A study on film properties of electrochemically deposited tin-silver-copper (SnAgCu) alloys was performed with an alkaline bath. This research focused on the bath and process development for dendrite-free, near-eutectic SnAgCu alloy deposition through the investigation of cathodic polarization, morphological transition, and film composition. Effects of process parameters on surface morphology, film composition, and diffusion-limited current density (LCD) were also examined. Ternary alloys were obtained only when the current density was driven beyond the mass-transfer limitation of noble metals (silver and copper), which seemed to cause the transition of surface morphology and film composition with increasing current density. The morphological transition occurred through four stages (dendrites, suppression of dendrites, nodules, and columns/dendrites), and the content of noble metals in the film tended to drop with increasing current density. With increasing the concentration of noble metals, bath temperature, and agitation, the morphology at low current densities became increasingly dendrite-dominated and the content of noble metals in the film was enhanced at a fixed current density. The morphology of stage four was influenced by the ratio of the applied current density to the LCD, where the LCD was significantly influenced by the metal concentration, bath temperature, and agitation. © 2002 The Electrochemical Society. All rights reserved.

The electrodeposition of near-eutectic SnAg solders for wafer level packaging was investigated with Shipley-Ronal’s EXP-0700 SnAg bath. Fundamental studies including polarization behavior, morphological transition, and compositional change were performed to investigate the alloy deposition mechanism. It was proven that the mass transfer limitation of silver ions at low potential drove the drastic change of morphology and composition with increasing current density. The morphological transition occurred through four stages (dendrites, suppression of dendrites, facets, and dendrites) and the content of silver in the deposit dropped with increasing current density. The deposition mechanism of SnAg alloys with this bath looks similar to that of SnAgCu alloys with an alkaline bath due to a similar polarization behavior. Pattern plating results including studs, mushrooms, and stacks can be summarized as fine-grained surface, high deposition rate, good uniformity, and repeatability. Two types of in situ stack plating, Cu/SnAg and Ni/SnAg, were successfully performed with no defects between two layers. Reflow tests conducted with near-eutectic SnAg solders on copper studs showed spherical shapes with smooth surfaces, where the average melting point of whole bumps in a wafer was 223.7°C, which is close to the melting point (221°C) of the eutectic composition. © 2003 The Electrochemical Society. All rights reserved.

Electrical waveform mediated through-mask deposition of solder bumps was investigated with several types of plating baths for wafer level packaging applications. The influence of varying duty cycle in the presence of additives on deposit properties including shape evolution within the cavity, abnormal growth, surface morphology, alloy composition, and thickness distribution was evaluated at a fixed, moderate frequency. Waveform mediation with properly selected duty cycles ͑i͒ improved surface flatness and morphology of deposits when the shape ratio with dc deposition was less than 1, ͑ii͒ suppressed the probability of abnormal growth ͑nonhomogeneous growth such as large nodules͒, ͑iii͒ reduced grain sizes resulting in smoother surfaces, and (iv) modulated alloy composition at a given bath and process condition. With decreasing duty cycle, the thickness distribution within the feature, pattern, and workpiece also changed due to the increased influence of primary current distribution. The fraction of current flowing along the cavity edge, die edge ͑when the space between dice is much larger than the bump pitch͒, and wafer edge seems to increase with decreasing duty cycle.

Interfacial adhesive energy was evaluated quantitatively in relation to the bonding temperature and subsequent thermal treatment to develop a Cu-Cu thermal compressed bonding process at low temperature for a threedimensional integration circuit (3D-IC) package. Two pieces of sputtered Cu films coated on a Si wafer were bonded at 300°C, 350°C, and 400°C. A high bonding temperature increased the interfacial adhesive energy, and the original interfacial layers of Cu film gradually disappeared, as observed in focus ion beam (FIB) images. Specimens of Cu to Cu bonding were thermally compressed at 300°C and were post-annealed at 200°C, 250°C, and 300°C in a N 2 environment for 1 h. As a result, the original interfacial layer of Cu disappeared at 300°C, and an interfacial adhesive energy value above 10 J/m 2 was obtained.

There is no question that 3D integration will be the next generation of packaging. This requires new technologies from ultra thin wafer handling to wafer to wafer bonding with 3D inter substrate connections.TSV is a process in which wafers are thinned, stacked and interconnected to significantly improve electrical performance such as signal transmission, interconnect density, reduced power consumption, form factor and manufacturing costs. TSV -the next generation of packaging Graph 2: comparison wire bonding to 3D stackingThe TSV process requires ultra thin wafers with less than 50µm to reduce the stack thickness and improve the performance of the IC Device. EVG has developed a solution for temporary bonding of wafers to carriers to be able to run in standard IC Fab's all processes for back grinding, etching, metallization, wafer bonding and solder ball formation. Ultra thin wafer handling solutionsDepending on the process requirements 2 different solutions are on the market: -lamination of tapes on carriers, Si or glass wafers; disadvantage of tapes are the limitation of process temperature of usually max 170°C as well as the poor edge protection -spin on adhesive materials on carriers with the advantage of high process temperature up to 250°C with excellent edge protection. Graph 3: edge protection by tape versa spin on materialEVG has developed systems for a fully automated lamination and bond process as well as de-bonding systems for high volume manufacturing.When high process temperature e.g. for metallization is required we prefer spin on materials from our partner Brewer Science. The materials from Brewer Science HT250 and HT10.10 have high chemical resistance as well as high thermal resistance up to 250°C.