Advanced plating photoresist development for semiconductor packages

In recent years, novel electronic products like mobile phones, tablets, and personal computer have shrunk dramatically and become highly functionalized. These market trends of smaller thinner devices, have put pressure on the complexity of packaging structures for semiconductors. To satisfy these requirements, packaging technologies such as 3D-TSV, 2.5D, PoP and Flip-chip wafer bumping are being used. We have developed negative tone photoresists (ELPAC THB series) for re-distribution layer, C4 and micro bumps. The THB series is negative tone resist which incorporates an acrylate cross-linker system with photo radical initiator. This formulation shows excellent chemical resistance to various plating solutions such as Cu, Ni, Sn/Ag and Au, with good stripability. The key technology of plating photoresists for advanced packages is high resolution, allowing for high aspect ratio patterning capability that covers a wide range of film thicknesses. An example of such applications is in advanced PoP package design which require a thick film material that has high resolution capability, along with high aspect ratio performance. In TSV technology, via filling and high dissolution rate are key for micro-bump formation. Additionally, high resolution re-distribution layer photoresists can be used to create fine pitch conditions which are necessary for package downsizing. Our THB series shows good patterning performance from below 10um to above 100um film thickness conditions. In this paper, material design and key properties of novel plating resist with high resolution and high aspect ratio performance with a wide range film thickness ranges are discussed.