Identification of the main surface (part surface) and auxiliary surface (soldering surface) of the motherboard PCBA can usually be done by the following methods:

1. Parts marking: on the main surface (part surface) of the PCBA ) usually have markings on electronic components, such as chips, resistors, capacitors, etc. The main surface can be judged by these markings.

2.

Component location: Usually, large or important components (such as chips) will be installed on the main surface of the PCBA, while smaller or minor components will be installed on the main surface of the PCBA. On the welding surface, the main surface can be preliminarily judged by observing the position of the components.

3. Text or graphic marks: Sometimes there may be text or graphic marks on the edges or corners of the PCBA to indicate the main surface or soldering surface. These markings may be placed by the PCB manufacturer, designer or assembler.

4. Manual or specification: Refer to the corresponding PCB design manual, specification or product documentation. These documents usually clearly indicate the identification or difference between the main surface and the auxiliary surface.

It should be noted that some PCBAs may not have clear markings or logos to distinguish the main surface and the auxiliary surface. In this case, you need to use other auxiliary means or contact the PCB manufacturer, designer or assembler for confirmation.

In addition, when looking at PCBA, the main surface usually shows features such as denser components and more obvious pins and connection lines of electronic components, while the soldering surface usually has more pads, soldering points and Traces of printed circuit traces. However, in some cases, the difference between the main surface and the welding surface may not be obvious and requires careful observation and identification.