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Okamoto Y.,COSEL Co. | Takayanagi T.,COSEL Co. | Sayama T.,Machinery and Electronics Research Institute | Ejiri Y.,Toyama Prefectural University | And 2 more authors.
Proceedings of the ASME InterPack Conference 2009, IPACK2009 | Year: 2010

Thermal fatigue damage of solder joints is believed to be closely related to microstructure evolution, that is phase growth. In the previous researches, the authors have obtained the following results. The phase growth is characterized by phase growth parameter S, which is defined as average phase size to the 4th power, and proceeds such that S increases proportional to the number of thermal cycles. And a simple power low relation was found between average number of cycles to thermal fatigue crack initiation lifetime and average increase in the phase growth parameter per cycle ΔS. In this paper, in order to apply the relation to the evaluation of the crack initiation lifetime in actual solder joints, thermal cycle tests were carried out by using fabricated printed circuit board (PCB) on which chip resistors were mounted by Sn-3.0Ag-0.5Cu solder. Periodically, the specimen was taken out from thermal shock chamber and the phase growth of the β Sn phase in the solder joints was observed by scanning electron microscope (SEM). The following results were obtained. The microstructure observation showed that the lifetime prediction based on the phase growth parameter measured by the data in low cycles of 20 to 100, was within the range of 90% confidence limits of the experimentally determined lifetime. Therefore, the estimation method by the phase growth parameter can be applied to the lifetime prediction of solder joint with sufficient accuracy. Copyright © 2009 by ASME.


Tsuritani H.,Japan Central Research Institute of Electric Power Industry | Sayama T.,Machinery and Electronics Research Institute | Okamoto Y.,COSEL Co. | Takayanagi T.,COSEL Co. | And 2 more authors.
Proceedings of the ASME InterPack Conference 2009, IPACK2009 | Year: 2010

An X-ray micro-tomography system called SP-μCT, which has a spatial resolution of 1μm, has been developed in SPring-8, the largest synchrotron radiation facility in Japan. In this work, SP-μCT was applied to the nondestructive evaluation of micro-crack propagation appearing as thermal fatigue damage in lead-free solder joints. The observed specimens include two typical micro-joint structures by Sn-3.0wt%Ag-0.5wt%Cu lead-free solder. The first is an FBGA (Fine pitch Ball Grid Array) joint specimen in which an LSI package is connected to a substrate by solder bumps 360 μm in diameter, while the second is a chip joint specimen in which chip type resistors 1.6 mm in length and 0.8 mm in width are mounted on a substrate. A thermal cycle test was carried out, and the specimens were picked up at fixed cycle numbers. The same solder joints were observed repeatedly using SP-μCT at beamline BL20XU in SPring-8. An X-ray energy of 29.0 keV was selected to obtain CT (Computed Tomography) images with high contrast among some components, and a refraction-contrast imaging technique was also applied to the visualization of fatigue cracks in the solder joints. In the FBGA type specimens, fatigue cracks appeared at the periphery of the interfaces between the solder and the UBM (Under Bump Metallization) on the LSI package. As the thermal cycle proceeds, the cracks propagate gradually to the inner region of the solder bumps in the vicinity of the interface. On the basis of the three-dimensional crack images, the fatigue crack propagation lifetime was accurately estimated by means of the average crack propagation rate. On the other hand, in the chip joint specimens, fatigue cracks appeared and propagated through the thin solder layer between the chip and substrate. In contrast to the FBGA specimen, many small voids roughly 5 to 10 μm in length were formed in the solder layer. The important observed fact is that these voids deform and connect to each other due to the thermal cyclic loading prior to crack propagation. Consequently, the obtained CT images clearly show the process of crack propagation due to the thermal cyclic loading of the same solder joint. In contrast, such information has not been obtained, whatsoever by industrially employed X-ray CT systems. Copyright © 2009 by ASME.


Takei S.,Toyama Prefectural University | Takei S.,Osaka University | Murakami G.,Richell Co. | Mori Y.,Toyama Prefectural University | And 7 more authors.
Journal of Micro/Nanolithography, MEMS, and MOEMS | Year: 2013

Nanopatterning of an ecofriendly antiglare film derived from biomass using an ultraviolet curing nanoimprint lithography is reported. Developed sugar-related organic compounds with liquid glucose and trehalose derivatives derived from biomass produced high-quality imprint images of pillar patterns with a 230-nm diameter. Ecofriendly antiglare film with liquid glucose and trehalose derivatives derived from biomass was indicated to achieve the real refraction index of 1.45 to 1.53 at 350 to 800 nm, low imaginary refractive index of <0.005 and low volumetric shrinkage of 4.8% during ultraviolet irradiation. A distinctive bulky glucose structure in glucose and trehalose derivatives was considered to be effective for minimizing the volumetric shrinkage of resist film during ultraviolet irradiation, in addition to suitable optical properties for high-definition display. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.


