Industrialization of a New Adhesion Promoter Process for Leadframe

Substrate-based microelectronics have become common these days, but leadframe-based packages are still widely used in the semiconductor industry. Increased reliability requirements have led to extensive adoptions of "adhesion promoter" technologies on leadframes, to enhance the adhesion between leadframe metal surfaces and chip encapsulation materials, such as epoxy molding compounds (EMC). With the introduction of the most stringent requirement of the automotive electronics industry, many plastic packages, such as QFP, tend to show their weaknesses in delamination even during early reliability.Some degree of EMC delamination is usually found near the lead bonding areas on the leadframe, which are typically Ag-plated and Ag surfaces have very poor adhesion to EMC. If gold wires were used as the interconnects between the die and the leadframe, the gold wires may still be intact after package preconditioning due to their high ductility properties. Driven by cost initiatives, Cu wires have been introduced to replace gold wires. Cu wire introduction brings several workability challenges that require specific process optimizations on each leadframe finish [1]. Under such circumstances, severe problems of stitch bond cracks could occur and lead to serious package reliability issues due to the lower elongation of Cu wires.EMC adhesion can be improved acting on leadframe finishing: different plating stacks or roughening techniques can achieve a better adhesion, however those solutions will imply a significant leadframe cost increase, as well as the workability during IC assembly processes. In this paper, we will share the major challenges faced during the industrialization of a new adhesion promoter process, which is applicable to Ag surfaces and do not require surface etching or roughening; this study will also address the ultimate adhesion performance at high temperature of the new adhesion promoter and other key benefits of this noble process.