The Ultimate Guide to SMT and PCB Assembly Techniques

PCB assembly and SMT assembly

Surface Mount Technology (short for SMT) plays a very important role in the Printed Circuit Boards (PCBs) assembly industry nowadays. These advancements have adjusted the design and production of electronic devices, coming about in more efficient, more viable, less expensive and feature-rich items. We will analyze the history, applications, process, advantages, key qualifications, and the developing area of ​​electronic assembly as we dive deeply into the complexity of PCB assembly and SMT assembly.

A Brief History of PCB, PCB assembly and SMT Assembly

Efficiency and functionality characterize the process involved in the manufacture of circuit boards for PCBs and an assembly for SMT. We can start with a look at the history of how these technologies came into existence.

The Origins of PCBs

The use of point-to-point wiring is where the concept of a printed circuit board (PCB) was first made available in the early 20th century. Labor-intensive, susceptible to errors, and limited in its circuit complexity. Here comes Paul Eisler, an Austrian engineer who invented the first authentic PCB in 1936. He created one of the forefathers of the PCB using copper foil on any non-conducting substrate for making connections.

The Rise of SMT Assembly

Electronic manufacture was previously dominated by through-hole technology before SMT assembly. Nevertheless, the need for smaller and more compact devices led to the development of SMT assembly in the 1960s. Notably, IBM created the structural multithreading (SMT) used in such electronic products. They invented a revolutionary process where they stuck tiny parts on top of PCB without holes.

Understanding PCB Assembly

PCBs with SMT assembly

PCBs with SMT assembly

PCB Components

A PCB typically comprises several essential components:

  • PCB base material: Base laminate and prepreg used in PCB production, such as fiberglass (FR-4), aluminium, ceramic, polyimide, PTFE.
  • Conductive Traces: Copper foil designs scratched onto the substrate make electrical pathways.
  • Components: Resistors, capacitors, incorporated circuits, connectors, etc. are mounted on the PCB.
  • Surface finishes: A thin layer of metal to cover the pads from oxidation before PCB assembly.
  • Solder Mask: A defensive layer that covers the conductive follows, leaving just connection points uncovered.
  • Silkscreen: Recognizing markings like part names and values for gathering and upkeep.

The PCB Assembly Process

PCB assembly involves several key steps:

  • Design: Engineers create the diagram, PCB layout (better Gerber format) and BOM list
  • Component Procurement: All necessary electronic components are sourced, such as resistors, capacitors, IC chips, connectors, etc. We also consider PCB bare board as one type of components
  • Solder Paste Printing: Print a thin layer of solder onto the surface (pads) of the PCB bare board with an SMT stencil.
  • Component Placement: SMT pick & place machine places components accurately on the PCB.
  • Reflow Soldering: The PCB enters a high-temperature oven (usually with 8-12 temperature zones), where solder paste melts, creating permanent connections.
  • Quality Control: Rigorous testing ensures proper functionality and adherence to specifications, such as AOI testing, visual inspection, functional testing., etc.
Pick and place equipment in SMT assembly

Pick and place equipment in SMT assembly

Applications of PCB Assembly

PCB assembly is ubiquitous in electronics, serving in a wide range of applications:

  • Consumer Electronics: From LED and lighting, TVs, wearable devices, and smartphones to laptops, PCBs power everyday gadgets.
  • Medical Devices: The electronic control devices used on medical equipment always need to be high quality and highly precise, so they rely on precision PCB assembly.
  • Automotive Electronics: Modern cars contain numerous PCBs for control, safety and entertainment systems.
  • Industrial Automation: PCBs drive robotics and automation devices to achieve automatic production.
  • Aerospace and defense: PCBs are a dependency that defines critical systems, such as those in aircraft and military equipment. Very high-tech PCB materials, such as polyimide, PTFE, high TG, and high-frequency materials, are used in such applications.
  • Energy and power: PCBs play an important role in energy and power electronics, especially in the new energy industry, which includes solar panels, wind electricity generators, and electronic vehicles.

