A novel intermetallic compound insertion bonding to improve throughput for sequential 3D stacking

This article provides a novel 3-D die-to-wafer (D2W) bonding method using intermetallic compound (IMC) layer insertion into a soft Sn bump to generate mechanical connection of two dies, called insertion bonding. A 50% decrease in stacking time can be obtained. Using this process close to a 100% electrical yield of daisy chains containing 800 fine pitch bumps (20 $\mu \text{m}$ ) is achieved. Various challenges for insertion bonding, such as material selection, surface properties of microbumps, bonding optimization, and compatibility with underfill materials, are discussed in this article. In addition, the potential application of IMC insertion bonding to prevent oxide formation for Co-based under bump metallization and as protection layer is explored.