Cu Bump Interconnections in 20 μm-Pitch at Low Temperature Utilizing Electroless Tin-Plating on 3D Stacked LSI

Abstract

The electroless tin-plating on copper has the preferable characteristics for the thermal compression bonding, although it is easy to decrease in thickness by heating at the bonding because of the diffusion with copper.
Therefore, the bonding profile was determined to have lower pre-heating to evaluate the bondability with copper-bumps dressed thin tin-caps in 20 μm-pitch. Then, the possibility of the interconnections in 20 μm-pitch was confirmed. Bonding temperature was 150°C and bonding force was 24.5 N.
Finally, the tin-cap on a through-hole electrode (T-COTE) was performed in the electroless plating and the basic bonding condition was evaluated on the vertical interconnections.
The results showed the sufficient joint between the copper electrodes through the Si die and the adjacent copper bumps on the interposer.