Ni/Cu/Sn bumping scheme for fine-pitch micro-bump connections

• Published in: 2011 IEEE 61st Electronic Components and Technology Conference (ECTC) pp. 109 - 113
• Main Authors: Zhang, W., Limaye, B. D. P., Manna, A. L., Soussan, P., Beyne, E.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.05.2011
• Subjects: Aging; Bonding; Copper; Intermetallic; Nickel; Tin
• ISBN: 1612844979; 9781612844978
• ISSN: 0569-5503; 2377-5726
• DOI: 10.1109/ECTC.2011.5898499

3D integration requires a physical stacking of die/wafer onto another die/wafer while forming a permanent electrical and mechanical connection between the input/output pins of the devices. Tin-based micro-bump (μbump) connections using copper (Cu) or nickel (Ni) Under-Bump-Metallurgy (UBM) with interconnect pitches of 40 μm and smaller are generally considered to be the leading candidates for these high density Si-to-Si interconnects, particularly because of their tolerance to height variation, similarity to standard flip-chip solder joints and ease of processing. In this paper, a systematic study of the metallurgical interactions in the Ni/Cu/Sn system is presented, using both stacks of blanket films and μbumps. Furthermore, a novel Ni/Cu/Sn μbump scheme is developed to replace the conventional Cu/Ni/Sn or Cu/Sn schemes in order to improve the μbump solder joint quality and reliability. Here a very thin layer of Cu between Ni UBM and Sn solder is used to avoid the formation of (Ni, Cu) 3 Sn or Cu 3 Sn and significantly reduce void formation.