Bare chip stacking structure for MCM production

In order to obtain higher density and lower cost multichip modules (MCM), we have developed a simply structured bare-die stacking assembly technology. It provides a simple structure with thick epoxy layer to fix upper layer bare die, rather than custom structures such as notched dies or additional electrodes at die edge in the conventional structures. The developed technology can use exactly the same dies as those for wire bonding interconnection without any additional processing. All electrical connections of the upper and lower dies are achieved by wire-bonding to the substrate independently. We have performed this stacking assembly by precise control of epoxy layer thickness and wire loop shapes. This new technology was applied to the production of MCMs, including twelve memory dies. The assembled MCM was almost twice as dense as an MCM without a stacked-die structure. The MCM were verified to functional correctly. The assembly yield of MCM with this structure was high enough for production. As our technology includes a repair method for failed dies, fully tested KGD (known good die) are not necessary.