Cu Pillar Electroplating Using a Synthetic Polyquaterntum Leveler and Its Coupling Effect on SAC305/Cu Solder Joint...

Area of Science:

• Materials Science
• Electrochemistry
• Semiconductor Manufacturing

Background:

• Advanced semiconductor packaging requires precise copper (Cu) bumping technology for high-density interconnections.
• Cu electroplating additives are crucial for controlling pillar shape, crystal structure, and reliability.
• Kirkendall voids can form during reflow soldering, potentially due to impurities from electroplating additives.

Purpose of the Study:

• To investigate the effect of a self-synthesized polyquaternium (PQ) additive on Cu pillar electrodeposition.
• To explore the formation of Kirkendall voids in Cu pillars electroplated with PQ and reflowed.
• To understand the synergistic effects of PQ and bis-(sodium sulfopropyl)-disulfide (SPS) on Cu electroplating.

Main Methods:

• Patterned Cu pillar electroplating using PQ and SPS additives.
• Screen printing of Sn96.5/Ag3.0/Cu0.5 (SAC305) solder paste followed by reflow soldering.
• Scanning Electron Microscopy (SEM) for void observation and quantification, X-ray Diffraction (XRD), and Electron Backscatter Diffraction (EBSD) for microstructure analysis.

Main Results:

• The synthesized PQ additive demonstrated dual suppressor and leveler effects, influencing Cu pillar morphology.
• PQ's effectiveness was found to be dependent on liquid convection during electroplating.
• Synergistic action between PQ and SPS led to uneven adsorption on Cu pillar surfaces, increasing Kirkendall voids at corners compared to the center.

Conclusions:

• PQ shows promise as a dual-function additive in Cu pillar electroplating, but its performance is sensitive to process conditions.
• The interaction between PQ and SPS can lead to localized void formation, impacting the reliability of solder joints.
• Further optimization of additive formulations and electroplating parameters is needed to mitigate Kirkendall void formation.