A 2024 Ultimate Guide of SMD Electronic Components

Block-like electronic components are mounted on the surface of an assembled printed circuit board (PCB).

These electronic components are Surface Mount Devices (SMDs). In this blog, we will learn about SMD electronic components, SMD sizes, some common SMD components, the SMT process, and the value they provide.

What are SMD Electronic Components

Surface mount devices or SMDs are the electronic components that are directly placed and soldered on the surface of the PCBs.

The SMDs have smaller sizes than through-hole devices, whereas the through-hole devices take more space on the PCB, resulting in higher costs.

The following table compares the SMD electronic components and through-hole devices.

SMD components vs. through-hole components

From the above table, we can see that the SMD electronic components offer many advantages over through-hole components, especially their compact sizes.

Figure: Through-hole components assembled on a PCB

Let's look at the different sizes of the SMDs.

SMD Electronic Component Sizes

The SMD components come in various sizes, and they use the numeric coding system (like 01005,0402, etc.) to indicate their physical dimension. The format for these codes is:

LLWW

LL = the length of the component in hundredths of an inch

WW = the width of the component in hundredths of an inch

For example, 01005 can break down into:

Length = 01 x 0.01 = 0.01 inches

Width = 005 means 0.5 x 0.01 = 0.005 inches

Similarly, 0603 can break down into:

Length = 06 x 0.01 = 0.06 inches

Width = 03 x 0.01 = 0.03 inches

The above-mentioned sizes were in the Imperial coding system. Now let's look at the common sizes (Imperial code) of the SMD and their applications.

Besides the imperial coding system for representing the sizes of SMD electronic components, there is the metric coding system. It uses millimeters instead of inches for the SMD size units.

To convert inches to millimeters, you can use the conversion equivalent:

1 inch = 25.4 millimeters

For example,

01005 represents 0.01" × 25.4 = 0.254mm length and 0.005" × 25.4 = 0.127mm width.

0201 represents 0.02" × 25.4 = 0.508mm length and 0.01" × 25.4 = 0.254 mm width.

Relationship between SMD Sizes and PCB Footprints

Each SMD size corresponds to a specific PCB footprint, which is the designated area on the PCB, where the components will be soldered.

The footprint ensures that the SMD electronic component is securely attached and properly aligned

The PCB footprint for an SMD component includes the pads where soldering occurs, and it is designed to match the component's dimensions.

For instance, a 0603 SMD size will have a footprint with pads that accommodates a length (0.06" x 25.4 = 1.54mm rounded off to) 1.60 mm and a width of (0.03" in x 25.4=0.76mm rounded off to) 0.80mm.

SMD sizes are directly proportional to the PCB footprints. The smaller components such as 01005 or 0201 require smaller footprints, whereas larger components such as 1206 or 1210 require bigger PCB footprints.

To summarize the relationship, SMD sizes influence the PCB footprint, which in turn affects the overall PCB size and design. Smaller SMDs contribute to a more compact PCB, whereas larger SMDs provide easier handling and better heat dissipation.

Now let's view the common SMD components.

Common SMD Electronic Components

SMD components vary not only in size but also in type, each serving specific purposes in electronic circuits, ranging from simple signal processing to complex integration. Here is a brief overview of common SMD components and their typical use:

SMD LEDs

SMD LEDs are compact light-emitting diodes used for indicators and displays. They provide feedback in electronic devices.

SMD LEDs have different types based on the size and brightness of the LED. For example, SMD LED 352 is known for its power output of 6 to 8 lumens and a consumption of just 0.20W, offering a low light output suitable for specific applications.

They are small, rectangular, or oval-shaped packages with two or more terminals as shown in the following figure.

Figure: SMD LED and LED schematic symbol

SMD resistors

SMD resistors control the current flow in the circuits. They limit current and divide voltage. They are flat, rectangular packages with two terminals on the short sides as shown in the following image (R100 represents 100 ohms).

Figure: SMD resistors and resistor schematic symbol

SMD capacitors

SMD capacitors store and filter electrical charge. They are used for stabilizing voltages and filtering noise, ensuring smooth operation of electronic circuits.

SMD capacitors are flat, rectangular, or square packages with two terminals on short sides as shown in the following figure (270 represents 27 pF).

Figure: SMD capacitor and capacitor schematic symbol

SMD diodes

Diodes allow current to flow in one direction only and are used for protection and rectification.

SMD diodes are small and rectangular packages with two terminals as shown in the following figure.

Figure: SMD Diode and Diode schematic symbol

SMD transistors

Transistors amplify or switch electronic signals. They regulate electronic signals and power various parts of a circuit.

SMD transistors typically have three terminals and are rectangular or square as shown in the following figure.

Figure: SMD Transistor and Transistor schematic symbol

SMD ICs

Integrated circuits combine multiple functions into a single package. They control and manage the circuit as the core components.

ICs often have a large number of pins or pads for connections as shown in the below figure.

Figure: SMD Integrated Circuit (IC)

Assembly of SMD Components

To assemble the SMD components on the PCB, a process called surface mount technology (SMT) is used.

SMT assembly is fully automated and continuous. Here are the key steps involved in the SMT process.

• Solder paste printing: Solder paste is applied to the PCB's pads with an SMT stencil. The thickness, position, and size of the paste are inspected for quality control.
• Component placement: SMD electronic components are placed onto the PCB using high-speed mounters for small components and functional mounters for larger ones.
• X-ray inspection: An X-ray machine is used to detect the solder balls of the BGA.
• Reflow soldering: After placement, the PCB with SMD components is passed through a reflow oven. In this process, the solder paste is heated to melt and form solid solder joints with the copper pad.
• Automated optical inspection (AOI): 3D AOI is used to detect any surface defects of the PCBA. The AOI machine is in the SMT line.

The above process explains how the SMD electronic components are assembled on the PCB. After SMT assembly, the PCB is soldered with through-hole components on the other production line - the PTH line.

One-Stop PCBA Manufacturer PCBONLINE

Whether you want to buy SMD electronic components or electronic manufacturing and assembly, you can do it at PCBONLINE.

PCBONLINE is a one-stop PCBA manufacturer, providing advanced PCB fabrication, SMD and PTH component sourcing, PCB assembly, value-added services (IC burn-in, conformal coating...), and box-build assembly to be the final products.

To get a quote for the SMD electronic components and PCBA manufacturing for your project, don't hesitate to contact info@pcbonline.com.

Conclusion

Understanding SMD electronic components is crucial for designing and manufacturing modern electronic devices. Using the SMDs, surface mount technology (SMT) achieves compact design capabilities. For high-quality SMD PCB fabrication and assembly, work with the one-stop advanced PCBA manufacturer PCBONLINE.