Self-Assembly of Chip-Size Components with Cavity Structures: High-Precision Alignment and Direct Bonding without Thermal Compression for Hetero Integration

Abstract

New surface mounting and packaging technologies, using self-assembly with chips having cavity structures, were investigated for three-dimensional (3D) and hetero integration of complementary metal-oxide semiconductors (CMOS) and microelectromechanical systems (MEMS). By the surface tension of small droplets of 0.5 wt% hydrogen fluoride (HF) aqueous solution, the cavity chips, with a side length of 3 mm, were precisely aligned to hydrophilic bonding regions on the surface of plateaus formed on Si substrates. The plateaus have micro-channels to readily evaporate and fully remove the liquid from the cavities. The average alignment accuracy of the chips with a 1 mm square cavity was found to be 0.4 mm. The alignment accuracy depends, not only on the area of the bonding regions on the substrates and the length of chip periphery without the widths of channels in the plateaus, but also the area wetted by the liquid on the bonding regions. The precisely aligned chips were then directly bonded to the substrates at room temperature without thermal compression, resulting in a high shear bonding strength of more than 10 MPa

Surface tension-driven self-alignment

“…In some applications, the receptor is fractioned into several separated parts, due to the requirements of electrical functionality, structure of the device, or to remove excessive amount of liquid after alignment. 62,63 The working principle for such single-component to multi-receptor embodiment is analogous to the standard single-component to single-receptor self-alignment configuration, except for the mechanism of meniscus formation, which may slightly differ due to the segmented shape of the receptor. 62…”

“…A capillary approach was also applied to the fluidic assembly of a GaAs-based microcantilever spin injector, 70 microcantilever for atomic force microscopy, 71 and of millimeter-sized components with inner cavities. 63 In this case the hydrophilic receptors, coated with a thin layer of water-diluted hydrofluoric acid, matched only the perimeter of the components. The receptors contained additional microchannels for liquid evacuation, so that an interior area free of liquid could safely be maintained to host additional structures.…”

“…Capillary self-alignment can easily achieve sub-micron registration accuracy. 28,[59][60][61]63,74 Whereas the highest absolute accuracy is normally achieved for submillimeter components, millimetre-sized components have also achieved similarly high relative accuracy.…”

Integrated Flexible Electronic Devices Based on Passive Alignment for Physiological Measurement

“…To overcome these limitations, existing literature has suggested self-alignment between the components and the interconnect layer. However, this may require a complicated fabrication process of three-dimensional structures [ 16 , 17 ]. Therefore, a simpler method of alignment is needed to perform efficient fabrication of functional electronic devices.…”

Capillary Self-Alignment of Microchips on Soft Substrates

“…One promising approach toward preventing liquid spreading is to use a patterned surface where a large wetting contrast between patterns and their surrounding is preferred. Capillary self-alignment has been reported as achieving high-precision assembly on patterned oleophilic/superoleophobic surfaces [ 1 ], protruding patterns [ 2 , 3 ], hydrophilic/hydrophobic patterned surfaces [ 4 , 5 , 6 , 7 , 8 , 9 ], hydrophilic/superhydrophobic patterned surfaces [ 10 , 11 ] and all-hydrophobic patterns [ 12 ]. Moreover, high yield self-assembly has been reported in water [ 13 ].…”