SMD components are a standard choice in the modern electronic industry. As a PCB assembly manufacturer, we use many SMD parts in our SMT assembly production. So what is SMD and what is SMT? We can better understand the electronics assembly industry only when we know their definitions.
What are SMD components?
The full name of SMD is Surface Mount Devices. SMD device is a type of SMT (Surface Mount Technology) component that is directly mounted on the surface of a bare board.
You can also call SMD to be SMC (Surface Mount Component).
SMD components adopt various packaging forms, most of which have been standardized in production, this enables us to use automated machines to assemble PCB circuit boards.
SMD vs SMT
SMDs are components in electronics, while SMT is a production technology. It is easy to find their difference. SMT’s full name is Surface Mount Technology. We use SMT to assemble the SMD chips on bare boards. SMT is a new-generation PCB assembly technology.
In today’s electronics manufacturing service, SMT is a popular PCB assembly technology.
We need the following equipment for SMT assembly production:
- Solder paste printer
- Pick-and-place machine
- Reflow soldering oven
- AOI machine
- Dispensing machine, etc.
Surface assembly technology has high requirements for the production workshop environment. To make high-quality PCBA, we need a dust-free workshop. It must have constant temperature and humidity control. Workers must wear dust-free clothing, anti-static shoes, and gloves.
Two SMT processes are commonly used. They are single-sided assembly and double-sided assembly.
SMD components on the shelf
SMD vs THT
THT’s full name is through-hole technology (THT). In THT production, we insert components’ pins into drilled holes on the blank PCB. We then solder them on the other side of the circuit board. This forms reliable joints and establishes long-term connections. The PCB board distributes the THT component and solder joints on both sides. SMD and THT are distinct concepts. SMD is a surface mount electronic component, while THT is an assembly method.
Insert components into PCB (THT)
SMD Components Size
With the development of SMT technology, the industry has formed a series of standard parts that are easy to operate. All SMD parts suppliers manufacture surface mount devices according to this standard.
The standard SMD component sizes are as follows.
| COMMON PASSIVE SMD PACKAGE DETAILS | ||
| SMD PACKAGE TYPE | DIMENSIONS (MM) | DIMENSIONS (INCHES) |
| 2920 | 7.4 x 5.1 | 0.29 x 0.20 |
| 2725 | 6.9 x 6.3 | 0.27 x 0.25 |
| 2512 | 6.3 x 3.2 | 0.25 x 0.125 |
| 2010 | 5.0 x 2.5 | 0.20 x 0.10 |
| 1825 | 4.5 x 6.4 | 0.18 x 0.25 |
| 1812 | 4.6 x 3.0 | 0.18 x 0.125 |
| 1806 | 4.5 x 1.6 | 0.18 x 0.06 |
| 1210 | 3.2 x 2.5 | 0.125 x 0.10 |
| 1206 | 3.0 x 1.5 | 0.12 x 0.06 |
| 1008 | 2.5 x 2.0 | 0.10 x 0.08 |
| 0805 | 2.0 x 1.3 | 0.08 x 0.05 |
| 0603 | 1.5 x 0.8 | 0.06 x 0.03 |
| 0402 | 1.0 x 0.5 | 0.04 x 0.02 |
| 0201 | 0.6 x 0.3 | 0.02 x 0.01 |
| 01005 | 0.4 x 0.2 | 0.016 x 0.008 |
SMD Components List
There are numerous SMD types. Each type has a different packaging. Let’s introduce the SMD components we often use below.
Note: The letters in brackets represent their markings on the PCB board.
- Chip resistor(R)
Generally, the three-digit number on the surface mount resistor represents its resistance value. Its first and second digits are significant digits. Its third digit represents a multiple of 10. For example, “103” represents “10K Ω”, “472” represents “4700 Ω”, and the letter “R” represents the decimal point; R15 represents 0.15 Ω.
10K Ω Chip resistor picture
- Network Resistor (RA/RN)
Network resistors encapsulate several resistors with the same parameters together. Network resistors are generally used in digital circuits. The identification method of Network Resistors is the same as that of patch resistors.
Network Resistor picture
- Capacitor（C）
The most commonly used capacitor is MLCC (Multi-layer Ceramic Capacitors). MLCC can be divided into COG (NPO), X7R, and Y5V according to their materials. Among them, COG (NPO) is the most stable. The other two special capacitors we use are tantalum capacitors and aluminium capacitors, but it is important to distinguish the polarity of the two types.
Multi-layer ceramic capacitor picture
SMD Aluminium capacitor picture
Tantalum capacitors are relatively expensive SMD components.
