PCB production

Whether you’re designing automotive control modules, telecom infrastructure, or industrial equipment, press fit technology offers a proven path to reliable, manufacturable connections. The upfront engineering effort pays dividends in reduced defects, lower rework rates, and longer product lifetimes.