Novel high-density interconnection technology for the CBM Silicon Tracking System

In the Silicon Tracking System of the Compressed Baryonic Matter experiment at the future accelerator facility FAIR, double-sided microstrip sensors with sizes up to 62mm x 124mm will be connected to the readout electronics by means of up to 50 cm long lightweight microcables. The well-established aluminum to aluminum TAB bonding technology between die and microcable is highly manual and time-consuming. Therefore, a novel high-density interconnection technology based on a copper-polyimide flex microcable has been developed. It combines gold stud bumping on the die with solder paste printing on the microcable and a flip chip interconnection process. Shear strength and cross-section analysis have been performed on the bonded structures to optimize the solder paste reflow as well as the flip chip bonding process. First underfill application studies have been conducted successfully.