Flexible Techniques of Medium to Small Pitch 3D and 2.5D Integration for Prototypes and Small-Scale Production

In a research facility, we often face the task of testing a single idea or concept which is especially challenging in the field of semiconductor microfabrication as the majority of the activities typically require full-wafer processing. The process steps that require the best accuracy can only be performed on an entire wafer, making prototype development complex and resource-intensive. To bridge the gap between initial concepts and full-wafer production, we have established a roadmap to introduce technologies that enable efficient prototype fabrication and small-scale production. In the field of 3D and 2.5D integration technologies, we are focusing on electroless deposition of nickel, palladium, and gold to form under-bump metallization (UBM) layers suitable for solder material deposition. As the next step, we will incorporate two key technologies for solder deposition: (1) Solder ball laser placement system – that deposits preformed solder balls of arbitrary composition, ranging in size from 30 µm to 250 µm; and (2) Solder ink printing system – that dispenses solder ink of arbitrary composition, with a maximum solid particle size of approximately 5 µm. Both systems use single-spot, one-by-one deposition, inherently limiting production to low volumes. However, this limitation is also advantageous when only a small number of prototypes are needed, as neither technology requires lithography or full-wafer access. Moreover, these technologies support a wide range of bump sizes and interconnection pitches, from 50 µm to approximately 1 mm. The final steps of the planned 3D integration are flip chip bonding (thermocompression or thermo-sonic compression) and finally wire bonding. As a result, our back-end line shall be able to bond chips with highly variable integration sizes - an essential capability for research activities that demand diverse product integration requirements.