Nondestructive Observation of Thermal Fatigue Crack Propagation in FBGA and Die Attached Solder Joints by Synchrotron Radiation X-Ray Laminography

2015 ◽  
Author(s):  
Hiroyuki Tsuritani ◽  
Toshihiko Sayama ◽  
Yoshiyuki Okamoto ◽  
Takeshi Takayanagi ◽  
Masato Hoshino ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Synchrotron Radiation ◽  
Crack Propagation ◽  
Thermal Fatigue ◽  
Solder Joints ◽  
Fatigue Cracks ◽  
Three Dimensional ◽  
X Ray ◽  
Micro Cracks ◽  
Solder Bumps

The reliability of solder joints on printed circuit boards (PCBs) is significantly affected by thermal fatigue processes due to downsizing and high density packaging in electronic components. Accordingly, there is a strong desire in related industries for development of a new nondestructive inspection technology to detect fatigue cracks appearing in these joints. The authors have applied the SP-μCT, a synchrotron radiation X-ray microtomography system, to the nondestructive observation of such cracks. However, for planar objects such as PCB substrates, reconstruction of CT images is difficult due to insufficient X-ray transmission along the parallel axis of the substrate. In order to solve this problem, a synchrotron radiation X-ray laminography system was developed to overcome the size limits of such specimens. In this work, this system was applied to the three-dimensional, nondestructive observation of thermal fatigue cracks in solder joints, for which X-ray CT inspection has been extremely difficult. The observed specimens included two typical joint structures formed using Sn-3.0Ag-0.5Cu solder: (1) a fine pitch ball grid array (FBGA) joint specimen in which an LSI package is connected to a substrate by solder bumps 360 μm in diameter, and (2) a die-attached specimen in which a 3 mm square ceramic chip is mounted on a substrate. The optical system developed for use in X-ray laminography was constructed to provide a rotation axis with a 30° tilt from the right angle to the X-ray beam, and to obtain X-ray projection images via the beam monitor. The same solder joints were observed successively using the laminography system at beamline BL20XU at SPring-8, the largest synchrotron radiation facility in Japan. In the FBGA type specimen, fatigue cracks were clearly observed to appear at the periphery of the joint interface, and to propagate gradually to the inner regions of the solder bumps as thermal cycling proceeded. In contrast, in the die-attached joint specimen, micro-cracks were observed to appear and propagate through the thin solder layer. An important observation was that these micro-cracks become interconnected prior to propagation of the main fatigue crack. The fatigue crack propagation lifetime was also estimated in both specimens by measuring the crack surface area and calculating the average crack propagation rate through the three-dimensional images. Consequently, the sectional images obtained by the laminography system clearly show the process of crack propagation due to thermal cyclic loading.

Three Dimensional and Nondestructive Evaluation of Thermal Fatigue Crack Propagation Process in Complex-Shaped Solder Joints by Synchrotron Radiation X-Ray Micro-Tomography

2011 ◽  
Author(s):  
Hiroyuki Tsuritani ◽  
Toshihiko Sayama ◽  
Yoshiyuki Okamoto ◽  
Takeshi Takayanagi ◽  
Kentaro Uesugi ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Synchrotron Radiation ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Solder Joints ◽  
Fatigue Cracks ◽  
Propagation Process ◽  
X Ray ◽  
Micro Cracks ◽  
Crack Propagation Process

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.

Application of Synchrotron Radiation X-Ray Laminography to Nondestructive Evaluation of the Fatigue Crack Propagation Process in Flip Chip Solder Joints

2013 ◽  
Author(s):  
Hiroyuki Tsuritani ◽  
Toshihiko Sayama ◽  
Yoshiyuki Okamoto ◽  
Takeshi Takayanagi ◽  
Kentaro Uesugi ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Synchrotron Radiation ◽  
Crack Propagation ◽  
Flip Chip ◽  
Solder Joints ◽  
Fatigue Cracks ◽  
Propagation Process ◽  
X Ray ◽  
Micro Cracks ◽  
Crack Propagation Process

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 lead-free 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.

