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 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.