Fire safe epoxy composite with low dielectric properties from a combination of fluoro-phosphonium salt, melamine and copper hydroxystannate

•A novel fluorine containing phosphonium salt tetraphenylphosphine hexafluorophosphate flame retardant was synthesized.•Tetraphenylphosphine hexafluorophosphate prevented dripping of epoxy system.•Epoxy composites reached V0 rate at very low phosphorus loadings with melamine and copper hydroxystannate as co-additives.•Cone calorimeter coupled with FTIR method was adopted to observe the reduction of heat release rate and toxic gases intensity.•Epoxy composites showed lower dielectric constant and dielectric loss.