When selecting a PCB relay for an electronic design, engineers often face an important decision: Should you choose a surface-mount PCB relay or a through-hole PCB relay?

Although both relay types perform the same basic switching function, their mounting methods, mechanical strength, manufacturing processes, electrical characteristics, and application environments are quite different.

Choosing the wrong PCB relay type may lead to problems such as insufficient mechanical reliability, higher production costs, or difficulties during PCB assembly.

As an experienced PCB relay supplier, we will explain the key differences between surface-mount and through-hole relays and help you determine which option is best for your application.

1. Physical Structure: SMT Relay vs Through-Hole Relay

The biggest difference between surface-mount and through-hole PCB relays is how they connect to the printed circuit board.

Through-Hole PCB Relay

A through-hole relay uses metal pins or terminals that pass through holes drilled into the PCB.

During assembly, the relay pins are inserted through the board and soldered on the opposite side.

This traditional mounting method creates a strong mechanical connection between the relay and PCB.

Advantages of Through-Hole Relays

Strong Mechanical Reliability

Because the relay terminals physically pass through the PCB, through-hole relays provide excellent resistance against:

Vibration

Mechanical shock

Physical stress

For this reason, through-hole relays are commonly used in:

Industrial control equipment

Automation systems

Power control systems

Automotive electronics

For example, a high-current relay such as a 24V 30A PCB relay is typically designed with a through-hole structure because applications requiring higher current switching also require stronger mechanical stability.

Surface-Mount PCB Relay

A surface-mount relay (SMT relay) is mounted directly onto the surface of the PCB.

Instead of passing through holes, the relay terminals are soldered onto copper pads on the PCB surface.

This design allows manufacturers to create smaller and more compact circuit assemblies.

Advantages of Surface-Mount Relays

Smaller Size

The compact structure of SMT relays allows engineers to:

Reduce PCB size

Increase component density

Create smaller electronic products

They are widely used in:

Consumer electronics

Compact controllers

Smart devices

Portable equipment

For example, subminiature PCB relays are commonly selected when space limitations are a major design requirement.

2. Manufacturing Process Differences

The mounting method also affects PCB manufacturing.

Through-Hole Relay Assembly Process

The production process usually includes:

PCB drilling

Relay lead insertion

Wave soldering

Inspection

The soldering process creates a very strong connection, but the additional drilling and insertion steps increase manufacturing complexity.

Advantages

Strong solder joints

Suitable for large components

Easier manual assembly and repair

Limitations

Requires PCB holes

Uses more board space

Less suitable for ultra-high-density designs

Surface-Mount Relay Assembly Process

Surface-mount relay production uses SMT technology.

The typical process includes:

Applying solder paste to PCB pads

Pick-and-place machine positioning

Reflow soldering

Automatic inspection

This highly automated process enables:

Faster production

Higher accuracy

Lower labor costs

Advantages

Ideal for mass production

Supports compact PCB layouts

Allows components on both PCB sides

3. Electrical Performance Comparison

Many engineers assume that surface-mount and through-hole relays have completely different electrical performance.

However, the relay's electrical capability mainly depends on:

Contact material

Coil design

Rated voltage

Rated current

Switching frequency

The mounting method mainly affects mechanical and manufacturing characteristics.

Signal Integrity

Surface-mount relays generally have shorter electrical paths.

This reduces:

Parasitic inductance

Parasitic capacitance

Therefore, SMT relays can provide better performance in applications requiring fast signal switching.

Typical applications include:

Communication equipment

Measurement systems

High-speed electronic circuits

Power Handling Capability

Through-hole relays often have advantages in higher-power applications.

Their larger terminals provide:

Better current carrying capability

Improved heat dissipation

Stronger mechanical support

They are commonly used in:

Industrial equipment

Motor control

Power supply systems

4. Cost Comparison

Cost depends not only on the relay itself but also on the entire manufacturing process.

Through-Hole Relay Cost

Through-hole relays may have higher PCB assembly costs because they require:

PCB drilling

Additional assembly steps

More manual processing

However, they can be more economical for:

Low-volume production

Industrial equipment

Repair-friendly designs

Surface-Mount Relay Cost

SMT relays are usually more cost-effective for high-volume production.

Reasons include:

Fully automated assembly

Reduced labor requirements

Smaller PCB size

For manufacturers producing thousands or millions of units, SMT technology often provides significant cost advantages.

5. Design Flexibility

When Through-Hole Relays Are Better

Through-hole relays are ideal when you need:

Easy Maintenance

Technicians can easily:

Identify components

Replace damaged relays

Repair circuit boards

Strong Mechanical Stability

They are better suited for:

Industrial machinery

Equipment exposed to vibration

Harsh environments

When Surface-Mount Relays Are Better

SMT relays are preferred when you need:

Miniaturization

Suitable for:

Compact electronic devices

Space-limited PCB designs

High Component Density

SMT allows:

More components on smaller boards

Double-sided PCB assembly

Advanced electronic designs

Surface Mount Relay vs Through Hole Relay Comparison Table

How To Choose Between Surface-Mount and Through-Hole PCB Relay?

Choose Through-Hole PCB Relays If You Need:

✔ High current switching
✔ Strong mechanical durability
✔ Industrial reliability
✔ Easy maintenance
✔ Resistance to vibration and shock

Typical applications:

Industrial automation

Power controllers

Automotive systems

Factory equipment

Choose Surface-Mount PCB Relays If You Need:

✔ Compact PCB design
✔ Automated manufacturing
✔ High component density
✔ Smaller electronic products

Typical applications:

Consumer electronics

Smart devices

Compact control systems

Communication equipment

Frequently Asked Questions

Is a surface-mount relay better than a through-hole relay?

Not necessarily.

The best choice depends on the application.

Surface-mount relays are better for compact, high-volume PCB manufacturing, while through-hole relays are better for applications requiring mechanical strength and higher reliability.

Can SMT relays replace through-hole relays?

Only if:

Electrical specifications match

PCB footprint is compatible

Mechanical requirements are satisfied

The replacement should always consider the complete system design.

Which PCB relay is better for industrial applications?

For industrial environments involving vibration, high current, and long operating times, through-hole PCB relays are often the preferred choice.

Conclusion

The main difference between surface-mount PCB relays and through-hole PCB relays is their mounting technology.

Surface-mount relays provide advantages in size reduction, automated production, and high-density PCB designs.

Through-hole relays provide superior mechanical strength, easier maintenance, and better suitability for demanding industrial applications.

Before selecting a PCB relay, engineers should evaluate:

Electrical requirements

PCB design

Manufacturing process

Operating environment

Choosing the correct relay type ensures better reliability, lower production costs, and longer product life.