TPI (Thermoplastic Polyimide) features polyimide film, coated on both sides with a B-staged modified polyimide adhesive or polyimide adhesive. TPI is similar to Dupont bondply, which coated on both sides with proprietary B-staged modified acrylic adhesive. You also can think TPI or bondply has one more sheet of adhesive coated on the non-adhesive side of the coverlay.
