The invention provides a circuit substrate and a package structure. The circuit substrate includes a molding compound having a chip-side surface and a solder ball-side surface opposite from the chip side surface. A first conductive bulk is formed embedded in the molding compound. The first conductive bulk has a first number of first chip-side bond pad surfaces and a second number of first solder ball-side surfaces exposed from the chip side surface and the ball-side surface, respectively. The width of the first conductive bulk is greater than the first width of the first chip-side bond pad surfaces and the second width of the first solder ball-side surfaces.