How is a circuit board assembly made step by step?

 Abstract: Circuit board assembly refers to the process of mounting, inserting and soldering bare PCB components. The production process of PCB Assembly board needs to go through a series of processes to complete the production. This article will introduce the various processes of circuit board assembly production by Kingford.

The PCBA production process can be divided into several major processes, SMT soldering processing → DIP plug-in processing → circuit board assembly testing → finished product assembly → Quality control inspection.

Table of Contents

1. SMT soldering processing

2. DIP plug-in processing

3. Circuit board assembly testing

4. Finished product assembly

5. Quality control inspection

 

1. SMT soldering processing

The process of SMT patch processing is: solder paste mixing → solder paste printing → SPI → placement → reflow soldering → AOI → rework

1) Solder paste mixing

After the solder paste is taken out of the refrigerator and thawed, it is stirred by hand or machine to suit printing and soldering.

2) Solder paste printing

Place the solder paste on the stencil, and use a squeegee to print the solder paste onto the PCB pads.

3) SPI

SPI is the solder paste thickness detector, which can detect the printing of solder paste and control the effect of solder paste printing.

4) Placement

SMD components are placed on the feeder, and the placement machine head accurately mounts the components on the feeder on the PCB pads through identification.

5) Reflow soldering

The mounted PCB board is subjected to reflow soldering, and through the high temperature inside, the paste-like solder paste is heated to become liquid, and finally, it is cooled and solidified to complete the soldering.

6) AOI

AOI is an automatic optical inspection, which can detect the welding effect of PCB board through scanning, and can detect the defects of the board.

7) Repair

Repair the defects detected by AOI or manually.

 

2. DIP plug-in processing

The process of DIP plug-in processing is: plug-in→wave soldering→cutting feet→post-welding processing→washing board→quality inspection

1) Plug-in

Process the pins of the plug-in materials and insert them on the PCB board

2) Wave soldering

Pass the inserted board through wave soldering. In this process, liquid tin will be sprayed onto the PCB board, and finally it will be cooled to complete the soldering.

3) Cut feet

The pins of the soldered board are too long and need to be trimmed.

4) Post welding processing

Use an electric soldering iron to manually solder the components.

5) Wash the plate

After wave soldering, the board will be dirty, so it needs to be cleaned with washing water and washing tank or washing with a machine.

6) Quality inspection

The PCB board is inspected, the unqualified products need to be repaired, and the qualified products can enter the next process.

 

3. Circuit board assembly testing

Circuit board assembly test can be divided into ICT test, FCT test, aging test, vibration test, etc.

PCB Assembly board test is a big test. According to different products and different customer requirements, the test methods used are different. The ICT test is to detect the welding of components and the on-off conditions of the circuit, while the FCT test is to detect the input and output parameters of the PCB Assembly board to see if it meets the requirements.

 

4. Finished product assembly

The PCB Assembly board with the test OK is assembled on the shell, and then tested, and finally, it can be shipped.

Circuit board assembly production is one link after another. Any problem in any link will have a very large impact on the overall quality, and strict control of each process is required.

 

5. Quality control inspection

The circuit board assembly processing process involves a series of processes such as PCB board manufacturing, PCB incoming components procurement and inspection, SMT chip processing, plug-in processing, program firing, testing, aging, etc. The supply chain and manufacturing chain are long, and any link The defects of the PCB Assembly board will cause the mass quality of the PCBA board to fail and cause serious consequences. For such a situation, the quality control of PCBA patch processing is a very important quality guarantee in electronic processing, so what is the main quality control of PCBA processing?

1) PCB circuit board

It is particularly important to hold a pre-production meeting after receiving an order for PCBA processing. It is mainly to analyze the process of PCB Gerber files and submit a manufacturability report (DFM) according to different customer needs. Many small manufacturers do not pay attention to this, but tend to prefer Here. Not only is it prone to poor quality problems caused by poor PCB design, but also a lot of rework and repair work.

2) Purchase and inspection of circuit board assembly incoming components

It is necessary to strictly control the procurement channels of components and must obtain goods from large traders and original manufacturers, so as to avoid the use of second-hand materials and counterfeit materials. In addition, it is necessary to set up a special PCB Assembly board incoming material inspection post to strictly inspect the following items to ensure that the components are fault-free.

PCB: Check the temperature test of the reflow oven, whether the fly-line vias are blocked or leaking, whether the board surface is bent, etc.

IC: Check whether the screen printing is exactly the same as the BOM, and store it at constant temperature and humidity.

Other commonly used materials: check screen printing, appearance, power measurement, etc.

3) SMT assembly

Solder paste printing and reflow oven temperature control system are the key points of assembly, and laser stencils with higher quality requirements and better processing requirements are required. According to the requirements of PCB, some steel mesh holes or U-shaped holes need to be added or reduced, and steel mesh can be made according to process requirements. Among them, the temperature control of the reflow oven is very important for the wetting of the solder paste and the firmness of the steel mesh and can be adjusted according to the normal SOP operation guide.

In addition, strict implementation of the AOI test can greatly reduce the defects caused by human factors.

4) Plug-in processing

In the plug-in process, the mold design for wave soldering is the key. How to use the mold to maximize the yield rate is a process that PE engineers must continue to practice and summarize.

5) Program firing

In the previous DFM report, customers can be advised to set up some test points on the PCB (test points) in order to test the circuit continuity of the circuit in the PCBA processing after all the components of the PCB are soldered. If possible, you can ask the customer to provide the program and burn the program into the main control IC through the burner, which can test various touch actions more intuitively, so as to verify the integrity of the entire PCB Assembly board function.

6) PCBA processing board test

For orders with circuit board assembly test requirements, the main test content includes ICT (circuit test), FCT (functional test), burn test (aging test), temperature and humidity test, drop test, etc.