Taoyuan City, Taiwan
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Huang Y.T.,National Central University | Chen C.H.,National Central University | Lee B.H.,SHENMAO Technology Inc. | Chen H.C.,SHENMAO Technology Inc. | And 3 more authors.
Journal of Electronic Materials | Year: 2016

An in situ electromigration study has been conducted on U-groove Cu/Sn-3.5Ag/Cu and Ni/Sn-3.5Ag/Ni sandwich structures; the results were used to simulate microsolder joints passing current density of 1 × 104 A/cm2 at 150°C. The solder gap was only 15 μm, shorter than the critical length of Sn-3.5Ag solder. Backstress was proved to exist at critical solder lengths and to influence the electromigration mechanism. Theoretical calculations of the diffusivity of Cu and Ni in Sn solder indicated that the degree to which the dominant diffusion species (Cu or Ni atoms) diffused through the solder line is retarded by the backstress effect. The morphologies of intermetallic compounds (IMCs) were observed, and the grain boundaries in Sn solder were measured using electron backscatter diffraction to determine the kinetics of intermetallic growth. The results reveal that the unique electromigration characteristics of microbump joints, including the diffusivity, morphology, and backstress, can be determined. The retardation of atomic migration improves the reliability against electromigration. © 2016 The Minerals, Metals & Materials Society

Chen C.-H.,National Central University | Lee B.-H.,SHENMAO Technology Inc | Chen H.-C.,SHENMAO Technology Inc | Wang C.-M.,National Central University | Wu A.T.,National Central University
Proceedings - Electronic Components and Technology Conference | Year: 2016

In advanced 3D IC assembly, one of the key processes is to thin down the wafer for multiple-layer stacking vertically. Warpage is commonly seen in the IC chips due to the differences in coefficient of thermal expansion of the materials. The conventional peak temperatures for reflowing Sn-base Pb-free solders are above 230 °C. High temperature thermal processes would further induce severe warpage issues of the chips with thin wafers and cause failure and degrade the reliability. The development of new Pb-free alloys for low temperature assembly is important for the applications. In the previous years, Sn, In and Bi are the most common elements that are used for low temperature alloys. Setting the melting temperature at around 100 °C for the alloy is ideal for practical applications. The two alloys reported in this study show possible applications for the advanced packaging technology. Gallium has a melting temperature of 29.8 °C. Alloying Ga in Sn-Bi based solders could reduce the melting temperature to 128 °C when the composition is Sn62Bi32Ga6. The alloys reflowed on Cu substrates to investigate the microstructure. The microstructure of the cross-sectioned images and the electron probe micro-Analyzer (EPMA) analysis show that the initially formed intermetallic compound (IMC) is CuGa2. The IMCs became basin-Type due to fast dissolution of Cu into molten solders. The basin-Type IMC eventually became a continuous layer. The thermal aging tests at different temperatures yields the calculation of the activation energy, 2.82 kJ/mol. The relatively low value implies fast IMC growth and could be a possible candidate for the transient liquid phase bonding technique. Another low melting alloy, eutectic In-50wt% Bi (InBi), is developed for its melting temperature at around 95.7 °C. This study compares the properties with eutectic Sn-52wt% In (SnIn), melting point of 118 °C. Both alloys were reflowed on Cu substrates for cross-sectional microstructure investigation. The scanning electron microscopy (SEM) images revealed that the interfacial compounds were Cu6Sn5, Cu11In9 in eutectic Sn-In and In-Bi alloys, respectively. Shear tests were conducted on the samples with the alloys reflowed on OSP substrates. The results showed that InBi has almost twice the joint strength than the eutectic SnIn solders. © 2016 IEEE.

Chen C.-H.,National Central University | Lee B.-H.,SHENMAO Technology Inc. | Chen H.-C.,SHENMAO Technology Inc. | Wang C.-M.,SHENMAO Technology Inc. | Wu A.T.,National Central University
Journal of Electronic Materials | Year: 2015

A new ternary solder alloy Sn62Bi32Ga6 (in wt.%) with melting point of 128°C, which is 10°C lower than that of eutectic Sn-Bi, has been developed. The composition was obtained by adding the maximum possible amount of Ga without causing Ga segregation and the formation of a liquid phase inside the solder. Solders were reflowed on Cu substrates to investigate their interfacial morphologies during liquid reactions. The only intermetallic compound detected at the interfaces was CuGa2, which initially formed with a discrete basin type at the interfaces. As the reflow time was increased, the basin-type compound formed a continuous layer that inhibited Cu dissolution. Solid-state aging tests were also performed on the system, and the activation energy for the formation of CuGa2 was found to be 2.82 kJ/mol, which is much lower than that of the Cu-Sn compound. © 2015 The Minerals, Metals & Materials Society

Hsu H.-H.,National Central University | Wang C.-M.,Shenmao Technology Inc. | Lee H.-Y.,National Synchrotron Radiation Research Center | Wu A.T.,National Central University
2016 International Conference on Electronics Packaging, ICEP 2016 | Year: 2016

Warpage has become a very critical reliability problem for the advanced electronic packaging technique. One or more chips are stacked on the substrates for a device. The device thus contains materials that have different physical properties. The most prominent problem would be the differences in the thermal expansion coefficient for these materials. During fabrication, thermal energy was applied to the chips; the expansion of these materials would induce thermal stress and warpage on the chips that would be harmful to the long-term reliability. When a current is applied to the device, the Joule heating may further enhance the warpage of the chips. Si-on-Si interposer samples are introduced to minimize the issue. It is important to develop a quick and non-destructive method to insitu analyze the warpage level at different conditions. Synchrotron radiation X-ray is used for measuring the strain and the warpage of the Si dies. © 2016 The Japan Institute of Electronics Packaging.

Wang I.-T.,National Tsing Hua University | Duh J.-G.,National Tsing Hua University | Cheng C.-Y.,Shenmao Technology Inc. | Wang J.,Shenmao Technology Inc.
Materials Science and Engineering B: Solid-State Materials for Advanced Technology | Year: 2012

Sn3.0Ag0.5Cu solder doped with 0, 100, and 500 ppm Pd was reflowed with electroless Ni/immersion Au substrate. As Pd concentration increased in the solder, formation and growth of (Cu,Ni) 6Sn 5 were suppressed. After thermal aging, Cu 4Ni 2Sn 5 and Cu 5NiSn 5 were observed at interface of Sn3.0Ag0.5Cu-xPd/Au/Ni systems. As compared to Cu 4Ni 2Sn 5, more Pd dissolved in Cu 5NiSn 5. In addition, Pd doping enhanced the growth of Cu 4Ni 2Sn 5 and slowed the formation of Cu 5NiSn 5, which would stabilize the intermetallic compound. Based on quantitative analysis by field emission electron probe microanalyzer, the correlation between Pd doping and elemental redistribution in solder joints was probed and discussed. This study described a possible mechanism of the formation of different intermetallic compounds in Pd-doped lead-free solder. © 2011 Elsevier B.V. All rights reserved.

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