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Flip-chip solder joints have become the most important technology for high-density packaging in the microelectronic industry. As the size of the joints progressively shrinks, the carried current density increases. The octagonal passivation opening is now used in packaging industry. The shape effect of passivation opening on its electric behavior during electromigration is clear. This study investigates...
In this study, the temperature map distribution in the Sn3.0Ag0.5Cu solder bump with Cu column under current stressing is directly examined using infrared microscopy. It is the radiance changes between the different materials of the surface that cause the unreasonable temperature map distribution. By coating a thin layer of black optical paint which is in order to eliminate the radiance changes, we...
The requirement for smaller devices but with much greater performance leads to a boost in current density and damage caused by electromigration. Recently, some researches show that the grain orientation changes during current stressing. In this study, the solder of SnAg2.6 with 2 um-thick UBM layer of Ni and 20 um-thick copper pad is used. Electron Backscattered Diffraction (EBSD) is applied to investigate...
The Joule heating effect at various stages of electromigration of flip-chip Sn3.5Ag solder joints was investigated under a current of 0.5 Amp at 100??C. During various stages of electromigration, voids may form and propagate and Joule heating effect may vary at different void sizes. To verify the void nucleation and propagation on Joule heating effect during electromigration process, the solder bump...
Thermomigration in Pb-free SnAg solder joints is investigated during accelerated electromigration tests under 9.7times103 A/cm2 at 150degC. Different from Pb-containing solders, it is found that Cu-Sn intermetallic compounds (IMCs) migrate toward the cold end on the substrate end and thus voids accumulate in the passivation opening for the bump with current flowing from the substrate end to the chip...
The authors demonstrate a Ni/Cu bilayer structure for the under-bump-metallization (UBM) in Sn-Ag flip chip solder joints to enhance the electronmigration lifetime. The Ni layer provides two main contributions for the lifetime improvement. First, since Ni is a good diffusion barrier for Cu, it reduces the electromigration failure by UBM dissolution. Furthermore, the Ni layer limits the current crowding...
Several simulation studies reported that a hot spot exists in flip-chip solder bumps under accelerated electromigration. Yet, there are no experimental data to verify it. In this paper, the temperature distribution during electromigration in flip-chip SnAg3.5 solder bumps is directly inspected using infrared microscopy. Two clear hot spots are observed in the bump. One is located at the region with...
It is well known that Ni and its alloys possess a lower reaction rate with Sn than Cu and Cu alloys. Therefore Ni-based under bump metallization have attracted attention in recent years. In this study, the diffusion-controlled reaction between eutectic Sn-3.5Ag flip chip solder joints between electroplated-Ni (EP-Ni) and electroless-Ni (EL-Ni) has been investigated. Morphology and growth kinetics...
In this paper, the temperature distribution during electromigration in flip-chip SnAg3.5 solder bumps is directly examined using infrared microscopy. Two clear hot spots are observed in the bump. One is located at the region with peak current density, and the other one is at the bump edge under the current-feeding metallization on the chip side. Under a current stress of 1.06 times 104 A/cm2, the...
The electromigration in flip chip joints of Cu column bump with two different kinds of solder bumps; eutectic SnPb or eutectic SnAg was studied. The Cu columns were 50 mum thick and 50 mum diameter for eutectic SnPb solders and 80 mum thick and 85 mum diameter for eutectic SnAg solders. We observed that these flip chip joints did not fail after 1 month at 100 degC with a current density of 1times10...
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