Electrode application in piezoelectric ceramics -- HE SHUAI.

The main methods for electrode application in piezoelectric ceramics are chemical plating and vacuum plating.

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(1) Chemical plating

Chemical plating is a self-catalytic process that does not require electricity. Based on the principle of oxidation-reduction reactions, strong reducing agents are used in a solution containing metal ions to reduce the metal ions to metal and deposit a dense coating on various material surfaces.

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(2) Vacuum Plating

Vacuum plating mainly includes several types such as vacuum evaporation, sputtering, and ion plating. They all involve depositing various metal and non-metal films on the surface of the object in a vacuum environment through distillation or sputtering. This method can achieve very thin surface coatings and has the advantages of fast speed and good adhesion. However, it is relatively expensive, has a limited range of applicable metals, and is generally used for functional coatings on high-end products.

Differences between Chemical Plating and Vacuum Plating for Piezoelectric Ceramics:

Electroless plating is widely used due to its simple process and less stringent equipment and environmental requirements compared to vacuum ion plating.

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So far, many heavy metals can be deposited from aqueous solutions through the process of electroless copper plating. From an economic perspective, electroless copper plating has the lowest cost and is therefore widely adopted. The appearance of the electroless copper layer is copper-red and cannot be used as a decorative or protective layer. It is usually used as a conductive layer for non-metallic materials, printed circuit board hole metallization, and other electroplating thickening layers. Electroless copper plating can only provide a thin conductive layer for piezoelectric ceramic components. If other layers need to be further thickened, the electroless copper layer must be electroplated with copper to increase its thickness. Acidic copper plating or alkaline copper plating can be used for electroplating copper. After electroplating copper on the piezoelectric ceramic component, other metal layers can be electroplated as needed.

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In contrast to chemical plating, vacuum plating is more environmentally friendly, safe, energy-efficient, and does not generate wastewater. Vacuum plating allows for better control of coating thickness and enables the preparation of various functional coatings. The bond between vacuum-plated coatings and the substrate is stronger and less prone to detachment. Vacuum plating provides dense, pure coatings with better adhesion.

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Currently, the most commonly used method in the production process of piezoelectric ceramics is chemical plating. Besides the low cost, another reason is for better soldering of the piezoelectric ceramic components. The metal coating deposited by chemical plating is thicker, making it easier for soldering. However, chemical plating on the surface of piezoelectric ceramics can sometimes leave watermarks or scratches, which may affect the aesthetics.

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Vacuum plating is a more advanced technology but requires specialized equipment and involves more complex operations. Generally, we use vacuum magnetron sputtering to deposit nickel metal onto piezoelectric ceramics, followed by a choice of further gold or copper plating. The vacuum-plated coating on piezoelectric ceramics is thinner, which is not conducive to soldering. However, this can be resolved by multiple plating cycles, although it increases the cost. Additionally, the surface of vacuum-plated piezoelectric ceramics is very smooth and aesthetically pleasing.

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Conclusion

Chemical plating and vacuum plating are the main methods for electrode application on piezoelectric ceramics. Currently, chemical plating is the preferred method due to its low cost and simplicity. However, vacuum plating is a more advanced technology, albeit with higher equipment costs and the need for multiple coating cycles. With technological advancements in the future, vacuum plating is expected to become the primary method for electrode application on piezoelectric ceramics.

HE SHUAI team

2024.09.02