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  • 1.
    Dejanovic, Slavko
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Hesselbom, Hjalmar
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Norberg, Gunnar
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Manufacturing of Via Holes in Silicone ElastomerManuscript (Other (popular science, discussion, etc.))
    Abstract [en]

    In this work a possibility of making via holes in silicone elastomer was investigated. The methods that were taken into consideration were punching, mechanical drilling, laser drilling and RIE. Laser drilling and RIE were found to be viable and both were tried. Laser drilling of silicone elastomer has shown a big problem with burnt residues and has to be investigated much further to be usable. RIE of silicone elastomer is reported in this work. Several phenomena were observed. The etch-residues can be removed by washing them away in an ultra sonic water bath and subsequently totally removed by using a lift-off process based on wet Cu etch. A good anisotropy was achieved by applying CF4 plasma. Gradually broadening of the openings in the etch mask has contributed to a favorable etch profile and thus easier metallization of side-walls of via holes.

  • 2.
    Hesselbom, Hjalmar
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Norberg, Gunnar
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dejanovic, Slavko
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Haglund, Daniel
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Solder and adhesive free chip assembly using elastic chip sockets: Concept, Manufacture and Preliminary Investigations2004In: Proceedings of 2004 International IEEE Conference on the Asian Green Electronics (AGEC), Piscataway, NJ, USA: IEEE , 2004, p. 12-17Conference paper (Other academic)
    Abstract [en]

    Flip Chip connections enormously reduces the amount of solder as compared to mounting packaged devices, apart from also offering superior high frequency properties and placement density. However, when assembling chips to substrates having different thermal expansion coefficient, the solder balls are exposed to strain, the more so the denser the connections (and consequently smaller balls), and the higher the power densities, resulting in wider temperature cycles. This will usually result in loss of contact reliability. Using other materials than solder or using underfills may partially improve the situation, but causes other problems. In order to test another concept maintaining or exceeding the excellent HF and density properties of conventional Flip Chip, while practically eliminating the thermal mismatch problems and providing effortless chip replacement, the Elastic Chip Socket was developed. Silicone elastomer was molded in a precision mold made using anisotropic etching of Si. These structures were subsequently metallized and the metal patterned using electro plated resist. So far functional chip sockets with pin densities of 45 000 pins per cm2 (22 500 simultaneously functional connections to a 7 x 7 mm die) and more have been achieved which endure multiple repeated matings and quick temperature cycling between -40 °C and +90 °C. The following is a summary of the group's achievement this far, Oct. 2003

  • 3.
    Norberg, Gunnar
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dejanovic, Slavko
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media. KTH.
    Hesselblom, Hjalmar
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Very High Density Interconnect Elastomer Chip2006In: IEEE Transactions on Advanced Packaging, ISSN 1521-3323, E-ISSN 1557-9980, Vol. 29, no 2, p. 202-210Article in journal (Refereed)
    Abstract [en]

    The integration of more and more functionality into smaller and smaller form factor electronic products, drives the need for denser chip to substrate interconnect systems. As the number of I/O pins increases the use of area array chips or packages becomes inevitable. Metal patterned elastomer chip sockets have now been improved to work with contact densities as high as 80 000 contacts/cm2 corresponding to a pitch of 36 µm. Sockets with 10 000 contacts and a 72 µm pitch have survived more than 400 cycles in air to air thermal cycling chambers as well as freezing shocks caused by dipping into liquid nitrogen. Although the daisy chain test circuits breaks for temperatures lower than -50 C and higher than 90 C, they always return to the initial resistance values when entering the normal temperature range. The combination of a gold to gold contact interface and the elastic features of the contact bumps, makes this socket an ideal compliance layer between bare chips and different types of carrier substrates, reducing the problems caused by thermomechanical mismatch between the substrate and the chip. Bad dies can easily be replaced, since the chip is not soldered or glued to the socket. The size and the possibility to control the geometry of the contacts, provides means to maintain a good high frequency characteristic impedance matching all the way to the chip pad.

  • 4.
    Norberg, Gunnar
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dejanovic, Slavko
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Hesselbom, Hjalmar
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Contact Resistance of Thin Metal Film Contacts2006In: IEEE transactions on components and packaging technologies (Print), ISSN 1521-3331, E-ISSN 1557-9972, Vol. 29, no 2, p. 371-378Article in journal (Refereed)
    Abstract [en]

    To be able to reduce the size of products having electronic devices, it becomes more and more important to miniaturize the electro-mechanical parts of the system. The use of micro mechanical connectors and contact structures implies the need of methods for estimating the properties of such devices. This work will, by use of finite element modeling, treat the influence of a thin film constituting at least one of the contacting members of an electrical contact. The error introduced by using the traditional Maxwell/Holm contact constriction resistance theory will be investigated. Numerical methods are used to present a way to approximate the total resistance for the thin metal film contact.

  • 5.
    Norberg, Gunnar
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dejanovic, Slavko
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Hesselbom, Hjalmar
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Elastomer Chip Sockets for Reduced Thermal Mismatch Problems and Effortless Chip Replacement, Preliminary Investigations2003In: IEEE Transactions on Advanced Packaging, ISSN 1521-3323, Vol. 26, no 1, p. 33-40Article in journal (Refereed)
    Abstract [en]

    To avoid the problem with thermo-mechanical stress induced fatigue using conventional flip-chip mounting of bare chips, an elastic chip socket has been developed. The socket is made by casting silicone elastomer into micro structured silicon molds to form micro bump arrays. After the elastomer is cured and released from the mold, a metal layer is deposited and patterned. A chip is placed in the socket utilizing guiding structures for chip self alignment. The chip is then held in place by a spring loaded back-plate which can also serve as a heat sink for highly effective chip cooling. Since no adhesives, underfills or solders are used, the rework process becomes very simple and it can also be repeated many times for the same socket. Initial contact resistance and thermo-mechanical robustness measurements indicates that this type of sockets could work as a superior replacement for conventional flip-chip technologies in many applications. The particular design of the contact bumps results in metal structures that resemble (although up side down) and are scalable as those in the Chip-First technology. Preliminary thermal shock experiments from room temperature to liquid nitrogen and back show good survival. Thus, this new chip interconnect method indicates the possibility of getting the advantages of the Chip-First technology while eliminating the demand of placing the chip first. The concept will work for chips with rim positioned pads as well as for high density area arrays.

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