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Research Papers

Laser-Based Target Preparation in 3D Integrated Electronic Packages

[+] Author and Article Information
Stefan Martens, Walter Mack

 Infineon Technologies AG, 93049 Regensburg, Germany

Frédéric Courtade, Philippe Perdu

 Centre National d’Etudes Spatiales, CNES, 31401 Toulouse, France

Juergen Wilde

Department of Microsystems Engineering (IMTEK), Laboratory for Assembly and Packaging, University of Freiburg, 79110 Freiburg, Germany

Friedemann Voelklein

Institute of Microtechnologies, IMtech, University of Applied Sciences Wiesbaden, 65197 Wiesbaden, Germany

J. Electron. Packag 131(3), 031006 (Jun 23, 2009) (6 pages) doi:10.1115/1.3144157 History: Received December 02, 2008; Revised April 22, 2009; Published June 23, 2009

The trend toward 3D integration in electronic packaging requires that failure analysis procedures and target preparation methods are adapted from conventional discrete packages to these emerging packaging technologies. This paper addresses the feasibility of laser-based target preparation in 3D integrated devices, especially stacked-die packages. Various laser technologies such as ultrashort-pulse lasers, excimer lasers, and diode-pumped solid-state (DPSS) lasers with different wavelengths and pulse durations were evaluated. In particular, it was found that ultrashort-pulse lasers with pulse durations in the femtosecond range were not suitable for ablation of the molding compound (MC). Picosecond lasers were applicable with certain constraints. It was found that for MCs with high filler content, DPSS lasers with pulse durations in the nanosecond range were the best choice. For the removal of stacked silicon dies, the laser wavelength was the most important factor in artifact-free thinning. Laser cross sections through several silicon dies with remarkably small heat-affected zones were also demonstrated. The distinct removal of the MC, silicon dies, and metal interconnected with a single laser source offers new opportunities for laser-based target preparation in 3D integrated electronic packaging devices.

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Copyright © 2009 by American Society of Mechanical Engineers
Topics: Lasers , Silicon
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Figures

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Figure 1

Typical configuration and dimensions of stacked-die packages

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Figure 2

Optical top view image after five scans with different pulse energies of the femtosecond laser system; boxes size: 0.5×0.5 mm2, upper row (left to right): 2.1 μJ, 5 μJ, and 16 μJ, bottom row: 26 μJ, 36 μJ, and 46 μJ

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Figure 3

Scanning electron microscope (SEM) image of an IC surface machined with 16 μJ pulse energy of the femtosecond laser. Surrounding burst particles are up to 150 μm away.

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Figure 4

Silicon die surface after 100 area scans. Pulse energy of the picosecond laser system was 80 μJ; note massive hole occurrence in the bulk silicon.

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Figure 5

Mechanical cross section of a hole, probably induced by phase explosion or explosive boiling. Massive tensile cracks by molten and annealed silicon after ten area scans with a pulse energy of 125 μJ can be observed for the picosecond laser system.

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Figure 6

Mechanical cross section showing deep craters of excimer laser-induced damage in the IC structures down to the fourth engraved die; the material of the top silicon die remains.

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Figure 7

Top view image of the silicon die after 30 laser scans with 532 nm DPSS laser. With increasing number of scans, the irregularities increase.

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Figure 8

Tilted view on one edge of the area machined with a 355 nm DPSS laser through the molding compound and the two upper silicon dies (dies 2 and 3)

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Figure 9

Mechanical cross section through the laser edge machined with a 355 nm DPSS laser, including detailed view of the cut IC structures with small HAZ

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