Metallurgical challenges in microelectronic 3D IC packaging technology for future consumer electronic products

Metallurgical challenges in controlling the microstructural stability of Cu and solder microbumps in 3D IC packaging technology are discussed. Using uni-directional 〈111〉 oriented nanotwinned Cu, the controlled growth of oriented Cu66n5 on the nanotwinned Cu and its transformation to Cu3Sn without Kirkendall voids have been achieved. In order to join a stack of Si chips into a 3D device, multiple reflows of solder microbumps may be required; we consider localized heating to do so by the use of self-sustained explosive reaction in multi-layered Al/Ni thin films of nano thickness. It avoids re-melting of those solder joints which have been formed already in the 3D stacking structure.