Understanding SMT Assembly

  • SMT assembly boasts a different set of components compared to traditional through-hole assembly:
  • Surface-Mount Components: These smaller ones also have small, flat leads or even without leads, which can be placed directly at the surface of PCB boards.
  • Solder Paste: It is a kind of muddy solder which can be adhered to the PCB pads.
  • Stencils: Accurate application of solder paste is achieved by using precision-cut stencils as solder masks.
  • Reflow Soldering: Soldering happens through this step as it melts the solder paste to ensure strong joints. A reflow oven with 8-12 temperature zone is needed.

The SMT assembly Process

The SMT assembly process differs significantly from traditional assembly:

  • Solder paste printing: Print solder paste on the PCB pads with a stencil.
  • Component Placement: SMT components are placed by automated machines using a great accuracy pick & place machine.
  • Reflow Soldering: Then, the PCB undergoes a reflow oven, which causes meltdown of the solder paste into liquid forms of solder joints.
  • Inspection and Testing: Quality assurance is delivered by AOI, visual inspection, functional testing and others.

Advantages of SMT Assembly

SMT assembly offers many advantages:

  • Size and Weight Reduction: SMT components are smaller and lighter which suit miniature and little devices.
  • Higher Component Density: The absence of holes allows for tighter component placement, expanding circuits and functions in a small PCB.
  • Cost Effectiveness: Diminished physical work and high speed and high efficiency make SMT assembly more conservative.
  • Improved Performance: A high-accuracy pick and place machine can always place the small SMD components on the PCB pads correctly, which can greatly improve the quality compared to PTH soldering with component plug by hand.

Key Differences and Choosing the Right Method

PTH Assembly vs. SMT Assembly

  • Parts: PTH assembly used the components with leads. In contrast, SMT assembly uses just surface-mount parts. But usually, PCB assembly accommodates both through-hole and SMT parts.
  • Size and Density: SMT gathering succeeds in miniaturization and part thickness. PTH need a bigger size since PTH holes are needed.
  • Cost and Productivity: SMT assembly is often more practical and proficient for high-volume creation. PTH is usually suitable for prototypes since it can be soldered by hand.
  • Flexibility: PTH assembly is adaptable and can be done by one person.  However, SMT assembly need a pick-and-place machine, a reflow oven and experienced workers.
Wave soldering in SMT assembly

Wave soldering in SMT assembly

Choosing the Right Method

The choice between PTH assembly and SMT assembly depends on your project’s specific needs. But nowadays, both PTH and SMT assembly are used in the PCB assembly process usually.

  • PTH Assembly: Ideal for prototypes, low-volume creation, or components that need very robust usage, such as connectors that need to plug in and out frequently.
  • SMT assembly: Preferred for high-volume production, scaled-down plans, and applications where execution and space are critical.

The Future of PCB and SMT Assembly

As technology advances, so does the world of PCB assembly and SMT assembly. The future promises exciting developments:

  • Miniaturization: Smaller, more remarkable components will continue to demand SMT assembly.
  • More advanced equipment: More functions and smaller PCBs are needed, so more advanced equipment is needed to place very small components such as 01005.
  • High-level smaller materials: Advancements in materials will improve PCB execution, so components can be smaller.
  • Automation and artificial intelligence: Brilliant assembling methods will smooth out production further and increase efficiency.
  • Environmental Considerations: Sustainable practices will turn out to be progressively significant.


When it comes to electronics manufacturing, PCB and SMT assembly stand as a demonstration of human ingenuity and our tireless quest for advancement. These advances have formed the cutting edge world, empowering the making of once unbelievable products. Whether you pick PTH assembly for its adaptability or SMT assembly for its effectiveness in your PCB assembly demands, understanding their assets and applications is significant in the present high-speed electronics industry. As we look forward, what’s to come holds considerable additional thrilling prospects, and PCBs and SMT assemblies will without a doubt assume a critical part in forming it.

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