A new era in manufacturable, low-temperature and ultra-fine pitch Cu interconnections and assembly without solders

This paper presents the first demonstration of a high-throughput die-to-panel assembly technology to form Cu interconnections without solder at temperatures below 200°C. This interconnection technology, previously established with individual single-chip packages on both organic and glass substrates, at pitches down to 30μm, is brought up to a significant manufacturable level by two major innovations: 1) ultra-fast thermocompression bonding (TCB) process with pre-applied polymer, in air, and without any prior surface activation; 2) die-to-panel assembly process with heating from die side exclusively for reduced substrate warpage. The initial proof of concept reported in this paper consists of assembly of 15 silicon dies with Cu bumps at 100 μm pitch, on a 3” × 5” organic substrate, by sequential TCB at 210°C for 3 seconds, and 190°C for 10 seconds. X-ray analysis, C-SAM imaging, cross-section observation with optical microscopy and SEM, and electrical yield characterization indicate the formation of strong metallurgical interconnections. This pioneering technology addresses many manufacturability challenges presently hindering the technology-transfer of direct Cu-Cu bonding, the “holy grail” in the semiconductor industry, by offering a potentially low-cost, high-throughput solution, compatible with industry-standard assembly lines. Scalable to ultra-fine pitches onto low-CTE glass, silicon or organic packages, it has the potential to become a major enabler for the next two or more decades.