Highly-reliable, 30µm pitch copper interconnects using nano-ACF/NCF

Abstract

Flip chip packaging of ultra fine pitch integrated circuits (ICs) on organic substrates aggravates the stress-strain concerns, requiring a fundamentally different system approach to interconnections, underfill, interfaces, and the substrate. This work demonstrates a novel interconnection solution with excellent reliability for ultra-fine pitch (~30 mum) silicon (Si) on organic first level interconnections by using copper (Cu) pillar with nano-anisotropic conductive film (nano-ACF)/non conductive Film (NCF). Novel nano-ACF/NCF materials were developed and evaluated for package level reliability criterion for mobile or portable electronics systems at ultra-fine first level interconnect pitch of 30 mum. Various additives were added to the formulation to enhance the reliability performance. Test vehicles (TVs) with 30 mum bump pitch were designed with 3 mm times 3 mm chip to extract both daisy chain resistance and single bump resistance data. As assembled bump resistivity was measured and the interconnect reliability performance was evaluated using the novel adhesive materials for flip-chip on organic packages. Performance of these test vehicles was studied for High Temperature Storage Life Test (HTS), Unbiased- Highly Accelerated Stress Test (U-HAST) and is currently being tested for Thermal Cycling Test (TCT). Test results showed that the interconnect resistance is better than or comparable to most common solders for both as assembled and U-HAST tested assemblies. The TVs depicted excellent reliability results in both HTS and U-HAST. Insulation resistance measurements showed that these adhesives are near perfect insulators and there is negligible difference in nano-ACF and NCF in terms of leakage current. On the basis of the results, nano-adhesive materials, proposed in this work provide unique opportunities for ultra fine pitch and high electrical performance interconnects.