Pad redistribution technology for flip chip applications

Flip chip applications typically involve solder joint interconnections between the device chip and different substrates. In most cases, the I/O's on the device chip require to be relocated to a new format such as area array in order to match the corresponding pad locations on the substrate. In this paper, we describe one implementation of the pad redistribution technology, using aluminium interconnect lines, a photosensitive polyimide insulating layer and a wettable layer of underbump metallization (UBM) for the subsequent solder bumping applications. A test vehicle employing the flip chip on board (FCOB) assembly was fabricated and subjected to the thermal cycling reliability test. A useful simulation model was applied to understand the solder joint reliability in FCOB.