Understanding the Behavior of SnAg Bumps at 10 µm Pitch and Below for Imaging and Microdisplay Application

The finer pitch of 10 μm and below is currently explored by Microdisplays and Imaging industries. There are many contenders for achieving assembly at this pitch e.g. Cu-diffusion, Microtubes[1], and SnAg bumps. Among the contenders, SnAg bumps are tested for larger bumps but their capabilities for the finer pitch are yet to be explored. In this paper, behavior of SnAg for smaller bumps for the finer pitch is studied and compared to the larger bumps. Different reflow conditions such as environment, different type of flux, and temperature profile are examined. During this study, some particular bumps were observed, which we called as hedgehog bumps and their behavior is discussed in this paper. The conclusions drew from the reflow studies have been used to achieve assembly. The behavior of SnAg alloy during the assembly is also explored.