Versatile Lead-Free Solder Electroplating Products for Advanced Bumping Technologies

Abstract

Lead-free SnAg solder bumps deposited by electroplating are used extensively in high volume production lines for a number of new bumping technologies including C4 bumps, Cu pillars capped with SnAg solder and 3D microbumps. New bumping technologies present their challenging requirements such as tightly controlled thickness uniformity, alloy composition uniformity and avoidance of reflow voids to create high yields and low defects. To meet these requirements, SnAg plating chemistry must deliver strong performance over a wide range of applications. Traditional device manufacturers, wafer foundry companies and Outsourced Assembly and Test (OSAT) companies are manufacturing a number of different types of bumped wafers in their production lines; a diverse range of die design and pattern densities, thin and thick resist film wafers, mushroom and in-via plating, and wide range of plating rate. The variety and complexity of bumping wafers have challenged SnAg plating chemistries to meet tight requirements in terms of running cost saving and high production yield. Hence, development of versatile and robust chemistries for electroplating is critical to overcome these challenges In view of all these challenges and unmet needs in the market, Dow focused its efforts on developing a brand-new additive system for SnAg plating. On the one hand, we tapped into our know-how on solder plating to establish correlations between various types of end-user requirements and experiences to fundamental electrochemistry response. On the other hand, 300mm in-house plating and process tools are leveraged to speed up the feedback process and provide pilot run data. At the end, this highly iterative approach enabled us to optimize the performance of the chemistry without sacrifice on design space. In this paper, we will discuss next generation of SnAg electroplating products capable of achieving versatile performance requirements over a wide range of applications. The bump height WID co-planarity% ((hmax-hmin)/2havg ×100) was achieved less than ±5% over the wide range of current density from 4 ASD to 12 ASD. Smooth surface morphology, narrow Ag alloy composition distribution less than ±0.2% across the 300mm wafers, and reflow void free were observed. An optimized formulation of the next generation SnAg products was successfully demonstrated plating capability on various bumping technologies such as C4 bumping, Cu pillars capped SnAg solders and micro bumps meeting plating requirements.