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PCB pink circle

Shenzhen Inno Circuit Co.,Ltd | Updated: May 26, 2018

PCB pink circle

First, the definition of pink circle


After the oxidation of the board, a fluff layer (copper oxide and cuprous oxide) is formed. In essence, the villi are eroded by acid or reducing liquid, making the original black or reddish-brown villi appear red copper;


After the board is pressed and drilled and other follow-up processes, there is a clear contrast ring of copper color in the villi around the hole, which is called the pink circle.


The “pink circle” is a “pink circle” in the pink bare copper surface produced by the dissolution of the oxide on the surface of the copper foil on the inner layer of the multilayer printed circuit board manufacturing process.


Second, the cause of the pink circle


1. Darkening—Because the shape of the blackened fluff and the thickness of the fluff may cause pink circles of varying degrees, such blackened fluffs cannot effectively prevent the occurrence of pink circles.


2. Compression—Insufficient adhesion between the resin and the oxide layer due to poor pressure (pressure, temperature increase rate, fluidity, etc.) causes the formation of an acid invasion void path.


3. Drilling—Due to the stress and high heat in the borehole, the resin and the oxide layer are stratified or broken, so that the acid solution invades and erodes.


4, chemical copper --- in the process of the presence of a hole in the presence of acid, which makes the villi dissolved.


Third, the influence of the pink circle


1. Appearance: In the trend of small holes, it can no longer effectively cover up and cause poor appearance.

2, on the quality --- pink circle represents a partial layer, more porous.

3. Process - The emergence of pink circles under the increasingly high precision demand represents the instability of the process.

4. On the cost, the number of drilled holes on the drilling machine and the use of different film bases containing glue components are affected.


Fourth, to improve the pink circle occurred


1, improve the oxidation fuzz thickness and shape

2. Storage and use of substrates

3, improvement of lamination process conditions

4. Improvement of drilling conditions

5, the improvement of the wet process


To solve this kind of problem, apply the practice to prove that the following methods can achieve good results:


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


2. Treatment of copper surface whiskers with a sodium hyposulfite reducing solution with a pH of 3-3.5, acid leaching and passivation

The ESCA produces a coating of copper and cuprous oxide mixture;


3. Treat the inner layer with a mixture of 1-2% hydrogen peroxide, 9-20% inorganic acid, 0.5-2.5% tetraamine cation surfactant, 0.1-1% corrosion inhibitor and 0.05-1% hydrogen peroxide stabilizer. Copper surface after the lamination process;


4. The electroless tin plating process is used as a cover layer on the surface of the inner layer copper foil.