Through Hole and Surface Mount Soldering Techniques

What are the distinctions between through-hole and surface-mount soldering techniques?

Through-hole technology (THT) and surface mount technology (SMT) are both employed in conjunction with printed circuit boards (PCBs). Despite this commonality, significant distinctions exist between these two mounting techniques, along with clear rationales for preferring one over the other depending on specific application requirements.

Through Hole vs Surface Mount

We shall begin by examining the through-hole method. Just like the name suggests, the component leads are placed through pre-drilled holes on the PCB and then soldered to secure the component in place. On large scale productions using through hole components, wave soldering is used. This is when the circuit board moves through a solder wave tank, resulting in the application of molten solder to the component pins. A strong bond is created when running the leads through the board, resulting in a component that’s able to withstand harsh mechanical and environmental stress or high heat.

A THT component is easy to change out for testing and prototyping applications that require manual adjustments. Through hole soldering can be done manually or using automated processes, making it suitable for both small-scale and large-scale production.

Now, let’s examine the surface mount method. The surface mount method allows one or thousands of tiny electrical components to attach to their copper contact pads, after which the entire assembly is subjected to a controlled heat.

Solder paste is placed on the circuit board and then the components are added directly onto the PCB. The whole circuit board is then heated up to allow the flux paste to liquify and then solidify to form a bond with the contact pad and components. This method of soldering is known as reflow soldering.

No pre-drilled holes are required, the SMT components are typically smaller and can be mounted from both sides of the board.

Why Use Through Hole vs Surface Mount?

Through-hole mounting, while generally more expensive and time-consuming due to the necessity of pre-drilling holes, offers superior reliability and durability for applications subjected to mechanical movement and elevated temperatures. Through hole mounting switches can be placed on both sides of the board in low density.

Through hole soldering is an older technology and is commonly used for components like connectors, switches and some larger components. It requires more PCB space due to the holes and leads, which may limit the design flexibility.

SMT components can be placed up to 10 times faster than THT, so it’s seen as more economical. Paste and switches are quickly placed on the board and moved through the oven and conveyor track, and SMT switches can be placed on both sides of the PCB in higher density.

Surface mount technology is highly suitable for automated manufacturing, allowing for high-speed and high-volume production. SMT components are smaller, which enables miniaturization of electronic devices and greater design flexibility while also having improved thermal characteristics, allowing for better heat dissipation and the ability to operate at higher frequencies.

The selection between through-hole and surface-mount soldering methodologies hinges on a multitude of factors, including the nature of the components utilized, production scale, design specifications, and economic considerations. Although through-hole soldering remains pertinent for specific applications, surface-mount technology has emerged as the predominant choice in contemporary electronics manufacturing, owing to its compact form factor, superior automation capabilities, and cost efficiency in large-scale production environments.

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