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Recently, the dimensions of the flip-chip solder bumps reduce to about 20-30 micrometers, also known as "micro-bumps" sandwitched between two Si chips. In such a structure, electromigration and thermomigration behaviors in the micro-bumps are not clear now. In this study, the temperature map distribution of Al traces and Al pads in CoC and C4 structures during current stressing was directly...
Electromigration of flip-chip solder joints has been studied extensively in recent years. It was investigated in plenty of studies that the current crowding effect takes place at the corner near the traces due to huge differences in cross-section area between traces and solder joint. The local high current density, which has been known as a serious reliability issue, causes the failure such as void...
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...
Electromigration of flip-chip solder joints has been studied extensively in recent years. It was investigated in plenty of studies that the current crowding effect takes place at the corner near the traces due to huge differences of dimensions between traces and solder joint. The local high current density, which has been known as a serious reliability issue, causes the failure such as void formation...
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 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...
This study investigates the effect of passivation opening design on electromigration reliability issue in flip-chip solder joints by using statistical analysis. Eutectic SnAg solder joints were used in this study with two different filling condition of polyimide (PI), ie with or without contact opening. The bump height is 50 ??m. The four point probe method was used to monitor the bump resistance...
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 simulation results show that larger contact opening may not benefit on relieving current crowding effect in the flip-chip solder joints. For the solder joints with a 10-mum thick Cu UBM, the diameter of the contact opening for the lowest current crowding effect is 60 mum. It means that using larger or smaller diameter will increase the current density in the solder bumps. In addition, the optima...
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...
This study investigates electromigration study of eutectic SnPb flip-chip solder joints on ceramic substrates. The under bump metallization (UBM) structure consists of 5-mum Cu / 3-mum Ni under bump metallization (UBM). Under the current stressing by 0.9 A at 150degC, we did not find void formation but a large amount of intermetallic compound (IMC) of Cu6(Sn,Ni)5 were formed when the bump resistance...
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...
With the portable devices becoming smaller and more compact in size, flip-chip technology has been adopted for fine-pitch packaging in microelectronics industry. Area array of tiny solder joints can be fabricated on Si chips to achieve high-density packaging. In addition, as the required performance continues to increase, the input/output (I/O) pin count of flip-chip products has dramatically increased...
This study employs three-dimensional simulation to investigate the Joule heating effect under accelerated electromigration tests in flip-chip solder joints. It was found that the Joule heating effect was very serious during high current stressing, and a hot spot exists in the solder bump. The hot spot may play important role in the void formation and thermomigration in solder bumps during electromigration
In flip-chip solder joints, Cu has been used as a under-bump metallization (UBM) for its excellent wettability with solders. In addition, electromigration has become a crucial reliability concerns for fine-pitch flip chip solder joints. In this paper, 3D finite element method was employed to simulate the current density distribution for the eutectic SnPb solder joints with 5 mum, 10 mum, and 20 mum...
As the prediction that the I/O pitch will decrease from 60 um in 2004 to 20 um beyond 2010 by ITRS roadmap, flip chip interconnection by traditional ACF containing conductive particles with micro-meter size will face more and more challenges. One of many possible solutions is using high aspect-ratio metal posts or flake instead of conductive particles for electrical interconnection between chip and...
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