Which, between through-hole vs. SMT assembly technologies, offers more benefits? Also, when is it best to use each? We compared the two PCBA manufacturing methods on various fronts, from joint reliability needs to production costs.
What is Through-Hole Technology?
Through-hole technology (THT) is a PCB assembly method that involves inserting component leads into holes drilled on the board. The leads are then soldered on the opposite side.
Soldering is either automated, using a process called wave soldering, or manual. It creates robust joints and has been used widely to mount large components with higher anchoring requirements.
Through-hole components include large electrolytic capacitors, some resistors, and diodes. There are also mechanical types, such as relays, transformers, inductors, connectors, heat sinks, and housings.
What is SMT Technology?
Surface mount technology (SMT) is where you mount components directly on the PCB’s surface. It usually begins with attaching the part to the board using solder paste, a sticky material containing solder and flux.
The PCB with the mounted components then goes to a reflow oven, where controlled heat melts the solder in the paste. A cooling stage hardens the solder, bonding the component pins to the PCB.
Surface-mount components are wide and varied. Most are integrated circuits (ICs) and chip-based resistors, capacitors, and diodes. There are also SMT inductors, LEDs, and RF components.
Through Hole vs. SMT
A PCB’s assembly method influences its application suitability, cost, and various other outcomes. The decision whether to use THT or SMT, therefore, depends on your specific requirements. Here’s their quick comparison.
Component Mounting
The main difference between SMT and THT is how components attach to the board. Surface-mount devices require no holes; only solder pads. It facilitates high-speed automation, making it ideal for large-scale manufacturing.
THT components need holes. The drilled holes go through the board, emerging on the other side of the board where the pads are located. The process limits automation, especially if the components are bulky or multi-leaded.
Component Size and Weight
SMT mainly mounts small, lightweight, and low-profile components. They allow you to reduce a PCB’s overall weight and size. This benefit is critical in most modern electronics, from handheld devices to spacecraft systems.
Through-hole devices are typically leaded, tall, and heavy. The method anchors them more robustly to the board, preventing damage from mechanical shock. It also improves heat dissipation to avoid thermal damage.
Space and Routing
SMT components take up little space, saving a PCB’s real estate. This benefit makes them suitable for high component density boards. The lack of mounting holes also frees up the available routing space in the layers.
Through-hole components require more area, being large and long-leaded. Their leads traverse the layers, disrupting routing and creating placement challenges. It affects their suitability for miniaturized boards.
Mechanical Strength
Surface mount technology attaches components to the surface. These are more likely to peel, especially if the component experiences repeated tugging.
Larger SMT parts often require reinforcement to withstand stress. The reinforcement usually comes in the form of adhesive plastics, such as epoxy.
Sometimes, the parts have the bonding material applied to the corners. It reinforces them while also preventing unnecessary weight increase.
THT components produce joints that withstand mechanical stress better. They are more suitable for specific components, such as connectors.
Assembly Speed
SMT is an automation-friendly PCB assembly method. It requires no holes to assemble components, which makes it faster by eliminating drilling steps. It also allows automation, further reducing the assembly time.
Through-hole assembly is slower, given that it includes a drilling stage. It also has various manual steps, especially when the leaded parts are too large or complex. These often require manual finishing for accuracy.
Cost Difference
SMT reduces assembly costs through automation. However, this is only true if you assemble the boards in volumes. That’s because it requires expensive preparations, such as manufacturing custom stencils for solder paste.
Through-hole technology increases the cost of the bare board due to the drilling required, but is cheaper for assembly in low volumes , such as when prototyping.
In such cases, the low tooling costs reduce the amount of money spent assembling the boards, including making adjustments.
Resource: https://www.youtube.com/watch?v=y0Qk8nNxyXY
Through-Hole or SMT – The Verdict
The short answer is it depends. While SMT excels in most cases, THT still has its place. Some situations call for surface-mount components, while some require through-hole types for robust joints and reliability.
The component or mounting method to use depends on various factors, such as usage environments and production volumes. Below, we share cases where a specific assembly method would apply.
When to Use Surface-Mount Assembly
Most electronics today use SMT, thanks to its automation and cost-saving benefits. These include high-reliability applications, such as military and aerospace.
In these applications, the components must withstand application stresses, such as acceleration and collisions. They are, therefore, usually bonded to the board using underfill or a polymer-based adhesive.
Surface mount assembly is also the method to use when manufacturing high-density boards. It saves space, enabling the mounting of close circuits and micro-components.
When to Use Through-Hole Assembly
One advantage of through-hole technology is in applications with extreme heat levels and temperature fluctuations. Through-hole technology is preferred for high-power applications. Large power components (like transformers and power resistors) that generate significant heat often require the mechanical stability and air-flow spacing that THT provides.
Another scenario where THT outshines SMT is when attaching components that experience constant mechanical stress, such as connectors. The technology makes them withstand the stress better than SMT.
Some components are also available as through-hole types, necessitating their mounting with the assembly method. Other application areas include one-off boards or prototypes, where it reduces costs.
Conclusion
A PCB has two assembly technologies, through-hole (THT) and surface-mount (SMT). Each method has its advantages and disadvantages. These variations define PCBA production choices. SMT has a higher initial cost, but expenses are low in high production runs. THT, on the other hand, is cheaper for low volumes.
