Electroless nickel bath for wafer bumping: influence of additives

Aluminium bond pads on silicon wafers have two distinct features: small area and thin material. This necessitates special considerations for the design of the electroless nickel (EN) bath chemistry to deposit EN metallization or bumps on such small and delicate substrates for flip chip packaging applications. It also calls for special quality control practices and care during EN plating to produce consistent and high quality nickel deposits on the bond pads. The majority of the commercial EN solutions and processes that perform well on bulk aluminium have been observed to be incapable of plating acceptable nickel bumps. A specially formulated EN bath catering for nickel bumping applications is in demand in the electronics packaging industry. This study investigated the influence of EN bath chemistry on the quality of electrolessly deposited nickel-phosphorus bumps on wafers. A special EN solution and process has been developed which is capable of producing quality EN metallization and bumps