Development of Fluxless Micro-Bonding and Narrow Gap Filling Process

$2.\times \mathrm{D}$
and 3D packages require to connect chips and components in high density, therefore, both wiring pitch and vertical interconnect dimension must be finer and finer. Copper-to-copper bonding technologies, such as hybrid bonding, are being considered as the high-density connection method for various functional chips, nevertheless, there are still many challenges before realizing it into the mass production. On the other hand, solder bump interconnection by TCB (Thermal Compression Bonding) has already been studied extensively and mass-produced widely. However, to achieve high-yields in the fine pitch, the selection of bump formation material and optimization of the process conditions and bump metal compositions are critical. It is also important to verify the appropriate encapsulant material such as CUF (Capillary Underfill) to fill the narrow gaps between components after micro-bonding in order to achieve high reliability. In this study, we examined bump formation, bump bonding, and underfilling with a minimum
$10\ \mu\mathrm{m}$
pitch, and discussed the limitations of underfillability. In addition, we focused on the decrease in flux cleanability at fine bump pitches and investigated a fluxless bonding process with a simple pretreatment.