Tantalum capacitor picture
Tantalum has a standard size series represented by the letters Y, A, X, B, C, and D.
| COMMON SMD TANTALUM CAPACITOR PACKAGE DETAILS | |
| SMD PACKAGE TYPE | DIMENSIONS (MM) |
| Size A | 3.2 x 1.6 x 1.6 |
| Size B | 3.5 x 2.8 x 1.9 |
| Size C | 6.0 x 3.2 x 2.2 |
| Size D | 7.3 x 4.3 x 2.4 |
| Size E | 7.3 x 4.3 x 4.1 |
Note: Tantalum capacitors with the same capacitance value but different specifications and models cannot be substituted. For example, the 10UF/16V “B” type cannot replace the 10UF/16V “C”.
The end with a horizontal line on the surface of the tantalum capacitor is the anode.
- Diode（D）
Diode is a widely used SMD component. Generally, a color ring is used to indicate the direction of the cathode on the diode body.
diode picture
- LED（LED）
LEDs are divided into ordinary LEDs and high-brightness LEDs. The colors of LED light include white, red, yellow, blue, etc. If we want to determine the polarity of an LED, we need to follow the specific LED’s datasheet.
LED picture
- Triode（Q）
The typical structures of a triode are NPN and PNP, including BJT, FET, MOSFET, etc. The most commonly used packages for SMD components are SOT-23 and SOT-223 (larger).
Triode picture
- Inductor（L）
Inductors are mainly composed of magnetic cores and copper wires. Some inductors have magnetic covers. The inductance value is usually directly printed on their body.
Inductance picture
- Transformer (T)
Transformer uses the principle of electromagnetic induction to change the AC voltage. Its main components include primary coil, secondary coil, and iron core (magnetic core). In electrical equipment and wireless circuits, transformers have functions such as voltage regulation, impedance matching, and safety isolation.
Transformer
- Crystal oscillator（X）
We mainly use crystal oscillators to generate oscillation frequencies in various circuits.
Crystal oscillator picture
- Fuse
When the current in the circuit exceeds the rated value, the fuse will melt. The fuse
can cut off the circuit and protect electronic devices from damage or prevent fires from occurring.
fuse picture
- IC(U)
The full name of IC is integrated circuit. It is the most important functional component of electronic products. IC integrate various electronic components onto semiconductor chips. We generally use the packaging form of IC to classify its types.
Here are the basic IC types:
SOP (small outline package)
SOJ (small outline J-lead package)
QFP (quad flat package)
PLCC (plastic leadless chip carrier)
BGA (ball grid array)
CSP (chip scale package)
We generally use the format of “type + number of pins” to name IC. For example, we have SOP14PIN, SOP16PIN, SOJ20PIN,QFP100PIN,PLCC44PIN, etc.
There is often a small concave dot or a small notch on the surface of the IC. They are used to indicate IC polarity. In our actual PCBA production process, the polarity of the IC must be consistent with the marking on the PCB board.
IC orientation picture
Components Package Types and Charts
Here are the electronic components package charts.
Components Package Chart (1)
Components Package Chart (2)
Components Package Chart (3)
Components Package Chart (4)
How to check the quality of SMD components?
At PCBbee, our inspection department conducts sampling inspections to check the quality of surface mount devices, including solderability, pin coplanarity, and usability. In the solder-ability testing of SMD parts, we clamp SMD components with stainless steel tweezers and immerse them in tin pots at 235 ± 5 ℃ or 230 ± 5 ℃, and remove them after 2 ± 0.2s or 3 ± 0.5s. Then we examined the solder adhesion at the solder joints under a 20x microscope, and we required SMD components to have over 90% solder adhesion at the solder joints.
As a PCB SMT assembly manufacturer, we also conduct the following visual inspections:
1. We use a magnifying glass to check whether the solder terminals or pin surfaces of the SMD chips are oxidized or contaminated.
Oxidized SMD components
2. We check whether the nominal value, specifications, model, accuracy, external dimensions, etc. of the SMT components are consistent with the product process requirements.
3. We require that the pins of SOT and SOIC cannot be deformed. We require that the pin capillarity of multi lead QFP devices with lead spacing of 0.65mm or less must be less than 0.1mm.
deformed pins of SMD component
4. For products that require cleaning, we will ensure that the markings on the surface mount devices do not fall off after cleaning and do not affect the performance and reliability of the SMD components (visual inspection after cleaning).
If you have any questions or inquires about SMD components, please feel free to send an email to service@pcbbee.com. Our electronic components engineers have 15 years experience, and we will reply to you within half a day.
