PCB Technical - Why does the edge of PCB burn during electroplating

Why is the edge of the PCB scorched during electroplating of the PCB multi-layer circuit board?

PCB electronics factory you to understand that because electronic products require sophisticated technology and a certain degree of environmental and safety adaptability, it has promoted considerable progress in PCB plating technology. In the electroplating of PCB multilayer circuit boards, the chemical analysis of organic matter and metal additives is becoming more and more complicated, and the chemical reaction process is becoming more and more precise.
But even so, when PCB multilayer circuit boards are electroplated, the side of the board will still be burnt from time to time. So what is the source of the problem?
The reasons for the scorching of the edge of the PCB during electroplating of multi-layer circuit boards are rough as follows:

1. The current density is too high
Each plating solution has its best current density range.
The current density is too low, the grains of the coating are coarsened, and the coating cannot even be deposited. When the current density increases, the cathodic polarization effect increases, so the coating is dense and the coating speed increases. But if the current density is too large, the coating will be burnt or scorched;

2. The tin-lead anode is too long
When the anode is too long and the workpiece is too short, the power lines at the lower end of the workpiece are too dense and easy to scorch; when the distribution of anodes in the horizontal direction is much longer than the length of the workpiece placed horizontally, the power lines at both ends of the workpiece are dense and easy to scorch.

3. Insufficient tin-lead metal content
The metal content is insufficient, the current is slightly larger, H+ is easily discharged by the machine, and the diffusion and electromigration speed of the plating solution body becomes slow, leading to scorching.

4. Insufficient additives
In simple salt electroplating, if the additive is added too much, the additive film layer produced by adsorption is too thick, and the main salt metal ions are difficult to penetrate the adsorption layer and discharge, but H+ is a small proton that easily penetrates the adsorption layer and discharges hydrogen, and the coating is easy Burnt. In addition, too many additives have other side effects, so any additives and brighteners must adhere to the principle of adding less frequently.

5. Insufficient circulation or stirring of tank liquid
agitation is the main means to increase the speed of convective mass transfer. Using the cathode to move or rotate, there can be a relative flow between the liquid layer on the surface of the workpiece and the plating solution at a distance; the greater the stirring intensity, the better the convective mass transfer effect. When the stirring is insufficient, the surface fluid will flow unevenly, which will cause the coating to burn.
In addition, there are also reasons for the scorching
Organic pollution; metal impurity pollution; too much lead in the coating; anode mud falls into the tank; fluoroboric acid hydrolysis produces lead fluoride particle adhesion.