PCBA Tech - Burning procedure? Key points of quality in PCBA processing

In the PCBA processing process, in order to enable the PCB board to achieve certain specific functions, in addition to the hardware is no problem, it is also necessary to add software functions. At this time, we need to "burn" the program. Before programming, we need to test whether the PCB board is qualified, and then select the appropriate programming method. The current burning methods are generally divided into offline burning and online burning.

Program burning is to load the original program into the computer after being compiled and processed, and let the computer execute the program you wrote. For example, when the microcontroller program is burned, the .hex file is loaded, stored in the microcontroller, and the written program can be realized after booting. To put it simply, the process of enabling the microcomputer to execute your program is program burning.

Offline programming: through the adapter and different packaged chips link, the chip and the adapter can be used together to achieve the programming of the program. The nature of the adapter is similar to a precision fixture, and different packaged chips need to be matched with different adapter seats.

If an error occurs during the PCBA production test and the production retrospective re-correction is performed, the chip needs to be removed from the adapter and re-burned in accordance with the prescribed process, which consumes a lot of manpower and material resources, is costly, and is more prone to problems., So offline burning is generally not recommended.

Online programming: Online programming uses the chip's standard communication bus, such as USB, SWD, JTAG, UART, etc. The interface is generally fixed, and there are few pins that need to be connected during programming. Because the interface communication rate is not high, the programming can be completed by using ordinary wires without high consumption.

Online programming is to program programming through wire connection. If an error is found during the PCBA production test, the programming can be performed again without disassembling the chip. It not only saves production costs, but also increases the efficiency of programming. Therefore, online burning is generally used now.

The main points of PCBA process control and quality control

1. PCB circuit board production

After receiving the PCBA order, analyze the Gerber file, pay attention to the relationship between the PCB hole spacing and the board's load-bearing capacity, do not cause bending or breakage, and whether the wiring considers key factors such as high-frequency signal interference and impedance.

2. Procurement and inspection of components

The procurement of components requires strict control of channels, and must be picked up from large traders and original factories, and 100% avoid second-hand materials and fake materials. In addition, a special inspection post for incoming materials is set up, and the following items are strictly inspected to ensure that the components are free of faults.

PCB: Reflow soldering furnace temperature test, no flying leads, whether the vias are 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 ratio is generally 1-3%

3. SMT Assembly processing

Solder paste printing and reflow oven temperature control are key points, and it is very important to use laser stencils of good quality and meeting process requirements. According to the requirements of PCB, some steel mesh holes need to be enlarged or reduced, or U-shaped holes are used to make steel mesh according to process requirements. The furnace temperature and speed control of the reflow soldering is very critical to the solder paste infiltration and soldering reliability. It can be controlled in accordance with the normal SOP operation guidelines. In addition, AOI testing needs to be strictly implemented to minimize the defects caused by human factors.

4. Plug-in processing-circuit board welding processing

In the plug-in process, the mold design for wave soldering is a key point. How to use the mold to maximize the probability of good products after the furnace is a process that PE engineers must continue to practice and summarize 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 PCB and PCBA circuit continuity after soldering all components. If you have conditions, you can ask the customer to provide a program, and burn the program into the main control IC through a burner (such as ST-LINK, J-LINK, etc.), and you can more intuitively test the effects of 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 content includes ICT (In Circuit Test), FCT (Function Test), Burn In Test (aging test), temperature and humidity test, drop test, etc., according to the customer's test plan. And summarize the report data.