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What is SMT PCB assembly?

Most of the high-tech control systems we use are almost produced by SMT equipment, such as HDI PCB. The biggest advantage is that each part has a very high wiring density per unit area and shortens the connection line. Thereby improving electrical performance.
PCBA Manufacturing's SMT (Surface Mount Technology) is an electronic junction technology that uses professional automatic assembly equipment to directly paste and solder surface-mounted electronic components to the surface of the circuit board. It is currently the most popular in the electronic assembly industry. Kind of technology and craftsmanship.
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 of the electronic 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 Electronic 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 undesirable phenomena such as small tin, leakage, and excessive tin.
　　04 Patch
　The Electronic Components SMD is 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 electronic components with large lead spacing and small electronic components.
　　 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 Components SMD and PCB board be firmly soldered 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, the location can be not fixed, it can 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 Electronic Components to use substitute materials or components of designated brands and brands; IC, Electronic Resistor and Capacitor, switches and other directional components Whether the direction is correct; defects after welding: short circuit, open circuit, fake parts, fake welding.
　　09 Rework
　　 Its function 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.
　　 SMT 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.

PCBA Manufacturing selects the appropriate assembly method according to the specific requirements of PCB assembly products and the conditions of PCB assembly equipment, which is the basis for efficient and low-cost PCB assembly production and the main content of SMT chip processing design. The so-called surface assembly technology refers to the placement of chip-shaped components or miniaturized components suitable for surface assembly on the surface of the printed circuit board according to the requirements of the circuit, using soldering processes such as reflow soldering or Wave Solder for PCBA Assemble, constitute the assembly technology of electronic components with certain functions.
On the traditional THT printed circuit board, the components and solder joints are located on both sides of the board, while on the SMT patch printed circuit board, the solder joints and components are on the same side of the board. Therefore, on the SMT patch printed circuit board, Through-Hole Assembly is only used to connect the wires on both sides of the circuit board. The number of holes is much smaller, and the diameter of the holes is much smaller, which can increase the assembly density of the circuit board. Greatly improved.
1. SMT single-sided Mixed Assembly method
The first type is single-sided Mixed Assembly, that is, SMC/SMD and through-hole plug-in components (17HC) are distributed on different sides of PCB Mixed Assembly, but its soldering surface is only single-sided. This type of assembly method uses single-sided PCB and wave soldering (currently double wave soldering is generally used), and there are two specific assembly methods.
(1) Paste first. The first assembly method is called the first-attach method, that is, the SMC/SMD is attached to the B side (welding side) of the PCB first, and then the THC is inserted on the A side.
(2) Post-sticking method. The second assembly method is called post-attachment method, which is to first insert THC on the A side of the PCB, and then mount the SMD on the B side.
2. SMT double-sided hybrid assembly method
The second type is double-sided hybrid assembly. SMC/SMD and T.HC can be mixed and distributed on the same side of the PCB. At the same time, SMC/SMD can also be distributed on both sides of the PCB. Double-sided hybrid assembly adopts double-sided PCB, double wave soldering or reflow soldering. In this type of assembly method, there is also a difference between SMC/SMD or SMC/SMD. Generally, it is reasonable to choose according to the type of SMC/SMD and the size of the PCB. Usually, the first method is more. Two assembly methods are commonly used in this type of assembly.
(1) SMC/SMD and FHC on the same side, SMC/SMD and THC are on the same side of the PCB.
(2) SMC/SMD and iFHC have different side methods, put the surface mount integrated chip (SMIC) and THC on the A side of the PCB, and put the SMC and the small outline transistor (SOT) on the B side.
In this type of assembly method, the SMC/SMD is mounted on one or both sides of the PCB, and the leaded components that are difficult to be surface-assembled are inserted into the assembly, so the assembly density is quite high.

The PCB assembly method and process flow of SMT chip processing mainly depend on the type of surface mount component (SMA), the types of components used and the conditions of assembly equipment. In general, SMA can be divided into three types: single-sided Mixed Assembly, double-sided Mixed Assembly, and full-surface assembly, a total of 6 assembly methods. Different types of SMA have different assembly methods, and the same type of SMA can also be assembled differently.

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