Facile Synthesis of Conductive Flexible Composite Sn@Ag Microspheres and their Application in Anisotropic Conductive Films

Abstract

Composite microspheres with noble metal nanoshells are advantageous in flexible circuit connections, flip chips, and chemical sensors. It is difficult for Polystyrene microspheres to cover a complete Ag layer, and hard metal microspheres have no deformability. These two reasons have contributed to this research. This report demonstrates a facile synthesis route that chemically deposits an Ag layer on the surface of 30 µm Sn microspheres to form a composite Sn@Ag double‐layer structure, which is suitable for anisotropic conductive films (ACFs) with linewidths greater than 100 µm. Scanning electron microscope analysis reveals that the surface Ag coating thickness can be controlled within the range of 737 nm–5.62 µm by varying the amount of Ag source applied, and trace free Ag particles are produced during the preparation process. An anisotropic conductive adhesive film is successfully fabricated and hot‐pressed after the film‐on‐film flexible circuit board. The microspheres form an ACF single‐layer structure after hot pressing. Hot pressing in the range of 10–20 MPa can ensure deformation and avoid Ag shell cracking, and the deformation is determined when Sn@Ag is in contact with the circuit surfaces at both ends. This approach provides a potential method of preparing low‐cost and high‐performance ACFs.

Microwave Bonding of Thin Polymer Substrates Using Carbon Nanotubes for Flexible Interconnections

“…Several studies have highlighted the importance of the mechanical reliability of electronic packages against dynamic bending, twisting, and folding, which can induce the formation of cracks inside the joint area. − Conventional bonding methods for flexible packaging include organic adhesives such as epoxies due to their strong adhesion force, lightweight, and low cost. − Recently, anisotropic conductive film (ACF) technologies have been actively developed for flexible applications. The ACFs consist of insulating epoxy resin and various conductive particles and have a high potential to realize flexible devices such as chip-on-flex (COF). − However, organic-adhesive-based bonding techniques have inevitable limitations, including bending stiffness and mechanical reliability. The thick adhesive layer of the epoxy material, even though the thickness is less than 100 μm, results in a significant increase in bending stiffness and low flexibility.…”

Shell structure control of monodisperse polystyrene‐silver composite microspheres and synthesis of epoxy resin‐based anisotropic conductive adhesives

“…These ACAs were pasted between printed circuit boards (PCBs), and the measured resistance in the vertical direction was less than 10 ohms. Zhang et al 10 have deposited silver on 30‐μm Sn microspheres to obtain a composite microsphere with a core‐shell structure, which has been used as a conductive filler to prepare an anisotropic conductive adhesive film (ACF) suitable for line widths greater than 100 μm. However, the conductive particles in large‐scale industrial‐grade ACAs are typically compound microspheres with a desirable monodisperse size in the range of 3–10 μm 11,12 .…”

Mechanical stability and insulation reliability of polymeric layers constructed by thermal fusion of polymer shell particles heterocoagulated on conductivenickel‐platedcore particles

“…11,14,[16][17][18][19] In addition to the conventional display applications, recent studies have focused on radio frequency identification mounting 20 and stretchable ACF applications. 21 Furthermore, new concepts of conductive particles are also being investigated, such as micropolystyrene particles and nickel-copper particles, 22 tin-silver particles, 23 composite particles of carbon nanotubes-gold nanoparticles. 24 In addition, to allow a narrower space between electrodes, it is necessary to ensure not only connection reliability but also electrical insulation.…”