In fact, electronic components are available in a variety of packages, and components in different packages are mounted differently on the PCB. Conventional electronic components are mostly pin-type and bulky. For such components, they need to be drilled in the PCB before they can be installed. The component leads are drilled from the drilled holes to the pads on the other side of the PCB, and the excess pins are trimmed after soldering.
But nowadays computer boards use more low-cost, small-size SMD surface mount components, so there is no need to drill holes in the PCB, as long as they are stuck in the designed position, the components can be soldered on the pads. In addition to being solderable directly to the PCB, the components can be mounted through a socket. For example, most of the well-known BIOS chips are installed on the motherboard with sockets.
The concept of component faces and weld faces is often mentioned in some materials. The so-called component surface is the surface on which the electronic component is located. The soldered surface is the surface on which the component's pins are connected by solder to the pads on the PCB. It is used for soldering. For pin-type components, the solder joints and components are on both sides of the PCB, and the components can only be on the component side, otherwise it will cause great trouble for soldering. For SMD components, the solder joints and components are on one side, so the components can be on either or both sides of the PCB.