The invention relates to a method of determining a reinforcement position of a circuit substrate and a substrate assembly. The method of determining a reinforcement position of a circuit board includes: setting a numerical model of a circuit board in which an electronic component is mounted in a front surface by bumps, and a reinforcing member is attached to a position corresponding to a bump located in a corner part of the electrical component in a back surface; incorporating information about a stud that is located in a periphery of the electronic component and fixes the circuit board to a chassis of the electronic device; performing a simulation for obtaining values of stresses generated in bumps of corner parts when a force is applied to the electronic component from a back side of the circuit board; and determining an arrangement of the reinforcing member in accordance with a position of the stud based on the values of stresses obtained by the simulation.