Why do ceramic PCBs tend to use an immersion gold finish over gold plating?

2025-08-02 During the PCB (printed circuit board) manufacturing process, surface treatment is often required to improve oxidation resistance and effectively protect the circuitry. Both immersion gold and gold plating are common surface treatment methods. In ceramic PCBs, the substrate is an inorganic material, so immersion gold is more widely used than gold plating when choosing a surface treatment. This article will explore the reasons for this phenomenon and the key differences between the two.

Ceramic PCB surface treatment processes typically include: bare board (untreated), rosin board, OSP (organic solder preservative), tin-spray (including lead-tin and lead-free tin), gold plating, immersion gold, and immersion silver. Each of these processes has its own characteristics, meeting the needs of different application scenarios.

Definition and Process of Immersion Gold and Gold Plating
Gold plating generally refers to "electroplated gold," "electroplated nickel gold," and "electrolytic gold," among other terms, and includes distinctions between soft gold and hard gold. The process involves dissolving nickel and gold (also known as gold salts) in a chemical solution. The circuit board is immersed in an electroplating tank and an electric current is applied, forming a nickel-gold coating on the copper foil of the circuit board. Electroplated nickel-gold is widely used in electronic products due to its high hardness, wear resistance, and oxidation resistance.

Immersion gold (Immersion Gold) is a chemical nickel-gold deposition method that uses a chemical redox reaction to form the coating, typically resulting in a thicker gold layer. The following is an analysis of the advantages, disadvantages, and differences between Immersion Gold (Immersion Gold) and gold plating for ceramic circuit boards:

Comparison of Immersion Gold and Gold Plating

Immersion gold is commonly used for ceramic circuit boards, primarily due to the solderability limitations of gold-plated boards. While some customers still opt for gold plating, the advantages of Immersion Gold make it a superior choice. The key differences between the two are as follows:

1. Thickness and Appearance: The film thickness of Immersion Gold is typically between 0.025 and 0.1 microns. Compared to gold plating, Immersion Gold produces a thicker, more pronounced golden-yellow layer, while gold plating, due to its thinner layer, has a slightly whitish appearance (due to the color of nickel). 2. Solderability: Compared to gold plating, immersion gold (Immersion Gold) boards are easier to solder and have a lower chance of soldering defects. This process is particularly reliable in ceramic packaging applications.
3. Signal Transmission: If the pads on an Immersion Gold board are coated with nickel and gold, the signal is transmitted within the copper layer and is not negatively impacted by the gold layer.
4. Oxidation Resistance: The crystal structure of Immersion Gold is relatively denser, making it more resistant to oxidation than gold plating.
5. Processing Precision: With increasing precision requirements for ceramic PCB processing, Immersion Gold (Immersion Gold) boards offer a significant advantage in preventing gold wire short circuits, especially when the line widths and spacing of specialty PCBs, such as Jinruixin, reach 2-6 mm.
6. Bond Strength: The bond between the pads and copper layer of an Immersion Gold board is more secure, allowing for engineering compensation without affecting trace distances.
7. Flatness and Service Life: For PCBs requiring high flatness, the Immersion Gold process typically provides better flatness. Immersion Gold boards also have a longer service life than gold-plated boards, which often exhibit black padding after assembly. In summary, the immersion gold process is used for the surface treatment of ceramic circuit boards mainly due to its significant advantages in welding performance, oxidation resistance, and processing accuracy, making it more suitable for the needs of modern high-end applications.