PCB Technical - SMT process and assembly method of its components

How do the mobile phones, computers, refrigerators, washing machines and other electronic products that people use every day come from? In fact, these electronic products need to be processed and assembled by SMT, so what does smt mean? What is the SMT production process and the assembly method of its components?

1. What does SMT mean?

Most of the high-tech control systems we use are almost produced by SMT equipment. The biggest advantage is that each of its parts has a very high wiring density per unit area, and the connection lines are shortened, thereby improving electrical performance . If the error-proof material control system is combined with the software of the intelligent maker, it will be twice the result with half the effort. Next, the editor of

SMT (Surface Mount Technology) is an electronic mounting technology that uses professional automatic assembly equipment to directly attach and solder surface mounted components to the surface of the circuit board. It is currently the most popular technology and process in the electronics assembly industry. .

2. SMT production process

01 Programmable placement machine

According to the sample BOM placement location map provided by the customer, proceed to program the coordinates of the placement components. Then the first piece is matched with the SMT patch processing data provided by the customer.

02 Printing solder paste

The solder paste is printed on the pads of the PCB board with a stencil to prepare for the soldering of the components. The equipment used is a screen printing machine (printing machine), located at the forefront of the SMT patch processing production line.

03 SPI

Solder Paste Detector, to detect whether the solder paste printing is good, whether there is any bad phenomenon such as little tin, leaking tin, excessive tin and so on.

04 Patch

The electronic components SMD are accurately installed on the fixed position of the PCB. The equipment used is a placement machine, located behind the screen printing machine in the SMT production line. Mounting machines are divided into high-speed machines and general-purpose machines.

High-speed machine: used to paste components with large and small lead spacing.

General purpose machine: small-pin pitch (pin dense), large-volume components.

05 High temperature solder paste melting

is mainly to melt the solder paste at high temperature, and after cooling, make the electronic component SMD and PCB board firmly welded together. The equipment used is a reflow oven, which is located behind the placement machine in the SMT production line.

06 Cleaning

Its function is to remove the solder residues such as flux that are harmful to the human body on the assembled PCB board. The equipment used is a washing machine, and the location may not be fixed, it may be online or offline.

07 AOI

Automatic optical detector, to detect whether the welded components have poor welding, such as tombstone, displacement, empty welding, etc.

08 Visual inspection

The key items of manual inspection: whether the PCBA version is the changed version; whether the customer requires components to use substitute materials or components of designated brands and brands; IC, diodes, transistors, tantalum capacitors, aluminum capacitors, switches, etc. Whether the direction of the directional components is correct; Defects after welding: short circuit, open circuit, fake part, fake welding.

09 Rework

Its role is to rework the PCB board that has failed to detect. The tools used are soldering irons, rework stations, etc. Configured at any position in the production line.

10 Pack

The qualified products will be packaged separately. The generally used packaging materials are anti-static bubble bags, electrostatic cotton, and blister trays. There are two main packaging methods. One is to use anti-static bubble bags or electrostatic cotton into rolls and separate packaging, which is currently the most commonly used packaging method; the other is to customize the blister tray according to the size of PCBA. Place the package in a blister tray, mainly for PCBA boards that are sensitive to needles and have vulnerable SMD components.

Patching is the core technology in the SMT manufacturing process. The speed of patching is often the bottleneck restricting production efficiency. The daily production capacity depends largely on the speed of patching. The placement machine is also the most expensive equipment in the entire production line. The quality of the placement machine is usually the standard to measure the quality of the production line.