Solder Sphere Transfer for Wafer Level Packaging

Solder bumps for interconnects can be applied to a wafer by various means. Common methods applied in the industry are:- Electrochemical deposition (“ECD”) - Solder printing-Individual solder ball transfer (“Solder Jetting”) - Wafer level solder ball transfer (“Sphere Transfer”)Bump size & pitch requirements, overall yield and cost will highly influence manufacturer's choice in determining the technology [1], [2], [3]. Solder sphere transfer has positioned itself as technology that bridges both the precision of electrochemical deposition with the low-cost approach of solder printing [4].This paper consists of three main sections. In the first part, we will compare solder sphere transfer with other solder technologies, especially under design consideration. The second part gives a brief explanation of tool and process characteristics of solder sphere transfer. The third part examines yield and defect data from a solder sphere transfer production process at PacTech Asia, demonstrating its robustness for mass production.