The introduction of PCB circuit board pink circle causes and solutions

After the PCB circuit board is oxidized, a fluff layer (copper oxide and cuprous oxide) is generated. In essence, the fluff will be corroded by acid or reducing solution, so that the original black or red-brown fluff appears red copper color; after the board is pressed and drilled in the subsequent process, the fluff around the hole appears obvious dissolution of copper with contrasting color The color circle is called the pink circle.


PCB circuit board pink circle

1. Blackening --- Because of the shape of the blackened fluff and the thickness of the fluff, it will cause pink circles of different degrees, but this kind of blackened fluff cannot effectively prevent the pink circle from happening.

2. Lamination-due to poor lamination (pressure, heating rate, glue flow, etc.) caused by insufficient bonding between the resin and the oxide layer, resulting in the formation of acid intrusion into the void path.

3. Drilling --- due to stress and high heat in the drilling, stratification or cracking between the resin and the oxide layer is caused, which causes the acid solution to invade and dissolve.

4. Chemical copper---In the process of the via hole, there is acid liquid, which causes the fluff to corrode.

 

To solve this kind of problem, the application practice proves that the following methods can achieve good results:


1. Reduce the oxidized surface of the copper foil of the inner layer with an alkaline solution containing dimethylborane as the main component. The reduced metal copper can enhance acid resistance and improve adhesion;

2. Treat the whiskers on the copper surface with a sodium thiosulfate reducing solution with a PH value of 3--3.5. After acid leaching and passivation, a mixture of copper and cuprous oxide is produced by ESCA;

3. Treat inner layer board with a mixture of 1-2% hydrogen peroxide, 9-20% inorganic acid, 0.5-2.5% tetraamine-based cationic surfactant, 0.1-1% corrosion inhibitor and 0.05-1% hydrogen peroxide stabilizer Lamination process after copper surface;

4. The chemical tin plating process is used as the covering layer on the copper foil surface of the inner layer.