(A) study on the magnetic dispersion of the conductive particles and the fine pitch interconnection properties of anchoring polymer layer(APL) anisotropic conductive films(ACFs)

Abstract

Fine pitch interconnection technology has become a very important part in packaging industry since the demands of smart electronic devices such as tablet personal computers and smart phones have risen dramatically. The packaging industry requires more competitive technology to fulfill customer needs in electronic devices with high performance, multi-functionality, and compactness. As a consequence, more input/output pins are required within the limited space resulting in the narrower pitch and bump space for further miniaturization of electronic devices.

However in fine pitch interconnections, there are electrical problems with the conventional ACFs bonding, as the pitch and space between bumps and electrodes have become finer and finer. Bumps shape with longer length and narrower width causes less number of conductive particles captured between the bump and the electrode resulting in high contact resistance problem. Moreover, narrow space between the bumps becomes a serious problem, because flown out conductive particles are agglomerated between bumps causing short circuit failures.

To solve this problem, the laboratory developed Anchoring Polymer Layer ACF (APL ACF), which suppresses the movement of conductive particles, to achieve stable electrical interconnection characteristics at the lowest pitch used in the display industry.

However, in fine pitch packaging, conductive particles agglomerates incorporated in APL ACFs form an electrical bridge between narrow bumps and bumps, creating the risk of short circuit failure. So the dispersion of conductive particles is essential to achieve stable electrical interconnection characteristics in fine pitch applications.

In this study, we tried to demonstrate stable electrical characteristics in fine pitch applications by dispersing conductive particle agglomerates in polyvinyl fluoride (PVDF) APL ACFs, which have already been studied in the laboratory. In the second chapter, the dispersion of conductive particles according to the direction and strength of the magnetic field and the viscosity of PVDF APL was examined, and a magnetic structure in which the vertical magnetic field was concentrated on the conductive particles having 80% dispersed particle was fabricated. In the third chapter, PVDF APL ACFs with dispersed conductive particles were fabricated by using that magnetic structure and compared with the PVDF APL ACFs with non-dispersed conductive particles to evaluate the electrical properties at actual fine pitch interconnections It was confirmed that the same capture rate, contact resistance and insulation characteristics were observed at $20 \mum$ pitch. And it was concluded that PVDF APL ACFs with dispersed conductive particles showed stable electrical interconnection characteristics without short circuit through the fine pitch capability test using the insulation characteristics at the lower pitch.