Evaluation of Cu-bumps with lead-free solders for flip-chip package applications

• Published in: Microelectronic engineering 2009-12, Vol.86 (12), p.2392-2395
• Main Authors: Lin, Kung-Liang, Chang, Edward-Yi, Shih, Lin-Chi
• Format: Article
• Language: English
• Subjects: Adhesion; Applied sciences; Brazing. Soldering; Copper; Copper bump; Cross-disciplinary physics: materials science; rheology; Design. Technologies. Operation analysis. Testing; Electrodeposition, electroplating; Electronics; Electroplating; Exact sciences and technology; Fatigue failure; Integrated circuits; Joining, thermal cutting: metallurgical aspects; Lead-free; Materials science; Metals. Metallurgy; Methods of deposition of films and coatings; film growth and epitaxy; Microelectronic fabrication (materials and surfaces technology); Physics; Seeds; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Shear; Solders; Tin; Titanium
• ISSN: 0167-9317; 1873-5568
• DOI: 10.1016/j.mee.2009.04.027

Low cost electroplated Cu-bump with environmental friendly Sn solder was developed for flip-chip applications. The seed layer used was Ti/WN x /Ti/Cu where WN x was used as the Cu diffusion barrier and Ti was used to enhance the adhesion between bump and the chip pad. Thick negative photoresist (THB JSR-151N) with a high aspect ratio of 2.4 was used for electroplating of copper bump and Sn solder. The Sn solder cap was reflowed at 225° for 6 min at N 2 atmosphere. No wetting phenomenon was observed for the Sn solder as evaluated by energy-dispersed spectroscopy (EDS). The Cu-bump with Ti/WN x /Ti/Cu seed layer not only have higher shear force than the Cu-bump with Ti/Cu seed layer but also has higher resistance to fatigue failure than the Au, SnCu, SnAg bumps.