For 8-layer PCB, the design choice of inner gold plating and outer immersion gold depends on the specific application requirements and manufacturing process.
First of all, gold plating is usually used for the inner layer because it has better electrical conductivity and corrosion resistance, and is suitable for areas requiring high electrical performance such as signal transmission and power circuits. At the same time, gold plating also has good adhesion and weldability, which facilitates subsequent welding and assembly.
The main function of the outer layer of immersed gold is to provide better appearance quality and corrosion resistance, as well as to enhance the conductive performance and signal integrity of the PCB. Immersion gold technology can make the PCB surface flatter and smoother, improve its solderability and reliability, and enable it to withstand harsh environmental conditions.
Therefore, for an 8-layer PCB, if high electrical performance and solderability are required, the inner layer can use the gold plating process; while the outer layer needs to have good appearance quality and corrosion resistance, the immersion gold process can be selected. Such a design can ensure PCB performance and reliability to meet a variety of application requirements.