The process of PCBA contract labor and material processing involves a series of processes such as PCB circuit board manufacturing, component procurement and inspection, patch processing, plug-in processing, program firing, testing, aging, etc. The supply and manufacturing chain is relatively long. Defects will cause a large number of bad PCBA boards, with serious consequences. Therefore, it is particularly important to control the entire PCBA manufacturing process. In this paper, we focuses on the analysis from the following aspects.
1. PCB Circuit Board Manufacturing
It is particularly important to hold a pre-production meeting after receiving a PCBA order, mainly to analyze the process of the PCB Gerber file, and to submit a manufacturability report (DFM) to the customer. Many small factories do not pay attention to this, but it is often easy to produce because of PCB Quality problems caused by poor design, resulting in a lot of rework and repair work. Production is no exception, it is necessary to think twice and make advance measures. For example, when analyzing PCB files, for some small and easy-to-fail materials, be sure to avoid higher materials in terms of structural layout, so that the soldering iron tip during rework is easy to operate; the relationship between the hole spacing of the PCB and the bearing capacity of the board, do not causes bending or breaking; whether the wiring takes into account key factors such as high-frequency signal interference and impedance.
2. Component Procurement and Inspection
The procurement of components needs to strictly control the channels, and must pick up the goods from large traders and original factories, and 100% avoid second-hand materials and fake materials. In addition, a special incoming material inspection post is set up, and the following items are strictly checked to ensure that the components are fault-free.
PCB: Reflow oven temperature test, prohibition of flying leads, whether the via hole is blocked or leaking ink, whether the board surface is bent, etc.
IC: Check whether the silk screen is completely consistent with the BOM, and keep it at constant temperature and humidity.
Other common materials: Check silk screen, appearance, power-on measurement, etc.
The inspection items are carried out according to the sampling method, and the proportion is generally 1-3%
3. SMT Processing
Solder paste printing and reflow oven temperature control are key points. It is very important to use laser stencils with good quality and in line with process requirements. According to the requirements of the PCB, some parts need to increase or decrease the stencil hole, or use a U-shaped hole to make the stencil according to the process requirements. The furnace temperature and speed control of reflow soldering is very critical to the infiltration of solder paste and soldering reliability, and it can be controlled according to the normal SOP operation guidelines. In addition, AOI testing needs to be strictly implemented to minimize defects caused by human factors.
4. Plug-In Processing
In the plug-in process, the mold design for wave soldering is the key point. How to use the mold can maximize the probability of providing good products after the furnace, which is a process that PE engineers must continue to practice and experience.
5. Program Firing
In the previous DFM report, customers can be suggested to set up some test points (Test Points) on the PCB, the purpose is to test the continuity of the PCB and the PCBA circuit after all components are soldered. If possible, you can ask the customer to provide the program, and burn the program into the main control IC through the programmer (such as ST-LINK, J-LINK, etc.), so that you can more intuitively test the effects brought by various touch actions. Functional changes to verify the functional integrity of the entire PCBA.
6. PCBA Board Test
For orders with PCBA test requirements, the main test contents include ICT (In Circuit Test), FCT (Function Test), Burn In Test (aging test), temperature and humidity test, drop test, etc., which are operated according to t
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