The electronics manufacturing industry is highly specialized. Those familiar with it often use basic abbreviations to express their needs, such as PCB (Printed Circuit Board), PCBA (Printed Circuit Board Assembly), and Through-Hole Technology (THT). This can be unfriendly to newcomers or electronics enthusiasts.

　 　What is SMT?

　　SMT stands for Surface Mount Technology, a new method for arranging components on a PCB. This technology is widely used in the PCBA industry; almost all companies that provide PCB assembly services can also provide SMT assembly services. In the early 1970s, electronics manufacturers used through-hole assembly to achieve component mounting and soldering, placing component leads into holes drilled in the bare PCB and using a soldering iron to achieve permanent through-hole component placement. However, with technological advancements, people gradually discovered that through-hole PCB assembly was not a good solution, and SMT assembly could serve as an alternative.

　　Unlike plug-in components, SMT technology uses a leadless assembly method, soldering components directly to the bare PCB. It's a faster and more economical assembly method. For some consumer electronics (mobile phones, computers, etc.), their update frequency is less than a year, meaning electronics manufacturers urgently need automated PCB assembly to achieve mass production, and SMT technology perfectly meets this requirement.

　　 SMT Assembly Process

　　Printing: The SMT equipment aligns the prepared stencil with the PCB that needs to be populated. As the squeegee spreads the stencil, solder paste is deposited onto the corresponding solder pads through the holes in the stencil.

　　Placement: SMD components are precisely positioned by a pick-and-place machine, using the solder paste as a temporary adhesive.

　　Reflow Soldering: At this stage, the solder paste is still semi-liquid and needs to be melted and solidified to form strong solder joints. Reflow soldering is commonly used in SMT processes to handle precision pin components such as BGAs and QFNs, providing precise temperature control and uniform heat distribution for highly reliable solder connections.

　　Testing and Inspection: Once the entire SMT process is complete, manufacturers perform a series of inspection methods to ensure soldering quality, including component alignment, solder bridges, and short circuits. These inspections involve manual inspection, AOI inspection, and other techniques.

　 　Characteristics of SMT

　　Reduces parasitic capacitance and inductance;

　　Reduces the number of components needed in PCBA projects;

　　New automated equipment enables fast and reliable mass production;

　　Promotes the development of miniature electronic devices or implantable devices.

　　In short, SMT is an assembly technology that involves using the right amount of solder paste to mount each component. It is also suitable for automation because machines can be programmed to mount components onto the PCB. This ensures accuracy and also speeds up the production process and accelerates delivery.

　　 What is SMD?

　　It is essential to understand how a PCB works. It consists of two main elements: the bare board and the components. The bare board is the platform where components are mounted and electrical pathways are established. When powered, current flows through the circuit and reaches the components, enabling their function. Therefore, the components themselves make a positive contribution to the functionality of the PCBA board. SMD represents a specific type of component.

　　SMD, or Surface Mount Device, is an electronic component soldered onto a printed circuit board, designed for direct mounting on the PCB. Currently, there are various ways to mount PCB components. Depending on the mounting method, PCB components can be divided into several types, including DIP components and SMD components, i.e., through-hole components and surface mount components. Influenced by the trend of miniaturization, SMD components are increasingly used in PCBA production today.

　　 Types of SMD Components

　　Surface mount components have gone from their inception to widespread popularity in just 20 years, now dominating the component field. Tracing the history of component development, the components in consumer electronic devices have evolved from passive components to active components and integrated circuits, finally leading to the dominance of SMDs today. Surface mount devices can be broadly classified into two categories: transistors and integrated circuits (SOP, SOJ, PLCC, LCCC, QFP, BGA, CSP, FC, MCM). Several common SMD components are categorized below.

　　 Resistors

　　These surface mount resistors are usually surface mounted using SMT technology, requiring special attention during mounting. Taking surface mount resistors on ceramic PCBs as an example, when mounting on ceramic PCBs, to prevent metal material overflow during soldering, a layer of glass passivation film needs to be applied to the surface.

　　 Ceramic Capacitors

　　Applications such as engine engines, military communication equipment, and aerospace equipment heavily rely on high-frequency circuits, so we need to use SMD mounting technology to mount SMD ceramic capacitors.

　　 Transistors (SOT)

　　Three-lead and four-lead SOT devices are considered among the pioneers of surface-mount active devices. Three-lead SOTs are identified as SOT 23 (EIA TO 236) and SOT 89 (EIA TO 243). Four-lead devices are called SOT 143 (EIA TO 253).

　　 Integrated Circuits

　　Integrated circuits, also known as IC chips, are collections of components such as resistors, capacitors, and transistors. Engineers integrate a "small PCB" with specific functions through IC programming and semiconductor processing. Commonly seen small-form-factor SMD active integrated circuits in daily life generally use shrink packaging. Small-form-factor ICs have lead centers of approximately 0.050 inches and are mainly used to accommodate larger ICs than SOT packages.

　　 SMD vs. SMT

　　 Differences

　　Conceptual Differences: SMT refers to a specific type of assembly technology, often associated with terms like assembly, soldering, and process. On the other hand, SMD represents an electronic component, commonly used with words like component and part.

　　Usage Differences: SMT processes are specifically designed for SMD components and cannot accommodate through-hole components. In contrast, SMD components can be mounted on circuit boards using various soldering processes, depending on their attributes and characteristics. These processes include manual soldering, hot air reflow, hot plate heating, and wave soldering.

　　Purpose Differences: The primary goal of SMT technology is to achieve automated and precise installation, leading to efficient production. The use of SMD electronic components primarily aims for miniaturization and high-density integration of electronic systems.

　　Although SMD and SMT represent different concepts, they complement each other in the field of electronics manufacturing. Considering the history of PCBA development, the decline of DIP components can be partly attributed to the limitations of manual soldering, which prompted the emergence of surface mount machines. While manual soldering was previously used for traditional SMD component assembly, the advent of surface mount machines rendered this method obsolete. In today's era, simplicity, efficiency, and cost-effectiveness are key factors for progress, and the integration of SMT and SMD precisely meets these requirements.

　　Automated production methods aim to optimize PCB assembly costs, and SMD provides a cost-effective solution in this regard.

　　SMT equipment can quickly install thousands of SMD components on a circuit board in a short time.

　　SMD components are small in size, increasing circuit board capacity, and SMT technology effectively leverages this advantage.

　　SMD components utilize lead-free soldering, allowing PCBA companies to reduce the occurrence of faults during assembly and improve the overall reliability of the SMT process.