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Ōsaka, Japan

Jo J.-L.,Osaka University | Nagao S.,Osaka University | Hamasaki K.,Osaka University | Tsujimoto M.,C. Uyemura and Co. | And 2 more authors.
Journal of Electronic Materials | Year: 2014

In this study, the morphological development of electroplated matte Sn and Sn-xBi (x = 0.5 wt.%, 1.0 wt.%, 2.0 wt.%) film surfaces was investigated under diverse testing conditions: 1-year room-temperature storage, high temperature and humidity (HTH), mechanical loading by indentation, and thermal cycling. These small Bi additions prevented Sn whisker formation; no whisker growth was observed on any Sn-xBi surface during either the room-temperature storage or HTH testing. In the indentation loading and thermal cycling tests, short (<5 μm) surface extrusions were occasionally observed, but only on x = 0.5 wt.% and 1.0 wt.% plated samples. In all test cases, Sn-2Bi plated samples exhibited excellent whisker mitigation, while pure Sn samples always generated many whiskers on the surface. We confirmed that the addition of Bi into Sn refined the grain size of the as-plated films and altered the columnar structure to form equiaxed grains. The storage conditions allowed the formation of intermetallic compounds between the plated layer and the substrate regardless of the Bi addition. However, the growth patterns became more uniform with increasing amounts of Bi. These microstructural improvements with Bi addition effectively released the internal stress from Sn plating, thus mitigating whisker formation on the surface under various environments. © 2013 TMS. Source


Jalkanen T.,University of Turku | Makila E.,University of Turku | Suzuki Y.-I.,C. Uyemura and Co. | Urata T.,Kyoto University | And 4 more authors.
Advanced Functional Materials | Year: 2012

Preparation of graded-index optical microcavities based on porous silicon is demonstrated, and chemical modifications for obtaining improved stability under alkaline conditions are studied. Four surface modification methods for stabilizing the samples are examined, and the effects on the optical properties are verified. Two different thermal carbonization treatments resulting in hydrophilic and hydrophobic surfaces are employed. In addition, modification with undecylenic acid is performed on as-prepared and thermally hydrocarbonized porous silicon surfaces. Stability and sensing capabilities of the modified samples are examined by subjecting them to different concentrations of methylamine and trimethylamine vapors. Vapor induced changes in the reflectance spectra are used for evaluating sensitivity and stability. Sensitivity towards ethanol vapor is also measured in order to compare the sensitivity to a normal organic solvent. The results show that the two carbonization treatments and the undecylenic acid functionalization of the hydrocarbonized surface result in greatly improved stability. In contrast, derivatization of as-prepared porous silicon with undecylenic acid does not protect the surface sufficiently against oxidation under the highly basic conditions produced by the amine vapors. Surface chemistry is also shown to have a large effect on sensitivity towards the examined vapors. X-ray photoelectron spectroscopy was used to assess changes in elemental composition of sample surface. The results suggest that thermally promoted addition of undecylenic acid on hydrocarbonized porous silicon is an effective method for producing highly stable optical structures with a carboxyl group functionalization. © 2012 WILEY-VCH Verlag erlag GmbH & Co. KGaA, Weinheim. Source


Jo J.-L.,Osaka University | Nagao S.,Osaka University | Sugahara T.,Osaka University | Tsujimoto M.,C. Uyemura and Co. | Suganuma K.,Osaka University
Journal of Materials Science: Materials in Electronics | Year: 2013

Whisker growths from matte tin electroplating have been observed during thermal cycling up to 1,000 cycles either in air or in vacuum. The density, length, and width of thermal stress whiskers depend on the plating thickness of 2 and 5 μm in the present study. Whiskers grown on the 2 μm plating are longer and thinner than those on 5 μm plating. In both cases, whiskers grow thinner and faster in vacuum than in air. These apparent variations come from the grain sizes and the thermal stress distributions in the electroplating, intrinsically different in 2 and 5 μm thick films. The grain structure of whisker root, particularly grain boundary cracks oxidized in air, determines the stress concentration to drive the whisker growth. Cracking caused by oxidation was rarely observed in vacuum hence causes thin and straight whiskers even from thick plating. Our results indicate that the stress concentration at whisker root grain is essential for controlling whisker growth morphology, and has a critical impact on various electronic applications. © 2013 Springer Science+Business Media New York. Source


Jo J.-L.,Osaka University | Kim K.-S.,Hoseo University | Sugahara T.,Osaka University | Nagao S.,Osaka University | And 3 more authors.
Journal of Materials Science: Materials in Electronics | Year: 2013

Long term surface evolution of matte tin electroplating has been investigated under room temperature to understand the tin whisker mitigation by a trace amount of lead addition. No whisker growth has been observed on all the Sn-xPb samples (1 ≤ x ≤ 10 wt%), while at least 3 wt% of Pb addition is required to alter the columnar grain structure of pure Sn plating to equiaxed grains. The mitigation mechanism by such a trace amount of Pb is not caused by the grain texture control, but is due to the less inter-metallic composite (IMC) growth; the segregated Pb at the columnar grain boundaries disrupts the IMC growth, and releases Sn grain boundary migrations to relax the internal stress. This mechanism of stress relaxation and whisker growth suppression suggests that lead-free Sn plating without whisker growth can be realized by co-plating Sn with a Pb-like metal element that precipitates at the grain boundary to interfere with the IMC growth. © 2013 Springer Science+Business Media New York. Source


Patent
C. Uyemura And Co. | Date: 2012-11-01

A manufacturing method of a buildup circuit board includes forming a wiring layer on an organic polymer insulating layer by copper electroplating and building up other organic polymer insulating layer on the wiring layer, wherein in a final step of the copper electroplating, a surface of the wiring layer is roughened by copper electroplating and the organic polymer insulating layer is formed directly on the roughened surface of the wiring layer. According to the invention, a specific etching step that is essential for enhancing adhesion between the organic polymer insulating layer and the wiring layer can be omitted and no expensive etching apparatus is necessary, thus being good in economy. In addition, if various types of copper sulfate plating baths containing different types of additives used for via fill plating are used as they are, irregularities on the surface can be made in various forms and roughnesses. Thus, it is necessary to select a specific type of etching solution depending on film characteristics ascribed to types of additives. Moreover, it is easy to form surface irregularities in conformity with the type of material and physical properties of the organic polymer insulating layer being built up.

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