SMT Assembly Process Flow Guide

In the era of rapid development of electronic products, the design and manufacturing process of electronic products is also in rapid development. The most important technology is PCB manufacturing. smt as an important process of electronic circuit board processing, for the processing of circuit board production laid the foundation. Today in this article, we will discuss what SMT is in detail.

What is SMT?

SMT is surface mount technology, which is one of the most popular technologies and processes in the electronic assembly industry.
It is a pinless or short lead surface assembly component, mounted on the surface of the printed circuit board or other substrate surface, by reflow soldering to be soldered to the assembly of the circuit assembly technology.

Why SMT?

SMT is a surface mount technology. It is currently a popular technology and process in the electronic assembly industry, it is a pinless or short lead surface assembly component, mounted on the surface of the printed circuit board or other substrate surface, by reflow soldering or dip soldering and other methods to be welded circuit assembly technology. Chip components; at the same time, production, product batch, production automation, manufacturers to achieve high output at low cost, produce good products to meet customer demand and strengthen market competitiveness. On the other hand, the development of electronic components, the development of integrated circuits, and the diversified application of semiconductor materials have also contributed to the development of SMT.

Background of SMT

1. The pursuit of miniaturization of electronic products, the previous use of through-hole plug-in components can not be reduced . Electronic products are more complete, the use of integrated circuits without perforated components, especially large-scale, highly integrated IC, must use surface mount components – product batch, production automation, low-cost, high-yield, to obtain high-quality products to meet customer demand and strengthen the competitiveness of market needs.

2. Development of electronic components, integrated circuit (IC) development, semiconductor materials for multiple applications.

Advantages of SMT

1. The high assembly density, small size and light weight of electronic products, the volume and weight of SMD components is only about 1/10 of the traditional cartridge components. Generally, after the use of SMT, the volume of electronic products is reduced by 40% to 60%, weight reduction of 60% to 80%.

2. High reliability, high impact resistance, low solder joint defect rate.

3. Good high frequency characteristics, reducing electromagnetic and radio frequency interference.

4. Easy to realize automation, improve production efficiency, reduce costs up to 30% ~ 50%, save materials and energy, equipment, manpower, time, space, etc.

Quickly understand the SMT process.

1.Programming and adjusting the monitor

According to the sample provided by the customer BOM patch location map, the coordinates of the location of the patch components to do the program. Then with the customer provided by the SMT chip processing information for the first piece.

2. Printing solder paste

The solder paste with steel mesh leakage printing to the PCB board needs to weld electronic components SMD pads, for the welding of components to prepare. Equipment for screen printing machines (printing machines), located in the SMT chip processing line **** front.


Solder Paste Inspection Instrument, test solder paste printing is good, there is no less tin, tin leakage, more tin and other bad phenomena.


SMD electronic components will be accurately mounted to the PCB’s fixed position. The equipment used for the SMD machine is located in the SMT production line behind the screen printing machine. SMD machines are divided into high-speed machines and general-purpose machines. High-speed machines are used to paste the pin spacing, small components.

General purpose machine: paste pin spacing is small (pin density), the volume of large components.

5. High temperature solder paste melting

Mainly solder paste through high temperature melting, cooling so that the electronic components SMD and PCB board are firmly welded together, the equipment used for the reflow oven, is located in the SMT production line in the back of the SMD machine.


Automatic Optical Inspection Instrument (AOI), detects whether there is any welding defects in the components after welding, such as marking, displacement, empty welding, etc..

7.Visual Inspection

Manual inspection to check the focus of the project: whether the the PCBA version is a modified version; whether the customer requires the components to use the replacement material or brand, brand components; IC, diodes, transistors, tantalum capacitors, aluminum capacitors, switches, and other components with the correct direction; defects after the welding: short circuit, open circuit, fake parts, false soldering.


Products that have passed the test are separated and packaged. Generally used packaging materials for bubble wrap, electrostatic cotton, blister disk. There are two main methods of packaging. One is to use bubble wrap or electrostatic cotton in a roll, separated from the packaging, is currently the most commonly used packaging method; the second is in line with the PCBA custom blister disc size. Placed in the blister disk packaging, mainly for the more sensitive needle, there are fragile SMD components of the PCBA board.

what are smt components?

Surface mount components differ from leaded components in that SMT components are not designed to be routed between two points, but rather are designed to be placed on and soldered to a circuit board.

Their leads do not pass through holes in the board like traditional leaded components. Different types of components come in different package forms. Roughly speaking, package types can be classified into three groups: passive components, transistors and diodes, and integrated circuits. These three types of SMT components are shown below.

Passive SMD:There is a wide variety of packages used for passive SMDs. However, most passive SMDs are either SMT resistors or SMT capacitors, and their package sizes have been fairly standardized. Other components, including coils, crystals and other components, tend to have more individual requirements and therefore have their own packages.

Resistors and capacitors are available in a variety of package sizes. Names for these include: 1812, 1206, 0805, 0603, 0402, and 0201. These numbers refer to dimensions in hundredths of an inch. In other words, the 1206 measures 12 x six hundredths of an inch.

Larger sizes like #1812 and #1206 were the first to be used. They are not widely used now because smaller components are usually required. However, they can find use in applications where higher power levels are required or other considerations call for larger sizes.

Connection to the printed circuit board is made through metallized areas at each end of the package.

Transistors and Diodes: SMT transistors and SMT diodes are typically contained in small plastic packages. These connections are made through leads from the package that are bent to make contact with the board. These packages always use three leads. In this way, it is easy to recognize in which direction the device must move.

Integrated Circuits:There are many types of packages used for integrated circuits. The package used depends on the degree of interconnection required. Many chips like simple logic chips may require only 14 or 16 pins, while others like VLSI processors and related chips may require up to 200 or more. Given the variety of requirements, there are many different software packages available.

Wired components have always been difficult to automate because the wires need to be pre-shaped to fit the associated hole spacing, and even then they are prone to placement problems.

Today, most components on a board are placed automatically during PCB assembly. Occasionally, some may require manual intervention, but this has been decreasing. Traditionally, some connectors and possibly some other components have required placement assistance, but the level of manual placement has been declining.