Detailed explanation of PCB proofing and electroplating

I believe that anyone who knows the production process of pcb proofing knows that electroplating is an indispensable and most important link in PCB, because the success of electroplating directly affects whether the PCB is qualified. Why can’t the quality be guaranteed in some PCB factories? It is because electroplating is not well controlled or well done, there will be copper or no copper in the electroplating hole, which will affect whether the circuit is open or closed. So today, pcbB PCB manufacturers will explain the adjustment in the process of electroplating.
PCB proofing plating additives include inorganic additives (such as cadmium salt for copper plating) and organic additives (such as coumarin for nickel plating). Most of the electroplating additives used in the early stage were inorganic salts, and then organic substances gradually gained a dominant position in the ranks of electroplating additives. According to the functional classification, electroplating additives can be divided into brighteners, leveling agents, stress relievers and wetting agents. Additives with different functions generally have different structural characteristics and action mechanisms, but multifunctional additives are also common. For example, saccharin can be used as a brightener for nickel plating and a common stress relieving agent. And additives with different functions may follow the same action mechanism. 1. Non-proliferation control mechanism of PCB proofing According to the dominant non-proliferation factors in electroplating, the non-proliferation control mechanism of additives can be divided into electro-adsorption mechanism, complex formation mechanism (including ion bridge mechanism), ion pair mechanism, Helmholtz potential change mechanism and electrode surface tension change mechanism. 2. PCB proofing diffusion control mechanism In most cases, the diffusion of additives to the cathode (rather than the diffusion of metal ions) determines the electrodeposition rate of metal. This is because the concentration of metal ions is generally 100~105 times that of additives. For metal ions, the current density of electrode reaction is far lower than its limit current density. In PCB proofing, under the control of additive diffusion, most additive particles diffuse and adsorb on the convex parts, active parts and special crystal faces of the electrode surface, which causes the adsorbed atoms on the electrode surface to migrate to the concave parts of the electrode surface and enter the crystal lattice, thus playing a role in leveling and brightening.