Novel Self-Assembly Process Using Magnetically Aligned $z$-Axis Anisotropic Conductive Adhesive for High-Density Vertical Interconnection

In this paper, a novel self-assembly packaging approach using a magnetically aligned
z
-axis anisotropic conductive adhesive (ACA) is introduced, enhancing the quality of interconnects and reducing packaging cost in fine-pitch electronic circuitry. This self-assembly process creates selectively agglomerated vertical columns on I/O pads and is first demonstrated using the magnetization interaction properties between ferromagnetic conductive particles and I/O pads in the presence of an external magnetic field. Experimentally, this packaging process is verified to be particularly beneficial in improving the environmental reliability of the self-aligned material. At 133 × 133-μm pad size, the resistance of the created interconnects only varies by 2.45 Ω over a 160°C temperature range. In addition, the breakdown current of the self-assembly
z
-axis ACA was measured to be 2.0 A at 1.3 V. Furthermore, this self-assembly process was demonstrated to still work at the extremely small pad size of 12×19-μm. Finally, through analysis of the design parameters of this self-assembly process, properties of the
z
-axis ACA material and I/O pad structure were suggested to create vertical interconnects for small pads of size in the order of 10 μm.