What is the PCB assembly process?

The basic process of PCB assembly

PCBA production, i.e., PCB bare board through the component placement, plug-in, and complete the welding process. This process covers a number of procedures, including SMT placement processing, DIP insertion processing, PCBA testing, three-proof coating, and the final visual inspection and packaging shipment. Each step is critical and works together to ensure the quality and performance of the PCBA.

pcb assembly

SMT SMD Processing

1. Board Drop
This link in the beginning of the SMT production line plays a crucial role, it ensures that the PCB boards can be transferred to the production line in an orderly and efficient manner, thus guaranteeing the continuity and efficiency of production.

2. Solder Paste Printing
Solder paste printing is a key part of SMT placement processing, which involves the precise printing of solder paste onto the circuit board by manual means through the stencil of the printing machine. This step not only requires professional printing machine (such as hand printing table) and squeegee, but also requires strict control of the composition of the solder paste, printing resolution, accuracy, and thickness and uniformity of the solder paste.

3. On-machine placement
On-machine placement is the SMD components in accordance with the process diagram or BOM requirements, through the SMD machine programming or manual alignment, accurate mounting to the circuit board has been printed with good solder paste.

4.Reflow soldering
In the solder paste printing and on the machine after the patch, in order to ensure that the components can be firmly soldered on the PCB board, reflow soldering must be carried out. This link through the high-temperature heating to melt the solder paste, so that the components and PCB pads closely together, so as to complete the welding.

5.AOI Inspection
Post-oven AOI is a key link in the production line. It is through the graphic recognition method will be stored in the AOI system standard digitized image and the actual detection of the image for comparison, so as to obtain the test results. The technical points of this link include inspection standard, detection force, false detection rate, sampling position, coverage rate and blind spot. Its inspection items cover a wide range of possible problems such as missing parts, reverse, upright, broken solder, wrong parts, less tin, warped legs, continuous tin and more tin.

DIP Insert Processing

DIP insertion, also known as DIP packaging or dual-row in-line packaging technology, is a process that packages integrated circuit chips in the form of dual-row in-line insertion.

1.Manual insertion
In this link, the PCB is passed through the rotation of the chain, and the workers need to insert the molded parts and components accurately and correctly to the corresponding position of the PCB according to the work instruction (applicable to through-hole components).

2. Wave soldering
Wave soldering is a kind of molten solder with the help of the pump, in the solder tank to form a specific shape of the solder wave process. During the soldering process, the PCB with components inserted passes through the conveyor chain and passes through the solder wave at a specific angle and immersion depth, thus realizing a solid connection of the solder joints.

3. Manual foot trimming
After the wave soldering is completed, the PCB board needs to be manually clipped. This step involves manual PCB board plug-in components on the surface of the pad exposed pins, in accordance with the provisions of the operating instructions for cutting. The purpose of cutting the foot operation is to ensure that the height of the component pins in the right place, while avoiding damage to the component body and its pad.

4. Manual soldering
In the manual welding process, the need for the PCB board soldering abnormalities, such as false soldering, leakage of solder, less tin, tin, etc., to repair in a timely manner. At the same time, for the components of the insertion of abnormalities, such as skewed, floating high, fewer pieces, wrong insertion, etc., also need to be dealt with accordingly to ensure the quality of welding.

DIP Insert Processing

Test link

1.ICT test

ICT test is designed to examine the basic characteristics of components to ensure good performance. During the testing process, NG (non-conforming) and OK (qualified) products are placed separately to facilitate subsequent processing. For the test results for the OK circuit board, the corresponding ICT test labels need to be affixed, and separated from the foam, in order to facilitate the subsequent tube.

2.FCT Test

FCT test is designed to comprehensively check the functional integrity of the circuit board. In the testing process, NG (defective) and OK (qualified) strictly differentiated, and are properly placed. For circuit boards with OK test results, they need to be labeled with the appropriate FCT test labels and isolated from the foam to facilitate subsequent tracking and management. At the same time, if you need to generate a test report, you should ensure that the serial number on the report corresponds to the serial number on the PCB board. For NG products, they need to be sent to the maintenance department for repair, and do a good job of recording the defective product maintenance report.

Coating of three-proof paint

Three-proof paint, as a kind of coating with special functions, is widely used in PCBA protection. Its role is to provide comprehensive protection for electronic components, effectively resist the erosion of moisture, salt spray and corrosive substances. By spraying three-proof paint, it not only ensures that the products work stably under the harsh environment of high humidity and high salt spray, but also significantly extends their service life.

Visual inspection for packing and shipping

Before packing and shipping, manual inspection must be carried out to ensure product quality, IPC610 standard is an important basis for inspection, focusing on checking whether the direction of the components on the PCBA is correct, such as IC, diodes, transistors, tantalum capacitors, aluminum capacitors and switches and so on. At the same time, it is also necessary to carefully check the defects after welding, such as short circuit, open circuit, fake parts, false welding, etc., to ensure that the products can work stably and meet customer requirements.