A flexible circuit board includes a substrate including a base layer and a bonding layer formed on each of opposite sides of the base layer. Each of the two bonding layers is formed by coating a bonding solution and drying the bonding solution. The bonding solution is composed of an adhesive and a solvent. A viscosity of the adhesive is 5000 millipascal-seconds. The adhesive is composed of a precursor having a mass fraction of 35%-65%, carboxyl modified polyphenylene oxide having a mass fraction of 10%-15%, bisphenol-F-epoxy resin having a mass fraction of 10%-15%, a silane coupling agent having a mass fraction of 0%-1.5%, silica filler having a mass fraction of 5%-20%, and a flame retardant filler having a mass fraction of 10%-20%.