PCB Technical - PCBA process flow chart and production steps

PCBA is a finished module processed by PCB through SMT and DIP procedures. The PCBA processing process mainly involves two aspects of SMT surface assembly and DIP packaging. Different surface assembly components have different specifications, so there will be different process requirements in inserting and assembly. Typical PCBA surface assembly processing methods include full surface assembly, single-sided mixed assembly, double-sided mixed assembly, etc. Common component assembly.

Full surface assembly process

The pcb assembly of all surface mount components is called full surface assembly, and the assembly of both plug-in components and surface mount components is called hybrid assembly (mixed assembly).

Full-surface assembly means that both sides of the PCB are all surface-mounted components (SMC/SMD),and there are two forms of single sided surface assembly and double-sided surface assembly. Single-sided surface assembly adopts single panel, and double-sided surface assembly adopts double panel.

Usually there are the following two different processes

1. Print solder paste on side B - mount components - reflow soldering - flip PCB - print solder paste on side A - mount components - reflow soldering

2. Print solder paste on side A - mount components - drying (curing) - reflow soldering on side A - (cleaning) - flip the PCB - print solder paste on side B (point patch glue) - mount components - bake Dry - reflow

Single-sided mixed packaging process

Single-sided mixed packaging means that there are both SMC/SMD and through-hole plug-in components (THC) on the PCB. THC is on the main side, while SMC/SMD can be on the main side. Also available in format.

1. SMC/SMD and THC are on the same side

Printing solder paste - patch - reflow soldering - plug-in - wave soldering

Printing solder paste - patch - reflow soldering - plug-in - wave soldering

Double-sided mixed installation means that both sides have SMC/SMD, and THC is on the main side, or there may be THC on both sides.

1.THC has SMC/SMD on side A and side A and B

Print solder paste on the A side of the PCB - patch - reflow soldering - flip board - apply patch glue on the B side of the PCB - patch - fixed phone - flip board - A side plug-in - B side wave soldering

2.Both sides A and B have SMC/SMD and THC

Print solder paste on the A side of the PCB - patch - reflow soldering - flip board - apply patch glue on the B side of the PCB - patch - fixed phone - flip board - A side plug-in - B side wave soldering - B side plug-in - wave weld

Factors to be considered in the PCBA processing process

The selection process is mainly based on the assembly density of PCBA components and the equipment conditions of the SMT production line. When the SMT production line has two soldering equipment, reflow soldering and wave soldering, you can refer to it.

Try to use reflow soldering, because compared with wave soldering, reflow soldering has the following advantages

1.Reflow soldering does not require the components to be directly immersed in the molten solder, and the thermal shock is relatively high.

2.Only need to apply solder on the pad, the user can control the amount of solder, reduce the generation of soldering defects such as false soldering and bridging, and have high reliability.

3.There is a self-positioning effect. When the component placement position is deviated to a certain extent, due to the surface tension of the molten solder, when all the solder ends or pins and the corresponding pads are wetted at the same time, it can play a role in the surface tension. Is automatically pulled back to the approximate target position.

4.Generally, no impurities are mixed into the solder. When using solder paste, the composition of the solder can be accurately ensured.

5.Local heating heat source can be used, so that different welding processes can be used for welding on the same substrate.

6.The process is simple, the workload of repairing the board is small, and it saves manpower, electricity and materials.

Under the mixed assembly conditions of general density, when the SMC/SMD and THC are on the same side of the PCB, the solder paste is printed on the A side, reflow soldering, and the wave soldering process on the B side is used. When THC is on the A side of the PCB and the SMC/SMD is on the B side of the PCB, the B side glue and wave soldering process is adopted.

In high-density hybrid assembly, when there is no THC or only a very small amount of THC, double-sided printing solder paste and reflow soldering process can be used, and a small amount of THC can be used with the attached method. When there are more THC on the A side, the PCBA processing sequence of printing solder paste on the A side, reflow soldering, and dispensing on the B side, fixed telephone, and wave soldering is adopted.

Complexity of the PCBA process

High technical threshold: the execution of PCBA process depends on professional equipment and high-level technical personnel. For example, the mounter needs to be equipped with a high-precision positioning system and a stable transmission system to ensure the accurate placement of components; the soldering process needs to accurately control the soldering temperature and time and other parameters, so as to avoid soldering defects or component damage.

Process management is difficult: As the PCBA process contains multiple steps, each step may affect the quality of the final product. Therefore, effective process management is the core to ensure product quality. This includes quality control of raw materials, maintenance of production equipment and continuous optimisation of the production process.

Quality inspection and traceability is crucial: in the production process of PCBA, quality inspection is a necessary part to ensure product quality. At the same time, for products with quality problems, it is equally important to carry out quality traceability to find out the root cause of the problem and take corresponding improvement measures. In order to do so, it is necessary to establish a complete quality management system and the corresponding technical means.

For the complexity of the PCBA process, we can take the following strategies:

Enhance the ability of technical personnel: to create a deep professional knowledge and rich practical experience of the technical team is to ensure that the PCBA process is the key to the smooth running of the key. Technicians should be proficient in all kinds of equipment and technical means, and have the ability to solve complex problems.

Introduction of advanced equipment and technology: the use of advanced equipment and technology can significantly improve production efficiency and product quality. For example, the use of high-precision mounter and welding equipment can significantly improve the placement accuracy and welding quality of components; and the application of automated testing equipment can reduce human error and improve testing efficiency.

Strengthen the process management: the establishment of a perfect process management system is to ensure the stable operation of the PCBA process basis. Process management should be carried out throughout the entire production process, from the procurement of raw materials to the delivery of the final product, all need to be strictly controlled and managed.

Build a comprehensive quality management system: quality management system is an important guarantee to ensure the quality of PCBA products. By building a comprehensive quality management system, we can carry out comprehensive monitoring and management of the production process, timely detection and resolution of problems, so as to ensure product quality and reliability.