Name: using synchrotron radiation microtomography to investigate multi-scale three-dimensional microelectronic packages
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The LLNL portion of this work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. The Intel Corporation authors would like to thank Pilin Liu, Liang Hu, William Hammond, and Carlos Orduno from Intel Corporation for some of the data collection and helpful discussions. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

Note: Protocol details described below were written specifically for work at beamline 8.3.2 at the ALS, Berkeley, CA. Adaptations may be required for work at other synchrotron facilities, which can be found around the world. Appropriate safety and radiation training is required for running experiments at these facilities and the guidelines for training can be found on each individual synchrotron facility&#39;s website. Any changes or updates to the tomography protocol (ALS, LBNL, Berkeley, CA) can be found on the beamline manual15...

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All of the steps described in the protocol section are critical to obtaining high-resolution images of multi-scale and multi-material samples. One of the most critical steps is the sample mounting and the focusing of optics, which are vital to obtaining quality images that can be used for quantification. Specifically, even slight movement of the sample would cause artifacts in the reconstructed image and defocusing would cause deterioration in resolution. To avoid issues with image quality it is important to reconstruct ...

In the microelectronics field, as in many other fields, non-destructive evaluation at the micrometer scale is necessary when characterizing samples. Specifically for the microelectronics industry there is interest in probing 3D microelectronics packages, containing multi-levels and multi-materials, and identifying failures in packages during thermal, electrical, and mechanical stressing of components. Around the world synchrotron radiation facilities have designated tomography and diffraction beamlines that are used for failure analysis of microelectronic packages. Some examples of this are imaging void formation caused by electromigration1-3, evaluating mechanisms for tin whisker growth4,5, in situ observations of undercooling and anisotropic thermal expansion of tin and intermetallic compounds (IMCs)6,7, in situ observation of solidification and IMC formation8-10, anisotropic mechanical behavior and recrystallization of tin and lead free solders10, voids in flip chip bumps, and in situ observations of Ag-nanoink sintering11. All of these studies have further advanced the understanding and development of components in the microelectronic industry. However, many of these studies have focused on small regions within the package. More information could be gleaned from testing and characterizing the full size package using high resolution SR&#181;T in order to further their development.
The electronic packages being produced now contain multiple layers of interconnects. These packages and devices are growing more and more complex which calls for a 3D solution for non-destructive evaluation with regard to failure analysis, quality control, reliability risk assessment, and development. Certain defects require a technique that can detect features less than 5 &#181;m in size, which include voids and cracks forming inside copper substrate vias, identifying non-contact open and nonwet solder pads in multilevel packaging12, locating and quantifying voids in ball grid arrays (BGAs) and C4 solder joints. During the substrate assembly process these types of defects must be identified and monitored extensively to avoid unwanted failures.
Currently CT systems using laboratory-based sources, also known as tabletop, are able to provide as high as ~1 &#181;m spatial resolution, and are being used to isolate failures in multilevel packages with promising results. However, tabletop CT systems have some limitations when compared to SR&#181;T setups13,14. Tabletop systems are limited to only imaging a certain density range of materials since they usually only contain one or two x-ray source spectrums. Also through-put-time (TPT) remains long for conventional tabletop CT systems requiring several hours of data acquisition time per 1-2 mm2 region of interest, which can limit its usefulness; for instance, analyzing failures in Through Silicon Vias (TSV), BGAs or C4 joints often require acquiring multiple Field of Views (FoV) or regions of interest at high resolution within the sample, resulting in total TPT of 8-12 hours, which is a show stopper for conventional tabletop CT systems when multiple samples have to be analyzed. Synchrotron radiation provides much higher flux and brightness than conventional x-ray sources, resulting in much faster data acquisition times for a given region of interest. Although SR&#181;T does allow for more flexibility with respect to types of materials that can be imaged and sample volume, it does have limitations, which are specific to the synchrotron source and setup used, specifically maximum acceptable thickness and sample size. For the SR&#181;T setup at the ALS the maximum cross-sectional area that can be imaged is &#60;36 x 36 mm and the thickness is limited by the energy range and flux available and is material specific.
This study is used to demonstrate how SR&#181;T can be utilized to image an entire multi-level system in package (SIP) with high resolution and low TPT (3-20 min) for use in inspecting 3D semiconductor packages. More details on comparing tabletop CT&#39;s to Synchrotron Source CT&#39;s can be found in references13,14.
Experimental Overview &#38; Beamline 8.3.2 Description: 
There are synchrotron facilities available for tomography experiments around the world; most of these facilities require submission of a proposal where the experimentalist describes the experiment, as well as its scientific impact. The experiments described here were all performed at the ALS at Lawrence Berkeley National Laboratory (LBNL) at beamline 8.3.2. For this beamline there are two energy mode options: 1) monochromatic in the energy range ~7-43 keV or 2) polychromatic &#34;white&#34; light where the entire available energy spectrum is used when scanning high density materials. During a typical scan at beamline 8.3.2 a sample is mounted on a rotational stage where x-rays penetrate the sample, then the attenuated x-rays are converted into visible light through a scintillator, magnified by a lens, and then projected onto a CCD for recording. This is done while the sample rotates from 0 to 180&#176; producing a stack of images that is reconstructed to obtain a 3D view of the sample with micrometer resolution. The resulting tomographic dataset size ranges from ~3-20 Gb depending on the scan parameters. Figure 1 shows a schematic of the hutch where the sample is scanned.
The following protocol presented here describes the experimental setup, data acquisition, and processing steps required for imaging an entire microelectronic package, but the steps can be modified to image a variety of samples. The modifications depend on the sample size, density, geometries, and features of interest. Tables 1 and 2 present the resolution and sample size combinations available at beamline 8.3.2 (ALS, LBNL, Berkeley, CA). For the microelectronic package investigated here the sample was imaged using a polychromatic (&#34;white&#34;) beam, which was selected due to the thickness and high-density of the sample&#39;s components. The sample was mounted in the horizontal orientation on a chuck mount, this orientation allowed for the entire sample to fit within the height of the beam, which is parallel with a height of ~4 mm and width of ~40 mm, therefore only requiring one scan to capture the entire sample.

