Localized Micro-Inserts Connection for Smart Card Secure Micro Packaging

Smart card integrated circuits are never completely immune against any invasive attack (chemical, physical or energetic), and a hardware protection of the chip could be necessary. One solution consists in shielding the devices at the wafer level with a silicon structured cap (Sishelltrade). In order to increase security, this cap can also comport active functions. In this case electrical connections between the two wafers are necessary. This paper presents a new solution to interconnect two wafers, compatible with smart cards integration requirements. Starting from a previous technology on anisotropic conductive film, hard localised Z axis micro-bumps are grown directly on wafer pads. Electrical contact and bonding are obtained simultaneously by thermo-compression at wafer level (top wafer on base wafer supporting the micro-bumps and glue). During this step, hard micro-bumps brake native oxide and create intimate contact with the top wafer Al pads. Two kinds of glue were implemented to obtain wafer bonding: epoxy and polyimide