Extended abstract :C4NP - solder bumps for flip chip and microbumps for 3D

Abstract

IBM's new lead-free solder bumping technology C4NP (Controlled Collapse Chip Connection - New Process) has originally been developed to replace solder electro-plating in traditional FlipChip bumping applications ranging from larger than 250um solder ball pitch down to below 150um pitch. This work reviews lead-free reliability data based on IBM's standard test vehicles. A UBM pad was formed and lead free solder was applied onto the test wafers using C4NP. The parts underwent full reliability stress testing. Also included in this work is comprehensive data about 300mm C4NP equipment performance and production yield based on a high-volume manufacturing environment. Besides FlipChip, more and more bumping applications fall into the 3D packaging and 3D integration space which is characterized by its tight pitch and high performance requirements. Feasibility of 50 μm fine pitch solder bumping of 300mm wafers using C4NP has been studied. Interconnection of TSV's is expected to drive the bump pitch requirements even lower. Glass molds were fabricated, filled with solder, inspected, and the solder transferred to a wafer with fine pitch UBM pads. Four molds have been fabricated with cavity top diameters ranging from ~33 to 40 μm., The molds were filled with binary SnAg solder using the mold fill tool, automatically inspected with the mold inspect tool, and wafers were bumped with the solder transfer tool. Characterization of the filled molds and bumped wafers is presented. The C4NP process utilizes glass molds with etched cavities according to the bump pattern on the wafer. The cavities are filled with pure molten solder (lead-free or leaded). After a mold inspection step, the mold and wafer are aligned and brought into contact for a single step solder transfer process. The process does not require liquid flux and is compatible with 300mm or smaller wafers. C4NP eliminates the complexities and cost associated with electroplating infrastructure. Data provided by IBM Systems and Technology Group.