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			<td class="xl64" height="20" style="height:15.0pt;width:87pt" width="116">Beamline 8.3.2</td>
			<td class="xl64" style="width:200pt" width="267">Advanced Light Source, Berkeley, CA, USA</td>
			<td style="width:81pt" width="108"></td>
			<td class="xl65" style="width:113pt" width="150">http://microct.lbl.gov/</td>
		</tr>
	</tbody>
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using synchrotron radiation microtomography to investigate multi-scale three-dimensional microelectronic packages

Synchrotron radiation micro-tomography (SR&#181;T) is a non-destructive three-dimensional (3D) imaging technique that offers high flux for fast data acquisition times with high spatial resolution. In the electronics industry there is serious interest in performing failure analysis on 3D microelectronic packages, many which contain multiple levels of high-density interconnections. Often in tomography there is a trade-off between image resolution and the volume of a sample that can be imaged. This inverse relationship limits the usefulness of conventional computed tomography (CT) systems since a microelectronic package is often large in cross sectional area 100-3,600 mm2, but has important features on the micron scale. The micro-tomography beamline at the Advanced Light Source (ALS), in Berkeley, CA USA, has a setup which is adaptable and can be tailored to a sample&#39;s properties, i.e., density, thickness, etc., with a maximum allowable cross-section of 36 x 36 mm. This setup also has the option of being either monochromatic in the energy range ~7-43 keV or operating with maximum flux in white light mode using a polychromatic beam. Presented here are details of the experimental steps taken to image an entire 16 x 16 mm system within a package, in order to obtain 3D images of the system with a spatial resolution of 8.7 &#181;m all within a scan time of less than 3 min. Also shown are results from packages scanned in different orientations and a sectioned package for higher resolution imaging. In contrast a conventional CT system would take hours to record data with potentially poorer resolution. Indeed, the ratio of field-of-view to throughput time is much higher when using the synchrotron radiation tomography setup. The description below of the experimental setup can be implemented and adapted for use with many other multi-materials.

The images captured using tomography occur due to the differential absorption of x-rays in the solder interconnects, metallic traces, and other materials in the microelectronic package as a function of the different attenuation lengths and thickness of these multi-materials. The SIP package consisted of a silicon die attached to a ceramic substrate with first level interconnect (FLI) flip chip C4 solder balls of approximately 80 &#181;m diameter; mid-level interconnect (MLI) solder balls of approximately 350 &#181;m conn...

Watch this Scientific Journal Video about Using Synchrotron Radiation Microtomography to Investigate Multi-scale Three-dimensional Microelectronic Packages at JoVE.com

Using Synchrotron Radiation Microtomography to Investigate Multi-scale Three-dimensional Microelectronic Packages

For this study synchrotron radiation micro-tomography, a non-destructive three-dimensional imaging technique, is employed to investigate an entire microelectronic package with a cross-sectional area of 16 x 16 mm. Due to the synchrotron&#39;s high flux and brightness the sample was imaged in just 3 min&#160;with an 8.7 &#181;m spatial resolution.

Synchrotron radiation micro-tomography (SR&#181;T) is a non-destructive three-dimensional (3D) imaging technique that offers high flux for fast data ...

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