The bonding process using the defect – dewetting phenomenon direct interconnection to achieve the microelectronic device
With the discovery of advanced manufacturing techniques and materials and improvements in the future, the electronic device will tend to miniaturization, tightly integrated within a limited area and interconnected to achieve the object of multi-functional, high performance and energy saving. However, when the electronic component (e.g. light-emitting diodes, transistors, and various sensors, etc.) become very small in scale, a common method of assembling (metal wire, metal welding and an anisotropic conductive film (the ACF)) during the integration process It will be subject to many restrictions. In recent years, researchers have metal coated polymer spheres, the ACF multilayer, non-conductive film (the NCF) and a silver ink and a eutectic gallium – indium variety of methods (eGain) the liquid metallic alloy coating, etc. to improve the interconnection section distance. However, these methods still exhibit various limitations, for example, a conductive metal-coated polymer spheres easily affected by heat, low reliability; thermal conductivity of the polymer is lower than that of the metal solder, so heat easily occurs the problem device; and the ACF NCF multilayer structure may improve the performance of the pitch, but the need for greater bonding pressure, the need for additional processing on the device in order to achieve the sidewall insulation, reducing the yield and throughput; although EGaIn auxiliary nano silver ink It may be interconnected at low temperatures, but because of the surface tension of the oxide layer and reducing the size and the ink pattern remains a challenge.
by means of selective adhesive desiccant electrically interconnected
Based on this, Sungkyunkwan University Tae-il Kim team using selective anisotropic conductive adhesive polymer dewetting developed a new and direct vertical electrical interconnection technique , the method is applicable to flexible electronic devices deterministic microelectronic assembly. The interconnection system consists of an adhesive polymer and an electrode structure of a composition containing metal nanoparticles. The adhesive by a simple spin-coating process is coated on a substrate, cured by ultraviolet light in the device is mounted on the device with selective conductivity and viscosity, the insulating layer is formed and the other portion of the protective layer. This technique can be applied to the electrode size and spacing of 20 μm or less in various miniature electronic devices, and can withstand severe temperature changes (- 40 to 85 ° C, 5 minutes, more than 300 cycles) and long-term high humidity environment (85 ° C, 85% RH, 300 hours). Further, on a flexible transparent substrate and monolithically integrated solidNow the display comprises preparing more than 10,000 micro light-emitting diodes (micro-LED) and commercialization of the microchip.
using the transfer printing technique Achievement of selective desiccant adhesives
first of preparing an acrylate-based ultraviolet (UV) curable adhesives for assembly of various electronic devices deterministic and transfer printing. The adhesive glycidyl ester of bisphenol A, diacrylate, a silane coupling agent KH570, SOG 500F and UV initiators, by changing the weight ratio of the components, diluted with a solvent or the spinning rate may be controlled based coating the thickness of the adhesive material. To prepare an anisotropic conductive adhesive (ACA) is achieved by adding 1 wt% of commercial adhesive in the above indium (In) nanoparticles (250 nm). On using the spinning method, a bar coating method or an inkjet method ACA uniformly coated on the Au electrodes, so that in a completely wet state. When the indium (In) coated nanoparticles embedded in the adhesive, the adhesive is stable and completely wet film state (Figure 1a). Then use polydimethyl siloxane (PDMS) are highlighted as a deterministic carrier with electronic components aligned and transfer (FIG. IB), due to the weak between the PDMS and the interaction of the electronic device, the latter can be printed by the transfer process, the electrons gently place the device on ACA coating (FIG. 1c). Since the adhesive – adhesion difference between the device and the device -PDMS, weak pressure (≈0.5 bar) applied to the device -ACA. By extrusion of an adhesive material, the thickness of the device is attenuated ACA. When the thickness is less than ACA dehumidifying threshold value, the polymeric binder becomes unstable and will trigger on the desiccant is pressed point. Such that the metal particles (indium) and exposed on the surface of the metal gasket electronics, to achieve a connection between the electronic device (the exposed metal particles act as a conventional metal bumps, but lower than those perpendicular to the circuit base plate preform use of the contact 100 times smaller). Finally, the exposed regions ACA lost its adhesive force inherent in the ultraviolet initiator of polymerization, an inert insulating layer; and an electronic device located below the ACA unexposed areas maintain bondForce, firmly hold the electronic component, the non-exposed areas cure slowly over time, to prevent electrical defect such as short circuit (FIG. 1d).
transfer device printing causes adhesive desiccant particles on the electrode or the structure of metal, while the adhesive in the electronic it will form capillary migration (Fig of 2AB) on the device side walls, which makes the electronic device having a stable interconnection and assembly at a desired position. 250 nm after transfer printing is exposed on the surface of metal nanoparticles, a polymer adhesive dewetting meniscus form a (red) around the particles, this is a major proof meniscus (FIG 2CD) dewetting phenomenon.
The method may be through a simple process of spin coating and the respective transfer printing electronic products directly interconnected (micro light-emitting diode, a mini-emitting diodes, infrared receiver, a microcontroller, a transistor); can also be integrated with different sizes and heights of the electronic components, or even may be integrated on a flexible transparent substrate, to have uniform electrical properties; thousands also be integrated electronic component, for transferring large area of the printing process (FIG. 3). In addition, this method proved very stable interconnect performance by moisture sensitive test and thermal shock test. Dewetting of instability although this method still has some challenging problems, such as structural height of the metal particle size, the weaker adhesion brought about. However, this study hopes to provide a new interconnect technology, the future can be used for large-scale integratedand uncertainties flexible wearable electronic devices in a limited circuit board. Original link: https: //onlinelibrary.wiley.com/doi/full/10.1002/adma.201908422