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|New Cleaning Technology Solutions for Lead-Free Micro-Bumping Processes|
|Keywords: Microbumping, photoresist removal, lead-free|
|Historically, the semiconductor industry has increased performance by decreasing the size of features on chips, thereby improving the cost per performance unit. This has led to the need for the adoption of copper and low-κ dielectric materials to gain improved performance. Being at or near the natural limits for copper presently and with the goals for the industry aggressively continuing to call for reduced energy consumption and smaller form factors, additional approaches need to be considered. One approach, which has garnered a lot of attention, is to re-engineer advanced wafer level packaging (WLP) and develop processes for manufacturing stacked and vertically interconnected device layers. The goals for this work have been and continue to be to improve density, reduce interconnect length and therefore transmission length, reduce power consumption and provide for improved thermal management with the ultimate goal of generating smaller, thinner and more efficient electronics as well as more efficient storage facilities. Many traditional WLPs are simultaneously being combined with 3-D technologies, providing many possible packaging schemes to meet a variety of product needs. In the world of 150 μm pitch solder bumping, the introduction of RoHS rules for non-leaded solder bump compositions and the integration of processes to support them, along with the continued migration of solder bump compositions towards lead-free (SnAg, SnAgCu) alloys has been relatively simple. However, new challenges are arising in the fabrication of SnAg micro-pillars (μ-pillars) or copper μ-pillars with lead free solder caps as the bump pitch approaches 25 µm. Individual processes that are involved in the total integration have been challenged to meet the demands, with no single process left unaffected. The focus of this paper is to identify the route to defect-free plated microbumps in applications compatible with advanced packaging schemes and provide integrated solutions for improving yields and reliability.|
|Kimberly D. Pollard, Ph.D., Director of Technology