Mixed PCB Assembly for complex products systems with SMT and THT lines

Mixed PCB Assembly: SMT + THT Optimization
What is Mixed PCB Assembly?
Mixed assembly is a flexible manufacturing approach that leverages the strengths of both assembly technologies.
◈ SMT components (such as high-density integrated circuits) save space and support miniaturization.
◈ THT components (including power resistors, connectors, and heavy parts) deliver stronger mechanical stability and reliability.
By combining both, manufacturers can achieve a balance between compact design and structural durability.

What are the Main Types of Mixed Assembly?

◈ Single-sided mixed assembly
SMT and THT components are placed on the same side of the PCB.
Suitable for simple, cost-effective designs.
◈ SMT on one side, THT on the other
SMT components are mounted on one side, while through-hole parts are placed on the opposite side.
This reduces thermal interference during wave soldering.
◈ Double-sided mixed assembly
Both sides include SMT and THT components.
Used in high-density, high-performance electronic devices.

What Are the Common Challenges in Mixed Assembly?

◈ Different soldering processes
SMT typically uses reflow soldering, while THT often relies on wave soldering.
Controlling thermal profiles to avoid component damage is critical.
◈ Thermal stress management
SMT chips and sensitive parts can be affected by the high temperatures required for THT soldering.
◈ Complex inspection requirements
Multi-sided, multi-height components demand advanced inspection such as AOI and X-ray inspection, especially for BGAs.
◈ Process sequence control
SMT is usually processed first to avoid shadowing and ensure reliable solder joints.

How Are Mixed Assemblies Used Across Applications?

◈ Industrial equipment: Power supplies and control systems use THT for durability and SMT for control logic.
◈ Automotive electronics: ECUs and control modules use THT for vibration resistance and SMT for high-speed processing.
◈ Aerospace & military: Avionics and communication systems operating under extreme conditions.
◈ Medical devices: Diagnostic and monitoring equipment requiring long-term stability.

How Can You Get the Best Mixed Assembly Solutions?

Early DFM (Design for Manufacturing)

Work with your manufacturer during PCB design to optimize layout and component placement.
Use precision soldering processes

Selective wave soldering is recommended for high-value or sensitive assemblies.
Rigorous testing & inspection

Ensure AOI, X-ray, and functional testing are included to verify solder quality and performance.
Choose an experienced manufacturer

Look for certified suppliers with specialized mixed-assembly capabilities.