In-Situ Monitoring via Synchrotron Radiation Laminography of Thermal Fatigue Cracks at Die-Attached Joints Under Cyclic Energization Loading

2017 ◽  
Author(s):  
Hiroyuki Tsuritani ◽  
Toshihiko Sayama ◽  
Yoshiyuki Okamoto ◽  
Takeshi Takayanagi ◽  
Masato Hoshino ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Thermal Fatigue ◽  
Fatigue Cracks ◽  
In Situ Monitoring ◽  
X Ray ◽  
Crack Propagation Process ◽  
Thermal Fatigue Cracks

Recently, due to the increasing heat density of printed circuit boards (PCBs), thermal fatigue damage in the joints has exerted a more significant influence on the reliability of electronic components. Accordingly, the development of a new nondestructive inspection technology is strongly desired by related industries. The authors have applied a synchrotron radiation X-ray micro-tomography system to the nondestructive observation of micro-cracks. However, the reconstruction of CT images is difficult for planar objects such as PCB substrates, due to insufficient X-ray transmission in the direction parallel to the substrates. In order to solve this problem, a synchrotron radiation laminography system was developed to relax size restrictions on the observation samples, and was applied to the three-dimensional nondestructive evaluation of several kinds of solder joints, which were loaded under accelerated thermal cyclic conditions via thermal shock tests. Moreover, the thermal fatigue crack propagation process that occurs under actual PCB energization loading conditions will differ from that under the usual acceleration test conditions. In this work, the possibility of in-situ monitoring of the thermal fatigue crack propagation process using the laminography system was investigated at die-attached joints subjected to cyclic energization loading, which is close to the actual usage conditions of PCBs. The optical system developed for use in the laminography system was constructed to provide a rotation stage with a tilt from the horizontally incident X-ray beam, and to obtain X-ray projection images via a beam monitor. In this manner, the X-ray beam is sufficiently transmitted through the planar specimen in all projections. The observed specimens included several die-attached joints, in which 3 mm square ceramic dies had been mounted on a 40 mm square FR-4 substrate using Sn-3.0wt%Ag-0.5wt%Cu solder. Consequently, the laminography system was successfully applied to the in-situ monitoring of thermal fatigue cracks that appeared in the solder layer under cyclic energization. This was possible because the laminography images obtained in the energization state have a quality that is equivalent to those obtained in a non-energized state, provided that the temperature distribution of the specimen is stable. In addition, the fatigue crack propagation process can be quantitatively evaluated by measuring the crack surface area and calculating the average crack propagation rate. However, in some cases, the appearance of thermal fatigue cracks was not observed in a solder layer that had been loaded by the accelerated thermal cycle test. This result strongly suggests that delamination occurred at the interface, which indicates that the corresponding fracture mode was significantly influenced by the type of thermal loading.

Nondestructive Evaluation of Thermal Fatigue Crack Propagation in Sn-Ag-Cu Solder Joints by Synchrotron Radiation X-Ray Micro-Tomography

2009 ◽  
Author(s):  
Hiroyuki Tsuritani ◽  
Toshihiko Sayama ◽  
Yoshiyuki Okamoto ◽  
Takeshi Takayanagi ◽  
Kentaro Uesugi ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Nondestructive Evaluation ◽  
Thermal Cycle ◽  
Solder Joints ◽  
Fatigue Cracks ◽  
Lead Free Solder ◽  
X Ray ◽  
Solder Bumps ◽  
Micro Tomography ◽  
Free Solder

An X-ray micro-tomography system called SP-μCT, which has a spatial resolution of 1 μm, 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.

Application of Synchrotron Radiation X-Ray Microtomography to Nondestructive Evaluation of Thermal Fatigue Process in Flip Chip Interconnects

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Hiroyuki Tsuritani ◽  
Toshihiko Sayama ◽  
Yoshiyuki Okamoto ◽  
Takeshi Takayanagi ◽  
Kentaro Uesugi ◽  
...  
Keyword(s):  
Synchrotron Radiation ◽  
Crack Propagation ◽  
Nondestructive Evaluation ◽  
Thermal Fatigue ◽  
Flip Chip ◽  
Fatigue Cracks ◽  
Nondestructive Inspection ◽  
Ct Images ◽  
Phase Growth ◽  
X Ray

