New reflow soldering and tip in buried box (TB2) techniques for ultrafine pitch megapixels imaging array

Flip chip is a high-density and highly reliable interconnection technology which is mandatory for the fabrication of high end heterogeneous imaging arrays. The control of ultra-fine pitch (<10 mum) and high bumps count flip-chip bonding technology represents a challenge on the roadmap of next generation devices (Kozlowski). This paper describes and compares in details two new flip- chip technologies that can address the challenges at the 10 mum pitch node: a modified reflow soldering technology and a thermocompression "tip in buried box" (TB2) insertion technology. The technological preparation of the flip-chipped devices is fully described including new maskless underbump metallization (UBM) technique, new maskless soft solder buried box filling technique and new "micro-tube" fabrication technique. First the flip chip experiments are described as well as two methods to evaluate minimum insertion force for the TB2 technology: 500times500 area arrays insertion/ pull out forces are measured as well as original "single tip into solder" insertion/ pull out forces. The reduction of the required thermocompression forces obtained with "micro-tube" is demonstrated, finally first reflow and thermocompression hybridization results are achieved and commented.