PCB Assembly Methods: Surface Mount vs. Through-Hole

Printed Circuit Board (PCB) assembly is the backbone of modern electronics manufacturing. From smartphones to industrial machinery, everything runs on some form of a PCB. The assembly process covers the entire process, from design and procurement to assembly and testing, ensuring that PCBs meet specific application requirements. The method used to attach components to PCBs can vary greatly—and the method used can affect everything from size and performance to cost and durability. Different copper thicknesses and flex PCBs are available to meet diverse application needs.

​In this blog, we’ll break down two primary PCB assembly methods: surface mount and through-hole. After the initial design, services such as layout and pcb fabrication are essential steps in delivering a finished product. We’ll also explore the advantages of each, the various mounting technologies used today, and how SMD and through-hole connectors differ. Our ability to deliver complete electronic product solutions—from schematic creation to finished assembly—ensures your project is in expert hands. If you’re trying to understand which method is right for your next electronics project, this guide will walk you through everything you need to know.

PCB assembly is the essential process that brings electronic devices to life by mounting electronic components onto a printed circuit board (PCB). This step transforms a bare printed circuit into a functional platform for everything from industrial new energy network systems to consumer electronics and telecommunications equipment. Our PCB assembly services are designed to meet the diverse needs of industries such as medical, automotive, aerospace, and network infrastructure, ensuring that every assembly meets the highest standards of quality and reliability.

​By leveraging advanced assembly equipment and rigorous quality control protocols, we deliver consistent quality across every board and project. Whether you require high-volume production or specialized assembly services for complex energy network applications, our team is committed to providing the expertise and precision needed for today’s demanding electronic products. From the initial design to the final assembled circuit, we focus on delivering reliable, high-performance solutions for every application.

The pcb assembly process begins with the careful selection of bare boards and electronic components. We work closely with authorized distributors to source only the highest quality components, including SMT components, through-hole components, and a variety of other leadless package parts. Our experienced team ensures that all the components chosen for your assembly process meet strict specifications and customer requirements, guaranteeing optimal performance and reliability.

​For customers who prefer to supply their own components, we offer flexible consigned assembly services. This approach allows you to provide all the components needed for your project, while we handle the precise assembly onto the bare boards. Whether you choose turnkey or consigned assembly, our focus remains on quality, traceability, and meeting your unique project needs. Every step of the process—from component selection to final assembly—is managed with attention to detail, ensuring your printed circuit boards are built to the highest standards.

At a high level, surface mount and through-hole technologies refer to how electronic components are attached to a printed circuit board. Manufacturers assemble electronic components onto the PCB using either through-hole or surface mount methods, often utilizing automated equipment to ensure precision and efficiency. The choice between these methods can significantly impact the overall manufacturing process, including factors such as speed, cost, and quality control.

Through-hole technology (THT) means inserting component leads into pre-drilled holes on the PCB. These leads are then soldered to pads on the opposite side of the board. This method has been around since the early days of electronics and is still used today in specific scenarios.

Surface mount technology (SMT) skips the drilling process. Components are placed directly onto the surface of the PCB, and soldered using reflow techniques. Instead of long leads, surface-mount devices (SMDs) use smaller, flat contacts.

Both SMT and through-hole methods can be used to assemble different quantity ranges, from prototypes to large-scale production.

The circuit board assembly process is a multi-stage operation that combines advanced technology with skilled craftsmanship. Our assembly services cover every aspect of board assembly, including SMT assembly, through-hole assembly, and mixed assembly for projects that require both technologies. Using high-speed pick and place machines, reflow ovens, and state-of-the-art solder paste inspection equipment, we ensure that every component is accurately placed and securely soldered.

​In addition to standard PCB assembly, we offer comprehensive electro-mechanical assembly services, such as cable assemblies and wire harnesses, to support complex system integration. Our team works closely with customers to understand their specific requirements and specifications, tailoring the assembly process to deliver the best possible results. Whether you need a simple single-sided board or a complex multi-layer assembly with both SMT and through-hole components, our process is designed for efficiency, quality, and flexibility.

Surface mount technology has largely replaced through-hole methods for most modern electronics. Here’s why:

​SMT can significantly reduce lead time for PCB assembly projects, allowing for faster turnaround and more efficient manufacturing.

