Novel Low Cost Bumping Process with Non-strip Type Photosensitive Resin and Injection Molded Solder (IMS) for Fine Pitch Flip Chip Joining

Fine pitch interconnect is one of key technology elements for 2.5D and 3D IC. Low cost and flexibility in technical aspects are also important, so that the technology can be used for wide range of applications. We have newly developed a non-strip type photosensitive resin and propose a novel IMS bumping process with it for finer pitch flip chip joining in a further cost-effective way. The photosensitive resin layer can be used for IMS bumping Mask and Underfill, and we named the resin layer a Mask and Underfill co-usable layer (MU layer). With this technology, several UBM fabrication methods can be chosen. One of options is electro-less plating after MU layer patterning, and in this case, both solder volume and UBM thickness can be designed flexibly without increasing a risk of UBM bridging as well as solder bridging. In this paper, we present detail results on bumping, bonding, reliability tests with this technology with the MU layer for 80 mm pitch test vehicles. Flip chip joining and temperature cycling reliability were demonstrated with electro-less plated Ni/Au UBM. In addition, we have confirmed that the technology is applicable to 40 μm pitch flip chip joints.