A substrate improving immobilization of ball pads for BGA packages mainly comprises a substrate core, a plurality of ball pads and a solder resist layer. Each of the ball pads has a metal pad and at least a metal nail. The metal pads are adhered on a surface of the substrate core and the metal nails are embedded into but not penetrate the substrate core. The solder resist layer is formed over the substrate core and exposes the metal pads. By utilizing the shapes of the ball pads to increase bonding area between the ball pads and the substrate core, a separation or crack occurring at the interface between the metal pads and the substrate core can be substantially avoided.