2009 Volume 50 Issue 7 Pages 1684-1689
In this paper, we discuss our design of a new class of low-melting-point alloy (LMPA)-filled anisotropically conductive adhesives (ACA) and a self-organized interconnection process for using these adhesives, and we demonstrate a good electrical conduction for the process. Flow, melting, coalescence, and wetting characteristics of LMPA fillers in the ACA facilitate this process. In order to exploit good coalescence and wetting characteristics of LMPA fillers, the polymer matrix has a sufficient fluxing capability against oxide films of both LMPA fillers and electrode materials. Furthermore, it is essential that the polymer have a low viscosity level around the melting point of the incorporated LMPA to achieve a good electrical conduction path.
In order to study coalescence and wetting characteristics, we formulated two types of ACA with different volume fractions of LMPA filler (10 vol% and 40 vol%). Our test board had an 18-μm thick Cu line-type pattern (10mm×0.1mm) and an area array-type pattern (square type: 0.1mm×0.1mm, circle type: \\varphi, 0.1 mm) with five different pitches (50 μm to 250 μm). We measured thermal properties of the ACA by differential scanning calorimetry (DSC), and we determined a temperature profile for the interconnection process. We then monitored coalescence and wetting characteristics of LMPA fillers and morphology of conduction path in ACA by using a microfocusing X-ray inspection system and an optical microscope.
We determined that the developed LMPA-filled ACA have good coalescence and wetting characteristics regardless of pattern types. In addition, we were able to achieve a good electrical conduction path because of the coalescence and wetting characteristics of the LMPA fillers in the ACA.