What difference between SMT (Surface Mount Technology) and SMD (Surface Mount Device)?

What difference between SMT (Surface Mount Technology) and SMD (Surface Mount Device)?

What are SMT and SMD? The difference between SMT and SMD is that SMD (Surface Mount Device) refers to an electronic component mounted on a PCB using SMT (Surface Mount Technology).

What do we mean by “SMT (Surface Mount Technology)” or “SMD (Surface Mount Device)” for the electronic manufacturing services industry? Workingbear never really thought about this question before, but since someone asked, it means there are still people out there who don’t know. So, let’s take a moment to talk about them. If you’re already familiar with this industry, feel free to skip this article.

Before we delve into the concept of SMT, let’s clarify the difference between SMD and SMT. Sometimes you might hear people use SMT, and other times they might refer to SMD. These terms are sometimes used interchangeably, but there are some basic distinctions:

  • SMD: Surface Mount Device       
    So this term represents components that can be used with SMT process or technology.

  • SMT: Surface Mount Technology       
    So this term refers to a technique of soldering electronic components onto the surface of a printed circuit board.

使用SMT製程的SMD零件We can use driving as an analogy. The car is a complete product, and it consists of various components such as tires, doors, and so on. These car components are equivalent to devices. On the other hand, driving is a skill, so when we say someone knows how to drive, it means they have the skill or technology of driving. Skills or technologies usually require learning and extensive practice to become proficient.

Alright, let’s talk about what SMT (Surface Mount Technology) means. Simply put, it’s a technique used to solder electronic components onto the surface of a Printed Circuit Board (PCB). It’s different from the through hole devices that used older process called “wave soldering”, which involved soldering components with pins that went through the board. Surface Mount Technology (SMT) has revolutionized electronic manufacturing by making devices smaller, lighter, and more compact. Think of it this way: through-hole devices were like old bulky vacuum tube TVs, while SMD is comparable to sleek LCD TVs.

In the past, electronic components could only be soldered using through-hole technology (THT) with larger pins. This meant the components had to be designed with extra pins to go through the PCB. However, these larger pins had size limitations and were prone to breakage if mishandled. Through-hole components were considered small if they reached a size of 5mm x 5mm. Nowadays, SMD (Surface Mount Device) components have taken miniaturization to a whole new level. The smallest SMD components, like the 01005 size (0.4mm x 0.2mm), are even smaller. This explains why early mobile phones, like the famous “brick” phones, were big and could only make calls. In contrast, today’s smartphones are incredibly compact, offering a wide range of features.

How does SMT (Surface Mount Technology) actually solder electronic components onto PCBs? The answer lies in solder paste. Solder paste is applied to the solder pads on the components, and then the components are placed on top. The terminals of the components should align with the solder paste. Next, the assembly goes through a reflow oven where the temperature is carefully controlled. The oven heats the solder paste to a temperature higher than its melting point but not so high as to damage the components. As a result, the solder paste melts and becomes liquid, enveloping the component leads. As the temperature cools, the solder paste solidifies, firmly soldering the components onto the PCB.

To visualize the process, think of it like painting with a stencil. Instead of paint, solder paste is applied to specific areas on the PCB. For more detailed guidance on printing solder paste, you can refer to the article of How to print solder paste on PC Board and screen printing notices?

What are the advantages and benefits of using Surface Mount Technology (SMT) in electronic products?

  • Smaller and more compact designs: SMT allows electronic products to be designed in a smaller and more streamlined form. The components used in SMT are smaller, resulting in reduced space requirements on the circuit board compared to traditional through-hole components.

  • Expanded possibilities: The small and thin nature of SMT components opens up opportunities for high-end products. They can be applied in various fields, such as miniature robots, faster CPUs, and portable electronic devices, offering enhanced performance and functionality.

  • Ideal for mass production: SMT eliminates much of the manual labor involved in component assembly. Instead, machines are used for precise placement, making it highly suitable for large-scale production. The process is more stable compared to through-hole components, ensuring consistent quality.

  • Cost-effective production: SMT reduces production costs by minimizing labor and time requirements. While through-hole components rely on manual placement, SMT utilizes automated machinery for efficient and accurate component mounting.

In addition to the solder paste printing machine, pick and placement machine, and reflow oven, a complete SMT production line also includes various inspection equipment to ensure high production yield. For a detailed understanding of the SMT process steps and important considerations, you can refer to the article “Introduction to SMT Surface Mounting: Processes and Precautions.”

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