PURPOSE: A package on package substrate is provided to increase the number of electronic devices to be mounted on a lower package by setting the space between an upper package and a lower package with a wanted height. CONSTITUTION: A lower package substrate(20) includes a lower pad unit and a solder resist unit in response to the lower pad unit. An electronic device is mounted on the lower package substrate. An upper package substrate(10) is stacked on the upper side of the lower package substrate by interposing a solder and includes a pad unit in response to the lower pad unit. A first solder resist layer is formed on the upper side of the lower package substrate in response to the lower pad unit. A second solder resist layer is formed on the first solder resist layer to expose the lower pad unit.
