SMT PCBA process quality management | SunzonTech

2021-04-02

The PCBA processing process involves a series of processes such as PCB board manufacturing, PCB incoming component procurement and inspection, SMT processing, DIP plug-in processing, post-welding processing, program loading, PCBA testing, aging, etc.  Supply chain and manufacturing chain are long, and any defect in any link will cause the quality of PCBA finished product to fail in large quantities, causing serious consequences. Therefore, the quality management of the entire pcba processing process is particularly important.
1. PCB circuit board manufacturing
It is particularly important to hold a pre-production meeting after receiving an order for PCBA processing, mainly for process analysis of PCB drawings and documents, and submitting a manufacturability report (DFM) according to different customer needs. Many small manufacturers do not pay attention to this. As a result, it is not only prone to poor quality problems caused by poor PCB design, but also a large amount of rework and repair work.
2. PCBA incoming components procurement and inspection
It is necessary to strictly control the procurement channels of components, and must obtain goods from large traders and original factories, so as to avoid the use of used materials and counterfeit materials. In addition, it is necessary to set up a special PCBA incoming material inspection post to strictly inspect the following items to ensure that the components are free of faults.
①PCB: Check the temperature test of the reflow oven, whether the vias without flying wires are blocked or leaking, whether the board surface is bent, etc.
②IC: Check whether the screen printing is completely consistent with the BOM, and store it at constant temperature and humidity.
③Other commonly used materials: check screen printing, appearance, power measurement, etc.
3. SMT mounting process
Solder paste printing and reflow oven temperature control are the key points of SMT assembly. Laser stencils with higher quality requirements and better processing requirements are required. According to the requirements of the PCB board, some steel mesh holes or U-shaped holes need to be added or reduced, and the steel mesh can be made according to the 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 PCBA, 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 process of plug-in processing, the details of the mold design for wave soldering are the key. How to use the mold carrier to greatly improve the yield rate is a process experience that PE engineers must continue to practice and summarize.
5. Program loading
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 continuity of the PCBA circuit after all the components of the PCB are soldered. If there are conditions, you can ask the customer to provide a program, burn the program into the main control IC through the machine, and test various touch actions more intuitively, so as to verify the integrity of the entire PCBA function.
6. PCBA board test
For orders with PCBA test requirements, the main test content includes ICT (circuit test), FCT (function test), aging test, temperature and humidity test, drop test, etc.
In fact, the knowledge of PCBA processing and PCBA incoming materials is far more than that, and each of the above points can be elaborated in a long space. This article only elaborates on the key points of quality control of PCBA custom processing from a macro perspective, hoping to be helpful to practitioners.

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