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.
- 3D IC packaging
- localized heating