The material of a CCGA solder ball is a three-layer composite structure: an inner layer of high-purity copper, a middle layer optionally plated with nickel, and an outer layer of tin-based solder plating (such as SAC305 or pure tin).
Copper Core Solder Ball (CCSB) is a high-performance interconnect material designed specifically for advanced 3D packaging. Its material composition directly determines its excellent performance in high-density, high-reliability scenarios.
Inner Layer: High-purity copper (Copper Core) Made of electrolytic copper, typically with a purity higher than 99.9%, and a diameter ranging from 0.03–0.5 mm.
Copper has a melting point as high as 1083℃, far exceeding the reflow soldering temperature (approximately 250℃), thus remaining solid during multiple thermal cycles, playing a crucial role in supporting the package space and preventing collapse.
Middle Layer: Nickel Plating (optional) Approximately 2–3 μm thick, deposited on the surface of the copper ball through electroplating. Its main function is to suppress intermetallic diffusion between copper and external tin-based solder, preventing the formation of brittle IMCs (such as Cu₆Sn₅) and improving the long-term reliability of the solder joint. Whether to add this layer depends on the substrate material and process requirements.
Outer layer: Solder coating
Commonly composed of SAC305 (Sn-3.0Ag-0.5Cu), pure tin (Sn), or SC alloy, with a thickness between 3–30μm.
During reflow soldering, it melts and forms a metallurgical bond with the PCB pads, achieving electrical and mechanical connections, while the internal copper core remains unchanged, achieving a stable soldering mechanism of "external melting and internal solidification".
