The core manufacturing process of copper core solder balls includes copper ball preparation, nickel electroplating and solder plating (nickel plating 2–3 μm, solder plating 3–30 μm such as SAC305), reflow soldering temperature profile and plating combination design. The entire process must balance structural precision and soldering reliability.
The manufacturing of copper core solder balls (CCSBs) is a high-precision composite process, mainly consisting of the following key steps:
Copper Ball Preparation: High Sphericity is the Primary Challenge Micron-sized copper balls, typically 0.03–0.5 mm in diameter, are prepared using atomization molding or electrolytic deposition methods.
Extremely high sphericity is required (deviation <1 μm) to ensure uniform contact with the pads during ball placement, avoiding cold solder joints or misalignment. The surface needs cleaning and activation treatment to improve the adhesion of subsequent plating layers.
Electroplating Process: Step-by-step deposition of functional layers
Nickel Plating Layer (2–3μm): A uniform nickel layer is formed on the surface of the copper ball through chemical plating or electroplating. Its main function is to inhibit the interdiffusion of copper and tin at high temperatures, prevent excessive growth of brittle intermetallic compounds (IMCs), and improve interface stability. This layer is optional and depends on the substrate material and reliability requirements.
Solder Plating Layer (3–30μm): The outer layer is plated with a solderable alloy, commonly lead-free solders such as SAC305 (Sn-3.0Ag-0.5Cu). The thickness is adjusted according to the solder joint height and wetting requirements. This layer melts during reflow soldering, completing the connection with the PCB or interposer pads.
