When observed at the submicroscopic level, the substrate surface is rough, full of pores and depressions. Liquid adhesives with good fluidity flow into and fill these pores and depressions, and form mechanical bonding forces such as anchoring, tenon connection, and riveting after drying and curing. The higher the roughness and the larger the surface area of the substrate, the greater the adhesion. Only when the adhesive fully penetrates the irregular interfaces of the rough surface is it beneficial to adhesion. As long as the coating has slight fluidity, few irreleasable stresses will be generated. However, with the increase in the viscosity and rigidity of the coating and the formation of adhesion to the substrate, a large amount of stress will be produced. The thickness of the adhesive at the uneven parts of the substrate is obviously different, and this difference leads to different physical properties. A non-uniform coating will generate significant internal stress and may even cause the coating to crack