Tsuritani H.,Machinery and Electronics Research Institute | Sayama T.,Machinery and Electronics Research Institute | Okamoto Y.,COSEL Co. | Takayanagi T.,COSEL Co. | And 2 more authors.
ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems, InterPACK 2011 | Year: 2011

The reliability or lifetime of micro-joints on printed circuit boards (PCBs) is significantly affected by fatigue processes, including fatigue crack initiation and propagation to failure. Accordingly, the industries producing electronic devices and components strongly desire a new nondestructive inspection technology, which detects micro-cracks appearing as thermal fatigue fractures in the joints. In this investigation, we applied a synchrotron radiation X-ray micro-tomography system called the SP-μCT to three-dimensionally and nondestructively evaluate the fatigue crack propagation process in complex-shaped solder joints. The observed specimens have a typical joint structure in which chip type resistors 1.0 mm in length and 0.5 mm in width are mounted on an FR-4 substrate by joining with Sn-3.0Ag-0.5Cu solder. A thermal cycle test was carried out, and specimens were collected at fixed cycle numbers. The same solder joints were observed successively using the SP-μCT at beamline BL20XU at SPring-8, the largest synchrotron radiation facility in Japan. An X-ray energy of 29.0 keV was selected to obtain computed tomography (CT) images with high contrast among some components, and a refraction-contrast imaging technique was also applied to the visualization of fatigue cracks in the solder joints. The following results were obtained. At the early stage in the fatigue process of normal joints, the main fatigue cracks were clearly observed to initiate from the region around the solder joint tip and the vicinity of the chip corner. Additionally, many micro-cracks roughly 5 to 10 μm in length also formed in the thin solder layer between the chip and substrate. The important observed fact is that these micro-cracks deform, grow, and connect to each other due to the thermal cyclic loading, prior to main crack propagation. On the other hand, in case of solder joints which included relatively larger initial voids, the voids deformed, and the fatigue cracks initiated and propagated from the surface of the voids. Furthermore, by employing the three-dimensional crack images, the crack dimensions were quantified straightforwardly by measuring the surface area of the fatigue crack, and the fatigue crack propagation process was also accurately evaluated via the average crack propagation rate. Consequently, the obtained CT images clearly illustrate the process of crack propagation due to the thermal cyclic loading of a solder joint. In contrast, such information has not been obtained in any form by industrially employed X-ray CT systems or finite element analyses. © 2011 by ASME.


Tsuritani H.,Machinery and Electronics Research Institute | Sayama T.,Machinery and Electronics Research Institute | Okamoto Y.,COSEL Co. | Takayanagi T.,COSEL Co. | And 3 more authors.
ASME 2013 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems, InterPACK 2013 | Year: 2013

The reliability and lifetime of micro-joints on printed circuit boards (PCBs) is significantly affected by fatigue processes, including fatigue crack initiation and propagation to failure. Accordingly, the industries producing electronic devices and components strongly desire the development of a new nondestructive inspection technology, which detects micro-cracks appearing as thermal fatigue fractures in these joints. Accordingly, the authors have demonstrated that the micro-cracks in the micro-solder joints can be observed using the SP-μCT synchrotron X-ray micro tomography system. However, in order for such solder joint micro-cracks to be observable by SP-μCT, the observation object must have a diameter of less than roughly 1 mm. In this investigation, we applied a synchrotron radiation X-ray laminography system to three-dimensionally and nondestructively evaluate the fatigue crack propagation process in flip chip solder micro-joints. X-ray laminography is a technique for nondestructively observing planar objects. The optical system developed for use in X-ray laminography was constructed to provide the rotation stage with a 20° tilt from the horizontally incident X-ray beam. For this reason, X-rays were sufficiently transmitted through the planar object, in all directions. The observed specimens had a flip chip structure, in which a 10.04 mm square LSI chip is connected to a 52.55 mm (length) × 30.0 mm (width) FR-4 substrate by 120 μm diameter Sn-3.0wt%Ag-0.5wt%Cu leadfree solder bumps. A thermal cycle test was carried out, and specimens were collected at fixed cycle numbers. The same solder joints were observed successively using the synchrotron radiation X-ray laminography system at beamline BL20XU at SPring-8, the largest synchrotron radiation facility in Japan. An X-ray beam energy of 29.0 keV was selected to obtain laminography images with high contrast among component. The obtained laminography images clearly show the evolution of cracks, voids, and the Ag3Sn phase due to the thermal cyclic loading of the solder joints. In addition, the surface area of the same fatigue cracks was also measured, to quantify the crack propagation process. However, the surface area change measured by laminography differed from the crack propagation results obtained by standard SP-μCT. This difference may be due to an inability to observe some micro-cracks, due to crack closure to beneath than the detection limit of synchrotron radiation X-ray laminography. Consequently, these results demonstrate the possibility that nondestructive observation of fatigue cracks in the solder bumps on a large size electronic substrate by synchrotron radiation X-ray laminography, although its detection ability for narrow cracks may be limited, compared to SP-μCT. Copyright © 2013 by ASME.

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