Design and manufacture of insoluble anode and its application in PCB industry？
Insoluble Anode Definition
When the current passes through the electroplating process, the anode itself does not dissolve and only undergoes an oxidation reaction, which are collectively referred to as insoluble anodes. Insoluble anode materials in electroplating include lead, carbon, platinum, graphite, nickel, stainless steel, platinum-plated titanium, tantalum-plated iridium, ruthenium-plated iridium, rhodium, etc.
The scenarios where insoluble anodes are applied in the circuit board industry mainly include copper electroplating, gold electroplating, silver electroplating, and environmental protection treatment of ammonia nitrogen and COD. The copper-plated insoluble iridium-tantalum anode for HDI boards, which is the most widely used for circuit boards, has high requirements on the consumption of light agent. The stability of the electroplating light agent in the electroplating process has a crucial impact on the quality of the electroplating.
The insoluble anode plays the role of anode conduction in the whole electroplating process, and precipitates oxygen or oxidized metal ions. There are two main effects of insoluble anodes for circuit boards on the bath liquid. Oxygen evolution on the surface of the first anode will cause additional loss of the electroplating agent at the same time. A direct oxidation reaction occurs on the surface of the anode catalytic coating. The main reaction is The hydroxide in the bath is catalyzed by the noble metal catalytic coating and loses an electron at a lower potential to become oxygen. At the same time, the organic matter in the bath also has the opportunity to discharge and be oxidized on the anode. The key point in the anode production process is to control the analysis. Oxygen potential, do not allow the organic matter in the bath to have the opportunity to be directly oxidized by discharging on the anode. The second affects the dissolved oxygen in the bath. Oxygen generated on the surface of the anode needs to escape from the anode as soon as possible and run out of the bath to reduce its residence time in the bath. (The reaction mechanism of pulsed iron-containing ions is different, and very little oxygen is precipitated).
2. Process requirements for insoluble anodes
The difference between the insoluble anodes we commonly use in circuit board electroplating and ordinary insoluble anodes lies in the loss of organic matter. This depends on the composition and structure of the noble metal coating, that is, the catalytic layer.
In the production process, two aspects need to be ensured. First, ensure a strong bonding force, which refers to the bonding force between the coating and the titanium substrate. Second, ensure the conversion rate of the precious metal of the coating into an effective catalyst.
In the first aspect, it is necessary to ensure the binding force: 1. Clean surface; 2. Appropriate surface roughness; 3. The crystal structure of the catalytic layer is similar to the crystal structure of the bottom layer (rutile structure). The combined structure can greatly enhance the binding force.
The second aspect is the conversion rate of coated precious metals. This requires a lot of actual measurement data on the formula and production process to find the best formula and production process.
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