Low-temperature bonding of surface-activated polyimide to Cu Foil in Pt-catalyzed formic acid atmosphere

Abstract

In this study, a two-step process involving oxygen plasma surface activation and thermos-compression in Pt-catalyzed formic acid gas was used to bond Cu foil and polyimide. The oxygen plasma was used to activate the polyimide surface to achieve strong adhesion with sputtered deposition film, and the Ptcatalyzed formic acid gas removed the oxides on the Cu surface effectively to promote bonding between Cu foil and polyimide. Via this method, a void-less bonding with a maximum shear strength of 20.31 MPa was achieved. The plasma bombardment was found to promote the formation of C-O-Cr and N-Cr bonds between polyimide and deposition metals, which improved their adhesion. After shear test, striped metal films remained on fracture surfaces at both polyimide and Cu foil sides, suggesting the fracture mainly occurred within adhered deposition metals rather than at bonding interface. This low-temperature bonding method is promising to achieve the direct integration between polyimide and copper foil without adhesive, which plays a key role in flexible device integration.

Cu-Cu joint with Sn-58Bi/Porous Cu/Sn-58Bi transient liquid phase bonding under formic acid atmosphere

“…In the case of using a Pt catalyst, as shown in Figure 11(b), most of HCOOH directly decomposes into CO 2 and hydrogen radicals without forming -COOH (ads) . HCOOH can directly decompose into hydrogen radicals with the aid of Pt catalyst, and the direct combination between hydrogen radicals and adsorbed OH facilitates the rapid extraction of O and the production of H 2 O (Meng et al , 2022; Chou et al , 2018; Yang et al , 2017). Hydrogen radicals exhibit higher reduction activity compared to H+ (Suga et al , 2014), and during the TLPB process in the FA atmosphere, they are more effective in reducing the oxides of subsequent SB, P-Cu foil and Cu substrate.…”

The Overlooked Role of Copper Surface Texture in Electrodeposition of Lithium Revealed by Electron Backscatter Diffraction

“…Cu foils are wildly used in batteries, electromagnetic shielding, and integrated circuits because of their high electrical conductivity and tensile strength. − In the current Li-ion batteries, the Cu foil functions as the current collector for the graphite-based anode. In order to increase the gravimetric energy density of the batteries, the thickness of the Cu foil has been reduced down to below 10 μm recently (i.e., the ultrathin Cu foil), which nevertheless leads to challenges in maintaining sufficient mechanical strength and corrosion resistance.…”