SMT allows components to be placed on both sides of the board. That means designers can fit more functionality into a smaller footprint—perfect for smartphones, tablets, and wearables.SMT is compatible with automated pick-and-place machines, making assembly faster and more cost-effective. While through-hole often requires human labor, SMT speeds up the process without sacrificing quality.

Fewer drilling steps and less labor means SMT is typically cheaper to manufacture at scale. Plus, smaller parts mean lower material costs.

Surface-mounted components have shorter leads, which reduces signal path lengths. That’s better for high-frequency applications.

Whether you’re making ten boards or ten thousand, SMT processes scale better. SMT is also ideal for rapid prototype assembly, enabling quick turnaround for early-stage design testing and iteration, as well as large-scale production. That’s a big win for manufacturers looking to ramp up production quickly.

​But it’s not a one-size-fits-all solution. Through-hole components are still the go-to for high-reliability applications like aerospace, automotive, and industrial controls where ruggedness and strength matter.

There are three main mounting technologies in PCB assembly: surface mount technology (SMT), through-hole technology (THT), and mixed technology. In addition to these, modern assembly processes also support advanced PCB types such as rigid flex, which combine flexible and rigid board sections for complex applications.

This traditional method is good for components that need strong mechanical bonds—like connectors or components that will be physically stressed.

The most common method today, SMT allows for compact, lightweight and high-speed assemblies. Components are mounted directly to the surface and soldered in place using a reflow oven, which is essential for ensuring reliable and high-quality solder joints.

In many cases both SMT and THT are used on the same board. For example, surface mount resistors and ICs might sit alongside through-hole connectors or transformers. This approach gives you the benefits of SMT while retaining the strength of through-hole where needed.

​Each has its place depending on the application, cost and mechanical requirements.

Connectors are interfaces between a PCB and other components like cables, switches or other boards. They can be either surface mount or through-hole and choosing the right one matters for long-term reliability.

These connectors have leads that go through the board, providing a stronger physical attachment. They’re good for applications that involve frequent plugging and unplugging or where mechanical stress is a concern—think industrial equipment or automotive electronics.

Surface mount connectors play a vital role in the pcb assembly process, especially as devices become smaller and more complex. We offer a broad selection of surface mount connectors, including micro BGA, QFN, and other leadless package parts, all chosen for their reliability and performance. Our assembly team ensures that these connectors are precisely aligned and expertly soldered onto the PCB, using advanced techniques to prevent defects such as solder bridges.

​To guarantee the integrity of every connection, we utilize automatic optical inspection (AOI) systems, including Yestech BX and X-ray inspection equipment. These tools allow us to detect even the smallest defects or misalignments, ensuring that every package, from micro BGA to other leadless package parts, meets our strict quality standards. With a focus on process control and defect prevention, we deliver assembled boards that are ready for the most demanding applications.

The final inspection and quality control phase is a cornerstone of our pcb assembly process, ensuring that every assembled board meets the highest standards before shipment. Our skilled inspectors and engineers conduct thorough examinations of all assembled boards, using a combination of functional testing, in-circuit testing, and environmental testing to verify performance and reliability.

​We employ advanced testing equipment, including ray testing, solder paste inspection, and specialized tools for inspecting other leadless package parts. This comprehensive approach allows us to identify and address any defects, solder issues, or inconsistencies before the final shipment. Each assembly process is documented, and customers receive detailed reports outlining the results of all inspections and tests. By maintaining rigorous quality control at every stage, we deliver consistent quality and peace of mind for every project, no matter the complexity or application.

Choosing the right PCB assembly method—SMT, through-hole or mixed—depends on your application. SMT is the norm in modern electronics due to size, speed and cost advantages. But through-hole still has its place where strength and reliability is non-negotiable.

Understanding the difference between SMD and through-hole connectors also helps your product perform in real world conditions. Whether you’re building a high-frequency comms device or a rugged industrial controller, match your PCB assembly method to your product requirements.

​At Sterling Technologies Inc., we specialize in custom PCB assembly solutions that balance speed, precision and durability. Contact us to see how we can help bring your next project to life with the right technology and expertise.