PTH is also called electroplating through-hole. Its main function is to deposit a thin layer of copper on the substrate in the insulating hole by chemical method to provide a conductive layer for subsequent electroplating, so as to achieve the conduction of the inner and outer layers.
Among them, the chemical reactions involved are as follows:
Activation: Pd2++2Sn2+→[PdSn]2+—reacts in solution to form unstable complexes
[PdSn]2+→Pd+Sn4++Sn2+——Most of the complex is reduced to metal palladium
SnCl2+H2→Sn(OH)Cl+HCl——Synthesis of SnCl2 to form basic stannate precipitate during water washing after activation
As the SnCl precipitates, the Pd core also deposits on the surface of the activated substrate.
Copper immersion: HCHO+OH-→H2+HCHOO-——Pd as a catalyst, this step can be carried out
Cu+H2+OH-→Cu+2H2O——copper ions are reduced to metallic copper under alkaline conditions