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  • 1. Khorramdel, Behnam
    et al.
    Liljeholm, Jessica
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems. Silex Microsystems AB.
    Laurila, Mika-Matti
    Lammi, Toni
    Mårtensson, Gustaf
    Ebefors, Thorbjörn
    Niklaus, Frank
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Mäntysalo, Matti
    Inkjet printing technology for increasing the I/O density of 3D TSV interposers2017In: Microsystems & Nanoengineering, E-ISSN 2055-7434‎, Vol. 3, p. 17002-Article in journal (Refereed)
    Abstract [en]

    Interposers with through-silicon vias (TSVs) play a key role in the three-dimensional integration and packaging of integrated circuits and microelectromechanical systems. In the current practice of fabricating interposers, solder balls are placed next to the vias; however, this approach requires a large foot print for the input/output (I/O) connections. Therefore, in this study, we investigate the possibility of placing the solder balls directly on top of the vias, thereby enabling a smaller pitch between the solder balls and an increased density of the I/O connections. To reach this goal, inkjet printing (that is, piezo and super inkjet) was used to successfully fill and planarize hollow metal TSVs with a dielectric polymer. The under bump metallization (UBM) pads were also successfully printed with inkjet technology on top of the polymer-filled vias, using either Ag or Au inks. The reliability of the TSV interposers was investigated by a temperature cycling stress test (-40 °C to +125 °C). The stress test showed no impact on DC resistance of the TSVs; however, shrinkage and delamination of the polymer was observed, along with some micro-cracks in the UBM pads. For proof of concept, SnAgCu-based solder balls were jetted on the UBM pads.

  • 2.
    Laakso, Miku
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.
    Bleiker, Simon J.
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.
    Liljeholm, Jessica
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems. Silex Microsystems AB.
    Mårtensson, Gustaf
    Mycronic AB.
    Asiatici, Mikhail
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems. EPFL École polytechnique fédérale de Lausanne, Processor Architecture Laboratory.
    Fischer, Andreas C.
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems. Silex Microsystems AB.
    Stemme, Göran
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.
    Ebefors, Thorbjörn
    Silex Microsystems AB.
    Niklaus, Frank
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.
    Through-Glass Vias for MEMS Packaging2018Conference paper (Other academic)
    Abstract [en]

    Novelty / Progress Claims We have developed a new method for fabrication of through-glass vias (TGVs). The method allows rapid filling of via holes with metal rods both in thin and thick glass substrates.

    Background Vertical electrical feedthroughs in glass substrates, i.e. TGVs, are often required in wafer-scale packaging of MEMS that utilizes glass lids. The current methods of making TGVs have drawbacks that prevent the full utilization of the excellent properties of glass as a package material, e.g. low RF losses. Magnetic assembly has been used earlier to fabricate through-silicon vias (TSVs), and in this work we extend this method to realize TGVs [1].

    Methods The entire TGV fabrication process is maskless, and the processes used include: direct patterning of wafer metallization using femtosecond laser ablation, magnetic-fieldassisted self-assembly of metal wires into via holes, and solder-paste jetting of bump bonds on TGVs.

    Results We demonstrate that: (1) the magnetically assembled TGVs have a low resistance, which makes them suitable even for low-loss and high-current applications; (2) the magneticassembly process can be parallelized in order to increase the wafer-scale fabrication speed; (3) the magnetic assembly produces void-free metal filling for TGVs, which allows solder placement directly on top of the TGV for the purpose of high integration density; and (4) good thermal-expansion compatibility between TGV metals and glass substrates is possible with the right choice of materials, and several suitable metals-glass pairs are identified for possible improvement of package reliability [2].

