In recent years, the creation of a more economical bumping process has been the focus. One of the most promising technologies is the low-cost stencil printing based flip-chip technology. It consists of electroless Nickel/Gold (Ni / Au) Under Bump Metallurgy (UBM) plated on an Aluminum bond pad, followed by selective solder paste printing, using the stencil mask, on top of the UBM. It eliminates the expensive photolithography with thick photoresist and the usage of vacuum sputtering. Ni/Au UBM is not only important in stencil printed bumping technology, but also widely used in some of the anisotropic conductive flip chip technologies as conductive mini bump for the anisotropic conductive film (ACF)....[ Read more ]

In recent years, the creation of a more economical bumping process has been the focus. One of the most promising technologies is the low-cost stencil printing based flip-chip technology. It consists of electroless Nickel/Gold (Ni / Au) Under Bump Metallurgy (UBM) plated on an Aluminum bond pad, followed by selective solder paste printing, using the stencil mask, on top of the UBM. It eliminates the expensive photolithography with thick photoresist and the usage of vacuum sputtering. Ni/Au UBM is not only important in stencil printed bumping technology, but also widely used in some of the anisotropic conductive flip chip technologies as conductive mini bump for the anisotropic conductive film (ACF).

The redistribution (RDL) technology facilitates the adaptation of chips designed for wire bonding to flip chip bonding, and relaxes the otherwise tight wire bond pitch to a loose area array pitch. RDLs are formed by adding passivation and metal layers on the top of die, relocating the pads according to the design rules of the solder bumping process. The basic redistribution process includes both a reroute metal layer and additional dielectric layers. The redistribution metal can be aluminum, copper, or other metals. The choice of the conductive material is determined by the substrate and the electrical requirements of the IC. The most popular dielectrics for redistribution technology are Benzocyclobutene (BCB) and Polyimide (PI). BCB has a number of properties that makes it suitable for thick passivation including low moisture uptake, a low dielectric constant and a high degree of planarization over the topography in IC chips.