Defluxing of Copper Pillar Bumped Flip-Chips

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[Ravi Parthasarathy & Umut Tosun]

Flip-chip technology is popular in the electronics industry due to its cost-effectiveness and improved performance. Copper pillar technology, replacing traditional solder bumps, offers benefits such as smaller device sizes and improved electrical performance. A study on cleaning flux residues from copper pillar bumped flip-chips provides valuable insights for future research on smaller bump pitches and denser package designs.

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Flip-chip technology is gaining popularity in the electronics industry due to its cost-effectiveness, increased package density, improved performance, and higher I/O density. However, traditional solder bump technology faces challenges below 125μm pitch, such as reduced standoff height, decreased joint reliability, and increased risk of shorts. To overcome these issues, copper pillar technology is emerging as a replacement for solder bumps. Copper pillar technology offers benefits like improved electrical performance, smaller device sizes, better control of standoff height, and reduced cost through fewer package substrate layers. The use of copper pillars allows for tighter pitches and lower standoffs, but it also raises concerns about flux residue removal to ensure product functionality and reliability. Flux residues can negatively impact underfill adhesion and hinder the flow of underfill material, potentially leading to delamination or void formation.

A study was conducted to investigate the cleaning of flux residues on copper pillar bumped flip-chips using DI-water and a low-concentration alkaline cleaning agent. The study’s findings can serve as a benchmark for future research involving smaller bump pitches and denser package designs, including 2.5D and 3D configurations


Naveen RavindranNaveen Ravindran, M.S.Ch.E. Application Engineer, ZESTRON Americas

Naveen Ravindran, M.S.Ch.E., is an Application Engineer at ZESTRON Americas. Mr. Ravindran is an active member of the SMTA as well as the IPC. He has contributed to multiple case studies performed in collaboration with major cleaning equipment manufacturers. Mr. Ravindran provides technical support to our customers, including cleaning process recommendations as well as onsite customer support for process implementations and optimizations. He also was a key contributor to the extensive technical paper series “Key to Low Standoff Cleaning” as well as the lead-free and eutectic screening series completed at ZESTRON’s Technical and Analytical Center in Manassas, VA. Mr. Ravindran graduated with a Bachelor’s Degree in Chemical Engineering from the University of Madras, India, and a Master’s Degree in Chemical Engineering from West Virginia University, Morgantown, WV. He has been with ZESTRON Americas since October 2006.

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