In hybrid sensors, detector and readout circuit is divided into two separate chips. The interconnections between the pixel detector and the readout integrated circuit chip (ROIC) are provided by small indium bumps and the use of flip chip technology. The approximately cylindrical shaped indium bumps intended for a pixel size of 38 x 38 mm have a diameter of 12 mm and a height of 7 mm. Both, detector and ROIC, were aligned and flip chip bonded under cold compression. Epoxy under filler was applied to the device mainly to improve adhesion and mechanical strength.
Because all interconnections are produced simultaneously, a very large number and high density of interconnections can be produced in a very efficient way. Up to 307 000 interconnections on a single hybrid sensor have been fabricated with a density of 160 000 interconnections/cm(2).
An advantage of hybrid 3D multi chip modules compared with monolithic devices is the fact that, the single chips can be optimised separately. This allows the combination of different device technologies and substrate materials that makes it attractive for many applications.