6 key points of PCBA process control and quality control
PCBA manufacturing process involves a series of manufacturing processes such as PCB board manufacturing, component procurement and inspection, patch processing, plug-in processing, program firing, testing, aging, etc. The supply and manufacturing chain is relatively long, and defects in any link will cause a large number of PCBA boards to be defective, resulting in serious consequences. Therefore, it is partICularly important to control the whole PCBA manufacturing process. This paper focuses on the following aspects.
It is particularly important to hold a pre production meeting after receiving the PCBA order. It is mainly to analyze the process of PCB Gerber documents and submit a manufacturability report (DFM) to the customer. Many SMAll factories do not pay attention to this, but it is easy to cause quality problems due to poor PCB design, resulting in a lot of rework and maintenance work. Production is no exception. We need to think twice before we act, and do a good job in advance. For example, when analyzing PCB files, for some small and fault prone materials, it is important to avoid higher materials in terms of structural layout, so that the soldering head can be easily operated during repair; The relationship between the hole spacing of PCB and the bearing capacity of the board shall not cause bending or fracture; Whether high frequency signal interference, impedance and other key factors are considered for wiring.
2. Procurement and inspection of components
The procurement of components needs to strictly control the channels, and must pick up the goods from large traders and the original factory to avoid 100% second-hand and fake materials. In addition, special incoming material inspection posts shall be set up to strictly check the following items to ensure that components are free of failure.
PCB: reflow soldering furnace temperature test, no flying wire, whether the via 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 store it at constant temperature and humidity
Other common materials: check silk screen, appearance, power on measurement, etc
The inspection items shall be carried out according to the sampling method, with the proportion of 1-3%
3. SMT assembly machining
The temperature control of solder paste printing and reflow soldering furnace is the key point. It is very important to use laser steel mesh with good quality and meeting the process requirements. According to the requirements of PCB, some of the steel mesh holes need to be increased or reduced, or U-shaped holes are used to make the steel mesh according to the process requirements. The temperature and speed control of reflow soldering furnace is very important for solder paste infiltration and welding reliability. It can be controlLED according to normal SOP operation guidelines. In addition, AOI detection needs to be strictly implemented to minimize defects caused by human factors.
4. Plug in processing
In the process of plug-in, the mold design of wave soldering is the key point. How to use the mold to maximize the probability of good products after the furnace is a process that PE engineers must constantly practice and summarize experience.
5. Programmed firing
In the previous DFM report, customers can be advised to set some test points on the PCB to test the continuity of PCB and PCBA circuit after all components are welded. If conditions permit, the customer can be asked to provide a program to burn the program into the main control IC through a burner (such as ST-LINK, J-LINK, etc.), so that the functional changes caused by various touch actions can be tested more intuitively, so as to check the functional integrity of the entire PCBA.
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. The specific operation is based on the customer's test plan and the report data is summarized.
The control knowledge of PCBA manufacturing process is far more than that, and each of the above points can be detailed in a long space. This article only looks at the key control points experienced by a PCBA board from a macro perspective, hoping to be helpful to practitioners.