    [1] M. Laakso et al., IEEE 30th Int. Conf. on MEMS, 2017. DOI:10.1109/MEMSYS.2017.7863517

    [2] M. Laakso et al., “Through-Glass Vias for Glass Interposers and MEMS Packaging Utilizing Magnetic Assembly of Microscale Metal Wires,” manuscript in preparatio

  • 3.
    Laakso, Miku J.
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.
    Bleiker, Simon J.
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.
    Liljeholm, Jessica
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.
    Mårtensson, Gustaf E.
    Mycronic AB, S-18353 Taby, Sweden..
    Asiatici, Mikhail
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems. Ecole Polytech Fed Lausanne, Sch Comp & Commun Sci, CH-1015 Lausanne, Switzerland..
    Fischer, Andreas C.
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.
    Stemme, Göran
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.
    Ebefors, Thorbjorn
    Silex Microsyst AB, S-17543 Jarfalla, Sweden.;MyVox AB, S-12938 Hagersten, Sweden..
    Niklaus, Frank
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.
    Through-Glass Vias for Glass Interposers and MEMS Packaging Applications Fabricated Using Magnetic Assembly of Microscale Metal Wires2018In: IEEE Access, E-ISSN 2169-3536, Vol. 6, p. 44306-44317Article in journal (Refereed)
    Abstract [en]

    A through-glass via (TGV) provides a vertical electrical connection through a glass substrate. TGVs are used in advanced packaging solutions, such as glass interposers and wafer-level packaging of microelectromechanical systems (MEMS). However, TGVs are challenging to realize because via holes in glass typically do not have a sufficiently high-quality sidewall profile for super-conformal electroplating of metal into the via holes. To overcome this problem, we demonstrate here that the via holes can instead be filled by magnetically assembling metal wires into them. This method was used to produce TGVs with a typical resistance of 64 m Omega, which is comparable with other metal TGV types reported in the literature. In contrast to many TGV designs with a hollow center, the proposed TGVs can be more area efficient by allowing solder bump placement directly on top of the TGVs, which was demonstrated here using solder-paste jetting. The magnetic assembly process can be parallelized using an assembly robot, which was found to provide an opportunity for increased wafer-scale assembly speed. The aforementioned qualities of the magnetically assembled TGVs allow the realization of glass interposers and MEMS packages in different thicknesses without the drawbacks associated with the current TGV fabrication methods.

  • 4.
    Laakso, Miku
    et al.
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Liljeholm, Jessica
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems. Silex Microsystems AB, Järfälla, SWEDEN.
    Fischer, Andreas
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems. Karlsruhe Institute of Technology (KIT), Germany.
    Stemme, Göran
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Ebefors, Thorbjörn
    Silex Microsystems AB, Järfälla, SWEDEN.
    Niklaus, Frank
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Maskless Manufacturing of Through Glass Vias (TGVs) and Their Test Structures2017In: Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS), 2017, p. 753-756, article id 7863517Conference paper (Refereed)
    Abstract [en]

    Through glass vias (TGVs) are a key component in glass-based interposers and microelectromechanical-system lid wafers. Magnetic-field-assisted self-assembly has been demonstrated earlier in fabrication of through silicon vias. Here we present an entirely maskless TGV fabrication process utilizing magnetic assembly. Femtosecond laser is used for ablative direct patterning of surface metal layers and for exposing the TGV conductors after wafer thinning. The proposed TGV structure is shown to be electrically functional by measuring the TGV resistance values.

  • 5. Larsson, S.
    et al.
    Johannisson, P.
    Kolev, D.
    Ohlsson, F.
    Nik, S.
    Liljeholm, Jessica
    KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.
    Ebefors, T.
    Rusu, C.
    Simple method for quality factor estimation in resonating MEMS structures2018In: Journal of Physics: Conference Series, Institute of Physics Publishing (IOPP), 2018, Vol. 1052, no 1, article id 012100Conference paper (Refereed)
    Abstract [en]

    The quality factor of a packaged MEMS resonating structure depends on both the packaging pressure and the structure's proximity to the walls. This type of mechanical constraints, which causes energy dissipation from the structure to the surrounding air, are applicable for oscillating energy harvesters and should be considered in the design process. However, the modelling of energy losses or the measurements of their direct influence inside a packaged chip is not trivial. In this paper, a simple experimental method to quantify the energy loss in an oscillating MEMS structures due to the surrounding air is described together with preliminary results. The main advantage of the method is the ability to characterize the damping contributions under different vacuum and packaging conditions without requiring any packaging of the harvester chip or fabrication of multiple devices with different cavity depths.

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