Interconnects based on metal coated polymer spheres for improved reliability
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Original versionSmart System Integration 2011
3D packaging and heterogeneous integration has revealed new opportunities with regard to where instrumentation can be applied. Extreme miniaturization of systems makes it possible to include sensors and electronics in regions where this was not possible earlier due to size or weight limitations. However, some of these new application areas represent a challenging combination of extreme demands for reliability in rough environments. Interconnects are known to be prone to failures as a result of thermo-mechanical stress and require a specific focus in any instrumentation system. In this presentation we will give three examples of cases where traditional interconnect technologies are replaced with solutions based on metal coated polymer spheres (MPS) in order to improve the reliability. The idea behind the work is that the larger compliance of the polymer core of MPS compared to solid metal will reduce the level of stress imposed on the interconnect during thermal cycling or shock loading. The interconnect challenges in the three cases were to mount a MEMS device onto a PCB, to mount a silicon planar sensor onto an ASIC, and to mount a ceramic carrier onto a PCB. In the first example silver epoxy was replaced with an isotropic conductive adhesive filled with 4-30 µm sized MPS. In the second example microbumps were replaced with an anisotropic conductive film filled with 6 µm sized MPS, and in the last example lead free solid solder BGA balls were replaced with 310 µm sized MPS. Results indicating increased reliability for the devices, especially with regard to thermal cycling and rough mechanical treatment, will be shown. All three technologies based on MPS are expected to represent valuable alternatives within several 3D packaging solutions, although 3D packing in itself is not the primary scope for the interconnect technology development at present.