Copper core solder balls (CCSBs) have a three-layer composite structure: an inner layer of high-purity copper balls (0.03–0.5 mm in diameter), a middle layer of 2–3 μm nickel plating (optional), and an outer layer of 3–30 μm solder plating (such as SAC305), providing both structural support and solderability.
Copper core solder balls (CCSBs) are high-performance interconnect materials specifically designed for high-density 3D packaging. Their unique structure solves the problems of collapse and short circuits that occur with traditional solder balls during repeated reflows.
Copper Core Ball: Providing Mechanical Support and Thermal Stability
Made of high-purity electrolytic copper, its diameter is typically between 0.03–0.5 mm, forming the rigid framework of the entire structure.
Copper has a melting point as high as 1083℃, far exceeding the reflow soldering temperature (approximately 250℃), thus remaining solid during multiple thermal cycles. This effectively maintains the physical space between chip stacks, preventing PKG (package body) compression and deformation.
Nickel Plating Layer: Inhibits Intermetallic Diffusion (Optional Functional Layer)
Typically 2–3 μm thick, it is deposited on the surface of the copper ball through electroplating or chemical plating.
Its main function is to prevent interdiffusion between copper and external solder (such as tin) at high temperatures, avoiding the formation of brittle intermetallic compounds (IMCs) and improving the long-term reliability of the solder joints.
This layer is an optional design, and its addition depends on the substrate material (such as OSP, ENIG) and process requirements.