New nondestructive inspection methods with high spatial resolution are expected to support the evaluation and enhancement of the reliability of microjoints on printed circuit boards. An X-ray microtomography system, the SP-μCT has been developed at the Super Photon ring-8 GeV (SPring-8), the largest synchrotron radiation facility in Japan. In this work, the SP-μCT was first applied to the nondestructive evaluation of thermal fatigue phenomena, namely microstructure evolution (i.e., phase growth) and microcrack propagation, appearing in actual solder microbumps of flip chip interconnects due to thermal cyclic loading. In addition, a refraction-contrast imaging technique was simultaneously applied to visualize the fatigue cracks with an actual opening of less than 100 nm. The observed specimen has a flip chip structure joined by Sn-37wt%Pb eutectic solder bumps 150 μm in diameter. Consequently, the process of phase growth and crack propagation was determined via observation of consecutive computed tomography (CT) images obtained in the same plane of the same specimen. As the thermal cycle proceeded, remarkable phase growth was clearly observed, followed by the appearance of fatigue cracks in the corners of the interfaces between the solder bump and Cu pad. Moreover, the CT images also enabled us to evaluate the fatigue lifetime of the bumps, as follows. The lifetime to fatigue crack initiation was estimated by quantifying the increase in the phase growth. The crack propagation lifetime to failure was then determined by measuring the average crack propagation rate. Such results have not been obtainable at all by X-ray CT systems for industrial use and demonstrate the possibility of nondestructive inspection by a synchrotron radiation X-ray microtomography system.

Application of Synchrotron Radiation X-Ray Micro-Tomography to Nondestructive Evaluation of Thermal Fatigue Damage in Flip Chip Interconnects

2007 ◽  
Author(s):  
Hiroyuki Tsuritani ◽  
Toshihiko Sayama ◽  
Yoshiyuki Okamoto ◽  
Takeshi Takayanagi ◽  
Kentaro Uesugi ◽  
...  
Keyword(s):  
Synchrotron Radiation ◽  
Fatigue Damage ◽  
Thermal Fatigue ◽  
Thermal Cycle ◽  
Flip Chip ◽  
Solder Bump ◽  
Fatigue Cracks ◽  
Phase Growth ◽  
X Ray ◽  
Solder Bumps

A synchrotron radiation X-ray micro-tomography system called SP-μCT with a spatial resolution of about 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 microstructure evolution; that is phase growth, and micro-crack propagation appearing as thermal fatigue damage in solder micro-bumps of flip chip interconnects. The observed specimens have a flip chip structure joined by Sn-37wt%Pb eutectic solder bumps 100μm in diameter. A thermal cycle test was carried out, and the specimens were picked up at any number of cycles. The solder bumps were observed by using SP-μCT at the beamlines BL47XU and BL20XU in SPring-8. An X-ray energy of 29.0 keV was selected to obtain absorption images with a high contrast between the Sn-rich and the Pb-rich phases. Additionally, a refraction-contrast imaging technique was applied to visualize fatigue cracks in the solder bumps. The obtained CT (Computed Tomography) images clearly show the process of phase growth and crack propagation due to the thermal cyclic loading of the same solder bump; such information has not been obtained at all by industrially-used X-ray CT systems. In the initial state, the Pb-rich phase was dispersed with characteristic shape, which appears in reflow soldering process. Remarkable phase growth was also observed clearly as the thermal cycle test proceeded. When the loading reached 300 cycles, fatigue cracks appeared in the corners of the interfaces between the solder bump and the Cu pad. The CT images enabled us to evaluate the lifetime of the bumps to the initiation of fatigue cracks by estimating the increase in a phase growth parameter, which corresponds to the accumulation of fatigue damage in the solder joints. The results showed that the estimated lifetime strongly agreed with the average value, which was determined by SEM (Scanning Electron Microscope) destructive observations. As the thermal cycle proceeded, the cracks propagated gradually to the inner region of the solder bump. From the CT images, the average propagation rate was calculated, and the mean of the total fatigue lifetime was estimated to be less than 1800 cycles. These results show the possibility that nondestructive testing by a synchrotron radiation X-ray micro CT system is useful for evaluating the thermal fatigue lifetime in micro-joints.

1928 Evaluation of Thermal Fatigue Micro-crack Propagation Process in Flip Chip Interconnects by Synchrotron Radiation X-ray Micro-tomography

2007 ◽  
Vol 2007.7 (0) ◽  
pp. 221-222
Author(s):  
Hiroyuki Tsuritani ◽  
Toshihiko Sayama ◽  
Yoshiyuki Okamoto ◽  
Takeshi Takayanagi ◽  
Kentaro Uesugi ◽  
...  
Keyword(s):  
Synchrotron Radiation ◽  
Crack Propagation ◽  
Thermal Fatigue ◽  
Flip Chip ◽  
Propagation Process ◽  
X Ray ◽  
Crack Propagation Process ◽  
Micro Tomography
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