PCB Tech - Why do we choose phosphor copper balls in PCB electroplating?

With the rapid development of electronic technology, the production demand for various circuit boards has greatly increased. Copper is an important raw material for electroplating anodes, and the demand has greatly increased. Among them, PCB precision circuit boards need phosphor copper balls as anodes. Phosphor copper balls are suitable for electronic circuit boards, especially high-precision multilayer circuit boards, which are indispensable important components of electronic products, and rely heavily on high-quality PCB phosphor copper ball anodes as the basic raw materials for manufacturing circuit boards. Therefore, the demand for phosphor copper anode balls is considerable. This article mainly introduces the phosphorous copper balls of PCB. Firstly, it introduces why phosphorous copper balls should be used for PCB electroplating. Secondly, it explains the application overview of phosphorous copper balls in PCB and the global market forecast of phosphorous copper balls. The specific follow-up Let's take a look at the editor.

Why use phosphorous copper balls for PCB electroplating

In the early stage, copper sulfate electroplating uses electrolytic copper or oxygen-free copper as the anode, and its anode switch copper ball power is as high as 100% or even more than 100%. This constitutes a series of problems: the copper content in the bath is constantly increasing, and the additives The cost is accelerated, the copper powder and anode mud in the bath increase, the anode power is reduced, and the coating is very easy to produce copper balls as burrs and rough defects.

The dissolution of copper anode is mainly to generate divalent copper ions. The research and experiment proved (rotating ring disk electrode and constant current method): the dissolution of copper in copper sulfate solution is carried out in two steps.

Cu-e--Cu+ elementary response 1

Cu+--e--Cu2+ elementary response 2

The oxidation of cuprous ions to divalent copper ions under the action of the anode is a slow response, and it can also generate divalent copper ions and elemental copper through the disproportionation reaction, just as in the chemical precipitation of copper. The resulting copper element is deposited in the plating layer by electrophoresis, resulting in copper powder, burrs, roughness, etc. When a small amount of phosphorus is added to the anode, a black phosphorous film is formed on the surface of the anode through electrolysis (or drag tank), and the dissolution process of the anode undergoes some changes:

1. The black phosphorous film has an obvious catalytic effect on the elementary response 2, which greatly accelerates the oxidation of cuprous ions, turns the slow response into a fast response, and greatly reduces the accumulation of cuprous ions in the bath. At the same time, the phosphor film on the surface of the anode can also block the cuprous ions from entering the bath, promote its oxidation, and reduce the cuprous ions entering the bath. The conductivity of the standard anode black phosphor copper film is 1.5&TImes;104Ω-1CM-1, which has metal conductivity and will not affect the conductivity of the anode, and the anode polarization of the phosphor copper anode wall spring copper anode is small, at Da At 1ASD, the anode potential of a copper anode containing 0.02---0.05% phosphorous is 50?80mv lower than that of an oxygen-free copper anode. The black anode phosphor film will not constitute anode passivation at the permitted current density.

2. The black phosphorous film on the surface of the anode will cause the anode to dissolve abnormally, the phenomenon of falling of fine particles is greatly reduced, and the operating power of the anode is greatly improved. When the anode current density is 0.4?1.2ASD, the phosphorus content on the anode has a linear relationship with the thickness of the black film. When the anode phosphorus content is 0.030 to 0.075%, the use power of the corrosion anode is the highest, and the anode black phosphorus film is the best.

The influence of phosphorus content on anode phosphorus film

1. Copper anodes with a phosphorus content of 0.030?0.075% have a moderate black film thickness, a fine structure, a strong combination, and are not easy to fall; copper anodes with too high phosphorus content before danger. Phosphorus is not uniformly distributed, and the dissolution will cause too much anode mud, which will contaminate the bath solution and block the anode bag holes, which constitutes a rise in the cell voltage. An increase in the cell voltage may cause the anode film to fall. In practice, burrs will simply occur when the anode is replaced while electroplating.

2. Phosphorus copper anode with a phosphorus content of 0.3% is unevenly distributed, the black phosphorus film is too thick, and the solubility of copper is poor. Therefore, it is often necessary to fill the anodes instead of making the area ratio of the anode and cathode to 1:1. In practice, there are more copper anodes hanging, and the copper content in the bath is still declining, and it is difficult to maintain a balance. It is necessary to add copper sulfate frequently, which is not economical in terms of the cost of electroplating. Electroplating prefers to hang more defective phosphor copper anodes, and if the anode slime increases, the practical cost will also increase.

3. In practice, the thickness of the black film produced by the copper anode with high phosphorus content is too thick, and the resistance is added, and the original current must be maintained and the voltage must be increased. The increase of the cell voltage is beneficial to the discharge of hydrogen ions, and the occurrence of pinholes increases. This phenomenon is rare for the domestic "MNSP.P.AEO" system, because there are more surface active agents, but for some imported light agents, the chance of pinholes will be greatly increased, and other supplements are needed. Add humidifier and try to lower the voltage.

4. In practice, the phosphorus content is high, the black film is too thick, and the distribution is uneven, and it will also form a low-current area that is not shiny and has a fine sandy shape.

Although the thickness of the black film of the 0.3% phosphorous copper anode can reduce the cuprous ions entering the bath, the effect is greatly reduced due to its loose structure and uneven distribution. There are chemical reversible reactions in other electrolytes:

Cu2++ Cu -- 2Cu+

At room temperature, the equilibrium constant of this response is K=(Cu+)2/(Cu2+)=0.5X10-4

The temperature rises, the cuprous ion concentration also rises. Cuprous ions exist in the bath as cuprous sulfate and will be oxidized when air is mixed. When the acidity drops, the cuprous sulfate hydrolyzes the cuprous oxide (copper powder), and the same powder stays in the high current area of the cathode, and the accumulation must be quantitative, and then burrs will occur; in the low current area, the current power decreases and the hydrogen ion discharges more. The acidity at this place decreases, and the hydrolysis proceeds in the direction of producing copper powder.

Cu2SO4+H2O=Cu2O+H2SO4

Overview of the application of phosphor copper balls in PCB

1. Phosphor copper balls are used in the primary and secondary copper processes of PCB boards, mainly to form the conductive copper layer of the through hole

PCB products with more than double layers, because the lines between different layers are not directly connected, the lines between different layers must be connected through the structure of via holes to facilitate electrical transmission.

In the PCB manufacturing process, after the inner layer board circuit production, multi-layer lamination and mechanical drilling, in order to make the drilling a conductive state, it is necessary to carry out the procedures of desmear, hair removal and chemical copper, Generate a thin copper layer. Afterwards, the primary copper plating and secondary copper plating were performed through electrolytic copper plating, and the thickness of the copper layer was increased to strengthen the conductive effect of the vias. Phosphor copper balls are the key material used for primary copper and secondary copper.

2. Phosphorus copper balls are the anode material for the PCB copper plating process. Phosphorus is added to the copper balls to prevent cuprous from affecting the quality of the coating.

Theoretically, in the PCB copper plating reaction, phosphorus does not directly participate in the reaction. The purpose of adding phosphorus is mainly to slow down the precipitation rate of copper atoms. If the dissociation rate of copper atoms is too fast, a large amount of cuprous ions will be produced, and the two cuprous ions will react with each other into copper atoms and copper ions. The copper atoms in the solution will be randomly adsorbed on the PCB board by electrophoresis, which affects the formation structure of the copper coating and degrades the quality of the copper coating.